Reversal of renovascular hypertension: a comparison of changes in blood pressure, plasma renin, and sodium balance in two models in rats.

Blood pressure changes produced by removal of the renal artery clip in two forms of experimental renovascular hypertension in the rat (two-kidney one-clip and one-kidney one-clip hypertension) have been studied in relation to sodium balance and the renin angiotensin system. Continuous records of arterial blood pressure in conscious, freely moving animals with hypertension of less than 6 weeks' duration showed similar baseline values. After unclipping, blood pressure fell to normal levels within 12 hours of operation, and the pattern of the fall was identical in both models. Plasma renin concentration was elevated in two-kidney hypertension and fell to normal by 24 hours after operation, remaining unchanged 6 days later, whereas in one-kidney hypertension it was normal before and after unclipping. Sodium balance became positive in two-kidney hypertension within 24 hours of unclipping and remained so at 7 days, and was significantly different from that in unclipped loose-clip controls (+2.54 +/- 0.55 mmol vs. +0.46 +/- 0.55 mmol at 7 days, P less than 0.05). In one-kidney hypertension, sodium balance was negative during the first 24 hours after operation, and remained slightly negative at 7 days compared with loose-clip controls (-0.34 +/- 0.23 mmol). The similarity in the pattern of blood pressure fall in these two models of renovascular hypertension, despite qualitative differences in the response of sodium balance and the renin-angiotensin system, suggests that a common mechanism is activated by unclipping. This mechanism cannot be explained solely in terms of changes in sodium balance or activity of the renin-angiotensin system.