Effect of preconditioning temperature on cardioprotection during global ischemia-reperfusion in the rat heart

BACKGROUND: Myocardial ischemic preconditioning (PC) is a protective intervention that aims to reduce the deleterious effects of ischemia-reperfusion injury. OBJECTIVES: : To assess the comparative efficacy of ischemic PC induced at hypothermic, normothermic and hyperthermic temperatures on the postischemic recovery of left ventricular contractile and coronary vascular functions in the aortic perfused rat heart model. METHODS: An isolated aorta-perfused (Langendorff) rat heart model was used. Hearts were studied in eight different groups (n=5 each). Unprotected ischemia for 60 min served as control. For the remaining seven groups, ischemia was preceded by PC at 10 degrees C, 20 degrees C, 30 degrees C, 34 degrees C, 37 degrees C, 40 degrees C and 42 degrees C achieved by two episodes of 5 min ischemia at the designated PC temperature and 10 min of reperfusion, respectively. The postischemic recovery in contractile (maximum developed pressure and left ventricular end-diastolic pressure) and coronary vascular functions (coronary flow and coronary vascular resistance) was assessed at the end of 30 min reperfusion. RESULTS: Hyperthermic PC provided optimal preservation and resulted in a 25% increase in the myocardial and 15% increase in the coronary vascular tolerance to ischemia. Normothermic PC resulted in a 21% increase in myocardial and 14% increase in coronary vascular tolerance to ischemia. Hypothermic PC was comparatively less effective and resulted in 11% increase in myocardial and 15% increase in the coronary vascular tolerance to ischemia. The temperature-dependence of PC may be summarized as: PC-42 degrees C > PC-40 degrees C > PC-37 degrees C > PC-34 degrees C > PC-30 degrees C > PC-20 degrees C > PC-10 degrees C. CONCLUSIONS: The results of the present study indicate that the extent of reversibility of the ischemic damage depends on the PC temperature and that optimal preservation occurred at the ideal PC temperature between 40 degrees C and 42 degrees C.