The ability of pimozide to prevent inhibition by dopamine analogs of cardioaccelerator nerves in cat hearts.
The dopamine receptor blocking agent, pimozide, antagonized inhibitory actions of apomorphine, N,N-dimethyldopamine and 5,6-dihydroxy-2-dimethyl-aminotetralin (M-7) on stimulation-induced positive chronotropic responses of cat hearts in both in vivo and in vitro experiments. Pimozide did not antagonize the inhibitory effect of clonidine in vitro experiments. Phentolamine, an alpha-adrenergic blocking agent, antagonized the inhibitory actions of dopamine analogs at 1.10 mug/ml concentration in in vitro experiments. Phentolamine, 0.3 mug/ml, only attenuated the response of N,  N-dimethyldopamine but did not antagonize the effects of apomorphine and M-7. Lower concentration of phentolamine, 0.1 mug/ml, showed marked inhibition to the inhibitory effect of clonidine. Both phentolamine and pimozide potentiated stimulation-induced positive chronotropic responses of cat right atria. Possibility of the presence of dopaminergic inhibitory system near the alpha-adrenergic inhibitory system in cardioaccelerator nerve terminal is discussed.
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D002415:Cats; D003000:Clonidine / Q000494:pharmacology; D004298:Dopamine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D010646:Phentolamine / Q000494:pharmacology; D010868:Pimozide / Q000494:pharmacology*
D010868:Pimozide; D003000:Clonidine; D001058:Apomorphine; D004298:Dopamine; D010646:Phentolamine