Evidence for the existence of prejunctional receptor sites for dopamine in the mouse vas deferens

The present work is focused on the effects of newly developed dopaminergic agonists and antagonists on the field-stimulated vas deferens. Both LY 171555 and SK and F 38393, relatively selective DA 2 and DA 1 receptor agonists, respectively, produced concentration-dependent inhibition of the field stimulation-evoked contractions in the mouse vas deferens; both compounds did not modify the baseline tone nor the contractile responses to exogenous noradrenaline. Control LY 171555 and SK and F 38393 concentration-response curves, were shifted rightward in a parallel manner in the presence of sulpiride (relatively specific DA 2 antagonist) and SCH 23390 (relatively specific DA 1 antagonist), respectively. Control concentration-response curves for dopaminergic agonists were not modified in the presence of specific blockers for H 1 and H 2 histamine receptors, serotonin receptors and α 2-adrenoceptors. These preliminary findings are suggestive of the existence of two dopaminergic receptor types both presumably located pre