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Role of Endothelium-Derived Relaxing Factor in Regulation of Vascular Tone and Remodeling Update on Humoral Regulation of Vascular Tone Jonathan P. Tolins, Pamela J. Shultz, and Leopoldo Raij In addition to preserving the permselectivity of the vascular wall and providing an antithrombogenic surface, the vascular endothelium contributes importantly to the regulation of vasomotor tone. Indeed, the endothelium participates in the conversion of angiotensin I to angiotensin II; the enzymatic inactivation of several plasma constituents such as bradykinin, norepinephrine, serotonin, and ADP; and the synthesis and release of vasodilator substances such as prostacyclin and the recently discovered endothelium-derived relaxing factor (EDRF). The diffusible EDRF released from the endothelium is nitric oxide or a substance closely related to it such as nitrosothiol. The endothelium also synthesizes and releases vasoconstrictive factors, including products derived from arachidonic acid metabolism and the recently discovered peptide endothelin. An increasing body of evidence from experimental and clinical studies indicates that EDRF and endothelium-derived contracting factors play an important role in vascular physiology and pathology. It has become apparent that the balance of these factors may be a major determinant of systemic and regional hemodynamics. Moreover, through generally opposite effects on growth-related vascular changes, contracting factors such as endothelin and relaxing factors such as EDRF also may be important determinants of the vascular response to injury in various disease states such as atherosclerosis and hypertension. It is clear that the vascular endothelium is a complex and dynamic organ. Understanding endothelium function in normal physiology and disease states is of potential clinical importance and should be the focus of future investigation. {Hypertension 1991;17:909-916)
H
istorically, the vascular endothelium was considered to be a structurally and metabolically simple cellular lining to blood vessels that was important only insofar as it contributed to regulation of vascular permeability and hemostasis. More recently, it has become overwhelmingly apparent that the endothelium represents a complex, dynamic organ with diverse functions, including the synthesis and release of vasoactive agents that play a role in modulating vascular tone.1-2 Moncada et al3 first demonstrated that vascular endothelial cells produce prostacyclin, a vasodilator prostaglandin. In 1980, Furchgott and Zawadzki4 demonstrated that vascular relaxation induced by the muscarinic agent acetylcholine was dependent on the presence of a functionally intact endothelium and From the Department of Medicine, Veterans Administration Medical Center and the School of Medicine, University of Minnesota, Minneapolis, Minn. Supported by funds from the Veterans Administration. Address for correspondence: Leopoldo Raij, MD, Renal Section 111 J, Veterans Administration Medical Center, One Veterans Drive, Minneapolis, MN 55417
postulated the release by endotheliaJ cells of a labile factor termed endothelium-derived relaxing factor (EDRF). Subsequent work in this area has made it clear that control of vascular function by the endothelium is quite complex and involves the synthesis and release not only of vasodilator substances such as prostacyclin and EDRF, but of vasoconstrictor substances such as endothelin and other less well-characterized endothelium-derived contracting factors (EDCFs) as well.5 The role of these substances in normal vascular physiology and disease states is the subject of this review. Endothelium-Derived Relaxing Factor
EDRF first was described as a labile, diffusible substance released by the endothelium in response to acetylcholine.4 Since this initial study, a variety of agonists, including thrombin, bradykinin, serotonin, ADP, and the calcium ionophore A23187, have been shown to induce release of EDRF from the endothelium of various vascular beds and endothelial cells grown in culture.1-2^,? A large body of evidence,
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Vol 17, No 6, Part 2 June 1991 Vascular Smooth Muscle or Mesangial Cell
Endothelial Cell
GTP
l-argininp Acetykholine Thrombin ADP Brady kin In Serotonin Adenosine A23187
NO L-NMMA
NO
(+) ^
Guanylate cyclase
(or nitrosothiol) cEMP
Relaxation
I
FIGURE 1.
Schematic of pos-
tulated metabolic pathway by which agonist stimulation of endothelial cells results in vascular smooth muscle cell relaxation. L-NMMA, Nc-monomethyl L-arginine; NO, nitnc oxide; cGMP, cyclic GMP.
Inhibition of Proliferation
including comparative pharmacological studies and direct measurements, supports the hypothesis that EDRF activity is due to release of nitric oxide (NO) by stimulated endothelial cells.8-10 Palmer et al11-13 demonstrated that the EDRF NO originates from the terminal guanidino nitrogen atom of the amino acid L-arginine. The characteristics of the NO synthase enzyme involved in this reaction in endothelial cells have been reviewed recently by Nathan and Stuehr.14 In endothelial cells, this enzyme is soluble, calcium- and NADPH-dependent, and can be inhibited by L-arginine derivatives such as A^-monomethyl L-arginine (LNMMA) or A^-nitro L-arginine.12-14 It is a constitutive enzyme, in that it requires no induction and synthesizes NO within seconds of agonist stimulation of the endothelial cell.14 The active product, NO, has a short half-life and decomposes rapidly to form mixtures of nitrite and nitrate in oxygenated solutions. The postulated metabolic pathway by which agonist stimulation of endothelial cells results in vascular smooth muscle cell relaxation is shown schematically in Figure 1. It should be kept in mind that other less well-characterized factors, such as endothelium-derived hyperpolarizing factor,15 may be released by agonist-stimulated endothelium and result in vasodilation as well. In this regard, Tare and coworkers16 have demonstrated recently that endothelium-derived NO can contribute to the hyperpolarization of vascular smooth muscle cells in response to acetylcholine. Thus, it is likely that NO is responsible for the majority of observed EDRF activity, and this substance will be the focus of the current review. It recently has become apparent that there is another subtype of NO synthase enzyme, designated as type I by Nathan and Stuehr.14 This enzyme has been found in macrophages,17 hepatocytes,18 and tumor cells19 and must be induced by cytokines such as interleukin-1, interferon gamma, and tumor necrosis factor or by microbial products, such as endotoxin.
A similar enzyme also may be present in endothelial cells20; however, the positive identification of an inducible NO synthase in endothelium remains to be demonstrated. Induction of this enzyme, and subsequent generation of NO, requires 4-18 hours of exposure to the immunostimulator and is dependent on protein synthesis. The amount of NO generated by these cell types is much larger than that generated by the NO synthase involved in EDRF responses and appears to mediate tumor cell cytostasis and macrophage-mediated bacterial killing.21 The NO generated by this system also may have vasodilator effects, because both endotoxin and interleukin-1 have been shown to inhibit contraction of and increase cyclic GMP (cGMP) levels in rat aortic rings in vitro,22 and LNMMA has been shown to inhibit the hypotension associated with intravenous infusion of tumor necrosis factor in dogs.23 It is likely that this system may be present within the glomerulus as well, because a preliminary report suggested that rat mesangial cells also can generate NO and demonstrate increased intracellular cGMP levels after exposure to endotoxin or interferon gamma.24 Both the NO generation and cGMP changes were prevented by LNMMA. Thus, it is possible that during glomerular inflammation or endotoxemia, NO may participate in the modulation of glomerular function. Murad et al25 reported that in vascular smooth muscle there is a positive correlation between an increase in cGMP levels and vascular relaxation. Subsequent work has shown that NO, as well as other nitrovasodilators, stimulates increases in cGMP levels in smooth muscle by activating soluble guanylate cyclase25-26 and that vascular relaxation is associated with an increase in tissue cGMP levels.27 Thus, it is apparent that NO released by stimulated vascular endothelium activates soluble guanylate cyclase in adjacent vascular smooth muscle cells, inducing a rise in intracellular cGMP levels and subsequent vascular
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Tolins et al
relaxation (Figure 1). The exact chemical form in which the endothelium releases NO remains controversial; more recent studies have suggested that endothelium-derived NO may be incorporated into a nitrosothiol.28 Uptake or degradation of this nitrosothiol carrier molecule at the vascular smooth muscle cell membrane would release NO and lead to subsequent stimulation of guanylate cyclase. Resolution of this issue awaits further study. The role of EDRF/NO in normal physiology has begun to be explored only recently. Investigation in this area has been facilitated by the development of EDRF/NO synthesis inhibitors that can be administered in vivo, such as LNMMA. In the rat29 and the rabbit,30 systemic bolus administration of LNMMA results in a marked and long-lasting increase in blood pressure, and this hypertensive effect is reversed by administration of L-arginine, the endogenous precursor to NO. This suggested that there is a basal rate of EDRF/NO synthesis by vascular endothelial cells that may be important in the modulation of systemic blood pressure. Tolins et al29 administered LNMMA to rats by continuous intravenous infusion and reported that arterial blood pressure and renal vascular resistance were increased and that the normal hypotensive and renal vasodilator responses to acetylcholine were prevented. Furthermore, they demonstrated that the vasodilator effects of acetylcholine were associated with increases in urinary cGMP excretion, a result not observed with endotheliumindependent vasodilators. They concluded that in vivo responses to endothelium-dependent vasodilators are due to stimulation of endogenous EDRF/NO release by vascular endothelium and that these responses are most likely mediated by changes in cGMP levels in vascular tissue. These same investigators infused LNMMA into the renal artery of the rat and demonstrated a decrease in glomerular filtration rate, marked renal vasoconstriction, and a rise in filtration fraction, suggesting an important role for EDRF/NO synthesis in the regulation of basal renal hemodynamics.31 The importance of EDRF/NO in the regulation of renal hemodynamic responses in vivo has been confirmed recently in the isolated perfused rat kidney32 and in the dog.33 Endothelial cells cultured from bovine glomeruli have been reported to be capable of producing EDRF.34 Within the glomerulus, the endothelial and mesangial cells are in close proximity, and it is possible that EDRF is an important mediator of endothelial-mesangial cell communication and thus of renal function. EDRF released from cultured endothelial cells, as well as exogenously applied NO, increases cGMP levels in cultured rat glomerular mesangial cells.35 NO also attenuates the mesangial cell contractile response to angiotensin II. Others have shown that EDRF can inhibit renin release from juxtaglomerular cells and therefore can limit the generation of angiotensin II.36 Because the state of mesangial contraction could affect the ultrafiltration coefficient (Kf) by altering the surface area
