OCCURRENCE OF EXCITATORY DOPAMINOCEPTORS IN THE RAT AND GUINEA-PIG VAS DEFERENS

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Abstract
1. Noradrenaline and dopamine produce contractions of isolated preparations of vasa deferentia from the rat or the guinea-pig. 2. Dopamine was three to five times as potent as noradrenaline on the rat vas deferens, but was considerably less potent than noradrenaline on the guinea-pig vas deferens. 3. Phentolamine antagonized responses to noradrenaline and dopamine of vasa deferentia of both species. On the rat vas deferens the pA2 values against noradrenaline and dopamine were 7.6 and 7.4, respectively. 4. Pimozide, a dopamine antagonist, antagonized responses to dopamine on vasa deferentia of both species, but was not significantly active in antagonizing responses to noradrenaline. On the rat vas deferens, the pA2 value against dopamine was 7.9. t. The beta-adrenoceptor blocking agents, propranolol and oxprenolol slightly enhanced dopamine-induced contractions on vasa deferentia of both species. 6. It is suggested that dopamine might act on both a-adrenoceptors and dopaminoceptors in the vas deferens, and that the component due to activation of dopaminoceptors is greater in the rat than the guinea-pig.