Effects of angiotensin-converting enzyme inhibition on blood pressure and plasma renin activity in essential hypertension.

Oral converting enzyme inhibitor SQ14225 was administered in 11 patients with essential hypertension, in order to investigate the role of the renin-angiotensin system in the regulation of blood pressure in essential hypertension. In the sodium-repleted state (150 mEq sodium intake for 6 days) in 11 patients, converting enzyme inhibitor decreased the average mean blood pressure from 113 +/- 2 to 106 +/- 2 mm Hg (p less than 0.001). Plasma renin activity increased with sodium depletion (30 mEq sodium intake for 3 days after furosemide treatment) from 1.26 +/- 0.07 to 3.26 +/- 0.48 ng/ml/hr (p less than 0.001). In the sodium-depleted state the hypotensive effect of SQ 14225 was more pronounced (mean blood pressure 108 +/- 2 to 93 +/- 3 mm Hg). The decrease in mean blood pressure caused by the inhibitor correlated to the basal plasma renin activity (r = -0.53, p less than 0.02, n = 22 measurements). The results indicate that the renin-angiotensin system participates in the regulation of blood pressure in essential hypertension, even in the sodium-repleted state. This role of the renin-angiotensin system in blood pressure regulation becomes more crucial during sodium depletion.