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available for glomerular filtration, this may represent another mechanism, distinct from direct hemodynamic effects, by which EDRF could modulate glomerular function. Recent studies have suggested that EDRF plays a role in the regulation of vascular tone in the pulmonary circulation.37'38 Brashers et al37 demonstrated that NO, bradykinin, and acetylcholine cause vasodilation in isolated, perfused lungs during hypoxic pulmonary vasoconstriction and conversely, that hypoxic vasoconstriction is enhanced by nonspecific inhibitors of EDRF action. Archer and coworkers38 reported that inhibition of EDRF/NO synthesis with LNMMA enhanced hypoxic vasoconstriction in the isolated perfused rat lung as well as in isolated pulmonary artery rings. In this same study, L-arginine rapidly reversed hypoxic vasoconstriction, especially when EDRF synthesis had been inhibited previously with LNMMA. They concluded that EDRF/NO synthesis is enhanced during hypoxia and acts as a balancing factor, limiting the constrictor response. Similarly, recent observations by Crawley et al39 suggest that vasoconstriction of human pulmonary arteries is attenuated by NO release. Further evidence has accumulated that EDRF/NO contributes to the control of resting tone in diverse vascular beds. Gardiner et al40 infused LNMMA intravenously into rats and noted a dose-dependent, sustained vasoconstriction in the carotid, mesenteric, renal, and hindquarters vascular beds. Vallance et al41 infused LNMMA into the brachial artery of human volunteers and noted a 50% fall in basal blood flow rate and inhibition of the vasodilator response to acetylcholine, suggesting that EDRF/NO contributes to control of basal peripheral arterial blood flow in humans. EDRF also has been reported to be important in modulating hemodynamic responses in the cerebral42 and coronary43-44 circulations. In addition to effects on vascular tone, EDRF/NO influences components of the blood coagulation system and cellular proliferative responses. In vessels with normal endothelium, thrombin, as well as serotonin and ADP released by aggregating platelets, binds to specific receptors and induces EDRF release.2-7 EDRF/NO inhibits platelet aggregation.45 The adhesion of platelets to cultured endothelial cells in vitro is decreased by the EDRF agonist bradykinin or exogenous NO.46 Furthermore, platelets themselves contain an NO synthase that can generate NO and increase platelet cGMP levels in response to activating stimuli.47 Therefore, acting synergistically with prostacylcin, NO may participate in the local regulation of coagulation responses. NO also has been shown to inhibit vascular smooth muscle and mesangial cell proliferation induced by serum- or platelet-derived growth factor in vitro48"50 and so could act as a limiting factor in vascular and glomerular responses to injury. Whether this antiproliferative effect is mediated by increases in cGMP is currently unclear.50
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Endothelium-Derived Contracting Factors
Since the discovery of EDRF, it has become clear that endothelial cells also release several substances that mediate contraction of vascular smooth muscle.5 Possible candidates for EDCFs include the cyclooxygenase products thromboxane A251-52 and prostaglandin H253 and superoxide anion.54 Vascular tissue also may have a locally active renin-angiotensin system that is capable of generating the vasoconstrictor angiotensin II.55 Furthermore, the vascular endothelium recently has been demonstrated to release endothelin, a 21-amino acid peptide with potent vasoconstrictive properties.56-57 Freshly isolated porcine arteries with intact endothelium release endothelin under basal conditions, and thrombin significantly enhances this release.5* Binding sites for endothelin have been described in blood vessels and in renal tissues.59 Recently, a radioimmunoassay for measurement of endothelin in plasma has been developed that should greatly facilitate further investigation into the role of this novel peptide in vivo. Preliminary reports using this radioimmunoassay have found detectable circulating levels of endothelin in normal humans, with increased levels noted in patients with essential hypertension and patients with renal insufficiency.60-61 In nephrectomized rats, the plasma clearance of endothelin is prolonged, and exogenously administered endothelin induces exaggerated responses, indicating that the kidney may play a role in the elimination of endothelin.62 It appears that, unlike EDRF, endothelin can circulate in the bloodstream and therefore may be released from one vascular bed and have vasoconstrictive effects in distant parts of the circulation. Recent experimental studies have focused on the systemic and renal hemodynamic effects of exogenously administered endothelin. When administered to "experimental animals" in pharmacological doses, endothelin induces a transient vasodilation followed by a marked and prolonged vasoconstriction, resulting in elevation of blood pressure and reduction in renal bloodflow.63-64The renal vascular bed appears to be 10-fold more sensitive to vasoconstriction by endothelin than are the coronary, femoral, or bronchial vascular beds.65 Endothelin also has been shown to stimulate atrial natriuretic peptide release66-67 and to increase plasma renin activity and aldosterone levels.67 The effect of endothelin on the glomerular microcirculation has been investigated with the use of micropuncture techniques. In this setting, endothelin has been shown to reduce single-nephron glomerular filtration rate and glomerular plasma flow by 3050%.64 Both afferent and efferent arteriolar resistances increase with endothelin64-68 and Kt has been reported to be reduced64 or unchanged.68 Several studies have investigated the effects of endothelin on glomerular mesangial cells in culture.64-69 In contrast to EDRF, endothelin stimulates mesangial cell proliferation especially when added in the presence of
low concentrations of serum.69 Endothelin stimulates rapidincreasesinmesangialcytosoliccalcium,phosphoinositide turnover, and intracellular alkalinization similar to many other vasoconstrictors and growth factors.69 In this regard, endothelin would fit the apparent pattern observed in studies of mesangial cells in which vasodilators (EDRF/NO, prostacyclin) are antiproliferative, whereas vasoconstrictors (angiotensin II, platelet-derived growth factor, endothelin) are pro-proliferatfve. Whether glomerular endothelial cells can synthesize endothelin remains to be determined, but because endothelin circulates within the bloodstream, the glomerulus could be exposed to this agent from various sites within the circulation. Thus, it appears that EDRF and endothelin exert a number of opposite effects on the glomerulus and mesangial cells, suggesting that they may have counterbalancing effects on glomerular function. Role of the Endothelium in Disease States
From the above discussion it is apparent that the control of vascular tone by the endothelium has proved to be much more complex than previously suspected and would appear to reflect a balance between locally acting mediators such as EDRF/NO and the various EDCFs, as well as circulating endothelium-derived factors such as endothelin. Furthermore, the interaction of EDRF and endothelin is of potential importance in both normal physiology and disease states. Several agonists, such as thrombin and A23187, stimulate simultaneous release of EDRF/NO and endothelin.2 In addition, recent studies have demonstrated that thrombin-induced release of endothelin is potentiated when NO synthesis is inhibited by LNMMA,58 suggesting that NO may exert an inhibitory effect on endothelin synthesis. On the other hand, endothelin may stimulate the release of EDRF and prostacyclin.70 Thus, it can be seen that in disease states in which the endothelium is injured, the delicate balance between endothelium-mediated vasodilation and vasoconstriction can be disrupted, leading to unopposed vasoconstriction. This imbalance may play a role in the pathophysiology of diseases such as hypertension and atherosclerosis. Arterial hypertension results in the exposure of the vascular endothelium to abnormal physical forces such as shear stress and stretch. As a result, endothelial cells from hypertensive animals and humans develop morphological and functional abnormalities.71-72 Abnormal vascular responses have been noted in experimental models of hypertension. Responses of vascular beds and isolated blood vessels to vasoconstrictor agonists generally are exaggerated,73 whereas relaxation after exposure to vasodilators such as nitroprusside and isoproterenol is decreased.74-76 It is apparent that abnormal endothelial function, with an imbalance of endothelium-dependent relaxations and contractions, could contribute to these abnormal vascular responses and the increased peripheral vascular resistance that is the central hemodynamic abnormality in hypertension.
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Tolwsetal
