Abstract
In the rabbit ear artery both dopamine and noradrenaline inhibit stimulation-induced (S-I) transmitter noradrenaline efflux. Pimozide, which is supported to be a specific dopamine receptor antagonist, was used to further study the efects of dopamine on transmitter efflux. In a concentration of 0.2 μM pimozide blocked the inhibition of S-I efflux produced by 0.5 μM dopamine but not that produced 0.5 μM noradrenaline. In a concentration of 10 nM, pimozide enhances transmitter release and vosoconstriction 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 μM, pimozide reduced transmitter release and vasoconstrictor responses to sympathetic nerve stimulation. Vasoconstrictor responses to noradrenaline and histamaine are antogonized by pimozide in a noncompetitive manner.
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