Prostaglandins Leukotrienes @ottgman Croup UK Ltd
and Essential 1991
Fatty
Acids
(1991) 43. 179-W
Vascular Eicosanoid Production in Experimental Hypertensive Rats with Different Mechanisms T. Ishimitsu, Y. Uehara, J. Iwai*, T. Sugimoto, Y. Hirata, H. Matsuoka and T. Sugimoto The 2nd Department of Internal Medicine, University of Tokyo, 7-3-l Hongo, Bunkyo-ku, Tokyo 113, Japan and *Brookhaven National Laboratory, Upton, New York, USA (Reprint requests to TI)
This study investigated the release of prostacyclin (PGIz) and thromboxane A2 (TXA2) from the aortic walls of various experimental hypertensive rats, e.g. spontaneously hypertensive rats (SHR), Dahl salt-sensitive (Dahl S) rats, deoxycorticosterone (DOCA)-salt hypertensive rats and renovascular (2-kidney, l-clip (2KlC) and l-kidney, l-clip (1KlC)) hypertensive rats. The PG12 generation was increased significantly in these hypertensive models, irrespective of the hypertensive mechanisms, when they developed established hypertension. Dahl S rats, having an impaired PGIz production on a low salt diet, restored PG12 generating capacity to the control level of Dahl salt-resistant rats when they were fed a high salt diet and developed salt-induced hypertension. On the other Laud, the TXA2 generation in the vascular walis was enhanced particularly in rat models for genetic hypertension, and this system was unaltered in the models for secondary hypertension, e.g. DOCA-salt and renovascular hypertension. Thus, it is suggested that the ekvation of blood pressure is associated with an increase in vascular PGI2 production, and that the increased vascular TXA2 production is a characteristic feature of genetic hypertension.
ABSTRACT.
INTRODUCTION
rats when they are fed a high salt diet and develop hypertension. A similar property is found in the vascular walls from spontaneously hypertensive rats (SHR) (10). These data lead to the hypothesis that hypertension per se exerts to increase the vasodepressor PGI2 synthesis in the vascular walls; if so, such changes in the .vascular eicosanoid system are likely to counteract the elevation of blood pressure or protect the vascular vessels from the damage in hypertension. In spite of this intriguing proposal, the relationship between the blood pressure elevation and vascular eicosanoid system is not fully proved. Moreover, most of the studies on the vascular eicosanoid system in hypertensive rats have been carried out in different experimental conditions. This makes it difficult to interpret the results or compare them each other. Thus, in this study, to reveal the possible correlation between vascular eicosanoid system and elevation of blood pressure, we examined, under constant experimental conditions, the alterations of eicosanoid synthesis in the vascular walls from various experimental hypertensive rat models with different mechanisms for hypertension.
There is an increasing amount of evidence that the arterial vessels are capable of producing various vasodepressor or vasoconstrictor substances, the balance of which is expected to play a role in modulation of the vascular contractility or remodeling of the arterial structure through platelet-vascular wall interactions. In this context, eicosanoids, e.g. prostacyclin (PGI,) and thromboxane (TXA& have attracted much attention because the vascular walls have a large capacity to generate these potent vasoactive substances (1, 2). In fact, there is some evidence that the vascular eicosanoid system is altered in experimental rat models for human hypertension (3-8). In Dahl saltsensitive (Dahl S) rats, vascular PGIz generation is lowered and the thromboxane production is enhanced even in a prehypertensive state (9). Moreover, the PGIz generating capacity is restored to the control level of Dahl salt-resistant (Dahl R)
Date received 19 December 1990 Date accepted 28 February 1991
179
180