Studies in hypertensive Dahl salt-sensitive rats have shown that relaxations to agonists of EDRF are significantly impaired when compared with responses of nonnotensive Dahl salt-sensitive and salt-resistant rats.75 In this same model, endothelium-independent relaxations to sodium nitroprusside also were impaired, but to a lesser degree.75 Spontaneously hypertensive rats also have abnormalities in endothelium-dependent responses. In fact, vessels from spontaneously hypertensive rats also develop endothelium-dependent contractions in response to acetylcholine.77 Indomethacin normalized the reduced endothelium-dependent relaxations and eliminated endothelium-dependent contractions in the spontaneously hypertensive rat,77-78 suggesting that the primary defect in this form of hypertension is not defective release of EDRF/NO but simultaneous increased release of cyclooxygenase-dependent contracting factors. A recent study by Panza and coworkers79 demonstrated that endothelium-dependent relaxations, determined by noninvasive techniques, are abnormal in patients with hypertension. In this study, forearm vascular relaxation was normal in response to nitroprusside but reduced with acetylcholine. Whether these abnormalities are secondary to hypertensive changes or are part of the pathogenesis of hypertension, or both, is an important question that will need to be addressed by future studies. It has become apparent that injury to the endothelium and the response of vascular tissue to endothelial injury are important in the pathogenesis of atherosclerosis.80'81 At an early stage in the development of the atherosclerotic plaque, monocytes migrate into the intima. These cell types are capable of releasing oxygen radicals,82 which could decrease the half-life and bioactivity of EDRF/NO,83 thus removing a vasodilator influence on vessel tone. In addition, oxidized low density lipoproteins, known to be important in atherosclerosis, have been reported to directly inhibit endothelium-dependent relaxations,84'85 further contributing toward a vasospastic tendency. The endothelium can sense changes or abnormalities in blood flows and pressures and can participate in vascular responses not only by rapid generation of vasoactive mediators, such as NO or prostacyclin, but also by modulating long-term structural responses of the smooth muscle in the vascular wall. The role of the endothelium in vascular remodeling has been reviewed recently by Gibbons and Dzau.86 Growth factors released by endothelial cells, monocytes, and platelets most likely stimulate vascular smooth muscle cell proliferation as part of the development of atherosclerotic lesions81 or the response to hypertension. Because EDRF/NO and prostacyclin have been demonstrated to have antiproliferative effects on vascular smooth muscle cells,50-87-88 decreased production of these agents due to endothelial injury and dysfunction could result in enhanced proliferation and accelerated atherogenesis. Thus, endotheliumderived substances may regulate vascular remodeling
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and play a role in the development of vascular disease. Functionally, vasoconstrictor responses of atherosclerotic vessels from experimental animals tend to be exaggerated, although this varies depending on the agonist used and the animal species studied.8990 Aortic rings from hypercholesterolemic rabbits with atherosclerosis have depressed responses to agonists of endothelium-dependent vasodilation, such as acetylcholine and ADP.91"93 Monkeys with diet-induced atherosclerosis have impaired endothelium-dependent relaxations to acetylcholine and thrombin.94 Atherosclerotic human coronary arteries have depressed endotheliumdependent relaxations when studied in vitro,95-97 whereas normal human coronary arteries in vivo dilate in response to acetylcholine. In coronary vessels with atherosclerosis, acetylcholine actually induces vasoconstriction despite the fact that organic nitrates still cause vasodilation.98 This suggests that endothelium-dependent but not endothelium-independent relaxations are impaired. In patients with hypercholesterolemia, impaired endothelium-dependent and endothelium-independent relaxations can be demonstrated in forearm resistance vessels that are not, themselves, injured by atherosclerosis.99 Furthermore, injury to the endothelium from atherosclerosis may stimulate release of EDCF.5 Thus, in certain vascular beds, vasospasm associated with atherosclerosis may not be due only to deficient vasorelaxation but also to an unbalanced production of vasoconstrictive agonists. Conclusions An increasing body of evidence from experimental and clinical studies indicates that EDRFs and EDCFs play an important role in vascular physiology. It has become apparent that the balance of these factors may be a major determinant of systemic and regional hemodynamics. Through generally opposite effects on hemostatic mechanisms and cellular proliferation, contracting factors such as endothelin and relaxing factors such as NO also may be important determinants of the vascular response to injury in various disease states such as atherosclerosis and hypertension. It is clear that the vascular endothelium is a complex and dynamic organ. Understanding endothelial function in normal physiology and disease states is of potential clinical significance and should be the focus of future investigation. References 1. Moncada S, Palmer RMJ, Higgs EA The discovery of nitnc oxide as the endogenous nitrovasodilator. Hypertension 1988; 12.365-372 2. Vane JR, Anggard EE, Botting RM Regulatory functions of the vascular endothelium. N Engi J Med 1990,323:27-36 3. Moncada S, Herman AG, Higgs EA, Vale C: Differential formation of prostacyclin (PGX or PGI2) by layers of the arterial wall- An explanation for the anti-thrombotic properties of vascular endothelium. Thromb Res 1977,11:323-344 4. Furchgott RF, Zawadzkj JV The obligatory role of endothelial cells in the relaxation of arterial smooth muscle by acetylcholine. Nature 198O;299.373-376
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5. Luscher T: The endothebum, target and promoter of hypertension' Hypertension 1990;15:482-485 6. Moncada S, Palmer RMJ, Higgs EA: Generation of prostacychn and endothehum-derived relaxing factor from endothehal cells, in Jalles G, Legrand JY, Nurden A (eds): Biology and Pathology of Platelet-Vessel Wall Interactions
London,
Academic Press, 1986, pp 289-304 7. Vanhoutte PM, Rubanyi GM, Miller VM, Houston DSModulation of vascular smooth muscle contraction by endothelium. Annu Rev Physiol 1986;48:307-320 8 Hutchinson PJA, Pahner RMJ, Moncada S: Comparative pharmacology of EDRF and nitric oxide on vascular strips. Eur J Pharmacol 1987;141:445-451 9. Palmer RMJ, Fcrrigc JAG, Moncada S: Nitric oxide release accounts for the biologic activity of endothehum-derived relaxing factor Nature 1987;327524-526 10. Amezcua JL, Dusting GJ, Pahner RMJ, Moncada S: Acetylcholine induces vasodilatation in the rabbit isolated heart through release of nitric oxide, the endogenous nitrovasodilator. BrJ Pharmacol 1988,95:830-834 11 Palmer RMJ, Ashton DS, Moncada S: Vascular endothelial cells synthesize nitnc oxide from L-arginine. Nature 1988;333664-666 12. Palmer RMJ, Rees DD, Ashton DS, Moncada S- L-Arginine is the physiologic precursor for the formation of nitric oxide in endothelium-dependent relaxation. Biochem Biophys Res Commun 1988;153:1251-1256 13 Palmer RMJ, Moncada S: A novel citrulline-forming enzyme implicated in the formation of nitric oxide by vascular endothelial cells. Biochem Biophys Res Commun 1989;158348-352 14. Nathan CF, Stuehr DJ: Does endothelium-denved nitric oxide have a role in cytokine-induced hypotension' / Natl Cancer Inst 1990;82:726-728 15. Feletou M, Vanhoutte PM: Endothelium-dependent hyperpolarization of canine coronary smooth muscle BrJ Pharmacol 1988,93:515-524 16. Tare M, Parkington HC, Coleman HA, Neild TO, Dusting GJ. Hyperpolarization and relaxation of arterial smooth muscle caused by nitric oxide derived from the endothelium Nature 1990;34669-71 17. Stuehr DJ, Marietta MA- Mammalian nitrate biosynthesis: Mouse macrophages produce nitrite and nitrate in response to Eschenchia colx lipopolysaccharide. Proc NatlAcad Sci U S A 1985;82:7738-7742 18. Curran RD, Billiar TR, Stuehr DJ, Hofmann K, Simmons RL. Hepatocytes produce nitrogen oxides from L-arginine in response to inflammatory products of Kupffer cells. / Exp Med 1989;1701769-1774 19. Amber IJ, Hibbs JB Jr, Taintor RR, Vavrin Z- Cytokines induce an L-arginine-dependent effector system in nonmacrophage cells. / Leukoc Biol 1988;44:58-65 20. Kilbourn RG, Belloni P: Endothelial cell production of nitrogen oxides in response to interferon-gamma in combination with tumor necrosis factor, interleukin-1, or endotoxin J Natl Cancer Inst 1990;82:772-776 21. Hibbs JB Jr, Taintor RR, Vavnn Z: Macrophage cytotoxicity: Role for L-arginine deiminase and unino nitrogen oxidation to nitrite. Science 1987,23:473-476 22. Beasley D- Interleukin 1 and endotoxin activate soluble guanylate cydase in vascular smooth muscle. Am J Physiol 1990;259:R38-R44 23. Kilbourn RG, Gross SS, Jubran A, Adams J, Griffith OW, Levi R, Lodato RF: /v^-methyl L-arginine inhibits tumor necrosis factor-induced hypotension' Implications for the involvement of nitric oxide. Proc Natl Acad Sci U S A 1990;87-3629-3632 24. Shultz P, Sweeney C, Tayeh M, Marietta M, Raij L: Activated rat mesangial cells (MC) synthesize nitnc oxide (NO) from L-arginine which results in autocrine increases in cGMP (abstract). J Am Soc Nephrol 1990;l:731 25. Murad F, Arnold WF, Mittal CK, Braughler JM: Properties and regulation of guanylate cyclase and some proposed
functions for cyclic GMP. Adv Cyclic Nucleoade Res 1979;11 175-204 26. Murad F, Mittal CK, Arnold WP, Katsuki S, Kimura H: Guanylate cyclase: Activation of azide, nitro compounds, nitric oxide and hydroxyl radical and inhibition by hemoglobin and myoglobin./ldv Cyclic Nucleoade Res 1978;9:145-158 27. Rappaport RM, Murad F: Agonist-induced endotheliumdependent relaxation m rat thoracic aorta may be mediated through cGMP Circ Res 1983^2 352-357 28. Myers PR, Minor RL, Guerra R, Minor RL Jr, Guerra R Jr, Bates JN, Harrison DG: Vasorelaxant properties of the endothehum-derived relaxing factor more closely resemble 5-nitrosocysteine than nitric oxide Nature 1990;345:161-163 29 Tohns JP, Palmer RMJ, Moncada S, Raij L: Role of endothelium-derived relaxing factor in regulation of renal hemodynamic responses Am J Physiol 1990;258H655-H662 30. Rees DD, Palmer RMJ, Moncada S: Role of endothehumderived nitnc oxide in the regulation of blood pressure. Proc Natl Acad Sci USA 1989;86:3375-3378 31. Tohns JP, Raij L- Effects of ammo acid infusion on renal hemodynamics. Role of endothehum-derived relaxing factor. Hypertension 1991,17.1045-1051 32. Radermacher J, Forstermann U, Frolich JC: Endothehumdenved relaxing factor influences renal vascular resistance. Am J Physiol 1990,259:F9-F17 33. Lahera V, Salom MG, Fiksen-Olsen MJ, Raij L, Romero JO Effects of A/°-monomethyl-L-argmine and L-arginine on acetylcholine renal response. Hypertension 1990;15:659-663 34. Marsden PA, Brock TA, Ballerman BJ Glomenjlar endothelial cells respond to calcium-mobilizing agonists with release of EDRF. Am J Physiol 1990;258:F1295-F1303 35. Shultz PJ, Schorer AE, Ray L Effects of endothehumderived relaxing factor and nitric oxide on rat mesangial cells Am J Physiol 1990;258:F162-F167 36. Vidal-Ragout M, Romero JC, Vanhoutte PM. Endothehumdenved relaxing factor inhibits renin release. Eur J Pharmacol 1988;149-4O1-4O2 37 Brashers VL, Peach MJ, Rose CE' Augmentation of hypoxic pulmonary vasoconstnction in the isolated perfused rat lung by in vitro antagonists of endothelium-dependent relaxation. JChn Invest 1988;82:1495-15O2 38. Archer SL, Tohns JP, Raij L, Weir EK: Hypoxic pulmonary vasoconstnction is enhanced by inhibition of the synthesis of an endothelium derived relaxing factor. Biochem Biophys Res Commun 1989;164:1198-1205 39 Crawley DE, Liu SF, Evans TW, Barnes PJ Inhibitory role of endothelium-denved relaxing factor in rat and human pulmonary artenes. BrJ Pharmacol 1990;101 166-170 40. Gardiner SM, Compton AM, Bennett T, Palmer RMJ, Moncada S- Control of regional blood flow by endotheliumderived nitnc oxide. Hypertension 1990;15486-492 41 Vallance P, Collier J, Moncada S: Effects of endotheliumderived nitnc oxide on peripheral arteriolar tone in man Lancet 1989,2.997-1000 42. Wei EP, Kontos HA: H2O2 and endothelium-dependent cerebral artenolar dilation: Implications for the identity of endothelium-denved relaxing factor generated by acetylcholine. Hypertension 1990^16:162-169 43. Forstermann U, Mugge A, Alheid U, Haverich A, Frolich JC. Selective attenuation of endothehum-mediated vasodilation in atherosclerotic human coronary artenes. Circ Res 1988;62: 185-190 44. Drexler H, Zeiher AM, Wollschlager H, Meinertz T, Just H, Bonzel T: Flow-dependent coronary artery dilatation in humans. Circulation 1989;80:466-474 45. Radomski MW, Palmer RMJ, Moncada S: Comparative pharmacology of endothelium-derived relaxing factor, nitnc oxide and prostacychn in platelets. BrJ Pharmacol 1987;92: 181-187 46 Radomski MW, Palmer RMJ, Moncada S. Endogenous nitnc oxide inhibits human platelet adhesion to vascular endothelium. Lancet 1987,2:1057-1058
