Protecting effects of m-nifedipine on isoproterenol-induced myocardial injury in rats

To test whether m-nifedipine (m-Nif) protects heart against myocardial injury induced by a single subcutaneous injection of isoproterenol (Iso) 30 mg/kg, male rats were injected subcutaneously twice daily with m-Nif 6 mumols/kg for 4 d. Hemodynamic changes, serum creatine kinase activity and ion contents of myocardial tissue and mitochondria were assessed about 6 h after Iso injection. While it did not notably influence blood pressure, heart rate and left ventricular contracting function of rats, m-Nif markedly attenuated calcium accumulation in myocardial tissue and mitochondria, reduced magnesium and potassium loss in myocardial tissue, depressed the release of creatine kinase and prevented the elevation of left ventricular end diastolic pressure. These beneficial effects of m-Nif were similar to those of nifedipine (Nif). However, m-Nif decreased minute tension-time index more significantly than the same dose of Nif. It is possible that m-Nif protects the rat heart from isoproterenol-induced injury by inhibiting transsarcolemmal calcium influx.