Influence of verapamil on cellular integrity and electrolyte concentrations of ischemic myocardial tissue in the cat.

Verapamil, at a dose of 1 mg/kg, was given intravenously to anesthetized cats one hour after coronary artery occlusion. Verapamil significantly reduced mean arterial blood pressure, but produced an increase in heart rate, partially offsetting the reduction in myocardial oxygen demand resulting from the reduction in pressure. Verapamil failed to prevent the elevations in the S-T segment of the electrocardiogram observed in cats subjected to myocardial ischemia (MI) and given only the vehicle for verapamil (i.e., 0.9% NaCl). Moreover, verapamil also did not prevent the accumulation of creatine phosphokinase (CPK) activity in the circulating blood after MI. Nevertheless, verapamil significantly prevented the loss in CPK and in amino-nitrogen observed in the ischemic region of the myocardium, indicating some protective effect on myocardial integrity. The major effects of verapamil on electrolyte content of ischemic myocardial tissue were a decrease in sodium and an increase in potassium. However, calcium gain by the heart was not prevented by verapamil. Verapamil, therefore, exerts a partial degree of protection of the ischemic myocardium but exerts some other effects which do not help prevent the spread of ischemic damage in the myocardium.