The effect of an acute or chronic treatment with indomethacin on the blood pressure of DOCA/salt and spontaneously hypertensive rats

Effect of elastase on blood pressure and urinary excretions of prostaglandins and catecholamines in the spontaneously hypertensive rat (SHR)

The effects of elastase on blood pressure (B.P.) and the urinary excretions of prostaglandins (PGs) and catecholamines in the spontaneously hypertensive rat (SHR) were investigated. Male SHRs (n = 20), castrated at 4 weeks of age, were divided into 2 groups. Elastase was then dissolved in saline (5 mg/ml) and injected subcutaneously (10 mg/kg of body weight) into the SHRs of one of the 2 groups (n = 10) at 5 to 13 weeks of age, and the same dose of saline only was injected subcutaneously into the SHRs of the other group (n = 10) as a control during the same period. B.P. was measured by the tail-cuff method every 2 weeks. Urine sampling and measurement of body weight (B.Wt.) were also performed every 2 weeks. The B.P. in the elastase-administered group (184.1 +/- 3.3 mmHg) was found to be significantly lower (p less than 0.02) than that of the control group (198.0. +/- 4.3) at 9 weeks of age. A significant difference (p less than 0.01) in B.P. between the control group (204.0 +/- 4.5) and the elastase-administered group (187.3 +/- 2.7) was also observed at 13 weeks of age. The urinary excretion of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) in the control group (5.1 +/- 0.4 ng/day/100 g B.Wt.) at 11 weeks of age was significantly lower (p less than 0.05) than that of the elastase-administered group (10.4 +/- 1.3).(ABSTRACT TRUNCATED AT 250 WORDS)

A possible role of gonad and renal prostaglandin E2 on the development of hypertension in spontaneously hypertensive rats

A possible role of prostaglandin E2 (PGE2) in the regulation of blood pressure in spontaneously hypertensive rats (SHR) was investigated. The inhibition of PG synthesis by chronic indomethacin treatment accelerated the elevation of blood pressure with the tendency to decrease renal PGE2. We, therefore, confirmed that PGE2 in SHR may play a role in the antihypertensive mechanism. In this connection, the participation of renal PGE2 in the retardation of the development of hypertension in male SHR induced by orchiectomy was examined. Urinary PGE2 which reflects the renal PGE2 level tended to keep a higher level in the castrated group. Urinary electrolytes excretion also inclined to augment in the castrated group throughout the experiment. These results indicate that renal PGE2 may participate in the gonads-mediated blood pressure regulation system, although the mechanism of the retardation of spontaneous hypertension induced by orchiectomy remains obscure.

Differences in arachidonic acid metabolism and effects of aspirin between one- and two-kidney Goldblatt hypertensive rats

Vasodepressor responses to prostacyclin, nitroprusside and arachidonic acid were compared in two groups of anaesthetized, two-kidney, one-clip Goldblatt rats. The groups were composed of rats which had high blood pressure (greater than 150 mmHg systolic) or normal blood pressure (less than 140 mmHg systolic). The vasodepressor effects of prostacyclin and nitroprusside and arachidonic acid did not differ significantly between hypertensive and normotensive groups when measured as percentages of resting blood pressure. Thus, in contrast to one-kidney Goldblatt hypertensive rats, there is no evidence for increased vascular conversion of arachidonic acid to prostacyclin in the two-kidney hypertensive model. The effect of cyclo-oxygenase inhibition on development of hypertension in one- and two-kidney Goldblatt rats was also studied by treating them daily with aspirin (200 mg/kg orally) from 3 days before until 3 weeks after clipping the renal artery. Aspirin-treated two-kidney rats developed significantly higher blood pressures than vehicle-treated controls, but the blood pressures of aspirin-treated one-kidney rats increased less after clipping than those of vehicle-treated controls. It appears paradoxical that transformation of arachidonic acid to prostacyclin is increased, while aspirin has a blood pressure lowering effect in one-kidney Goldblatt rats. It is suggested that there might be a more fundamental disturbance in arachidonate metabolism in hypertension which might contribute to increased vascular reactivity.

