Effects on plasma angiotensin-converting enzyme activity and circulating renin of lisinopril and enalapril alone and in combination with propranolol in healthy volunteers

The effects on plasma angiotensin-converting enzyme activity and renin activity of the two long-acting angiotensin-converting enzyme inhibitors, lisinopril and enalapril, alone and in combination with propranolol were studied. In an open, randomised, cross-over design 12 healthy volunteers received orally enalapril 20 mg alone, enalapril 20 mg in combination with propranolol 80 mg, lisinopril 20 mg alone, and lisinopril 20 mg in combination with propranolol 80 mg. Plasma angiotensin-converting enzyme activity and plasma renin activity were measured for 24 h after each treatment period. Lisinopril and enalapril reduced plasma angiotensin converting enzyme activity substantially and equally at six hr (-70%, P<0.05) and 12 hr (-65%, P<0.05), irrespective of combination with propranolol. At 24 hr plasma angiotensin-converting enzyme activity remained significantly suppressed only after lisinopril (-60%, P<0.05). Plasma renin activity increased almost ten times after ingestion of both angiotensin-converting enzyme inhibitors. but the effect lasted significantly longer after lisinopril than after enalapril. beta-Adrenergic blockade blunted the effect on the increase in plasma renin activity induced by both angiotensin-converting enzyme inhibitors. Our results show that the effect of lisinopril on plasma angiotensin-converting enzyme activity and plasma renin activity lasted longer than that of enalapril. beta-Adrenergic blockade suppressed the effect on elevated plasma renin activity, but did not influence the effect of angiotensin-converting enzyme inhibitors on plasma angiotensin-converting enzyme activity.