Abstract
The action of propranolol on cardiotoxicity produced by ouabain was studied in intact and isolated guinea pig hearts. The lethal event in the intact guinea pig was ventricular fibrillation; in the isolated heart it was asystole. Myocardial ouabain content at death was significantly higher in isolated preparations than in the intact heart. Propranolol was observed to alter the mode of death in the intact guinea pig from ventricular fibrillation to asystole. The myocardial ouabain content at the time of death was elevated in guinea pigs pretreated with propranolol to the level observed in isolated guinea pig heart preparations. Exposure of the isolated preparation to propranolol prolonged the time to the induction of cardiac rhythm disorders and death without changing myocardial ouabain content. These data suggest that propranolol, by eliminating neural influence transforms the cardiotoxicity of ouabain to an in vitro mechanism. In the isolated heart, propranolol prolongs the time to the induction of cardiac rhythm disorders by inhibiting the myocardial uptake of ouabain.
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