Central and Regional Vascular Hemodynamics Following Intravenous Milrinone in the Conscious Rat: Comparison with Dobutamine

This study examined the hemodynamic and regional vascular profile of intravenous (i.v.) milrinone during increasing doses (3, 6, 12 μg/kg/min, n = 8) and by intraindividual comparison of milrinone and dobutamine (n = 10) in normal conscious rats. At 3 μg/kg/min, Milrinone increased coronary and cerebral blood flow (radioactive microspheres 15 ± 5 μm) (7.7–9.8 and 1.05–1.27 ml/min/g respectively, both p < 0.05) without significant changes in systemic hemodynamics. At 6 μg/kg/min milrinone increased skeletal muscle blood flow (0.19–0.24 ml/min/g, p < 0.05) along with increases in cardiac output, stroke volume, and stroke work (all p < 0.05), while systemic vascular resistance decreased (-51|X%, p < 0.05). When compared with dobutamine, milrinone caused a greater increase in cardiac output ( + 26|X% vs. + 17|X%) and a greater reduction in systemic vascular resistance. Milrinone and dobutamine increased renal, intestinal, cerebral, and coronary flow to a similar extent, but only milrinone enhanced hepatic arterial blood flow (+ 26|X%, p < 0.05) and tended to increase flow to skeletal muscle (+ 35|X%, p = 0.07). We conclude that milrinone exerts significant regional vasodilating effects in a conscious rat model, being most prominent in the coronary and cerebral circulations at a dosage that does not alter central hemodynamics. At higher doses, milrinone causes a balanced increase in regional blood flow including enhanced flow to skeletal muscle. The hemodynamic (particularly as compared with dobutamine) and regional vascular profile of milrinone suggests a predominant vasodilating effect in the rat. Given a similar limited response of rat and diseased human myocardium to milrinone, these findings may have important clinical implications.