Existence and pharmacological properties of dopamine D-4 receptors in guinea pig vas deferens

This study was carried out to identify subtypes of dopamine D-2-like recept ors in guinea pig isolated vas deferens. Dopamine had no effect on the musc le tone in the presence of prazosin, an alpha(1)-adrenoceptor antagonist. H owever, contractile responses to adenosine triphosphate (ATP). noradrenalin e and acetylcholine were potentiated in a concentration dependent manner by dopamine in the presence of prazosin. This potentiation was not inhibited by raclopride, an antagonist for dopamine D-2 and D-3 receptors. However, t he potentiation of ATP- and noradrenaline induced contraction was inhibited by clozapine and 8-methyl-6-(4-methyl-1-piperazinyl)-11 H-pyrido[2-,3-b][ 1,4]benzodiazepine (JL-18), dopamine D-4 receptor antagonists. Further, the potentiation of noradrenaline- and acetylcholine-induced contraction was a lso inhibited by spiperone. an antagonist for dopamine D-2, D-3 and D-4 rec eptors. These results suggest that the dopamine D-4 receptor is located on the postsynaptic site of guinea pig vas deferens and that activation of the dopamine D-4 receptor enhances contractile responses to agonists without a ffecting muscle tone. (C) 1999 Elsevier Science B.V. All rights reserved.