Circulatory and Humoral Changes in the Reversal of Renovascular Hypertension in Sheep by Unclipping the Renal Artery

Abstract

The renal arterial clip was removed from 11 sheep with chronic experimental renovascular hypertension (previous unilateral nephrectomy, unilateral renal arterial constriction for 3 to 8 weeks, blood pressure elevated and stable). In five animals cardiac output, blood volume, plasma [Na⁺], and plasma renin concentration were measured the day before, 1 day after, and 4 days after unclipping. In the other six animals, plasma [Na⁺], plasma renin concentration, and blood angiotensin concentration were determined before and after unclipping. After unclipping, blood pressure returned to normal levels in 24 to 96 hours; cardiac output and blood volume were essentially unaltered during the period of observation. No natriuresis was seen, nor any change in plasma [Na⁺], plasma renin concentration, or blood angiotensin concentration, which remained within the appropriate normal ranges throughout. Nephrectomy of five similarly hypertensive animals, and six previously unilaterally nephrectomized normotensive sheep, was performed as a control. Variables similar to those measured before and after unclipping were determined at similar time intervals. The second nephrectomy of hypertensive animals was followed by maintained hypertension; and of normotensive animals by maintained normotension. The role of the kidney in the maintenance and reversal of chronic experimental renovascular hypertension is evaluated in the light of these results.