SPECIFIC ANTAGONISM BY METOCLOPRAMIDE OF DOPAMINE-INDUCED RELAXATION ON ISOLATED RABBIT MESENTERIC-ARTERIES CONTRACTED WITH PROSTAGLANDIN-F2-ALPHA

On isolated rabbit mesenteric arteries pretreated with phenoxybenzamine (10-5M) and contracted with prostaglandin F2α (PGF2α) dopamine (10-6M to 3×10-4M) and isoprenaline (10-9M to 10-5M) caused a dose-related relaxation. Pindolol (10-7M) significantly suppressed the effects evoked by isoprenaline, but did not affect those produced by dopamine. The dopamine receptor antagonist metoclopramide (5×10-5 and 10-4M), however, shifted the dose-response curve for dopamine-induced relaxation significantly to the right in a concentration dependent manner without affecting relaxations caused by isoprenaline or papaverine. These results demonstrate for the first time a specific antagonism to dopamine-induced relaxation on rabbit mesenteric arteries in vitro. They support the hypothesis of the existence of specific dopamine receptors in vascular smooth muscles. © 1979.