Identification and characterization of postsynaptic D1- and D2-dopamine receptors in the cardiovascular system

Measuring adenylate cyclase activity (AC) as a biochemical index of dopamine (DA) receptor function, we obtained evidence for the presence in rabbit vasculature of both D1 receptors associated with stimulation of AC and of D2 receptors coupled with AC in an inhibitory way. The cAMP generating system in rabbit mesenteric artery was stimulated by DA and several DA agonists, an effect antagonized by the D1-receptor blocker SCH 23390 and by other neuroleptic drugs. When activation of D1 sites was impeded by SCH 23390, DA, (-)apomorphine, and (-)NPA inhibited cAMP formation. In addition, selective D2 agonists inhibited basal AC activity even when there was no D1-receptor blockade. The relative order of potency of various neuroleptics in antagonizing bromocriptine-induced inhibition of AC confirmed the D2 nature of these binding sites. Inhibition of AC activity elicited by bromocriptine remained unchanged after chemical sympathectomy, suggesting that vascular D2 receptors inhibiting AC activity are located postsynaptically in the arterial wall.