Identification and characterization of postsynpatic 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 DNA 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.