Separation of peripheral dopamine receptors by a selective DA1 antagonist, SCH 23390

Intravenous (i.v.) infusions of SCH 23390 (R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7- ol) produced dose-related antagonism of dopamine (DA)-induced renal vasodilation in phenoxybenzamine-treated dogs at infusion rates of 0.05, 0.15, and 0.5 microgram/kg/min. The highest rate of infusion, 0.5 microgram/kg/min, resulted in pronounced antagonism of this DA1-receptor-mediated response. In contrast, a 10 times higher infusion rate, 5 micrograms/kg/min, did not antagonize the following DA2-mediated responses: increase in femoral blood flow produced by apomorphine and piribedil in untreated dogs; and N,N-di-n-propyl DA (DPDA)-induced inhibition of the tachycardia produced by cardiac accelerator nerve stimulation. Infusions of 0.5 micrograms/kg/min or greater of SCH 23390 did not affect the actions of agonists of alpha1-, alpha2-, beta1-, and beta2-adrenergic, histamine, serotonin, and cholinergic receptors, or the vasodilation produced by bradykinin. At the infusion rates used in these studies, SCH 23390 did not affect arterial blood pressure or heart rate. These data indicate that SCH 23390 is the most specific and selective antagonist of DA1 receptors thus far described. Accordingly, SCH 23390 should be extremely useful in investigations of potential physiological and pathological roles of DA and in the classification of DA receptors.