Prostaglandins Leukotrienes
and Essential Fatty Acids
MATERIALS AND METHODS Rat models for genetic hypertension Male spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) were bred at University of Tokyo, Tokyo, Japan. After weaning, the rats were fed a regular (0.6% NaCl) laboratory chow and given tap water ad libitum during the experiment and maintained for 5 weeks or 15 weeks. Male Dahl salt-sensitive (Dahl S) and Dahl saltresistant (Dahl R) rats were from Brookhaven National Laboratory, Upton, New York, USA. After weaning, Dahl rats were assigned to 1) rats fed a low salt (0.3% NaCl) diet or 2) rats fed a high salt (4%) diet. Tap water was given ad libitum. The rats were maintained for 8 weeks. Deoxycorticosterone (DOCA)-salt hypertensive rats Male heminephrectomized Wistar rats aged 7 weeks were assigned to 4 groups; 1) control rats given only water, 2) salt rats given 1% saline ad libitum, 3) DOCA rats given 100 mg deoxycorticosterone acetate (DOCA)/kg body weight and tap water and 4) DOCA-salt rats given 100 mg DOCA/kg body weight and 1% saline. The rats were fed a regular laboratory chow and maintained for 1 or 8 weeks. Renovascular hypertensive rats Two-kidney, l-clip (2KlC) and l-kidney, l-clip (1KlC) models of renovascular hypertension were developed, using 7-week-old and 11-week-old male Wistar rats, respectively. To establish 2KlC hypertension, a 0.2 mm silver clip was introduced in the left main renal artery without manipulating the contralateral renal artery under pentobarbital anesthesia (50 mg/kg body weight). In the shamoperated, control rats, the left renal artery was carefully isolated. To establish 1KlC hypertension, the right kidney was totally removed and the left renal artery was partially constricted by a 0.25 mm silver clip. In the sham-operated, control rats, the right kidney was nephrectomized and the left renal artery was isolated without clipping. The rats were fed a regular laboratory chow and given tap water. 2KlC rats were maintained for 8 weeks and 1KlC rats for 4 weeks.
titia was carefully removed using forceps, and approximately 50 mm* aortic strips were prepared. The aortic strips were incubated in 2 ml of D-PBS (pH 7.35) at 37°C for 30 min. The amounts of PG12 and TXA2, released from the aortic strip into the media, were measured by radioimmunoassay method in the forms of 6-keto-prostaglandin F1, (6-keto-PGF,,) and thromboxane B2 (TXB2), respectively (9). Briefly, the assay mixture consisted of 0.1 ml of (3H)eicosanoid (lo4 dpm), 0.1 ml of a diluted sample or standard solution, and 0.1 ml of a diluted antibody solution. The assay mixture was incubated at 4°C for 24 h. To separate the bound from the free (3H)eicosanoid, 0.1 ml of a dextrancoated charcoal solution (2.5% charcoal and 0.25% dextran) was added, and the mixture was immediately spun at 1000 g at 4°C for ‘5 min. The radioactivity of the bound (3H)eicosanoid was counted using an automatic liquid scintillation counter. The antisera were all raised in rabbits in our laboratory, using eicosanoid-coupled thyroglobulin and complete Freund’s adjuvant as the immunogens. The immunization was repeated every 2 weeks for 4 months. Anti-6-keto-PGFi, serum crossreacted 1% with PGEz, 2% with PGFz,, 0.08% with PGD,, 0.01% with TXB2 and less than 0.001% with arachidonate. Anti-TXB, serum crossreacted 0.005% with 6-keto-PGFi,, 0.007% with PG&,, 0.018% with PGFz,, 0.06% with PGD2 and less than 0.001% with arachidonate. Reagents Reagents were all of analytical grade. (3H) eicosanoids were purchased from Amersham International, Buckinghamshire, UK. Authentic eicosanoids for radioimmunoassay were gifts from Ono Pharmaceutical Co Ltd, Osaka, Japan. Statistical analysis The values are expressed as means + SEM. The difference was assessed by the Student’s t-test or one way analysis of variance. A p value less than 0.05 was considered as statistically significant.
