Hypertension after ending captopril administration: pathogenesis in 2-kidney, 1-clip rat

We have previously shown that continuous captopril administration prevents hypertension from developing in the two-kidney, one-clip (2K, 1C) rat. The present investigation was designed to determine the mechanism(s) producing the hypertension. In one series of experiments captopril prevented pressure from increasing during an 8-wk treatment period. Relative to the last day of treatment, mean arterial pressure and total peripheral resistance (TPR) were increased and cardiac output was unchanged at 3, 7, and 28 days after captopril cessation. Plasma renin activity (PRA) was unchanged 3, 7, and 14 days after captopril cessation but was elevated at 28, 49, and 56 days after captopril cessation only in 2K, 1C rats with severe hypertension (systolic blood pressure greater than 180 mmHg). Guanethidine (45 mg/kg po, bid) did not prevent the development of 2K, 1C hypertension but did prevent the hypertension from developing after cessation of captopril. Blockade of the prostaglandin system with indomethacin (5 mg/kg + 50 micrograms X kg-1 X min-1) and of the kallikrein-kinin system with aprotinin (25,000 KIU + 150 KIU X kg-1 X min-1) for 2 h had no effect on captopril's antihypertensive effect. Additionally, no change in sodium or water balance was observed after captopril cessation. Taken together these data demonstrate that hypertension after captopril cessation is due to an increase in TPR. Additionally, the rise in TPR is due to both the sympathetic nervous and the renin-angiotensin systems since both systems must be functional before pressure rises.