The influence of dopamine and dopaminergic agonists on the contractions of field stimulated rat vas deferens.

: In isolated field stimulated rat vas deferens frequency-response curves were shifted to the right by noradrenaline, dopamine, apomorphine, bromocriptine and nomifensine. Piribedil was found to be inactive. Phentolamine antagonized the effect of each active drug. The inhibition due to dopamine and apomorphine was also counteracted by haloperidol and sulpiride, while that caused by bromocriptine and nomifensine only by sulpiride. On the basis of these results an interaction was suggested between the presynaptic alpha and dopaminergic receptors: in the rat vas deferens dopaminergic receptors might activate alpha 2 receptors. The agonists increased the slope of the frequency-response curves. The drugs had a reversible activity on the vas deferens, except for bromocriptine which could not be removed by repeated wash-outs from the organ.