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Tolins et al 47. Radomski MW, Palmer RMJ, Moncada S- An L-argintne/ nitnc oxide pathway present in human platelets regulates aggregation. Proc Natl Acad Sci U S A 199O;87:5193-5197 48. Garg UC, Hassid A; Nitnc oxide-generating vasodilators and 8-bromo-cychc guanosme monophosphate inhibit mitogenesis and proliferation of cultured rat vascular smooth muscle cells. J Chn Invest 1989;83 1774-1777 49. Garg UC, Hassid A: Inhibition of rat mesangial cell mitogenesis by nitric oxide-generating vasodilators. Am J Physiol 1989,257:F60-F66 50 Shultz PJ, Ruble D, Ray L: S-nitroso-zi-acetylpenicillamine (SNAP) inhibits mitogen-induced mesangial cell proliferation (abstract). Kidney Int 1990;37.203 51. Miller VM, Vanhoutte PM: Endothehum-dependent contractions to arachidonic acid are mediated by products of cyclooxygenase in carune veins. Am J Physiol 1985.248.H432-H437 52. Shirahase H, Usui H, Kurahashi K, Fujwara M, Fukui K; Possible role of endothehal thromboxane A2 m the resting tone and contractile responses to acetylchohne and arachidonic acid in canine cerebral arteries. / Cardwvasc Pharmacol 1987;10:517-522 53 Kato T, Iwama Y, Okumura K, Hashimoto H, Ito T, Satake T. Prostaglandin H2 may be the endothehum-derived contracting factor released by acetylchohne in the aorta of the rat. Hypertension 1990;15:475-481 54 Katusic ZS, Vanhoutte PM: Superoxide anion is an endotheuum-denved contracting factor. Am J Physiol 1989, 257:H33-H37 55. Dzau VJ- Significance of the vascular renin-angiotensm pathway. Hypertension 1986,8:553-559 56. Hickey KA, Rubanyi G, Paul RJ, Highsmith RF: Characterization of a coronary vasoconstrictor produced by cultured endothehal cells. Am J Physiol 1985;248:C550-C556 57. Yanagisawa M, Kurihara H, Kunura S, Mitsue Y, Kobayashi M, Wantanabe TX, Masaki T: A novel potent vasoconstrictor peptide produced by vascular endothehal cells. Nature 1988; 332.411-415 58. Boulanger C, Luscher TF- Release of endothelin from the porcine aorta. / Chn Invest 1990,85:587-590 59 Martin ER, Marsden PA, Brenner BM, Ballerman BJ: Identification and characterization of endothelin binding sites in rat renal papillary and glomerular membranes. Bwchem Biophys Res Commun 1989,162.130-137 60 Cernacek P, Stewart DJ: Immunoreactive endothelin in human plasma. Marked elevations in patients in cardiogenic shock. Bwchem Biophys Res Commun 1989;161.562-567 61. Kohno M, Yasunan K, Murakawa KI, Yokokawa K, Hono T, Kunhara N, Takeda T: Plasma immunoreactive endothelin in essential hypertension. Am J Med 1990;88:614-618 62. Kohno M, Murakawa KI, Yasunan K, Yokokawa K, Horio T, Kunhara N, Takeda T: Prolonged blood pressure elevation after endothelin administration in bilaterally nephrectomized rats. Metabolism 1989,38712-713 63 King AJ, Brenner BM, Anderson S- Endothelin: A potent renal and systemic vasoconstrictor peptide. Am J Physiol 1989;256:F1051-F1058 64. Badr KF, Murray JJ, Breyer M, Takahashi K, Inagami T, Harris RC: Mesangial cell, glomerular and renal vascular responses to endothelin in the rat kidney / Chn Invest 1989;83:336-342 65. Pernow J, Boutier JF, Franco-Cerecedia A, LaCroix JS, Matran R, Lundberg JM: Potent selective vasoconstnctor effects of endothelin in the pig kidney in vivo Acta Physiol Scand 1988;134:573-574 66. Fukada Y, Hirata Y, Yoshima H, Takatsugu K, Koliayashi Y, Yanagisawa M, Masaki T: Endothelin is a potent secretagogue for atnal natnuretic peptide in cultured rat atnal myocytes. Biochem Biophys Res Commun 1988;155167-172 67. Miller WL, Redfield MM, Burnett JC J r Integrated cardiac, renal, and endocnne actions of endothelin. / Chn Invest 1989;83:317-320 68. Kon V, Yoshioka T, Fogo A, Kon V, Ichikawa I: Glomerular actions of endothelin in vivo. / Chn Invest 1989;83:1762-1767
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69. Simonson MS, Wann S, Mene P, Dubyak GR, Kester M, Nakazatoy Y, Sedor J Jr, Dunn MJ Endothelin stimulates phosphohpase C, Na + /H + exchange, c-fos expression, and mitogenesis in rat mesangial cells. J Chn Invest 1989,83: 708-712 70. DeNucci G, Thomas R, D'Orleans-Juste P, Antunes E, Walder C, Warner TO, Vane JR: Pressor effects of circulating endothelin are limited by its removal in the pulmonary circulation and by the release of prostacyclin and endothelium-derived relaxing factor Proc Natl Acad Sci USA 1988; 85:9797-9800 71 Haudenschild CC, Prescott MF, Chobanian AV- Effects of hypertension and its reversal on aortic intima lesions of the rat. Hypertension 1979,2:33-44 72. Huttner I, Gabbiani G: Vascular endothelium in hypertension, in Genest J, Kuchel O, Hamet P (eds): Hypertension. New York, McGraw-Hill Book Co., 1983, pp 473-488 73. Vanhoutte PM, Luscher TF: Penpheral mechanisms in cardiovascular regulation. Transmitters, receptors and the endothelium, in Taraa RC, Zanchetti A (eds): Handbook of Hypertension. Volume 8, Physiology and Pathophyswlogy of Hypertension—Regulatory Mechanisms. Amsterdam, Elsevier Science Publishers, 1987, pp 96-123 74. Cohen ML, Berkowitz BA: Decreased vascular relaxation in hypertension./PharmacolExp Ther 1976;196396-406 75 Luscher TF, Ray L, Vanhoutte PM: Endothehum-dependent responses in normotensive and hypertensive Dahl rats Hypertension 1987;9 157-163 76. Konishi M, Su C Role of endothelium in dilator responses of spontaneously hypertensive rat artenes. Hypertension 1983^5: 881-885 77. Luscher TF, Vanhoutte PM: Endothehum-dependent contractions to acetylcholine in the aorta of the spontaneously hypertensive rat Hypertension 1986;8:344-348 78 Luscher TF, Romero JC, Vanhoutte PM- Bioassay of endothehum-derived vasoactive substances in the aorta of normotensive and spontaneously hypertensive rats. / Hypertens 1986;49(suppl 6).81-83 79. Panza JA, Quyumi AA, Brush JE Jr, Epstein SE: Abnormal endothehum-dependent vascular relaxation in patients with essential hypertension. New Engl J Med 1990;323 22-27 80. Ross R, Harker L: Hyperlipidemia and atherosclerosis: Chronic hyperlipidemia initiates and maintains lesions by endothehal cell desquamatton and lipid accumulation Science 1976;193:1094-1100 81. Ross R: The pathogenesis of atherosclerosis An update. N Engl J Med 1986;314-488-500 82. Davies PF- Biology of disease: Vascular cell interactions with special reference to the pathogenesis of atherosclerosis Lab Invest 1986^5:5-24 83. Gryglewski RJ, Palmer RMJ, Moncada S. Superoxide anion is involved in the breakdown of endothehum-derived vascular relaxing factor. Nature 1986^320454-456 84. Andrews HE, Bruckdorfer KR, Dunn RC, Jacobs M: Lowdensity hpoproteins inhibit endothehum-dependent relaxation in rabbit aorta. Nature 1987,327-237-239 85. Simon BC, Cunningham LD, Cohen RA: Oxidized low density hpo-proteins cause contraction and inhibit endothelium-dependent relaxation in the pig coronary artery / Chn Invest 1990;86:75-79 86. Gibbons GH, Dzau VJ: Endothehal function in vascular remodeling, in Warren JB (ed): The Endothehum New York, Wiley-Liss, Inc, 1990, pp 91-93 87. Garg UC, Hassid A: Nitnc oxide-generating vasodilators and 8-bromo-cyclic guanosine monophosphate inhibit mitogenesis and proliferation of cultured rat vascular smooth muscle cells. / Chn Invest 1989;83:1774-1777 88. Mene P, Dunn MJ: Prostaglandins and rat glomerular mesangial cell proliferation. Kidney Int 1990;37-1256-1262 89. Heistad DD, Armstrong ML, Marcus ML, Piegors DJ, Mark AL: Augmented responses to vasoconstrictor stimuli in hypercholesterolemic and atherosclerotic monkeys. Ctrc Res 1984,54:711-718
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90. Henry PD, Yokayama M: Supersensitrvity of atherosclerotic rabbit aorta to ergonovine: Mediation by a serotonergic mechanism. / Chn Invest 1980;66 306-313 91. Habib JB, BossaUer C, WeUs S, Williams C, Mornsett JD, Henry PD: Preservation of endotheuum-dependent vascular relaxation in cholesterol-fed rabbit by treatment with the calcium blocker PN200110. Circ Res 1986^8:305-309 92. Verbeuren TJ, Jordaens FH, Zonnekeyn LL, Van Hoole CE, Coene MC, Herman AG Effect of hypercholesterolemia on vascular reactivity in the rabbit I Endothehum-dependent and endothelium-independent relaxations in isolated arteries of control and hypercholesterolemic rabbits. Circ Res 1986; 58 552-564 93. Verbeuren TJ, Coene MC, Jordaens FH, Van Hove CE, Zonnekeyn LL, Herman AG. Effect of hypercholesterolemia in vascular reactivity in the rabbit: II Influence of treatment with dipyndamole on endothelium-dependent and endothelium-independent responses in isolated aortas of control and hypercholesterolemic rabbits. Circ Res 1986^9:496-504 94 Harrison DG, Armstrong ML, Freimann PC, Heistad DD. Restoration of endothelium-dependent relaxation by dietary treatment of atherosclerosis. / Chn Invest 1987;8O.18O8-1811
95. Ginsburg R, Bristow MR, Davis K, Dibiase A, Bilungham ME: Quantitative pharmacologic responses of normal and atherosclerotic isolated human epicardial coronary arteries Circulation 1984;69:430-440 96. Ginsburg R, Zera PH- Endothelial relaxant factor in the human epicardial coronary artery (abstract). Circulation 1986;70(suppl 11)11-122 97. Chester AH, OTMeil GS, Moncada S, Tadjkarimi S, Yacoub MH. Low basal and stimulated release of nitnc oxide in atherosclerotic epicardial coronary arteries. Lancet 1990,336: 897-900 98. Ludmer PL, Sehvyn AP, Shook TL, Wayne RR, Mudge GH, Alexander RW, Ganz P: Paradoxical vasoconstnetion induced by acetylcholine in atherosclerotic coronary arteries. N EnglJ Med 1986;315 1046-1051 99. Creager MA, Cooke JP, Mendelsohn ME, Gallagher SJ, Coleman SM, Loscalzo J, Dzau V' Impaired vasodilation of forearm resistance vessels in hypercholesterolemic humans / Chn Invest 1990;86:228-234 KEY WORDS
• endothelium • vascular endothelium • nitric
oxide
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Role of endothelium-derived relaxing factor in regulation of vascular tone and remodeling. Update on humoral regulation of vascular tone. J P Tolins, P J Shultz and L Raij Hypertension. 1991;17:909-916 doi: 10.1161/01.HYP.17.6.909 Hypertension is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231 Copyright © 1991 American Heart Association, Inc. All rights reserved. Print ISSN: 0194-911X. Online ISSN: 1524-4563
The online version of this article, along with updated information and services, is located on the World Wide Web at: http://hyper.ahajournals.org/content/17/6_Pt_2/909
