Cardiovascular properties of a new cardiotonic agent, MDL 19205

The cardiovascular properties of a new cardiotonic agent, MDL 19205, were investigated in anesthetized and conscious dogs and in a dog heart-lung preparation. MDL 19205 (0.1-1 mg/kg), administered to anesthetized dogs by intravenous injection, produced a dose-related increase in cardiac contractile force lasting up to 1 h. It also produced a relatively minor increase in heart rate and a brief decrease in blood pressure. These effects did not involve beta-adrenergic receptor stimulation, as they were observed in dogs after a myocardial-depressant dose of propranolol. Given orally to conscious dogs, MDL 19205 (1 and 3 mg/kg) produced a dose-related increase in dP/dt without producing a significant alteration in heart rate or blood pressure. When administered to anesthetized dogs by constant intravenous infusion, MDL 19205 (0.1 mg/kg/min) produced a marked and sustained increase in cardiac contractile force and decreases in blood pressure and left atrial pressure, but did not produce a significant change in cardiac output or stroke volume, indicating an enhancement of cardiac pump function. Intravenous MDL 19205 reversed the hemodynamic characteristics of heart failure produced by propranolol in anesthetized dogs. In addition, it reversed the depressant effect of pentobarbital on cardiac function in a dog heart-lung preparation. These studies show that MDL 19205 is a potent, direct-acting cardiotonic agent in animals.