Intrarenal role of angiotensin [des-Asp’langiotensin II

II and

JOHN E. HALL, THOMAS G. COLEMAN, ARTHUR C. GUYTON, J. WILLIAMSON AND HELIO C. SALGADO Department of Physiology and Biophysics, University of Mississippi School of Medicine, Jackson, Mississippi 39216 HALLJOHN E., THOMASG. COLEMAN,ARTHURC.GUYTON, J. WILLIAMSON BALFE, AND HELIO C. SALGADO. Intrarenal role of angiotensin II and [des-Asp’langiotensin II.. Am. J. Physiol. 236(3): F252-F259,1979 or Am. J. Physiol.: Renal Fluid Electrolyte Physiol. 5(3): F252-F259, 1979.-The relative importance of angiotensin II (AII) and its heptapeptide fragment [des-Asp’]AII (AIII) in regulating renal hemodynamics and electrolyte excretion was investigated in anesthetized dogs. Intrarenal infusion of the heptapepfide antagonist [desAsp1,11e8]AII for 90 min in seven sodium-depleted dogs caused no significant changes in renal hemodynamics, electrolyte excretion, or arterial pressure. In contrast; renal arterial infusion of the converting enzyme inhibitor SQ 20881 caused marked increases in renal blood flow (RBF) (32%), as well as urinary excretion of sodium (450%), potassium (56%), and water (60%), small increases in glomerular filtration rate (GFR) (ll%), and no significant changes in plasma aldosterone concentration. When renal artery pressure (RAP) was reduced, RBF * and GFR were effectively autoregulated in normal and sodium-depleted control dogs and in dogs infused with AI11 antagonist. Innormal and sodium-depleted dogs infused with SQ 20881, RBF was also effectively autoregulated, but GFR, filtration fraction, and calculated efferent arteriolar resistance decreased progressively as RAP was reduced; These data suggest that the renin-angiotensin system has an important intrarenal role in cohtrolling electrolyte excretion and in autoregulation of GFR, probably via an efferent arteriolar mechanism. However, AIII,.:when compared to AII, plays a relatively minor role in the renal response to sodium depletion and reduced RAP. sodium excretion; renal blood flow; glomerular filtration rate; renal autoregulation; efferent arterioles; converting enzyme inhibition

OFTENBEEN assumedto bethe primary active component of the renin-angiotensin system, but several investigators htive recently suggested that the heptapeptide fragment of AII, [des-Asp’]AII

ANGIOTENSINII(AII)HAS

(AIR), may mediate the renal and adrenal responses to activation of the renin-angiotensin system (4, 8-10). Goodfriend and Peach (10) have recently reviewed a substantial amount of evidence which suggests that AI11 plays a physiological role in regulating aldosterone secretion. The importance of AI11 in regulating renal hemodynamics and electrolyte excretion, however, has not been widely studied. [des-Asp’]AII has been reported to decrease renal blood flow and renin secretion when infused intraveF252

BALFE,

nously or into the renal artery at rates ranging from 10 to 100 rig/kg per min (8, 9, 25). However, recent studies . in which the concentrations of AI1 and AI11 were measured in man and dog indicate that only small amounts of the heptapeptide are present in plasma (5, 24)~ Goodfriend’ and Peach (10) have estimated the circulating levels of [des-Asp’]AII to be less than 4-25 pg/ml of plasma. It is still uncertain, therefore, whether there is enough endogenously produced AI11 present either in plasma or in renal tissue to regulate renal hemodynamics and electrolyte excretion. To our knowledge there has been only one attempt to study the effects of endogenously produced AI11 on renal function. Taub et al. (25) recently reported that infusion of the heptapeptide analogue [des-Asp’,Ile’]AII in dogs with acute partial constriction of the thoracic inferior vena cava increases renal blood flow, suggesting that endogenous levels of AI11 can alter renal blood flow under these experimental conditions. However, there has been no report on the effects of blockade of endogenously formed AI11 on the control of glomerular filtration rate (GFR) and electrolyte excretion or on the control of renal blood flow under other physiological conditions during which the renin-angiotensin system is activated. In the present study the importance of .endogenously formed AI11 in controlling renal, hemodynamics and electrolyte ,excretion during sodium deprivation and reduced renal perfusion pressure was examined after intrarenal infusion of the heptapeptide antagonist [des-Asp’,Ile’]AII. The importance of AI1 in regulating renal hemodynamits as well as water and electrolyte excretion has been demonstrated in several previous studies from our laboratory (14,15,28). Intrarenal infusion of the AI1 analogue [Sar’,Ile8]AII caused marked increases in renal blood flow and electrolyte excretion in sodium-depleted or water:deprived dogs. In addition to its effects on electrolyte excretion, endogenously produced AI1 may also play an important role in regulating GFR during reductions in renal artery pressure. After renin depletion caused by chronic salt loading and administration of deoxycorticosterone acetate, or after AI1 blockade in sodium-depleted dogs, GFR autoregulation is markedly impaired although renal blood flow autoregulation remains intact, suggesting that AI1 plays an essential role in maintaining efferent art&oh tone and effective filtration pressure during reductions in renal artery !pressure (13, 15). Several other investigators have also reported that AI1

