COMPARISON OF THE EFFECTS OF DOPAMINE(1)-RECEPTOR AND DOPAMINE(2)-RECEPTOR AGONISTS ON THE CAMP GENERATING-SYSTEM IN CANINE CORONARY-ARTERIES AND RENAL-ARTERIES

To further evaluate the functional significance of dopamine (DA) recep tors in different vasculature, in this study we compared the effects o f D-1- and D-2-receptor agonists on canine coronary and renal arteries by measuring adenylate cyclase (AC) activity as a biomedical index of DA receptor function. It was found that both the selective D-1-recept or agonist, fenoldopam, and the D-2-receptor agonist, propyl-butyl-dop amine (PBDA), induced a dose-related increases in cAMP formation in co ronary and renal arteries; however the magnitude of increase in the re nal artery was remarkably greater than that in the coronary artery. Th e stimulatory effect on AC activity of fenoldopam was significantly mo re potent than that of PBDA. The selective D-1-receptor antagonist, SC H23390, blocked fenoldopam- and PBDA-induced cAMP production, while th e selective D-2-receptor antagonist, domperidone, was without effect o n the increase of cAMP elicited by PBDA. After beta-adrenergic blockad e with propranolol, fenoldopam still increased the cAMP level signific antly but to a much lesser degree. The existence of postsynaptic D-2-r eceptor associated with inhibition of cAMP formation could not be demo nstrated in this study. These data suggest the presence of D-1-recepto rs associated with stimulation of AC activity in both renal and corona ry arteries. However there are much fewer receptor sites in the corona ry artery than in the renal artery, suggesting less physiological impo rtance of such receptors in the coronary artery than in the renal arte ry.