Cardiac inotropic as well as coronary and pulmonary artery actions of epinine in human isolated tissues.

The present study was aimed to characterize the effects of epinine, the metabolite of the p.o. active dopamine derivate ibopamine in human cardiovascular tissues such as myocardium, coronary artery and pulmonary artery. Isometric force of contraction was studied in electrically driven papillary muscle strips from nonfailing (brain death), moderately failing (New York Heart Association class II-III, mitral valve replacement) and terminally failing human myocardium (New York Heart Association class IV, heart transplants) as well as in auricular trabeculae (aortocoronary bypass operation). Epinine increased force development in a concentration-dependent manner. In comparison to isoprenaline, epinine had a significantly lower potency but a similar efficacy to enhance force of contraction. Depending on the degree of myocardial failure, the effectiveness of epinine was reduced, whereas the potency was similar. Only in nonfailing myocardium, epinine increased force of contraction as effectively as Ca++. Prestimulation with forskolin or milrinone enhanced the potency of the epinine-mediated inotropic effect. In contrast, the beta-1-selective antagonist CGP 207.12A [2-hydroxy-5-(2-(hydroxy-3-(4-((1-methyl-4-trifluoromethyl)-1-H-imidazol -2-yl)-phenoxy)-propyl)-aminoethoxyl)-benzamide] and the beta-2-selective antagonist ICI 118.551 [erythro-(+-)-1-(7-methylindan-4-yloxy)-3- isopropylaminobutan-2-ol-hydrochloride] shifted the concentration-response curve of epinine significantly to the right, indicating action at both beta-2 and beta-1 adrenoceptors. Epinine exerted higher affinity at beta-2 compared to beta-1 adrenoceptors in radioligand binding experiments ([125I]iodocyanopinodolol). In human coronary artery rings and pulmonary artery rings epinine alone as well as epinine in the presence of propranolol initiated a concentration-dependent increase in tension development in precontracted (prostaglandin F2 alpha, 0.3 mumol/l) as well as in non-precontracted rings. These results suggest that epinine exerts no direct vasodilatory activity in human coronary and pulmonary arteries at concentrations which are capable to produce positive inotropic activity. The supposed beneficial effects of ibopamine in the treatment of heart failure may not be due to positive inotropic actions as the concentrations producing positive inotropy are much higher than the clinically observed plasma concentrations.