EFFECTS OF DOPAMINE ON ISOLATED FAILING RAT-HEART

Dopamine has been used for many years to treat patients with severe he art failure. it is not clear whether improvements of cardiac function may be due to a direct action on heart. This study was aimed to invest igate the direct action of dopamine on failing heart. We chose male Wi star rats which had undergone uninephrectomy under ether anaesthesia t o induce hypertension to result in heart failure. After 5 weeks the he arts were excised and perfused according to Langerdoff's technique. He art rate, systolic and diastolic ventricular pressures, the derivative of the intraventricular pressure lime ratio, and coronary flow were m easured at baseline, at 2 and 5 min and then every 5 min during a 30-m in period. Rat hearts were divided into 4 groups of 5 hearts: group 1, perfused without drug; group 2, perfused with dopamine at 4 mu g/kg/m in; group 3, perfused with dopamine at 8 mu g/kg/min; group 4, perfuse d with dopamine al 8 mu g/kg/min and with 100 nM I. C.I. 118.551 (beta 2-ant: beta-2 receptors antagonist) at the same time. Our results sho w that dopamine induced a negative inotropic effect and a reduction oi coronary flow. Moreover, there was a significant chronotropic action even when dopamine was administered at high concentrations. So we foun d no positive dopamine effect on isolated failured hearts of rat. This might be explained by both alpha-1-induced vasoconstriction and the s timulation of alpha-1B receptors. We conclude that the favourable effe cts or dopamine in heart failure could be due to DA1 vasodilation rath er than to a direct inotropic action on the heart.