Effect of enalapril on renin, angiotensin converting enzyme activity, aldosterone and prostaglandins in patients with hypertension.

Enalapril (MK-421) was administered orally as a single dose of 2.5, 5.0, 10 and 20 mg to 13 patients with either essential or renovascular hypertension. At these doses, enalapril produced a moderate reduction in both supine and standing blood pressure as well as a significant reduction in angiotensin I-converting enzyme activity, an increase in peripheral plasma renin activity and a decrease in plasma aldosterone concentration 4 to 8 hours after administration of the drug. Plasma levels of prostaglandins E1 and E2 were unchanged. The calculated ratio of urinary Na/K was increased in the patients with renal artery stenosis after enalapril. Creatinine clearance was increased in the patients with essential hypertension and reduced in the patients with renal artery stenosis. No adverse effects occurred in these patients treated with single doses of enalapril.