RESULTS Spontaneously hypertensive rats
Eicosanoid production by aortic walls Systolic blood pressure was measured by the tailcuff method of Friedman (11). At the end of feeding period, the descending thoracic aortae were quickly removed from the decapitated rats. The aortae were placed in ice-chilled Dulbecco’s phosphate-buffered saline solution (D-PBS; Gibco Laboratories, Grand Island, NY, USA). The adven-
Table 1 presents the averaged systolic blood pressure of SHR and WKY. Although 5-week-old SHR remained completely normotensive, the systolic blood pressure was 10 mmHg higher than the agematched WKY (p < 0.01). In contrast, 15-week-old SHR established systolic hypertension, as compared with the age-matched WKY (189 vs 134 mmHg, p < 0.001).
Eicosanoid and Hypertension Tat& 1 Averaged systolic bloods pressure of SHR and WKY Strain
181
Table 2 Averaged systolic blood pressure of Dahl S and Dahl R rats
Systolic blood pressure (mmHg) Strain
WKY SHR
5-week-old
15week-old
109 f 3 (20) 119 f 2* (20)
134 rf: 3 (10) 189 + 4** (10)
Numbers in a parenthesis represent the numbers of rats. *p c 0.01, **p < 0.001 vs the respective control values of WKY.
Dahl R Dahl S
Systolic blood pressure (mmHg) 0.3% NaCl diet
4% NaCl diet
130 + 3 (10) 143 + 2* (10)
124 f 2 (10) 166 + 3** (10)
Numbers in a parenthesis represent the numbers of rats. *p. < 0.005, **I) < 0.001 vs the respective control values of dahl R rats. ’
I‘XA,
I
P< 0.661
0
WKY SUK S-w&-old
WKY SHK l%ue,k-old
SHR S*l,ak-old
; YKY
WKY SHII 1 S-weak-old
Fig. 1 Vascular eicosanoid generation in SHR and WKY. The left graph shows the production of PGIz in the aortic walls and the right graph vascular TXA, generating capacity. The open bars and solid bars represent WKY and SHR, respectively.
The amounts of PG12 and TXA2 generated by the aortic strips from SHR and WKY are shown in Figure 1. In the prehypertensive state, there was no difference in the PG12 production between SHR and WKY (left graph, Fig. 1). In contrast, the aortic strips from 15-week-old, hypertensive SHR exhibited a larger capacity to generate PGI,! than those of 15week-old, normotensive WKY (32.3 + 3.9 vs 17.6 + 1.0 ng/mg/30 min, p < 0.002). With regard to the vascular TXAz generation in SHR, the production was significantly increased in both prehypertensive and hypertensive states, compared with the respective controls (365 f 26 vs 245 f 16 pg/mg/30 min for prehypertensive rats, p < 0.001; 350 f 16 vs 297 + 14 pg/mg/30 min for hypertensive rats, p < 0.02) (right graph, Fig. 1).
Fig. 2 Vascular eicosanoids generation in Dahl rats. .The left graph illustrates PGIz generating capacity of the aortic walls and the right graph vascular TXA, production. The open bars (R) and solid bars (S) represent Dahl R and Dahl S rats, respectively.
(10.2 + 1.5 vs 16.8 f 2.7 ng/mg/30 min, p < 0.03). In contrast, when Dahl S rats were fed a high salt diet, the PGIt generation was restored to the control level of Dahl R rats (15.3 f 2.9 vs 15.0 f 2.2 ng/mg/30 min). On the other hand, the vascular TXA2 production was enhanced in Dahl S rats when compared with Dahl R rats, irrespective of the hypertensive state. DOCA-salt hypertensive rats Table 3 shows the systolic blood subgroups in DOCA-salt study. difference in the averaged systolic among the groups when the rats 1 week after the loading. However,
pressures of 4 There was no blood pressure were examined after 8 weeks,
Dahl rats As shown in Table 2, Dahl S rats stayed in a prehypertensive state on a low salt diet although the blood pressure was 13 mmHg higher than control Dahl R rats. When Dahl S rats were challenged with a high salt diet for 8 weeks, the blood pressure was significantly elevated, compared with normotensive, control Dahl R rats. Vascular eicosanoid production in Dahl rats is illustrated in Figure 2. The aortic strips from Dahl S rats on a low salt diet had a significantly lowered production of PGI2, as compared with Dahl R rats
PROST.
