Influence of sublingual captopril on plasma catecholamine levels during hypertensive emergencies and cold immersion.

Experimental evidence of captopril-induced inhibition of sympathetic activity, mediated by decrease in angiotensin II production, is presented. The blood pressure, plasma catecholamine, plasma renin activity, and plasma aldosterone responses to a single dose of sublingual captopril in 23 patients with hypertensive emergencies were evaluated. The major correlation found was between the captopril-induced decrease in blood pressure and the decrease in plasma norepinephrine levels (r = 0.57, p less than 0.01). In another 11 hypertensive patients with normal or high renin levels, captopril lowered by 65 percent the increase in plasma norepinephrine induced by cold immersion of the forearm. In both circumstances, plasma renin and aldosterone levels changed in accordance with the expected inhibition of angiotensin converting enzyme activity. These data suggest that, in selected circumstances in hypertensive patients, captopril exhibits a depressive influence on sympathetic activity along with the inhibition of the renin-angiotensin system.