A discrepancy between the effects of a single oral dose of captopril on blood pressure, plasma renin activity, and serum angiotensin-converting enzyme levels

Abstract

The effects of a single oral dose (100 mg) of the angiotensin-converting enzyme (ACE) inhibitor, captopril (SQ 14,224), on blood pressure (BP), plasma renin activity (PRA), plasma aldosterone (PA), and serum ACE were investigated in 18 patients with essential hypertension (EH) and in 4 with renovascular hypertension (RVH). in most patients, SQ 14,225 caused a significant reduction of BP during the subsequent 6 h, particularly in RVH patients. A significant correlation between basal PRA levels and BP reduction was observed only by considering all the patients together. After ACE blockade, a significant increase of PRA was observed in RVH and in normal-renin EH patients, but not in EH patients with lower PRA. Maximal serum ACE inhibition (over 50%) occurred after 2 h but diminished after 4 h and 6 h, whereas the BP decrease persisted for 6 h. After 3-day treatment with indomethacin (six patients) captopril's antihypertensive action was blunted, despite a reduction of baseline PRA levels and of captopril-induced PRA elevation. The antihypertensive effects of SQ 14,225 in low-renin EH patients, the lack of effect of ACE blockade on renin secretion in these patients, and the reduction of the antihypertensive effects of SQ 14,225 after indomethacin refute the interpretation of purely angiotensin-related antihypertensive mechanism.