c
Table 3 Systolic blood pressure of DOCA-salt hypertensive rats Group of rats
Control 1% saline DOCA DOCA-salt
Systolic blood pressure (mmHg) l-week stage
g-week stage
119 + 116 + 112 f 121 +
120 f 120 + 149 + 183 +
l(6) 4 (6) 5 (6) 5 (6)’
5 3 5* 7**
(6) (7) (7) (7)
Numbers in a parenthesis represent the numbers of rats. F values are 0.97 for l-week stage (p > 0.1) and 36.74 for &week-study (p < O.OOl), respectively. *p ‘)7- IOI in Clinical Pharmacoloav of Prostacvclin. il.cwis P J, O’Grady J eds) Ravyn Press. Ne& York, 1981. Suhhiah M 1’ K, Bale L K. Dinh D M. Kottkc B A. Dcitemcycr I). Regional aortic diffcrcnccs in
184
7.
8.
9.
10.
11.
12.
13.
14.
Prostaglandins Leukotrienes and Essential Fatty Acids
atherosclerosis-susceptibility: changes in prostaglandin biosynthesis and cholesterol accumulation in response to desoxycorticosterone (DOCA)-salt induced hypertension. Virchows Archives 37: 309-315, 1981. Botha J H, Leary W P, Asmal A C. Enhanced release of ‘PGI,-like’ substance in experimental hypertension. Prostaglandins and Medicine 3: 251-252,1979. Taube C h, Hoffman P, Forster W. Enhanced thromboxane production in the aorta of spontaneously hypertensive rats in vitro. Prostaglandins Leukotrienes and Medicine 4: 431-438,198O. Uehara Y, Tobian L, Iwai J, Ishii M, Sugimoto T. Alterations of vascular prostacyclin and thromboxane A, in Dahl genetical strain susceptible to salt-induced hypertension. Prostaglandins 33: 727-738,1987. Soma M, Manku M S, Jenkins D K, Horrobin D F. Prostaglandins and thromboxane outflow from the perfused mesenteric vascular bed in spontaneously hypertensive rats. Prostaglandins 29: 323-333,1985. Friedman M, Freed S C. Microphonic manometer for indirect determination of systolic blood pressure in the rat. Proceedings of the Society for Experimental Biology and Medicine 70: 670-672, 1949. Botha J H, Leary W P. Mechanical reduction in pressure and pulse pressure decreases the ability of hypertensive rat aortas to produce ‘PGIr-like’ activity. Prostaglandins and Medicine 6: 267-268, 1981. Uehara Y, lshimitsu T, Ishii M, Sugimoto T. Prostacyclin synthase and phospholipases in the vascular wall of experimental hypertensive rats. Prostaglandins 34: 423-432, 1987. Lansman J B, Hallam T J, Rink T J. Single stretch-activated ion channels in vascular
15.
16.
17.
18.
19.
20.
21.
22.
