Effect of isoproterenol on myocardial creatine kinase activity in rats

Isoproterenol (0.1-500 mg/kg) decreased the myocardial creatine kinase (CK) activity in rats. The maximum effect was already reached with 10 mg/kg, decreasing the enzyme activity to 58.5% of the control values. The beta-blocking agents propranolol and practolol, and also glucocorticosteroids inhibited the isoproterenol effect. The relative CK isoenzyme composition of the myocardium was not grossly altered by isoproterenol, as shown by DEAE-Sephadex A-50 macrocolumn chromatography. --Serum CK was increased significantly after the administration of the excessive dose of 500 mg isoproterenol/kg.