Digoxin induced release of creatine kinase from isolated guinea-pig hearts.

In isolated perfused guinea-pig hearts, digoxin produced a concentration dependent release of creatine kinase (ATP-creatine-transphosphorylase; CK). A corresponding decrease of the CK activity in the myocardium was obtained. The enzyme release seems to be a sign of glycoside intoxication, as its extent paralleled the severity of digoxin induced arrhythmias. Especially high CK activities were liberated when ventricular fibrillation occurred. Likewise, electrically induced fibrillation, in control hearts, led to enzyme release. However, the digoxin effect was not matched. Reserpine pretreatment antagonized the CK release by electrical fibrillation, whereas it increased excessively the enzyme liberating effect of higher digoxin concentrations. Also, propranolol decreased the enzyme release due to electrical fibrillation. The glycoside induced CK liberation, however, was not diminished, although the ventricular fibrillation was prevented. Increase of the potassium concentration of the perfusion fluid prevented the glycoside induced fibrillation, and reduced the enzyme release. The significance of the enzyme loss from the myocardium, and the mechanisms of enzyme release are discussed.