0363-6127/79/0000-OOOOooo$Ol.25Copyright 0 1979 the American Physiological Society

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F253

ROLE OF AII AND AIII

blockade does not markedly alter renal blood flow autoregulation (1,2,18), but in the few studies in which GFR has been measured the results have been complicated by the use of isolated kidney preparations (W, or because they were conducted under conditions of marked diuresis (2) instead of in the normal hydropenic condition. Schnermann and his colleagues (22, 23) have reported that regulation of superficial nephron GFR is impaired when the renin-angiotensin system is nonfunctional, but they did not measure renal plasma flow and, therefore, could not determine whether. impairment of GFR autoregulation was due to a lack of angiotensin effect on afferent or efferent arterioles. In the present study, autoregulation of GFR and renal blood flow were studied in normal and sodium-depleted dogs after intrarenal infusion of the angiotensin converting enzyme inhibitor SQ 20881. One- criticism of our previous studies (13, 15) was that some unknown effect of salt loading and administration of deoxycorticosterone acetate, unrelated to renin depletion, may have caused the impairment of GFR autoregulation; also, infusion of an AI1 antagonist would not uncover the full effects of blockade of the renin-angiotensin system if the agonistic effects of the blocker was substantial or if [de&Asp’]angiotensin II played a significant role in regulating GFR. However, SQ 20881 has no known agonistic effects, and it also blocks the formation of AI11 as well as AII. If AI11 does play an important role in regulating renal hemodynamics and electrolyte excretion during sodium deprivation or reduced renal perfusion pressure, the effects of SQ 20881 on renal function should be greater than the effects of AI1 blockade alone. Therefore, in addition to providing information on the renal effects of converting enzyme inhibition, the data obtained after intrarenal infusion of SQ 20881, when compared to data obtained after AI1 blockade alone, provides another means of assessing the relative importance of AI1 and AI11 in regulating renal function during sodium deprivation and reduced renal perfusion pressure. METHODS

Experiments were conducted on 39 male mongrel dogs weighing 18-28 kg. Twenty-two dogs (groups I, II, and III) were fed a sodium-deficient diet (h/d dietary animal food, Riviana Foods, Inc.) which provided approximately 5 meq sodium/day for 3 wk, while the remaining dogs (groups IV and V) were fed a standard kennel ration (Purina high protein dog meal). Dogs in groups I, II, and III were also injected intramuscularly with 20 mg furosemide at the end of the 2nd wk of sodium depletion. At the time of the experiment, the dogs were anesthetized with sodium pentobarbital (25-30 mg/kg i.v.) and rectal temperature was maintained constant by warming the table on which the dog rested. The left kidney was exposed through a retroperitoneal flank incision, and small sections of the ureter and spermatic vein were isolated. Renal venous blood samples were collected from a catheter inserted into the spermatic vein and advanced into the renal vein. The ureter was cannulated and urine was directed through a photoelectric drop counter and collected. Renal blood flow was measured with an electromagnetic flow transducer connected to a square-wave

