Effects of pimozide on noradrenergic transmission in rabbit isolated ear arteries.
In the rabbit ear artery both dopamine and noradrenaline inhibit stimulation-induced (S-I) transmitter noradrenaline efflux. Pimozide, which is reported to be a specific dopamine receptor antagonist, was used to further study the effects of dopamine on transmitter efflux. In a concentration of 0.2 micrometer pimozide blocked the inhibition of S-I efflux produced by 0.5 micrometer dopamine but not that produced by 0.5 micrometer noradrenaline. In a concentration of 10 nM, pimozide enhances transmitter release and vasoconstrictor responses to sympathetic nerve stimulation; this may be due to blockade of feedback inhibition of transmitter release by endogenous dopamine. In a concentration of 1 micrometer, pimozide reduced transmitter release and vasoconstrictor responses to sympathetic nerve stimulation. Vasoconstrictor responses to noradrenaline and histamine are antagonized by pimozide in a noncompetitive manner.
D000818:Animals; D001001:Anura; D001158:Arteries / Q000294:innervation*; D003042:Cocaine / Q000494:pharmacology; D004298:Dopamine / Q000494:pharmacology; D004347:Drug Interactions; D004558:Electric Stimulation; D006325:Heart Atria / Q000187:drug effects; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D009638:Norepinephrine / Q000502:physiology*; D010868:Pimozide / Q000494:pharmacology*; D011817:Rabbits; D013564:Sympathetic Nervous System / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects*; D014662:Vasoconstrictor Agents
D014662:Vasoconstrictor Agents; D010868:Pimozide; D006632:Histamine; D003042:Cocaine; D004298:Dopamine; D009638:Norepinephrine