Effects of m-nisoldipine on arterial baroreflex sensitivity in anesthetized rats

Baroreflex sensitivity (BRS) in anesthetized rats was measured as the slope of the regression line of the concomitant maximal change in heart rate (delta R-R) and blood pressure (delta BP) induced by bolus i.v. phenylephrine or sodium nitroprusside, m-nisoldipine (m-Nis) i.v. 5, 10, 20 micrograms.kg-1 depressed the BRS (2.6 +/- 0.2, 2.4 +/- 0.3, 1.6 +/- 0.2, or 1.7 +/- 0.1, 1.6 +/- 0.2, and 1.4 +/- 0.2 ms.kPa-1, respectively) compared with before medication (P < 0.01). m-Nis may act directly on carotid sinus to depress the BRS, but not through cardiac beta or M receptor nor through central nervous system.