Chronic converting enzyme inhibition facilitates baroreceptor resetting to hypertensive levels

We investigated the acute and chronic effects of converting enzyme inhibitors (captopril or enalapril) and of angiotensin II receptor blockade (DuP 753) on rapid (30-minute) baroreceptor resetting elicited by a prompt and sustained hypertensive response provoked by aortic constriction. Pressure-nerve activity curves, pressure at 50% of maximal baroreceptor activity, baroreceptor gain (slope of the curve), and systolic threshold pressure for baroreceptor activation were determined as indexes of baroreceptor function. A slight fall in mean arterial pressure after acute treatment with the converting enzyme inhibitor or DuP 753 was accompanied by a partial leftward curve shift, which is associated with a partial threshold shift and increase in gain. A maintained hypertensive stimulus caused a partial rightward curve shift and partial (49% to 56%) threshold shift to hypertensive levels in both acutely treated and control rats. The hypertensive stimulus provoked a partial rightward curve shift and complete (88% to 94%) threshold shift to hypertensive levels in chronically treated rats. The effect of enalapril on baroreceptor function was unaltered by the bradykinin antagonist Hoe 140. These data demonstrate that chronic inhibition of converting enzyme or blockade of angiotensin II receptors facilitates rapid resetting of the baroreceptors to hypertensive levels caused by partial aortic constriction without a change in baroreceptor sensitivity.