endothelial cells as mechanotransducers? Nature 325: &X1-813,1987. Adams D J, Barakeh J, Laskey R, Van Breemen C. Ion channels and regulation of intracellular calcium in vascular endothelial cells. The FASEB Journal 3: 2389-2400,1989. Ishimitsu T, Uehara Y, Ishii M, Matsuoka H, Ikeda T, Sugimoto T. Roles of endogenous vasodepressor prostaglandins in growth of vascular smooth muscle cells in spontaneously hypertensive rats. Japanese Circulation Journal, in press. Gonik H C, Kramer H J, Paul W, Lu E. Circulating inhibitor of sodium-potassium-activated adenosine triphosphate after expansion of extracellular fluid volume in rats. Clinical Science and Molecular Medicine 53: 329-334, 1977. Kojima I, Yoshihara S, Ogata E. Involvement of endogenous digitalis-like substance in genesis of deoxycorticosterone-salt hypertension. Life Science 30: 1775-1781,1982. Uehara Y, Kobayashi T, Ishii M. Relationship between Na+ ,K+-ATPase and release of prostacyclin and thromboxane A, in the vascular wall. p 23-27 in Prostaglandin and Membrane Ion Transport. (Braquet P, Garay R P, Frolich J C, Nicosia S eds) Raven Press, New York, 1985. Uehara Y, Ishii M, Ishimitsu T, Sugimoto T. Salt-induced plasma factor that inhibits platelet thromboxane AZ release and renal prostaglandin E, production in rats. Hypertension 9(Suppl III): 6-12, 1987. Nakajima M, Toda N. Prejunctional and postjunctional actions of prostaglandins Frr and I, and carbocyclic thromboxane A, in isolated dog mesenteric-arteries. European Journal of Pharmacoloev 120: 309-318. 1986. Ishimitsu T,?_Jehara Y, Ishii M, Ikeda T, Matsuoka H, Sugimoto T. Thromboxane and vascular smooth muscle cell growth in genetically hypertensive rats. Hypertension 12: 46-51, 1988.
and Essential 1991
Fatty
Acids
(1991) 43. 179-W
Vascular Eicosanoid Production in Experimental Hypertensive Rats with Different Mechanisms T. Ishimitsu, Y. Uehara, J. Iwai*, T. Sugimoto, Y. Hirata, H. Matsuoka and T. Sugimoto The 2nd Department of Internal Medicine, University of Tokyo, 7-3-l Hongo, Bunkyo-ku, Tokyo 113, Japan and *Brookhaven National Laboratory, Upton, New York, USA (Reprint requests to TI)
This study investigated the release of prostacyclin (PGIz) and thromboxane A2 (TXA2) from the aortic walls of various experimental hypertensive rats, e.g. spontaneously hypertensive rats (SHR), Dahl salt-sensitive (Dahl S) rats, deoxycorticosterone (DOCA)-salt hypertensive rats and renovascular (2-kidney, l-clip (2KlC) and l-kidney, l-clip (1KlC)) hypertensive rats. The PG12 generation was increased significantly in these hypertensive models, irrespective of the hypertensive mechanisms, when they developed established hypertension. Dahl S rats, having an impaired PGIz production on a low salt diet, restored PG12 generating capacity to the control level of Dahl salt-resistant rats when they were fed a high salt diet and developed salt-induced hypertension. On the other Laud, the TXA2 generation in the vascular walis was enhanced particularly in rat models for genetic hypertension, and this system was unaltered in the models for secondary hypertension, e.g. DOCA-salt and renovascular hypertension. Thus, it is suggested that the ekvation of blood pressure is associated with an increase in vascular PGI2 production, and that the increased vascular TXA2 production is a characteristic feature of genetic hypertension.
ABSTRACT.
INTRODUCTION
rats when they are fed a high salt diet and develop hypertension. A similar property is found in the vascular walls from spontaneously hypertensive rats (SHR) (10). These data lead to the hypothesis that hypertension per se exerts to increase the vasodepressor PGI2 synthesis in the vascular walls; if so, such changes in the .vascular eicosanoid system are likely to counteract the elevation of blood pressure or protect the vascular vessels from the damage in hypertension. In spite of this intriguing proposal, the relationship between the blood pressure elevation and vascular eicosanoid system is not fully proved. Moreover, most of the studies on the vascular eicosanoid system in hypertensive rats have been carried out in different experimental conditions. This makes it difficult to interpret the results or compare them each other. Thus, in this study, to reveal the possible correlation between vascular eicosanoid system and elevation of blood pressure, we examined, under constant experimental conditions, the alterations of eicosanoid synthesis in the vascular walls from various experimental hypertensive rat models with different mechanisms for hypertension.
