The inhibitory action of dopamine on the anterior tibialis muscle preparation antagonized by pimozide and chlorpromazine.

In the cat anterior tibialis muscle preparation dopamine produces a decrease on indirectly evoked twitch contraction when it is administered intraarterially but not on intravenous injection. Edrophonium (0.3 mg/kg) exerts only a brief antagonism to the dopamine-induced inhibition. The phenothiazine derivative, chlorpromazine (CPZ, 400 mug/kg) which possesses both alpha and dopaminergic blocking properties significantly reduces the action of dopamine on skeletal muscle. However, phentolamine (1 mg/kg), an alpha adrenergic blocker is without effect, possibly indicating that the dopaminergic blocking characteristic of CPZ is responsible for decreasing the action of dopamine. A more selective dopaminergic blocking agent, pimozide (100 and 200 mug/kg) is an effective antagonist to the paralysis caused by dopamine on the anterior tibialis muscle. The results of this investigation suggests the possibility that a dopaminergic receptor may be present in or on skeletal muscle.