EVIDENCE FOR A ROLE OF INHIBITION OF SYMPATHETIC NEUROTRANSMISSION INTHE CARDIOVASCULAR EFFECTS OF INTRAVENOUSLY ADMINISTERED VERAPAMIL

The effects of intravenous administration of verapamil, nifedipine and diltiazem on sympathetic stimulation-induced increase in heart rate ( HR) and blood pressure (BP) have been investigated in chloralose-anaes thetized and artificially-ventilated cats. Verapamil (300 mu g kg(-1) i.v.) produced a significant inhibition of sympathetically-induced tac hycardia and presser responses, The same dose of verapamil did not sig nificantly alter adrenaline (2 mu g kg(-1) i.v.) induced increase in H R and BP. In contrast, neither the sympathetically-induced nor the adr enaline-induced presser and tachycardiac responses were significantly affected by nifedipine or diltiazem. These results demonstrate that pe ripherally administered verapamil but not nifedipine and diltiazem can inhibit cardiovascular sympathetic neurotransmission and this can pos sibly contribute to its effects on HR and BP.