There is an increasing amount of evidence that the arterial vessels are capable of producing various vasodepressor or vasoconstrictor substances, the balance of which is expected to play a role in modulation of the vascular contractility or remodeling of the arterial structure through platelet-vascular wall interactions. In this context, eicosanoids, e.g. prostacyclin (PGI,) and thromboxane (TXA& have attracted much attention because the vascular walls have a large capacity to generate these potent vasoactive substances (1, 2). In fact, there is some evidence that the vascular eicosanoid system is altered in experimental rat models for human hypertension (3-8). In Dahl saltsensitive (Dahl S) rats, vascular PGIz generation is lowered and the thromboxane production is enhanced even in a prehypertensive state (9). Moreover, the PGIz generating capacity is restored to the control level of Dahl salt-resistant (Dahl R)
Date received 19 December 1990 Date accepted 28 February 1991
179
180
Prostaglandins Leukotrienes
and Essential Fatty Acids
MATERIALS AND METHODS Rat models for genetic hypertension Male spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) were bred at University of Tokyo, Tokyo, Japan. After weaning, the rats were fed a regular (0.6% NaCl) laboratory chow and given tap water ad libitum during the experiment and maintained for 5 weeks or 15 weeks. Male Dahl salt-sensitive (Dahl S) and Dahl saltresistant (Dahl R) rats were from Brookhaven National Laboratory, Upton, New York, USA. After weaning, Dahl rats were assigned to 1) rats fed a low salt (0.3% NaCl) diet or 2) rats fed a high salt (4%) diet. Tap water was given ad libitum. The rats were maintained for 8 weeks. Deoxycorticosterone (DOCA)-salt hypertensive rats Male heminephrectomized Wistar rats aged 7 weeks were assigned to 4 groups; 1) control rats given only water, 2) salt rats given 1% saline ad libitum, 3) DOCA rats given 100 mg deoxycorticosterone acetate (DOCA)/kg body weight and tap water and 4) DOCA-salt rats given 100 mg DOCA/kg body weight and 1% saline. The rats were fed a regular laboratory chow and maintained for 1 or 8 weeks. Renovascular hypertensive rats Two-kidney, l-clip (2KlC) and l-kidney, l-clip (1KlC) models of renovascular hypertension were developed, using 7-week-old and 11-week-old male Wistar rats, respectively. To establish 2KlC hypertension, a 0.2 mm silver clip was introduced in the left main renal artery without manipulating the contralateral renal artery under pentobarbital anesthesia (50 mg/kg body weight). In the shamoperated, control rats, the left renal artery was carefully isolated. To establish 1KlC hypertension, the right kidney was totally removed and the left renal artery was partially constricted by a 0.25 mm silver clip. In the sham-operated, control rats, the right kidney was nephrectomized and the left renal artery was isolated without clipping. The rats were fed a regular laboratory chow and given tap water. 2KlC rats were maintained for 8 weeks and 1KlC rats for 4 weeks.
titia was carefully removed using forceps, and approximately 50 mm* aortic strips were prepared. The aortic strips were incubated in 2 ml of D-PBS (pH 7.35) at 37°C for 30 min. The amounts of PG12 and TXA2, released from the aortic strip into the media, were measured by radioimmunoassay method in the forms of 6-keto-prostaglandin F1, (6-keto-PGF,,) and thromboxane B2 (TXB2), respectively (9). Briefly, the assay mixture consisted of 0.1 ml of (3H)eicosanoid (lo4 dpm), 0.1 ml of a diluted sample or standard solution, and 0.1 ml of a diluted antibody solution. The assay mixture was incubated at 4°C for 24 h. To separate the bound from the free (3H)eicosanoid, 0.1 ml of a dextrancoated charcoal solution (2.5% charcoal and 0.25% dextran) was added, and the mixture was immediately spun at 1000 g at 4°C for ‘5 min. The radioactivity of the bound (3H)eicosanoid was counted using an automatic liquid scintillation counter. The antisera were all raised in rabbits in our laboratory, using eicosanoid-coupled thyroglobulin and complete Freund’s adjuvant as the immunogens. The immunization was repeated every 2 weeks for 4 months. Anti-6-keto-PGFi, serum crossreacted 1% with PGEz, 2% with PGFz,, 0.08% with PGD,, 0.01% with TXB2 and less than 0.001% with arachidonate. Anti-TXB, serum crossreacted 0.005% with 6-keto-PGFi,, 0.007% with PG&,, 0.018% with PGFz,, 0.06% with PGD2 and less than 0.001% with arachidonate. Reagents Reagents were all of analytical grade. (3H) eicosanoids were purchased from Amersham International, Buckinghamshire, UK. Authentic eicosanoids for radioimmunoassay were gifts from Ono Pharmaceutical Co Ltd, Osaka, Japan. Statistical analysis The values are expressed as means + SEM. The difference was assessed by the Student’s t-test or one way analysis of variance. A p value less than 0.05 was considered as statistically significant.
