Cardiac and hemodynamic profile of the new cardiotonic agent, DPI 201-106, in the conscious dog.

The cardiac and hemodynamic effects of increasing doses (0.1-3 mg/kg i.v.) of the novel cardiotonic agent, DPI 201-106 (DPI), were investigated over a 60 min period in conscious dogs chronically instrumented for the measurement of arterial pressure, heart rate, left ventricular pressure (LVP), LV (+) dP/dtmax and cardiac output. LV (+) dP/dtmax, cardiac output and stroke volume were significantly increased by DPI whereas the total peripheral resistance was significantly decreased. These effects were dose-dependent in intensity and in duration. The mean arterial pressure and heart rate remained unaffected, except by the 3 mg/kg dose, which increased them slightly. Autonomic blockade with hexamethonium, atropine and propranolol did not alter the positive inotropic properties of DPI but unmasked its intrinsic bradycardic effect. At equipotent positive inotropic doses, DPI (0.3 mg/kg), milrinone (40 micrograms/kg) and dobutamine (5 micrograms/kg per min) induced similar increases in cardiac output and similar decreases in total peripheral resistance, but only dobutamine and milrinone accelerated the heart rate, whereas ouabain (17.5 micrograms/kg) induced a strong rise in the total peripheral resistance and markedly lowered the heart rate and cardiac output. After coadministration of DPI and ouabain, LV (+) dP/dtmax was further increased whereas the ouabain-induced bradycardia, the rise in the total peripheral resistance and the decrease in cardiac output were reinforced, halved and unaltered, respectively. We conclude that (a) DPI exhibits potent and direct positive inotropic properties, associated with a peripheral vasodilating action, and almost no positive chronotropic effects, and (b) coadministration of DPI and ouabain results in synergistic positive inotropic effects.