Effect of chronic inhibition of angiotensin converting enzyme on baroreceptor reflex in essential hypertension.

We examined baroreflex function and plasma angiotensin II (Ang II) before and after the treatment with an angiotensin converting enzyme inhibitor (ACEI) in eight inpatients with essential hypertension (EHT). Baroreflex sensitivity (BS), expressed as a slope of linear relationship between %-changes in mean blood pressure (BP) and those in plasma concentration of norepinephrine (pNE), was greater during BP reduction by sodium nitroprusside (SNP) than during BP elevation by phenylephrine (PE). Enalapril treatment for 7 days reduced BP without a significant change in heart rate and pNE. It also increased the BS in two cases during SNP infusion and in four cases during PE infusion. Ang II was not significantly reduced after enalapril, while plasma ACE activity was suppressed by about 80% and plasma renin activity (PRA) was elevated. The changes in BS did not correlate with the changes in Ang II. The shift of barofunction curve with an enhancement of BS by enalapril therapy might not be attributed solely to the interaction between circulating Ang II and central baroreflex mechanisms.