RESULTS Spontaneously hypertensive rats
Eicosanoid production by aortic walls Systolic blood pressure was measured by the tailcuff method of Friedman (11). At the end of feeding period, the descending thoracic aortae were quickly removed from the decapitated rats. The aortae were placed in ice-chilled Dulbecco’s phosphate-buffered saline solution (D-PBS; Gibco Laboratories, Grand Island, NY, USA). The adven-
Table 1 presents the averaged systolic blood pressure of SHR and WKY. Although 5-week-old SHR remained completely normotensive, the systolic blood pressure was 10 mmHg higher than the agematched WKY (p < 0.01). In contrast, 15-week-old SHR established systolic hypertension, as compared with the age-matched WKY (189 vs 134 mmHg, p < 0.001).
Eicosanoid and Hypertension Tat& 1 Averaged systolic bloods pressure of SHR and WKY Strain
181
Table 2 Averaged systolic blood pressure of Dahl S and Dahl R rats
Systolic blood pressure (mmHg) Strain
WKY SHR
5-week-old
15week-old
109 f 3 (20) 119 f 2* (20)
134 rf: 3 (10) 189 + 4** (10)
Numbers in a parenthesis represent the numbers of rats. *p c 0.01, **p < 0.001 vs the respective control values of WKY.
Dahl R Dahl S
Systolic blood pressure (mmHg) 0.3% NaCl diet
4% NaCl diet
130 + 3 (10) 143 + 2* (10)
124 f 2 (10) 166 + 3** (10)
Numbers in a parenthesis represent the numbers of rats. *p. < 0.005, **I) < 0.001 vs the respective control values of dahl R rats. ’
I‘XA,
I
P< 0.661
0
WKY SUK S-w&-old
WKY SHK l%ue,k-old
SHR S*l,ak-old
; YKY
WKY SHII 1 S-weak-old
Fig. 1 Vascular eicosanoid generation in SHR and WKY. The left graph shows the production of PGIz in the aortic walls and the right graph vascular TXA, generating capacity. The open bars and solid bars represent WKY and SHR, respectively.
The amounts of PG12 and TXA2 generated by the aortic strips from SHR and WKY are shown in Figure 1. In the prehypertensive state, there was no difference in the PG12 production between SHR and WKY (left graph, Fig. 1). In contrast, the aortic strips from 15-week-old, hypertensive SHR exhibited a larger capacity to generate PGI,! than those of 15week-old, normotensive WKY (32.3 + 3.9 vs 17.6 + 1.0 ng/mg/30 min, p < 0.002). With regard to the vascular TXAz generation in SHR, the production was significantly increased in both prehypertensive and hypertensive states, compared with the respective controls (365 f 26 vs 245 f 16 pg/mg/30 min for prehypertensive rats, p < 0.001; 350 f 16 vs 297 + 14 pg/mg/30 min for hypertensive rats, p < 0.02) (right graph, Fig. 1).
Fig. 2 Vascular eicosanoids generation in Dahl rats. .The left graph illustrates PGIz generating capacity of the aortic walls and the right graph vascular TXA, production. The open bars (R) and solid bars (S) represent Dahl R and Dahl S rats, respectively.
