1. Intra-arterial pressure, baroreflex sensitivity and the baroreflex set point were measured in eight patients with essential hypertension during a control period and then after acute treatment (2 h after a 30 mg oral dose) and after chronic treatment (at least 2 months) with nicardipine hydrochloride, a calcium channel antagonist.
2. Mean intra-arterial blood pressure fell after the acute treatment from 130 ± 14 (sd) control to 118 ± 11 mmHg, P<0.05, and after chronic treatment to 112 ± 19 mmHg, P<0.05. Heart rate increased from 72 ± 11 control to 81 ± 16 beats/min, P<0.05, during acute treatment indicating activation of the baroreflex control mechanism, but returned to control values with chronic treatment (72 ± 11 control vs 69 ± 9 beats/min chronic), indicating a significant shift to the left of the baroreflex set point. There was no change in baroreflex sensitivity after either acute or chronic treatment (control 4.7, acute 4.3, chronic 5.1 ms/mmHg, P not significant for all values).
3. Nicardipine significantly reduces mean intraarterial pressure both acutely and chronically; the latter is associated with a return of the heart rate to control values due to resetting of the baroreflex control mechanism.