[Studies on dose-dependent effect of ouabain on right ventricular function and pulmonary circulation]

The clinical utility of digitalis glycoside for the treatment of cor pulmonale induced by chronic pulmonary disease has not been clarified. In the present study, a rational use of this drug for the treatment of cor pulmonale was investigated especially concerning it's dose. In normal open-chested anesthetized dogs, the effect of ouabain was studied with special reference to pulmonary vascular resistance and right ventricular myocardial contractility by changing dose of 0.01 mg/kg, 0.02 mg/kg and 0.03 mg/kg. Pulmonary vascular resistance was increased extremely when the dogs were treated with 0.03 mg/kg, but not changed remarkably with 0.02 mg/kg and 0.01 mg/kg. On the other hand, right ventricular myocardial contractility was increased equally in dogs treated with 0.03 mg/kg and 0.02 mg/kg but slightly in dogs treated with 0.01 mg/kg. From these data, the existence of the optimum therapeutic dose of ouabain for cor pulmonale which increases myocardial contractility enough but has no significant pulmonary vasoconstrictive effect may be suggested. Then this dose of ouabain was given to acute experimental pulmonary hypertensive dogs (mean PA pressure 40-50 mmHg) due to recurrent miliary pulmonary embolization. The other group of pulmonary embolization was not treated with ouabain. Pulmonary vascular resistance was not increased in both groups, but myocardial contractility and cardiac output were increased significantly only in the ouabain treated group. In conclusion, though the dose-response relationship was observed in increasing myocardial contractility and pulmonary vasoconstriction by ouabain, the dose which increases myocardial contractility was less than that which evokes pulmonary vasoconstriction in normal and pulmonary hypertensive dogs.