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Role of Endothelium-Derived Relaxing Factor in Regulation of Vascular Tone and Remodeling Update on Humoral Regulation of Vascular Tone Jonathan P. Tolins, Pamela J. Shultz, and Leopoldo Raij In addition to preserving the permselectivity of the vascular wall and providing an antithrombogenic surface, the vascular endothelium contributes importantly to the regulation of vasomotor tone. Indeed, the endothelium participates in the conversion of angiotensin I to angiotensin II; the enzymatic inactivation of several plasma constituents such as bradykinin, norepinephrine, serotonin, and ADP; and the synthesis and release of vasodilator substances such as prostacyclin and the recently discovered endothelium-derived relaxing factor (EDRF). The diffusible EDRF released from the endothelium is nitric oxide or a substance closely related to it such as nitrosothiol. The endothelium also synthesizes and releases vasoconstrictive factors, including products derived from arachidonic acid metabolism and the recently discovered peptide endothelin. An increasing body of evidence from experimental and clinical studies indicates that EDRF and endothelium-derived contracting factors play an important role in vascular physiology and pathology. It has become apparent that the balance of these factors may be a major determinant of systemic and regional hemodynamics. Moreover, through generally opposite effects on growth-related vascular changes, contracting factors such as endothelin and relaxing factors such as EDRF also may be important determinants of the vascular response to injury in various disease states such as atherosclerosis and hypertension. It is clear that the vascular endothelium is a complex and dynamic organ. Understanding endothelium function in normal physiology and disease states is of potential clinical importance and should be the focus of future investigation. {Hypertension 1991;17:909-916)
H
istorically, the vascular endothelium was considered to be a structurally and metabolically simple cellular lining to blood vessels that was important only insofar as it contributed to regulation of vascular permeability and hemostasis. More recently, it has become overwhelmingly apparent that the endothelium represents a complex, dynamic organ with diverse functions, including the synthesis and release of vasoactive agents that play a role in modulating vascular tone.1-2 Moncada et al3 first demonstrated that vascular endothelial cells produce prostacyclin, a vasodilator prostaglandin. In 1980, Furchgott and Zawadzki4 demonstrated that vascular relaxation induced by the muscarinic agent acetylcholine was dependent on the presence of a functionally intact endothelium and From the Department of Medicine, Veterans Administration Medical Center and the School of Medicine, University of Minnesota, Minneapolis, Minn. Supported by funds from the Veterans Administration. Address for correspondence: Leopoldo Raij, MD, Renal Section 111 J, Veterans Administration Medical Center, One Veterans Drive, Minneapolis, MN 55417
postulated the release by endotheliaJ cells of a labile factor termed endothelium-derived relaxing factor (EDRF). Subsequent work in this area has made it clear that control of vascular function by the endothelium is quite complex and involves the synthesis and release not only of vasodilator substances such as prostacyclin and EDRF, but of vasoconstrictor substances such as endothelin and other less well-characterized endothelium-derived contracting factors (EDCFs) as well.5 The role of these substances in normal vascular physiology and disease states is the subject of this review. Endothelium-Derived Relaxing Factor
EDRF first was described as a labile, diffusible substance released by the endothelium in response to acetylcholine.4 Since this initial study, a variety of agonists, including thrombin, bradykinin, serotonin, ADP, and the calcium ionophore A23187, have been shown to induce release of EDRF from the endothelium of various vascular beds and endothelial cells grown in culture.1-2^,? A large body of evidence,
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Vol 17, No 6, Part 2 June 1991 Vascular Smooth Muscle or Mesangial Cell
Endothelial Cell
GTP
l-argininp Acetykholine Thrombin ADP Brady kin In Serotonin Adenosine A23187
NO L-NMMA
NO
(+) ^
Guanylate cyclase
(or nitrosothiol) cEMP
Relaxation
I
FIGURE 1.
Schematic of pos-
tulated metabolic pathway by which agonist stimulation of endothelial cells results in vascular smooth muscle cell relaxation. L-NMMA, Nc-monomethyl L-arginine; NO, nitnc oxide; cGMP, cyclic GMP.
Inhibition of Proliferation
including comparative pharmacological studies and direct measurements, supports the hypothesis that EDRF activity is due to release of nitric oxide (NO) by stimulated endothelial cells.8-10 Palmer et al11-13 demonstrated that the EDRF NO originates from the terminal guanidino nitrogen atom of the amino acid L-arginine. The characteristics of the NO synthase enzyme involved in this reaction in endothelial cells have been reviewed recently by Nathan and Stuehr.14 In endothelial cells, this enzyme is soluble, calcium- and NADPH-dependent, and can be inhibited by L-arginine derivatives such as A^-monomethyl L-arginine (LNMMA) or A^-nitro L-arginine.12-14 It is a constitutive enzyme, in that it requires no induction and synthesizes NO within seconds of agonist stimulation of the endothelial cell.14 The active product, NO, has a short half-life and decomposes rapidly to form mixtures of nitrite and nitrate in oxygenated solutions. The postulated metabolic pathway by which agonist stimulation of endothelial cells results in vascular smooth muscle cell relaxation is shown schematically in Figure 1. It should be kept in mind that other less well-characterized factors, such as endothelium-derived hyperpolarizing factor,15 may be released by agonist-stimulated endothelium and result in vasodilation as well. In this regard, Tare and coworkers16 have demonstrated recently that endothelium-derived NO can contribute to the hyperpolarization of vascular smooth muscle cells in response to acetylcholine. Thus, it is likely that NO is responsible for the majority of observed EDRF activity, and this substance will be the focus of the current review. It recently has become apparent that there is another subtype of NO synthase enzyme, designated as type I by Nathan and Stuehr.14 This enzyme has been found in macrophages,17 hepatocytes,18 and tumor cells19 and must be induced by cytokines such as interleukin-1, interferon gamma, and tumor necrosis factor or by microbial products, such as endotoxin.
A similar enzyme also may be present in endothelial cells20; however, the positive identification of an inducible NO synthase in endothelium remains to be demonstrated. Induction of this enzyme, and subsequent generation of NO, requires 4-18 hours of exposure to the immunostimulator and is dependent on protein synthesis. The amount of NO generated by these cell types is much larger than that generated by the NO synthase involved in EDRF responses and appears to mediate tumor cell cytostasis and macrophage-mediated bacterial killing.21 The NO generated by this system also may have vasodilator effects, because both endotoxin and interleukin-1 have been shown to inhibit contraction of and increase cyclic GMP (cGMP) levels in rat aortic rings in vitro,22 and LNMMA has been shown to inhibit the hypotension associated with intravenous infusion of tumor necrosis factor in dogs.23 It is likely that this system may be present within the glomerulus as well, because a preliminary report suggested that rat mesangial cells also can generate NO and demonstrate increased intracellular cGMP levels after exposure to endotoxin or interferon gamma.24 Both the NO generation and cGMP changes were prevented by LNMMA. Thus, it is possible that during glomerular inflammation or endotoxemia, NO may participate in the modulation of glomerular function. Murad et al25 reported that in vascular smooth muscle there is a positive correlation between an increase in cGMP levels and vascular relaxation. Subsequent work has shown that NO, as well as other nitrovasodilators, stimulates increases in cGMP levels in smooth muscle by activating soluble guanylate cyclase25-26 and that vascular relaxation is associated with an increase in tissue cGMP levels.27 Thus, it is apparent that NO released by stimulated vascular endothelium activates soluble guanylate cyclase in adjacent vascular smooth muscle cells, inducing a rise in intracellular cGMP levels and subsequent vascular
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Tolins et al
relaxation (Figure 1). The exact chemical form in which the endothelium releases NO remains controversial; more recent studies have suggested that endothelium-derived NO may be incorporated into a nitrosothiol.28 Uptake or degradation of this nitrosothiol carrier molecule at the vascular smooth muscle cell membrane would release NO and lead to subsequent stimulation of guanylate cyclase. Resolution of this issue awaits further study. The role of EDRF/NO in normal physiology has begun to be explored only recently. Investigation in this area has been facilitated by the development of EDRF/NO synthesis inhibitors that can be administered in vivo, such as LNMMA. In the rat29 and the rabbit,30 systemic bolus administration of LNMMA results in a marked and long-lasting increase in blood pressure, and this hypertensive effect is reversed by administration of L-arginine, the endogenous precursor to NO. This suggested that there is a basal rate of EDRF/NO synthesis by vascular endothelial cells that may be important in the modulation of systemic blood pressure. Tolins et al29 administered LNMMA to rats by continuous intravenous infusion and reported that arterial blood pressure and renal vascular resistance were increased and that the normal hypotensive and renal vasodilator responses to acetylcholine were prevented. Furthermore, they demonstrated that the vasodilator effects of acetylcholine were associated with increases in urinary cGMP excretion, a result not observed with endotheliumindependent vasodilators. They concluded that in vivo responses to endothelium-dependent vasodilators are due to stimulation of endogenous EDRF/NO release by vascular endothelium and that these responses are most likely mediated by changes in cGMP levels in vascular tissue. These same investigators infused LNMMA into the renal artery of the rat and demonstrated a decrease in glomerular filtration rate, marked renal vasoconstriction, and a rise in filtration fraction, suggesting an important role for EDRF/NO synthesis in the regulation of basal renal hemodynamics.31 The importance of EDRF/NO in the regulation of renal hemodynamic responses in vivo has been confirmed recently in the isolated perfused rat kidney32 and in the dog.33 Endothelial cells cultured from bovine glomeruli have been reported to be capable of producing EDRF.34 Within the glomerulus, the endothelial and mesangial cells are in close proximity, and it is possible that EDRF is an important mediator of endothelial-mesangial cell communication and thus of renal function. EDRF released from cultured endothelial cells, as well as exogenously applied NO, increases cGMP levels in cultured rat glomerular mesangial cells.35 NO also attenuates the mesangial cell contractile response to angiotensin II. Others have shown that EDRF can inhibit renin release from juxtaglomerular cells and therefore can limit the generation of angiotensin II.36 Because the state of mesangial contraction could affect the ultrafiltration coefficient (Kf) by altering the surface area