flowmeter (Carolina Medical Electronics). Distal to the flow transducer, a 23.gauge curved needle was inserted into the renal artery and maintained patent by the infusion of 0.1 ml/n& of isotonic saline. Renal artery pressure was measured and systemic arterial blood samples were collected from a catheter inserted into the femoral artery and advanced into the abdominal aorta just below the left renal artery. Mean systemic arterial pressure was measured from another femoral catheter advanced into the aorta above the renal arteries. Mean systemic and renal arterial pressures, renal blood flow, and urine flow were recorded continuously on a Grass polygraph (model 7C). Glomerular filtration rate was determined from the renal arteriovenous extraction of [ ‘251]iothalamate (Glofil, Abbott Laboratories). A priming dose of 0.45 ,uCi/ kg of iothalamate was injected intravenously, followed by a sustaining infusion of 0.003 pCi/kg per min in 1.0 ml/min of isotonic saline in normal dogs. In sodiumdepleted dogs, the sustaining infusion was administered in only 0.2 ml/mm of isotonic saline in order to maintain sodium depletion. Glomerular filtration rate was calculated as GFR = (1 - Hct) x RBF x [(A - V)/A] where Hct is the systemic arterial hematocrit measured by the microcapillary method, RBF is the renal blood flow, and A and V are the systemic arterial and renal venous 1251radioactivities, respectively. Duplicate 1.0.ml arterial and renal venous plasma samples were collected for measurement of A and V and for determination of plasma electrolytes and protein concentrations. Plasma and urine sodium and potassium concentrations were determined by flame photometry and plasma protein concentration was measured with a refractometer (American Optical). Plasma renin activity was measured by radioimmunoassay of angiotensin I and is expressed as nanograms angiotensin I per milliliter per hour of incubation ( 11) . Plasma aldosterone concentration was also measured by radioimmunoassay and is expressed as nanograms per deciliter (20). Each experiment consisted of two parts. First, in order to determine the effects of converting enzyme inhibition or blockade of the heptapeptide [des-Asp’]AII, either the converting enzyme inhibitor SQ 20881 or the heptapeptide inhibitor [des-Asp’,Ile’]angiotensin II was infused into the renal left artery for 90 min while changes in arterial pressure and renal fun&ion were examined. In this part of the experiment, a 60. to 9Omin stabilization period was allowed, followed by two sets of control measurements (at t = -30 and t = 0 min) and two experimental periods (at t -= 60 and t = 90 min). During the control periods, isotonic saline was infused into the renal artery at 0.1 ml/min in all groups of dogs. During the experimental periods the converting enzyme inhibitor SQ 20881 was infused into the renal artery at a rate of 4 clg/ kg per min in group V (normal dogs) and at a rate of 6 pg/kg per min in group III (sodium-depleted dogs). In group II (sodium-depleted dogs), the heptapeptide analogue [des-Asp’,Ile8]angiotensin II was infused into the renal artery during the experimental periods a.t a rate of 200 rig/kg per min. In group I, which served as a time control group for the sodium-depleted dogs, isotonic sa-

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HALL

F254 line was infused into the renal artery during the experimental as well as during the control periods. In the second part of each experiment, the effects of intrarenal infusion of converting enzyme inhibitor SQ 20881 or the heptapeptide antagonist [des-Asp’,ne”]angiotensin II on autoregulation of renal blood flow and GFR were examined. After 90 min of infusion of isotonic saline, SQ 20881, or heptapeptide antagonist, renal arterial pressure was reduced in steps to approximately 100,85, and 70 mmHg by tightening the aortic clamp. Renal function was permitted to stabilize for 15-20 min after each step decrease in pressure before the data were collected. In sodium-depleted and normal dogs, the effectiveness of intrarenal infusion of SQ 20881 in blocking the vasoconstrictor effect of exogenous angiotensin I was examined by injection of 0.5-2 pg (or approximately 25-100 rig/kg) of angiotensin I directly into the renal artery; no measurable changes in renal blood were noted in any of the dogs studied. Injection of 10 rig/kg of [des-Asp’]angiotensin II directly into the renal artery caused no change in renal blood flow in dogs infused with [desAsp1,11e8]angiotensin II for 90 min or longer, indicating that the dosage of heptapeptide antagonist was sufficient to block even a large pharmacological amount of AIII. In four control dogs renal arterial injection of 10 rig/kg of [des-Asp’]an&otensin II caused a 30.55% reduction of renal blood flow. Other investigators have also shown that this dosage of AI11 antagonist (0.2 pg/kg per min) effectively blocks large amounts of exogenous AI11 (25). The control data were compared with experimental data within each group by Dunnett’s t test for multiple comparisons (7). Statistical significance was considered to be P < 0.05. All data in text, tables, and figures are expressed as means * SE.

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FIG. 1. Changes in renal blood flow (RBF), glomerular filtration rate (GFR), and filtration fraction (FF) in sodium-depleted dogs during intrarenal infusion of isotonic saline (time control), SQ 20881, or [desAsp1,11e8]angioten& II (AIII antagonist). Values obtained at t = -30 and t = 0 min are control values and those obtaiqed at t = 60 and t = 90 min are experimental values. Asterisks indicate P < 0.05 relative to control (at t = 0 min).

