title: Prejunctional inhibitory dopamine receptors in the rat isolated vas deferens.
abstract: The effects of apomorphine, clonidine, dopamine and noradrenaline as well as their antagonists were studied on the neuronally stimulated rat vas deferens in vitro. All agonists investigated significantly inhibited neuronally induced contractions of the vas deferens. The following IC50 values were obtained: clonidine 4.2 nM, dopamine 16.9 nM, apomorphine 58 nM and noradrenaline 455 nM. Phentolamine, yohimbine and pimozide significantly enhanced, whilst haloperidol inhibited the twitch responses. All the antaganists reduced, to a varying degree, the twitch-inhibitory effect of the agonists. The twitch inhibition produced by apomorphine was, however, relatively resistant to antagonism by yohimbine, whilst the inhibition produced by clonidine and noradrenaline was relatively resistant to antogonism by pimozide. The results suggest that different prejunctional receptors mediate the effects of dopamine and apomorphine on the one hand, and noradrenaline and clonidine on the other hand.
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D004298:Dopamine / Q000494:pharmacology; D006220:Haloperidol / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D010868:Pimozide / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects; D011954:Receptors, Dopamine / Q000187:drug effects* / Q000502:physiology; D014649:Vas Deferens / Q000187:drug effects*
chemical_list: D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D011954:Receptors, Dopamine; D010868:Pimozide; D006220:Haloperidol; D004298:Dopamine