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available for glomerular filtration, this may represent another mechanism, distinct from direct hemodynamic effects, by which EDRF could modulate glomerular function. Recent studies have suggested that EDRF plays a role in the regulation of vascular tone in the pulmonary circulation.37'38 Brashers et al37 demonstrated that NO, bradykinin, and acetylcholine cause vasodilation in isolated, perfused lungs during hypoxic pulmonary vasoconstriction and conversely, that hypoxic vasoconstriction is enhanced by nonspecific inhibitors of EDRF action. Archer and coworkers38 reported that inhibition of EDRF/NO synthesis with LNMMA enhanced hypoxic vasoconstriction in the isolated perfused rat lung as well as in isolated pulmonary artery rings. In this same study, L-arginine rapidly reversed hypoxic vasoconstriction, especially when EDRF synthesis had been inhibited previously with LNMMA. They concluded that EDRF/NO synthesis is enhanced during hypoxia and acts as a balancing factor, limiting the constrictor response. Similarly, recent observations by Crawley et al39 suggest that vasoconstriction of human pulmonary arteries is attenuated by NO release. Further evidence has accumulated that EDRF/NO contributes to the control of resting tone in diverse vascular beds. Gardiner et al40 infused LNMMA intravenously into rats and noted a dose-dependent, sustained vasoconstriction in the carotid, mesenteric, renal, and hindquarters vascular beds. Vallance et al41 infused LNMMA into the brachial artery of human volunteers and noted a 50% fall in basal blood flow rate and inhibition of the vasodilator response to acetylcholine, suggesting that EDRF/NO contributes to control of basal peripheral arterial blood flow in humans. EDRF also has been reported to be important in modulating hemodynamic responses in the cerebral42 and coronary43-44 circulations. In addition to effects on vascular tone, EDRF/NO influences components of the blood coagulation system and cellular proliferative responses. In vessels with normal endothelium, thrombin, as well as serotonin and ADP released by aggregating platelets, binds to specific receptors and induces EDRF release.2-7 EDRF/NO inhibits platelet aggregation.45 The adhesion of platelets to cultured endothelial cells in vitro is decreased by the EDRF agonist bradykinin or exogenous NO.46 Furthermore, platelets themselves contain an NO synthase that can generate NO and increase platelet cGMP levels in response to activating stimuli.47 Therefore, acting synergistically with prostacylcin, NO may participate in the local regulation of coagulation responses. NO also has been shown to inhibit vascular smooth muscle and mesangial cell proliferation induced by serum- or platelet-derived growth factor in vitro48"50 and so could act as a limiting factor in vascular and glomerular responses to injury. Whether this antiproliferative effect is mediated by increases in cGMP is currently unclear.50
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Endothelium-Derived Contracting Factors
Since the discovery of EDRF, it has become clear that endothelial cells also release several substances that mediate contraction of vascular smooth muscle.5 Possible candidates for EDCFs include the cyclooxygenase products thromboxane A251-52 and prostaglandin H253 and superoxide anion.54 Vascular tissue also may have a locally active renin-angiotensin system that is capable of generating the vasoconstrictor angiotensin II.55 Furthermore, the vascular endothelium recently has been demonstrated to release endothelin, a 21-amino acid peptide with potent vasoconstrictive properties.56-57 Freshly isolated porcine arteries with intact endothelium release endothelin under basal conditions, and thrombin significantly enhances this release.5* Binding sites for endothelin have been described in blood vessels and in renal tissues.59 Recently, a radioimmunoassay for measurement of endothelin in plasma has been developed that should greatly facilitate further investigation into the role of this novel peptide in vivo. Preliminary reports using this radioimmunoassay have found detectable circulating levels of endothelin in normal humans, with increased levels noted in patients with essential hypertension and patients with renal insufficiency.60-61 In nephrectomized rats, the plasma clearance of endothelin is prolonged, and exogenously administered endothelin induces exaggerated responses, indicating that the kidney may play a role in the elimination of endothelin.62 It appears that, unlike EDRF, endothelin can circulate in the bloodstream and therefore may be released from one vascular bed and have vasoconstrictive effects in distant parts of the circulation. Recent experimental studies have focused on the systemic and renal hemodynamic effects of exogenously administered endothelin. When administered to "experimental animals" in pharmacological doses, endothelin induces a transient vasodilation followed by a marked and prolonged vasoconstriction, resulting in elevation of blood pressure and reduction in renal bloodflow.63-64The renal vascular bed appears to be 10-fold more sensitive to vasoconstriction by endothelin than are the coronary, femoral, or bronchial vascular beds.65 Endothelin also has been shown to stimulate atrial natriuretic peptide release66-67 and to increase plasma renin activity and aldosterone levels.67 The effect of endothelin on the glomerular microcirculation has been investigated with the use of micropuncture techniques. In this setting, endothelin has been shown to reduce single-nephron glomerular filtration rate and glomerular plasma flow by 3050%.64 Both afferent and efferent arteriolar resistances increase with endothelin64-68 and Kt has been reported to be reduced64 or unchanged.68 Several studies have investigated the effects of endothelin on glomerular mesangial cells in culture.64-69 In contrast to EDRF, endothelin stimulates mesangial cell proliferation especially when added in the presence of
low concentrations of serum.69 Endothelin stimulates rapidincreasesinmesangialcytosoliccalcium,phosphoinositide turnover, and intracellular alkalinization similar to many other vasoconstrictors and growth factors.69 In this regard, endothelin would fit the apparent pattern observed in studies of mesangial cells in which vasodilators (EDRF/NO, prostacyclin) are antiproliferative, whereas vasoconstrictors (angiotensin II, platelet-derived growth factor, endothelin) are pro-proliferatfve. Whether glomerular endothelial cells can synthesize endothelin remains to be determined, but because endothelin circulates within the bloodstream, the glomerulus could be exposed to this agent from various sites within the circulation. Thus, it appears that EDRF and endothelin exert a number of opposite effects on the glomerulus and mesangial cells, suggesting that they may have counterbalancing effects on glomerular function. Role of the Endothelium in Disease States
From the above discussion it is apparent that the control of vascular tone by the endothelium has proved to be much more complex than previously suspected and would appear to reflect a balance between locally acting mediators such as EDRF/NO and the various EDCFs, as well as circulating endothelium-derived factors such as endothelin. Furthermore, the interaction of EDRF and endothelin is of potential importance in both normal physiology and disease states. Several agonists, such as thrombin and A23187, stimulate simultaneous release of EDRF/NO and endothelin.2 In addition, recent studies have demonstrated that thrombin-induced release of endothelin is potentiated when NO synthesis is inhibited by LNMMA,58 suggesting that NO may exert an inhibitory effect on endothelin synthesis. On the other hand, endothelin may stimulate the release of EDRF and prostacyclin.70 Thus, it can be seen that in disease states in which the endothelium is injured, the delicate balance between endothelium-mediated vasodilation and vasoconstriction can be disrupted, leading to unopposed vasoconstriction. This imbalance may play a role in the pathophysiology of diseases such as hypertension and atherosclerosis. Arterial hypertension results in the exposure of the vascular endothelium to abnormal physical forces such as shear stress and stretch. As a result, endothelial cells from hypertensive animals and humans develop morphological and functional abnormalities.71-72 Abnormal vascular responses have been noted in experimental models of hypertension. Responses of vascular beds and isolated blood vessels to vasoconstrictor agonists generally are exaggerated,73 whereas relaxation after exposure to vasodilators such as nitroprusside and isoproterenol is decreased.74-76 It is apparent that abnormal endothelial function, with an imbalance of endothelium-dependent relaxations and contractions, could contribute to these abnormal vascular responses and the increased peripheral vascular resistance that is the central hemodynamic abnormality in hypertension.