increase was not as great as the rise in renal blood flow; therefore, the filtration fraction decreased significantly RESULTS after 60 and 90 min of SQ 20881 infusion. In group I, which served as a time-control group for the sodiumEffects of intrarenal infusion of [des-Asp’,Ile8]angiotensin II in sodium-depleted dogs. The changes in renal depleted dogs, there were no significant changes in renal blood flow, GFR, and filtration fraction that occurred blood flow, GFR, or filtration fraction. during intrarenal infusion of the heptapeptide analogue Renal ‘excretion of sodium, potassium, and water in[des-Asp1,11e8]AII (AI11 antagonist) are illustrated in Fig. creased markedly in sodium-depleted dogs during intra1. Renal blood flow increased slightly from 3.97 t 0.17 to renal infusion of SQ 20881 (Fig. 2). Sodium excretion 4.37 =f: 0.28 ml/min per kidney wt after 90. min of hepta- increased to more than 5 times the control level (from peptide antagonist infusion. However, no significant 0.097 to 0.536 peq/min per g kidney wt) after 90 min of Since kidney weight averchanges in GFR or urinary excretion of sodium, potas- converting enzyme inhibition. sium, or water were observed during intrarenal infusion aged 50.7 g, the total increase in sodium excretion caused of AI11 antagonist (Figs. 1, 2, and 3). Infusion of the by SQ 20881 infusion was approximately 27.2 peq/min heptapeptide antagonist also caused no significant per kidney. Urine flow, potassium excretion, and fracchanges in mean arterial pressure or serum electrolyte tional sodium and potassium excretion also increased concentrations. Accordingly, in the sodium-depleted dog, markedly during.intrarenal infusion of SQ 20881. Howblockade of endogenously formed AI11 has minimal ef- ever, there were no significant changes in any of these fects on renal hemodynamics and electrolyte excretion. variables in the time-control group (Figs. 2 and 3). Mean Effects of intrarenal infusion of SQ 20881 in sodiumarterial pressure decreased from a control value of 127 depleted dogs. The changes in renal blood flow, GFR, * 3 to 113 =t 3 mmHg after 90 min of SQ 20881 infusion and filtration fraction that occurred in eight sodiumin sodium-depleted dogs. depleted dogs during intrarenal infusion of SQ 20881 are Although plasma renin activity (PRA) increased from also shown in Fig. 1. Renal blood flow, which averaged 5.5 $- 1.6 to 28.1 k 7.5 ng AI/ml per h after 90 min of 3.98 & 0.41 ml/min per g kidney wt during the control converting enzyme inhibition, there were no significant period, increased approximately 32% after 90 min of changes in plasma aldosterone concentration. During the converting enzyme inhibition. Glomerular filtration rate control period, plasma aldosterone concentration averalso increased slightly during SQ 20881 infusion, but the aged 49.8 t 6.0 ng/dl and after 90 min of SQ 20881

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F255

ROLE OF AI1 AND AI11

infusion aldosterone concentration was 41.0 =f: 5.2 ng/dl. t 0.25 and 5.32 =f=0.25 ml/min per g kidney wt, respectively, although GFR did not change. Therefore, the There were also no significant changes in plasma sodium or potassium concentrations, hematocrit, or plasma pro- filtration fraction decreased significantly after 60 and 90 tein concentration during intrarenal infusion of SQ 20881. min of SQ 20881 infusion. Converting enzyme inhibition Effects of intrarenal infusion of SQ 20881 in normal also caused significant increases in urine flow and urinary dogs. The average changes in arterial pressure, renal excretion of sodium and potassium as well as increases in fractional sodium and potassium excretion. Sodium exfunction, PRA, and plasma aldosterone concentration that occurred in eight normal dogs during intrarenal cretion more than doubled during SQ 20881 infusion, infusion of SQ 20881 are illustrated in Table 1. After 60 increasing from a control value of 1.04 t 0.14 to 2.12 t and 90 min of converting enzyme inhibition, renal blood 0.22 peq/min per g kidney wt. Although PRA increased flow increased from a control value of 4.21 k 0.14 to 5.17 to more than 200% of the control value during converting enzyme inhibition, no significant changes in plasma alNo-DEPLETED DOGS dosterone concentration or arterial pressure were observed. 0 TIME CONTROL (N=f) 0 SO-20881 (N=8) Effects of intrarenal infusion of SQ 20881 or [des0.6 m Am ANTAGONIST(N=7) Asp ‘,IleO]angiotensin II on renal autoregulation in soit dium-depleted dogs. The changes in renal blood flow, No-DEPLETED

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Intrarenal role of angiotensin II and [des-Asp1]angiotensin II.

Intrarenal role of angiotensin [des-Asp’langiotensin II II and JOHN E. HALL, THOMAS G. COLEMAN, ARTHUR C. GUYTON, J. WILLIAMSON AND HELIO C. SALGADO...
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