(10.2 + 1.5 vs 16.8 f 2.7 ng/mg/30 min, p < 0.03). In contrast, when Dahl S rats were fed a high salt diet, the PGIt generation was restored to the control level of Dahl R rats (15.3 f 2.9 vs 15.0 f 2.2 ng/mg/30 min). On the other hand, the vascular TXA2 production was enhanced in Dahl S rats when compared with Dahl R rats, irrespective of the hypertensive state. DOCA-salt hypertensive rats Table 3 shows the systolic blood subgroups in DOCA-salt study. difference in the averaged systolic among the groups when the rats 1 week after the loading. However,
pressures of 4 There was no blood pressure were examined after 8 weeks,
Dahl rats As shown in Table 2, Dahl S rats stayed in a prehypertensive state on a low salt diet although the blood pressure was 13 mmHg higher than control Dahl R rats. When Dahl S rats were challenged with a high salt diet for 8 weeks, the blood pressure was significantly elevated, compared with normotensive, control Dahl R rats. Vascular eicosanoid production in Dahl rats is illustrated in Figure 2. The aortic strips from Dahl S rats on a low salt diet had a significantly lowered production of PGI2, as compared with Dahl R rats
PROST.
c
Table 3 Systolic blood pressure of DOCA-salt hypertensive rats Group of rats
Control 1% saline DOCA DOCA-salt
Systolic blood pressure (mmHg) l-week stage
g-week stage
119 + 116 + 112 f 121 +
120 f 120 + 149 + 183 +
l(6) 4 (6) 5 (6) 5 (6)’
5 3 5* 7**
(6) (7) (7) (7)
Numbers in a parenthesis represent the numbers of rats. F values are 0.97 for l-week stage (p > 0.1) and 36.74 for &week-study (p < O.OOl), respectively. *p ‘)7- IOI in Clinical Pharmacoloav of Prostacvclin. il.cwis P J, O’Grady J eds) Ravyn Press. Ne& York, 1981. Suhhiah M 1’ K, Bale L K. Dinh D M. Kottkc B A. Dcitemcycr I). Regional aortic diffcrcnccs in
184
7.
8.
9.
10.
11.
12.
13.
14.
Prostaglandins Leukotrienes and Essential Fatty Acids
atherosclerosis-susceptibility: changes in prostaglandin biosynthesis and cholesterol accumulation in response to desoxycorticosterone (DOCA)-salt induced hypertension. Virchows Archives 37: 309-315, 1981. Botha J H, Leary W P, Asmal A C. Enhanced release of ‘PGI,-like’ substance in experimental hypertension. Prostaglandins and Medicine 3: 251-252,1979. Taube C h, Hoffman P, Forster W. Enhanced thromboxane production in the aorta of spontaneously hypertensive rats in vitro. Prostaglandins Leukotrienes and Medicine 4: 431-438,198O. Uehara Y, Tobian L, Iwai J, Ishii M, Sugimoto T. Alterations of vascular prostacyclin and thromboxane A, in Dahl genetical strain susceptible to salt-induced hypertension. Prostaglandins 33: 727-738,1987. Soma M, Manku M S, Jenkins D K, Horrobin D F. Prostaglandins and thromboxane outflow from the perfused mesenteric vascular bed in spontaneously hypertensive rats. Prostaglandins 29: 323-333,1985. Friedman M, Freed S C. Microphonic manometer for indirect determination of systolic blood pressure in the rat. Proceedings of the Society for Experimental Biology and Medicine 70: 670-672, 1949. Botha J H, Leary W P. Mechanical reduction in pressure and pulse pressure decreases the ability of hypertensive rat aortas to produce ‘PGIr-like’ activity. Prostaglandins and Medicine 6: 267-268, 1981. Uehara Y, lshimitsu T, Ishii M, Sugimoto T. Prostacyclin synthase and phospholipases in the vascular wall of experimental hypertensive rats. Prostaglandins 34: 423-432, 1987. Lansman J B, Hallam T J, Rink T J. Single stretch-activated ion channels in vascular
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19.
20.
21.
22.
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