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Studies in hypertensive Dahl salt-sensitive rats have shown that relaxations to agonists of EDRF are significantly impaired when compared with responses of nonnotensive Dahl salt-sensitive and salt-resistant rats.75 In this same model, endothelium-independent relaxations to sodium nitroprusside also were impaired, but to a lesser degree.75 Spontaneously hypertensive rats also have abnormalities in endothelium-dependent responses. In fact, vessels from spontaneously hypertensive rats also develop endothelium-dependent contractions in response to acetylcholine.77 Indomethacin normalized the reduced endothelium-dependent relaxations and eliminated endothelium-dependent contractions in the spontaneously hypertensive rat,77-78 suggesting that the primary defect in this form of hypertension is not defective release of EDRF/NO but simultaneous increased release of cyclooxygenase-dependent contracting factors. A recent study by Panza and coworkers79 demonstrated that endothelium-dependent relaxations, determined by noninvasive techniques, are abnormal in patients with hypertension. In this study, forearm vascular relaxation was normal in response to nitroprusside but reduced with acetylcholine. Whether these abnormalities are secondary to hypertensive changes or are part of the pathogenesis of hypertension, or both, is an important question that will need to be addressed by future studies. It has become apparent that injury to the endothelium and the response of vascular tissue to endothelial injury are important in the pathogenesis of atherosclerosis.80'81 At an early stage in the development of the atherosclerotic plaque, monocytes migrate into the intima. These cell types are capable of releasing oxygen radicals,82 which could decrease the half-life and bioactivity of EDRF/NO,83 thus removing a vasodilator influence on vessel tone. In addition, oxidized low density lipoproteins, known to be important in atherosclerosis, have been reported to directly inhibit endothelium-dependent relaxations,84'85 further contributing toward a vasospastic tendency. The endothelium can sense changes or abnormalities in blood flows and pressures and can participate in vascular responses not only by rapid generation of vasoactive mediators, such as NO or prostacyclin, but also by modulating long-term structural responses of the smooth muscle in the vascular wall. The role of the endothelium in vascular remodeling has been reviewed recently by Gibbons and Dzau.86 Growth factors released by endothelial cells, monocytes, and platelets most likely stimulate vascular smooth muscle cell proliferation as part of the development of atherosclerotic lesions81 or the response to hypertension. Because EDRF/NO and prostacyclin have been demonstrated to have antiproliferative effects on vascular smooth muscle cells,50-87-88 decreased production of these agents due to endothelial injury and dysfunction could result in enhanced proliferation and accelerated atherogenesis. Thus, endotheliumderived substances may regulate vascular remodeling
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and play a role in the development of vascular disease. Functionally, vasoconstrictor responses of atherosclerotic vessels from experimental animals tend to be exaggerated, although this varies depending on the agonist used and the animal species studied.8990 Aortic rings from hypercholesterolemic rabbits with atherosclerosis have depressed responses to agonists of endothelium-dependent vasodilation, such as acetylcholine and ADP.91"93 Monkeys with diet-induced atherosclerosis have impaired endothelium-dependent relaxations to acetylcholine and thrombin.94 Atherosclerotic human coronary arteries have depressed endotheliumdependent relaxations when studied in vitro,95-97 whereas normal human coronary arteries in vivo dilate in response to acetylcholine. In coronary vessels with atherosclerosis, acetylcholine actually induces vasoconstriction despite the fact that organic nitrates still cause vasodilation.98 This suggests that endothelium-dependent but not endothelium-independent relaxations are impaired. In patients with hypercholesterolemia, impaired endothelium-dependent and endothelium-independent relaxations can be demonstrated in forearm resistance vessels that are not, themselves, injured by atherosclerosis.99 Furthermore, injury to the endothelium from atherosclerosis may stimulate release of EDCF.5 Thus, in certain vascular beds, vasospasm associated with atherosclerosis may not be due only to deficient vasorelaxation but also to an unbalanced production of vasoconstrictive agonists. Conclusions An increasing body of evidence from experimental and clinical studies indicates that EDRFs and EDCFs play an important role in vascular physiology. It has become apparent that the balance of these factors may be a major determinant of systemic and regional hemodynamics. Through generally opposite effects on hemostatic mechanisms and cellular proliferation, contracting factors such as endothelin and relaxing factors such as NO also may be important determinants of the vascular response to injury in various disease states such as atherosclerosis and hypertension. It is clear that the vascular endothelium is a complex and dynamic organ. Understanding endothelial function in normal physiology and disease states is of potential clinical significance and should be the focus of future investigation. References 1. Moncada S, Palmer RMJ, Higgs EA The discovery of nitnc oxide as the endogenous nitrovasodilator. Hypertension 1988; 12.365-372 2. Vane JR, Anggard EE, Botting RM Regulatory functions of the vascular endothelium. N Engi J Med 1990,323:27-36 3. Moncada S, Herman AG, Higgs EA, Vale C: Differential formation of prostacyclin (PGX or PGI2) by layers of the arterial wall- An explanation for the anti-thrombotic properties of vascular endothelium. Thromb Res 1977,11:323-344 4. Furchgott RF, Zawadzkj JV The obligatory role of endothelial cells in the relaxation of arterial smooth muscle by acetylcholine. Nature 198O;299.373-376
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5. Luscher T: The endothebum, target and promoter of hypertension' Hypertension 1990;15:482-485 6. Moncada S, Palmer RMJ, Higgs EA: Generation of prostacychn and endothehum-derived relaxing factor from endothehal cells, in Jalles G, Legrand JY, Nurden A (eds): Biology and Pathology of Platelet-Vessel Wall Interactions
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Academic Press, 1986, pp 289-304 7. Vanhoutte PM, Rubanyi GM, Miller VM, Houston DSModulation of vascular smooth muscle contraction by endothelium. Annu Rev Physiol 1986;48:307-320 8 Hutchinson PJA, Pahner RMJ, Moncada S: Comparative pharmacology of EDRF and nitric oxide on vascular strips. Eur J Pharmacol 1987;141:445-451 9. Palmer RMJ, Fcrrigc JAG, Moncada S: Nitric oxide release accounts for the biologic activity of endothehum-derived relaxing factor Nature 1987;327524-526 10. Amezcua JL, Dusting GJ, Pahner RMJ, Moncada S: Acetylcholine induces vasodilatation in the rabbit isolated heart through release of nitric oxide, the endogenous nitrovasodilator. BrJ Pharmacol 1988,95:830-834 11 Palmer RMJ, Ashton DS, Moncada S: Vascular endothelial cells synthesize nitnc oxide from L-arginine. Nature 1988;333664-666 12. Palmer RMJ, Rees DD, Ashton DS, Moncada S- L-Arginine is the physiologic precursor for the formation of nitric oxide in endothelium-dependent relaxation. Biochem Biophys Res Commun 1988;153:1251-1256 13 Palmer RMJ, Moncada S: A novel citrulline-forming enzyme implicated in the formation of nitric oxide by vascular endothelial cells. Biochem Biophys Res Commun 1989;158348-352 14. Nathan CF, Stuehr DJ: Does endothelium-denved nitric oxide have a role in cytokine-induced hypotension' / Natl Cancer Inst 1990;82:726-728 15. Feletou M, Vanhoutte PM: Endothelium-dependent hyperpolarization of canine coronary smooth muscle BrJ Pharmacol 1988,93:515-524 16. Tare M, Parkington HC, Coleman HA, Neild TO, Dusting GJ. Hyperpolarization and relaxation of arterial smooth muscle caused by nitric oxide derived from the endothelium Nature 1990;34669-71 17. Stuehr DJ, Marietta MA- Mammalian nitrate biosynthesis: Mouse macrophages produce nitrite and nitrate in response to Eschenchia colx lipopolysaccharide. Proc NatlAcad Sci U S A 1985;82:7738-7742 18. Curran RD, Billiar TR, Stuehr DJ, Hofmann K, Simmons RL. Hepatocytes produce nitrogen oxides from L-arginine in response to inflammatory products of Kupffer cells. / Exp Med 1989;1701769-1774 19. Amber IJ, Hibbs JB Jr, Taintor RR, Vavrin Z- Cytokines induce an L-arginine-dependent effector system in nonmacrophage cells. / Leukoc Biol 1988;44:58-65 20. Kilbourn RG, Belloni P: Endothelial cell production of nitrogen oxides in response to interferon-gamma in combination with tumor necrosis factor, interleukin-1, or endotoxin J Natl Cancer Inst 1990;82:772-776 21. Hibbs JB Jr, Taintor RR, Vavnn Z: Macrophage cytotoxicity: Role for L-arginine deiminase and unino nitrogen oxidation to nitrite. Science 1987,23:473-476 22. Beasley D- Interleukin 1 and endotoxin activate soluble guanylate cydase in vascular smooth muscle. Am J Physiol 1990;259:R38-R44 23. Kilbourn RG, Gross SS, Jubran A, Adams J, Griffith OW, Levi R, Lodato RF: /v^-methyl L-arginine inhibits tumor necrosis factor-induced hypotension' Implications for the involvement of nitric oxide. Proc Natl Acad Sci U S A 1990;87-3629-3632 24. Shultz P, Sweeney C, Tayeh M, Marietta M, Raij L: Activated rat mesangial cells (MC) synthesize nitnc oxide (NO) from L-arginine which results in autocrine increases in cGMP (abstract). J Am Soc Nephrol 1990;l:731 25. Murad F, Arnold WF, Mittal CK, Braughler JM: Properties and regulation of guanylate cyclase and some proposed
functions for cyclic GMP. Adv Cyclic Nucleoade Res 1979;11 175-204 26. Murad F, Mittal CK, Arnold WP, Katsuki S, Kimura H: Guanylate cyclase: Activation of azide, nitro compounds, nitric oxide and hydroxyl radical and inhibition by hemoglobin and myoglobin./ldv Cyclic Nucleoade Res 1978;9:145-158 27. Rappaport RM, Murad F: Agonist-induced endotheliumdependent relaxation m rat thoracic aorta may be mediated through cGMP Circ Res 1983^2 352-357 28. Myers PR, Minor RL, Guerra R, Minor RL Jr, Guerra R Jr, Bates JN, Harrison DG: Vasorelaxant properties of the endothehum-derived relaxing factor more closely resemble 5-nitrosocysteine than nitric oxide Nature 1990;345:161-163 29 Tohns JP, Palmer RMJ, Moncada S, Raij L: Role of endothelium-derived relaxing factor in regulation of renal hemodynamic responses Am J Physiol 1990;258H655-H662 30. Rees DD, Palmer RMJ, Moncada S: Role of endothehumderived nitnc oxide in the regulation of blood pressure. Proc Natl Acad Sci USA 1989;86:3375-3378 31. Tohns JP, Raij L- Effects of ammo acid infusion on renal hemodynamics. Role of endothehum-derived relaxing factor. Hypertension 1991,17.1045-1051 32. Radermacher J, Forstermann U, Frolich JC: Endothehumdenved relaxing factor influences renal vascular resistance. Am J Physiol 1990,259:F9-F17 33. Lahera V, Salom MG, Fiksen-Olsen MJ, Raij L, Romero JO Effects of A/°-monomethyl-L-argmine and L-arginine on acetylcholine renal response. Hypertension 1990;15:659-663 34. Marsden PA, Brock TA, Ballerman BJ Glomenjlar endothelial cells respond to calcium-mobilizing agonists with release of EDRF. Am J Physiol 1990;258:F1295-F1303 35. Shultz PJ, Schorer AE, Ray L Effects of endothehumderived relaxing factor and nitric oxide on rat mesangial cells Am J Physiol 1990;258:F162-F167 36. Vidal-Ragout M, Romero JC, Vanhoutte PM. Endothehumdenved relaxing factor inhibits renin release. Eur J Pharmacol 1988;149-4O1-4O2 37 Brashers VL, Peach MJ, Rose CE' Augmentation of hypoxic pulmonary vasoconstnction in the isolated perfused rat lung by in vitro antagonists of endothelium-dependent relaxation. JChn Invest 1988;82:1495-15O2 38. Archer SL, Tohns JP, Raij L, Weir EK: Hypoxic pulmonary vasoconstnction is enhanced by inhibition of the synthesis of an endothelium derived relaxing factor. Biochem Biophys Res Commun 1989;164:1198-1205 39 Crawley DE, Liu SF, Evans TW, Barnes PJ Inhibitory role of endothelium-denved relaxing factor in rat and human pulmonary artenes. BrJ Pharmacol 1990;101 166-170 40. Gardiner SM, Compton AM, Bennett T, Palmer RMJ, Moncada S- Control of regional blood flow by endotheliumderived nitnc oxide. Hypertension 1990;15486-492 41 Vallance P, Collier J, Moncada S: Effects of endotheliumderived nitnc oxide on peripheral arteriolar tone in man Lancet 1989,2.997-1000 42. Wei EP, Kontos HA: H2O2 and endothelium-dependent cerebral artenolar dilation: Implications for the identity of endothelium-denved relaxing factor generated by acetylcholine. Hypertension 1990^16:162-169 43. Forstermann U, Mugge A, Alheid U, Haverich A, Frolich JC. Selective attenuation of endothehum-mediated vasodilation in atherosclerotic human coronary artenes. Circ Res 1988;62: 185-190 44. Drexler H, Zeiher AM, Wollschlager H, Meinertz T, Just H, Bonzel T: Flow-dependent coronary artery dilatation in humans. Circulation 1989;80:466-474 45. Radomski MW, Palmer RMJ, Moncada S: Comparative pharmacology of endothelium-derived relaxing factor, nitnc oxide and prostacychn in platelets. BrJ Pharmacol 1987;92: 181-187 46 Radomski MW, Palmer RMJ, Moncada S. Endogenous nitnc oxide inhibits human platelet adhesion to vascular endothelium. Lancet 1987,2:1057-1058
