title: Existence and pharmacological properties of dopamine D4 receptors in guinea pig vas deferens.
abstract: This study was carried out to identify subtypes of dopamine D2-like receptors in guinea pig isolated vas deferens. Dopamine had no effect on the muscle tone in the presence of prazosin, an alpha1-adrenoceptor antagonist. However, contractile responses to adenosine triphosphate (ATP), noradrenaline 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 D2 and D3 receptors. However, the potentiation of ATP- and noradrenaline-induced contraction was inhibited by clozapine and 8-methyl-6-(4-methyl-1-piperazinyl)-11H-pyrido[2,3b][1,4]benzodiazepine (JL-18), dopamine D4 receptor antagonists. Further, the potentiation of noradrenaline- and acetylcholine-induced contraction was also inhibited by spiperone, an antagonist for dopamine D2, D3 and D4 receptors. These results suggest that the dopamine D4 receptor is located on the postsynaptic site of guinea pig vas deferens and that activation of the dopamine D4 receptor enhances contractile responses to agonists without affecting muscle tone.
authors.affiliation: Department of Pharmacology, School of Medicine, Fukuoka University, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Morishita
authors.forename: T
authors.initials: T
authors.lastname: Katsuragi
mesh_terms: D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology; D004298:Dopamine / Q000494:pharmacology; D004347:Drug Interactions; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D014649:Vas Deferens / Q000378:metabolism*
chemical_list: D002316:Cardiotonic Agents; D017448:Receptors, Dopamine D2; D004298:Dopamine