In-vivo effects of amrinone and milrinone on left ventricular dP/dt, intraventricular pressure and heart rate in pentobarbital-anesthetized guinea pigs.

The cardiovascular properties of amrinone and milrinone were investigated in pentobarbital-anesthetized guinea pigs (in vivo). A 19g needle, attached to a pressure transducer, was inserted through the chest wall into the left ventricle. Continuous monitoring of intraventricular pressure and heart rate was recorded. The first derivative of this pressure pulse was dP/dt, an index of inotropic state. At a dose of 500 ug/Kg, amrinone given intravenously caused an increase in the rate of rise in left ventricular pressure (LV dP/dt) by 28.7 +/- 7.8% (from 928 +/- 34 to 119 +/- 73 mm Hg/sec., p less than 0.05). At 50 ug/Kg, milrinone (i.v.) caused an increase in the left ventricular peak positive dP/dt by 15.3 +/- 3.4 (from 942 +/- 24 to 1086 +/- 32 mm Hg/sec., P less than 0.001). Both amrinone and milrinone, in addition to vasodilating effect, exerted a concentration-related manner with these positive inotropic actions.