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Tolins et al 47. Radomski MW, Palmer RMJ, Moncada S- An L-argintne/ nitnc oxide pathway present in human platelets regulates aggregation. Proc Natl Acad Sci U S A 199O;87:5193-5197 48. Garg UC, Hassid A; Nitnc oxide-generating vasodilators and 8-bromo-cychc guanosme monophosphate inhibit mitogenesis and proliferation of cultured rat vascular smooth muscle cells. J Chn Invest 1989;83 1774-1777 49. Garg UC, Hassid A: Inhibition of rat mesangial cell mitogenesis by nitric oxide-generating vasodilators. Am J Physiol 1989,257:F60-F66 50 Shultz PJ, Ruble D, Ray L: S-nitroso-zi-acetylpenicillamine (SNAP) inhibits mitogen-induced mesangial cell proliferation (abstract). Kidney Int 1990;37.203 51. Miller VM, Vanhoutte PM: Endothehum-dependent contractions to arachidonic acid are mediated by products of cyclooxygenase in carune veins. Am J Physiol 1985.248.H432-H437 52. Shirahase H, Usui H, Kurahashi K, Fujwara M, Fukui K; Possible role of endothehal thromboxane A2 m the resting tone and contractile responses to acetylchohne and arachidonic acid in canine cerebral arteries. / Cardwvasc Pharmacol 1987;10:517-522 53 Kato T, Iwama Y, Okumura K, Hashimoto H, Ito T, Satake T. Prostaglandin H2 may be the endothehum-derived contracting factor released by acetylchohne in the aorta of the rat. Hypertension 1990;15:475-481 54 Katusic ZS, Vanhoutte PM: Superoxide anion is an endotheuum-denved contracting factor. Am J Physiol 1989, 257:H33-H37 55. Dzau VJ- Significance of the vascular renin-angiotensm pathway. Hypertension 1986,8:553-559 56. Hickey KA, Rubanyi G, Paul RJ, Highsmith RF: Characterization of a coronary vasoconstrictor produced by cultured endothehal cells. Am J Physiol 1985;248:C550-C556 57. Yanagisawa M, Kurihara H, Kunura S, Mitsue Y, Kobayashi M, Wantanabe TX, Masaki T: A novel potent vasoconstrictor peptide produced by vascular endothehal cells. Nature 1988; 332.411-415 58. Boulanger C, Luscher TF- Release of endothelin from the porcine aorta. / Chn Invest 1990,85:587-590 59 Martin ER, Marsden PA, Brenner BM, Ballerman BJ: Identification and characterization of endothelin binding sites in rat renal papillary and glomerular membranes. Bwchem Biophys Res Commun 1989,162.130-137 60 Cernacek P, Stewart DJ: Immunoreactive endothelin in human plasma. Marked elevations in patients in cardiogenic shock. Bwchem Biophys Res Commun 1989;161.562-567 61. Kohno M, Yasunan K, Murakawa KI, Yokokawa K, Hono T, Kunhara N, Takeda T: Plasma immunoreactive endothelin in essential hypertension. Am J Med 1990;88:614-618 62. Kohno M, Murakawa KI, Yasunan K, Yokokawa K, Horio T, Kunhara N, Takeda T: Prolonged blood pressure elevation after endothelin administration in bilaterally nephrectomized rats. Metabolism 1989,38712-713 63 King AJ, Brenner BM, Anderson S- Endothelin: A potent renal and systemic vasoconstrictor peptide. Am J Physiol 1989;256:F1051-F1058 64. Badr KF, Murray JJ, Breyer M, Takahashi K, Inagami T, Harris RC: Mesangial cell, glomerular and renal vascular responses to endothelin in the rat kidney / Chn Invest 1989;83:336-342 65. Pernow J, Boutier JF, Franco-Cerecedia A, LaCroix JS, Matran R, Lundberg JM: Potent selective vasoconstnctor effects of endothelin in the pig kidney in vivo Acta Physiol Scand 1988;134:573-574 66. Fukada Y, Hirata Y, Yoshima H, Takatsugu K, Koliayashi Y, Yanagisawa M, Masaki T: Endothelin is a potent secretagogue for atnal natnuretic peptide in cultured rat atnal myocytes. Biochem Biophys Res Commun 1988;155167-172 67. Miller WL, Redfield MM, Burnett JC J r Integrated cardiac, renal, and endocnne actions of endothelin. / Chn Invest 1989;83:317-320 68. Kon V, Yoshioka T, Fogo A, Kon V, Ichikawa I: Glomerular actions of endothelin in vivo. / Chn Invest 1989;83:1762-1767
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69. Simonson MS, Wann S, Mene P, Dubyak GR, Kester M, Nakazatoy Y, Sedor J Jr, Dunn MJ Endothelin stimulates phosphohpase C, Na + /H + exchange, c-fos expression, and mitogenesis in rat mesangial cells. J Chn Invest 1989,83: 708-712 70. DeNucci G, Thomas R, D'Orleans-Juste P, Antunes E, Walder C, Warner TO, Vane JR: Pressor effects of circulating endothelin are limited by its removal in the pulmonary circulation and by the release of prostacyclin and endothelium-derived relaxing factor Proc Natl Acad Sci USA 1988; 85:9797-9800 71 Haudenschild CC, Prescott MF, Chobanian AV- Effects of hypertension and its reversal on aortic intima lesions of the rat. Hypertension 1979,2:33-44 72. Huttner I, Gabbiani G: Vascular endothelium in hypertension, in Genest J, Kuchel O, Hamet P (eds): Hypertension. New York, McGraw-Hill Book Co., 1983, pp 473-488 73. Vanhoutte PM, Luscher TF: Penpheral mechanisms in cardiovascular regulation. Transmitters, receptors and the endothelium, in Taraa RC, Zanchetti A (eds): Handbook of Hypertension. Volume 8, Physiology and Pathophyswlogy of Hypertension—Regulatory Mechanisms. Amsterdam, Elsevier Science Publishers, 1987, pp 96-123 74. Cohen ML, Berkowitz BA: Decreased vascular relaxation in hypertension./PharmacolExp Ther 1976;196396-406 75 Luscher TF, Ray L, Vanhoutte PM: Endothehum-dependent responses in normotensive and hypertensive Dahl rats Hypertension 1987;9 157-163 76. Konishi M, Su C Role of endothelium in dilator responses of spontaneously hypertensive rat artenes. Hypertension 1983^5: 881-885 77. Luscher TF, Vanhoutte PM: Endothehum-dependent contractions to acetylcholine in the aorta of the spontaneously hypertensive rat Hypertension 1986;8:344-348 78 Luscher TF, Romero JC, Vanhoutte PM- Bioassay of endothehum-derived vasoactive substances in the aorta of normotensive and spontaneously hypertensive rats. / Hypertens 1986;49(suppl 6).81-83 79. Panza JA, Quyumi AA, Brush JE Jr, Epstein SE: Abnormal endothehum-dependent vascular relaxation in patients with essential hypertension. New Engl J Med 1990;323 22-27 80. Ross R, Harker L: Hyperlipidemia and atherosclerosis: Chronic hyperlipidemia initiates and maintains lesions by endothehal cell desquamatton and lipid accumulation Science 1976;193:1094-1100 81. Ross R: The pathogenesis of atherosclerosis An update. N Engl J Med 1986;314-488-500 82. Davies PF- Biology of disease: Vascular cell interactions with special reference to the pathogenesis of atherosclerosis Lab Invest 1986^5:5-24 83. Gryglewski RJ, Palmer RMJ, Moncada S. Superoxide anion is involved in the breakdown of endothehum-derived vascular relaxing factor. Nature 1986^320454-456 84. Andrews HE, Bruckdorfer KR, Dunn RC, Jacobs M: Lowdensity hpoproteins inhibit endothehum-dependent relaxation in rabbit aorta. Nature 1987,327-237-239 85. Simon BC, Cunningham LD, Cohen RA: Oxidized low density hpo-proteins cause contraction and inhibit endothelium-dependent relaxation in the pig coronary artery / Chn Invest 1990;86:75-79 86. Gibbons GH, Dzau VJ: Endothehal function in vascular remodeling, in Warren JB (ed): The Endothehum New York, Wiley-Liss, Inc, 1990, pp 91-93 87. Garg UC, Hassid A: Nitnc oxide-generating vasodilators and 8-bromo-cyclic guanosine monophosphate inhibit mitogenesis and proliferation of cultured rat vascular smooth muscle cells. / Chn Invest 1989;83:1774-1777 88. Mene P, Dunn MJ: Prostaglandins and rat glomerular mesangial cell proliferation. Kidney Int 1990;37-1256-1262 89. Heistad DD, Armstrong ML, Marcus ML, Piegors DJ, Mark AL: Augmented responses to vasoconstrictor stimuli in hypercholesterolemic and atherosclerotic monkeys. Ctrc Res 1984,54:711-718
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90. Henry PD, Yokayama M: Supersensitrvity of atherosclerotic rabbit aorta to ergonovine: Mediation by a serotonergic mechanism. / Chn Invest 1980;66 306-313 91. Habib JB, BossaUer C, WeUs S, Williams C, Mornsett JD, Henry PD: Preservation of endotheuum-dependent vascular relaxation in cholesterol-fed rabbit by treatment with the calcium blocker PN200110. Circ Res 1986^8:305-309 92. Verbeuren TJ, Jordaens FH, Zonnekeyn LL, Van Hoole CE, Coene MC, Herman AG Effect of hypercholesterolemia on vascular reactivity in the rabbit I Endothehum-dependent and endothelium-independent relaxations in isolated arteries of control and hypercholesterolemic rabbits. Circ Res 1986; 58 552-564 93. Verbeuren TJ, Coene MC, Jordaens FH, Van Hove CE, Zonnekeyn LL, Herman AG. Effect of hypercholesterolemia in vascular reactivity in the rabbit: II Influence of treatment with dipyndamole on endothelium-dependent and endothelium-independent responses in isolated aortas of control and hypercholesterolemic rabbits. Circ Res 1986^9:496-504 94 Harrison DG, Armstrong ML, Freimann PC, Heistad DD. Restoration of endothelium-dependent relaxation by dietary treatment of atherosclerosis. / Chn Invest 1987;8O.18O8-1811
95. Ginsburg R, Bristow MR, Davis K, Dibiase A, Bilungham ME: Quantitative pharmacologic responses of normal and atherosclerotic isolated human epicardial coronary arteries Circulation 1984;69:430-440 96. Ginsburg R, Zera PH- Endothelial relaxant factor in the human epicardial coronary artery (abstract). Circulation 1986;70(suppl 11)11-122 97. Chester AH, OTMeil GS, Moncada S, Tadjkarimi S, Yacoub MH. Low basal and stimulated release of nitnc oxide in atherosclerotic epicardial coronary arteries. Lancet 1990,336: 897-900 98. Ludmer PL, Sehvyn AP, Shook TL, Wayne RR, Mudge GH, Alexander RW, Ganz P: Paradoxical vasoconstnetion induced by acetylcholine in atherosclerotic coronary arteries. N EnglJ Med 1986;315 1046-1051 99. Creager MA, Cooke JP, Mendelsohn ME, Gallagher SJ, Coleman SM, Loscalzo J, Dzau V' Impaired vasodilation of forearm resistance vessels in hypercholesterolemic humans / Chn Invest 1990;86:228-234 KEY WORDS
• endothelium • vascular endothelium • nitric
oxide
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Role of endothelium-derived relaxing factor in regulation of vascular tone and remodeling. Update on humoral regulation of vascular tone. J P Tolins, P J Shultz and L Raij Hypertension. 1991;17:909-916 doi: 10.1161/01.HYP.17.6.909 Hypertension is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231 Copyright © 1991 American Heart Association, Inc. All rights reserved. Print ISSN: 0194-911X. Online ISSN: 1524-4563
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