Effects of dopaminoceptor agonists and antagonists on the rat vas deferens "in vitro"

Dopamine, noradrenaline, tyramine, amantadine and apomorphine produced concentration-related contractions of the rat vas deferens "in vitro". pD2 values of 5.35 +/- 0.12, 5.20 +/- 0.08, 4.50 +/- 0.06, and 4.50 +/- 0.10 were obtained for dopamine, noradrenaline, tyramine and apomorphine respectively. Phentolamine, haloperidol and pimozide blocked the effects of dopamine, tyramine, amantadine and apomorphine, however, noradrenaline-induced contractions were resistant to pimozide. Guanethidine (4 micrograms/ml) induced supersensitivity towards noradrenaline, almost abolished the effect of tyramine, but did not influence the effects of dopamine, amantadine and apomorphine at this concentration. These results confirm earlier reports that there are distinct dopaminoceptors in the rat vas deferens in addition to the conventional noradrenoceptors.