Significance of kallikrein-kinin and renin-angiotensin systems in the hypotensive mechanism of angiotensin-I converting enzyme inhibitors in essential hypertensives.

This study was undertaken to further clarify the role of kallikrein-kinin and renin-angiotensin systems in the hypotensive mechanisms of the angiotensin-I converting enzyme inhibitor by using highly sensitive and specific radioimmunoassays in patients with essential hypertension. Captopril was administered for 14 days (chronic effect), and the acute effects of captopril, alacepril and ramipril were also studied in the in-patients with essential hypertension. All of these converting enzyme inhibitors rapidly decreased the blood pressure and plasma angiotensin II levels, and increased plasma and urinary kinin and plasma renin activity in the acute effect. Following the administration of captopril for 14 days, these decreases and increases were maintained. The change of blood pressure was significantly correlated negatively with that of plasma kinin levels and positively with that of plasma angiotensin II levels in both the acute and chronic effect of converting enzyme inhibitors. Urine volume and urinary sodium excretion were markedly augmented, while both the change of urine volume and that of urinary sodium excretion were negatively correlated with the change of blood pressure in the chronic effect. These findings suggest that the hypotensive effect of converting enzyme inhibitors might be caused by an increase of plasma kinin and a decrease of plasma angiotensin II, and in part by an augmentation of urine volume and urinary sodium excretion. In this drug treatment, the renal kallikrein-kinin system may also play some role in the increase of urine volume and urinary sodium excretion through the increased kinin in the kidney.