Possible mechanisms of the protective effect of pretreatment with anipamil in ischemic-reperfused isolated rat hearts.

Rats were given anipamil (5 mg/kg) or glucose, intraperitoneally twice daily for 5 days. During this period the mean arterial blood pressure and heart rate were measured daily. The heart was then isolated and perfused. Energy metabolism and intracellular pH were monitored by 31P nuclear magnetic resonance spectroscopy during 30 minutes of ischemia followed by 30 minutes of reperfusion, with a simultaneous isovolumetric measurement of left ventricular contraction. Myocardial norepinephrine and glycogen were assayed immediately after excision of the heart, after 15 minutes oxygenated perfusion, at the end of ischemia and at the end of reperfusion. Metabolic and functional recovery during reperfusion were significantly better in hearts pretreated with anipamil (p less than 0.0005 vs controls). However, protection was not preceded by an effect on mean arterial pressure or heart rate in vivo, or a negative inotropic effect during control perfusion of the isolated hearts. There was no energy sparing effect during ischemia; but intracellular pH during ischemia stabilized at a higher level (p less than 0.0005 vs controls). Myocardial norepinephrine and glycogen stores were not decreased by pretreatment with anipamil, and their release or degradation due to ischemia and reperfusion were also not different from controls. Commonly known mechanisms of myocardial protection by calcium antagonists fail to explain the protection by pretreatment with anipamil as observed in our experiments, and alternative mechanisms are to be considered.