Nicardipine causes sympathetic activation that does not involve baroreceptor reflex tachycardia in conscious sinoaortic-denervated dogs

Nicardipine-induced tachycardia is generally attributed to the involvement of the baroreflex. The effects of nicardipine on blood pressure (BP) and heart rate (HR) as well as on plasma catecholamine levels were studied in six conscious dogs made hypertensive by sinoaortic denervation. Nicardipine (50, 100 and 200 micrograms/kg i.v.) induced both a significant decrease in mean BP and a marked increase in HR in these dogs whereas the catecholamines rose significantly. Nicardipine-induced tachycardia cannot be explained by a baroreflex mechanism only. It is suggested that nicardipine induces an increase in HR and sympathetic tone, probably by a direct action on central cardiovascular mechanisms.