Metabolism of arachidonic acid in the aorta of spontaneously hypertensive rats

1. The metabolism of [14C]-arachidonic acid has been studied in isolated aortae from age-matched spontaneously hypertensive (SH) rats and their normotensive Wistar Kyoto (WK) controls. 2. High pressure liquid chromatography of extracts of the incubation mixture from both SH and WK rats revealed the presence of 6-oxo-prostaglandin F1 alpha, the hydration product of prostacyclin, and a single, broad peak of unknown metabolites. No thromboxane B2, or prostaglandins E2 of F2 alpha could be detected in aortic incubations. 3. The SH rats produced significantly more 6-oxo-prostaglandin F1 alpha than the WK rats, but there was no difference between the strains in the proportion of label appearing in the unknown peak of the chromatograms. 4. These data confirm that vascular tissue of SH rats has enhanced ability to transform arachidonic acid into prostacyclin. Induction of these enzymes may be an adaptive response to elevated blood pressure, but the mechanism of this effect has yet to be elucidated.

Increased conversion of arachidonic acid to vasodilator prostanoids in spontaneously hypertensive rats

1. Vasodepressor responses to intravenous injection of prostacyclin, arachidonic acid, and nitroprusside were examined in anaesthetized, spontaneously hypertensive rats (SHR) of the Okamoto strain, and in their normotensive Wistar-Kyoto (WKY) controls. 2. Depressor responses to prostacyclin and nitroprusside did not differ significantly between the two strains. 3. The vasodepressor effects of arachidonic acid were greater and much more prolonged in SHR than in WKY. In rats treated with indomethacin (2 mg/kg) arachidonic acid induced only transient depressor responses which did not differ significantly between these strains. 4. It is concluded that SHR do not differ from WKY in their sensitivity to prostacyclin but they have enhanced ability to transform exogenous arachidonic acid into vasodilator prostanoids.

Effects of prostaglandins E2, I2 and F2 alpha, arachidonic acid and indomethacin on pressor responses to norepinephrine in conscious rats

The effects of prostaglandins E2 (PGE2), I2 (PGI2) and F2 alpha (PGF2 alpha), arachidonic acid and indomethacin on pressor responses to norepinephrine were examined in conscious rats. Intravenously infused PGE2, (0.3, 1.25 micrograms/kg/min), PGI2 (50, 100 ng/kg/min), PGF2 alpha (1.8, 5.4 micrograms/kg/min) and arachidonic acid (0.7, 1.4 mg/kg/min) did not change the basal blood pressure. Both PGE2 and PGI2 significantly attenuated pressor responses to norepinephrine, whereas PGF2 alpha significantly potentiated them. Arachidonic acid, a precursor of the prostaglandings (PGs), significantly attenuated pressor responses to norepinephrine. Since the attenuating effect of arachidonic acid was completely abolished by the pretreatment with indomethacin (5 mg/kg), arachidonic acid is thought to exert an effect through its conversion to PGs. On the contrary, intravenously injected indomethacin (0.2--5.0 mg/kg) facilitated pressor responses to norepinephrine in a dose-related manner without any direct effect on the basal blood pressure. These results suggest that endogenous PGs may participate in the regulation of blood pressure by modulating pressor responses to norepinephrine in conscious rats.

Single-dose captopril administration in DOCA/salt rats: reduction of hypotensive effect by indomethacin

The effect of an oral angiotensin I converting enzyme inhibitor, SQ 14225 (Captopril) on blood pressure and plasma renin activity (PRA) was studied in deoxycorticosterone-salt (DOCA/salt) hypertensive rats. Intraperitoneal (ip) injection of captopril (1 mg/kg) produced a significant fall in systolic blood pressure (23.4 +/- 5.0 mm Hg, p < 0.001) whereas no significant change in blood pressure occurred in control rats. Indomethacin (IDM) (2.5 mg/kg ip) pretreatment significantly (p < 0.01) attenuated the hypotensive action of captopril in DOCA/salt rats. PRA was markedly suppressed in DOCA/salt rats (0.3 +/- 0.1 ng/ml/hr) when compared with the normotensive controls (4.4 +/- 2.2 ng/ml/hr, p < 0.001) at baseline. Captopril induced a significant rise in PRA in both groups of rats. These responses were not significantly altered by IDM pretreatment. The hypotensive effect of captopril in the DOCA/salt model may be mediated by prostaglandins since their synthesis is inhibited by indomethacin.