Differential effects of captopril and nicardipine on baroreflex control of sympathetic nerve activity and heart rate in renal hypertension

OBJECTIVE: To test the hypothesis that an angiotensin I converting enzyme inhibitor and a calcium channel blocker have different effects on the arterial baroreflex in renal hypertension. DESIGN AND METHODS: We examined the baroreflex control of renal sympathetic nerve activity and heart rate before and after blood pressure was reduced by a similar magnitude (11 +/- 1 mmHg) with intravenous captopril or nicardipine in two-kidney, one clip hypertensive (mean arterial pressure 92 +/- 2 mmHg, n = 12) and normotensive rabbits (mean arterial pressure 75 +/- 1 mmHg, n = 9) in the conscious state. Data obtained during activation and deactivation of baroreceptors were analysed with logistic function curves, and the maximum slope of the curve was taken as the sensitivity of the baroreflex. RESULTS: The maximum slopes of the curves relating mean arterial pressure to renal sympathetic nerve activity and to the heart rate in hypertensive rabbits were significantly smaller than the maximum slopes in normotensive rabbits. In renal hypertensive rabbits, the maximum slope of the mean arterial pressure-renal sympathetic nerve activity curve was increased with captopril compared with that with vehicle. In contrast, the maximum slope of the mean arterial pressure-heart rate curve was increased with nicardipine compared with that with vehicle. CONCLUSIONS: Our data indicating that the baroreflex control of renal sympathetic nerve activity was improved by captopril and that baroreflex control of the heart rate was potentiated by nicardipine suggest that these classes of antihypertensive agents had differential effects in conscious hypertensive rabbits.