Role of kallikrein-kinin system in the hypotensive mechanisms of converting enzyme inhibitors in essential hypertension.

Patients with essential hypertension were studied to clarify the role of the kallikrein-kinin system in the hypotensive actions of angiotensin I converting enzyme inhibitors. Captopril, alacepril, ramipril, and altiopril administered in single doses rapidly decreased blood pressure and plasma angiotensin II levels, and increased plasma and urinary kinins as well as plasma renin activity. Following administration of captopril for 14 days, similar effects were observed. Urine volume and urinary sodium excretion were augmented after acute and chronic administration of captopril. The patients who received ramipril and altiopril were divided into renin subgroups. In the normal-renin group, the change in blood pressure was accompanied by an increase in plasma kinin level and a decrease in plasma angiotensin II level. However, in the low-renin group, although these drugs reduced blood pressure and increased plasma kinin, no significant change was observed in plasma angiotensin II levels. These findings suggest that (a) in patients with normal renin activity, the hypotensive effect of converting enzyme inhibitors might be caused by an increase in plasma kinin and a decrease in plasma angiotensin II, but in the low-renin group, the increase in plasma kinin levels may be more important; and (b) the augmentation of urine volume and urinary sodium excretion may also be related to the hypotensive effects of the converting enzyme inhibitors during long-term administration.