Halothane Protects the Isolated Rat Myocardium Against Excessive Total Intracellular Calcium and Structural Damage During Ischemia and Reperfusion

Abstract

A recent study from our laboratory demonstrated halothane to be a powerful protectant of the isolated rat heart during reperfusion after normothermic cardioplegic arrest. It was speculated that this protective effect might be due to prevention of excessive intracellular calcium. The aim of the present study was to evaluate the effect of halothane on the total intracellular calcium (Ca2+) content and on myocardial structure both at the end of normothermic cardioplegic arrest and at the end of reperfusion. Isolated perfused rat hearts were perfused for a control period of 30 min, followed by 40 min of normothermic cardioplegic arrest with or without reperfusion for 30 min. Halothane (1.5%) was administered continuously before and after arrest. Halothane caused a significant decrease of intracellular Ca2+ at the end of normothermic cardioplegic arrest and after reperfusion. Myocardial morphology was assessed by extensive light microscopy and ultrastructure was evaluated by electron microscopy. Grading of ischemic damage showed that exposure to normothermic cardioplegia resulted in marked ischemic injury, regardless of whether the hearts were treated with halothane. Reperfusion in the presence of halothane caused a significant reversal of ischemic damage and almost complete ultrastructural repair, whereas untreated hearts still exhibited severe edema, contracture, and contracture bands. Our results indicate that the beneficial effects of halothane on myocardial structural recovery during reperfusion is associated with a reduction in excessive intracellular Ca2+. The exact mechanism of this protective action is under investigation.