The effect of captopril on renin, angiotensin II, cortisol and aldosterone during ACTH-infusion in man.

Abstract

Prolonged low-dose ACTH infusion (5 or 10 iU/24h) leads to a transient increase in plasma renin activity and angiotensin II concentration in normal man. In order to find out whether the increase in angiotensin II stimulates aldosterone secretion, 12 normal men received ACTH (10 IU/24h) for 34 hours altogether, 6 with and 6 without simultaneous administration of captopril, 50 mg every 6 hours. Captopril prevented the increase in plasma angiotensin II during ACTH infusion and lowered its levels below those on the control day two hours after a new dose of the converting enzyme inhibitor was given. The increase in plasma cortisol was similar in both groups. The increase in plasma aldosterone was significantly blunted by captopril. The early blood pressure rise and the kaliuresis during ACTH infusion were also significantly decreased in the captopril group. These results suggest that angiotensin II mediates in part the effect of ACTH on aldosterone and blood pressure during the first 2 days of infusion. Since captopril reduced plasma angiotensin II for some time below normal, it is alternatively possible that ACTH requires normal plasma angiotensin II levels for a full effect on aldosterone secretion.