Epinine (N-methyl-dopamine, the active metabolite of ibopamine), is a full agonist at dopamine (DA)-receptors and ~-and fi-adrenoceptors. To study whether in vivo DA-receptor mediated effects can be separated from 0~-and fi-adrenoceptor effects we compared in 10 male volunteers the effects of i.v. epinine (0.5; 1; 2; 4 lag/kg/min for 15 min each) on DA-receptor (changes in serum prolactin)-and ~-and fi-adrenoceptor (changes in systolic [-Psyst3 and diastolic blood pressure [Pdiast'] and heart rate)-mediated effects with those of dopamine before and after propranolol (5 mg i.v. 45 rain pre-infusion), bisoprolol (15 mg p.o. 2 h preinfusion) and domperidone (10 mg p.o. 1 h pre-infusion). At the 0.5 and 1 lag doses dopamine and epinine did not affect Psyst, Pdiast and heart rate but significantly decreased prolactin levels. At the higher dose both dopamine and epinine significantly increased Psyst and heart rate, while only epinine significantly increased Pa~ast. In addition, both dopamine and epinine significantly increased diuresis and natriuresis; in contrast, only dopamine, but not epinine, dose-dependently increased plasma noradrenaline levels. Domperidone did not affect dopamine-and epinine-evoked blood pressure-and heart rate-changes, but antagonized their prolactin-effects (at least at the lower doses). Bisoprolol and propranolol significantly reduced dopamine-in-