Hypotensive effect of water restriction in the two-kidney one-clip hypertensive rat

In two-kidney one-clip hypertensive rats we evaluated the effect of water restriction on the development and maintenance of severe hypertension (systemic blood pressure 200-230 mmHg). After application of renal arterial clips in rats allowed access to water for 1 or 2 h daily, BP stabilized at 180-190 mmHg. No increase in water intake occurred and plasma renin activity(PRA) (measured before the drinking period) was significantly below the levels observed in ad libitum-drinking hypertensive rats. In rats administered 4 ml water/100 g body weight twice daily by gavage, development of hypertension was more clearly suppressed. Blood pressure increased slowly and reached levels of only 150-170 mmHg. Furthermore, PRA was significantly lower in this group compared with ad libitum-drinking hypertensive animals. In rats with established (4-5 wk) renal hypertension, restriction of water intake to 1 or 2 h daily resulted in a rapid decrease in BP of about 30 mmHg. Daily administration of Pitressin tannate to hypertensive rats allowed free access to water induced a similar decrease in BP as well as suppression of PRA. These results indicate that the hypotensive effect of water restriction in the two-kidney one-clip hypertensive rat model may be mediated, at least in part, through elevated circulating levels of vasopressin that subsequently inhibit renin release.