Stereospecific antagonism by d-butaclamol of dopamine-induced relaxation of the isolated rabbit mesenteric artery.
We characterized the properties of vascular dopamine receptors on isolated rabbit mesenteric arteries preincubated with phenoxybenzamine (10(-5) M) and contracted with prostaglandin F2 alpha (PGF2 alpha). The dose-response curve for dopamine-induced relaxation was shifted to the right by the dopamine receptor antagonist d-butaclamol (10(-7)--3 X 10(-6) M) in a concentration-dependent manner. The pA2 value for d-butaclamol was calculated as 6.77. In contrast, even a very high concentration (3 X 10(-6) M) of l-butaclamol had no effect, indicating that vascular dopamine receptors require stereospecificity of antagonists. In the same preparation the mechanism of relaxation by 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene (A-6,7-DTN; 3 X 10(-7)--10(-4) M) and bromocriptine (10(-6)--3 X 10(-4) M) was found to be dopaminomimetic, since only the dopamine receptor antagonists droperidol (10(-5) M) and metoclopramide (5 X 10(-5) M) could inhibit relaxations, whereas the beta-adrenoceptor antagonists pindolol (10(-7) M) and propranolol (10(-6) M) were without effect. It is concluded that receptors specific for dopamine exist on the rabbit mesenteric artery, which may tentatively be classified as belonging to the D1-type.
D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology; D002069:Butaclamol / Q000494:pharmacology*; D003986:Dibenzocycloheptenes / Q000494:pharmacology*; D018492:Dopamine Antagonists; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects; D011817:Rabbits; D011954:Receptors, Dopamine / Q000187:drug effects; D013237:Stereoisomerism; D013764:Tetrahydronaphthalenes / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects*
D003986:Dibenzocycloheptenes; D018492:Dopamine Antagonists; D011954:Receptors, Dopamine; D013764:Tetrahydronaphthalenes; D001971:Bromocriptine; C011639:ADTN; D002069:Butaclamol