Comparison of the effects of dopamine1- and dopamine2-receptor agonists on the cAMP generating system in canine coronary and renal arteries.

To further evaluate the functional significance of dopamine (DA) receptors in different vasculature, in this study we compared the effects of D1- and D2-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 D1-receptor agonist, fenoldopam, and the D2-receptor agonist, propyl-butyl-dopamine (PBDA), induced a dose-related increases in cAMP formation in coronary and renal arteries; however, the magnitude of increase in the renal artery was remarkably greater than that in the coronary artery. The stimulatory effect on AC activity of fenoldopam was significantly more potent than that of PBDA. The selective D1-receptor antagonist, SCH23390, blocked fenoldopam- and PBDA-induced cAMP production, while the selective D2-receptor antagonist, domperidone, was without effect on the increase of cAMP elicited by PBDA. After beta-adrenergic blockade with propranolol, fenoldopam still increased the cAMP level significantly but to a much lesser degree. The existence of postsynaptic D2-receptor associated with inhibition of cAMP formation could not be demonstrated in this study. These data suggest the presence of D1-receptors associated with stimulation of AC activity in both renal and coronary arteries. However, there are much fewer receptor sites in the coronary artery than in the renal artery, suggesting less physiological importance of such receptors in the coronary artery than in the renal artery.