Potentiation of isoproterenol cardiotoxicity by corticoids

In order to determine whether glucocorticoids share the ability of mineralocorticoids in sensitizing the myocardium to the arrhythmogenic property of isoproterenol, albino rats were implanted subcutaneously with prednisone or desoxycorticosterone acetate (DCA). Water was compared with 1% saline as drinking fluid in order to assess the role of a high sodium intake in the development of myocardial sensitization. At predetermined intervals during corticoid exposure, unanesthetized animals were challenged with a single subcutaneous dose of isoproterenol. In DCA-saline pretreated rats the LD50 of isoproterenol was determined to be 14.5 ug/kg. At a dose of 150 ug/kg isoproterenol, ventricular fibrillation was elicited in all DCA-saline pretreated animals, but in only 50% of rats implanted with predisone, receiving saline as drinking fluid. Substitution of water for saline did not prevent the development of myocardial sensitization. It is concluded that predisone pretreatment also sensitizes the rat myocardium to isoproterenol though to a lesser extent than DCA and that high sodium intake is not an absolute requirement for the development of this phenomenon by either corticoid.