Effects of isoflurane preconditioning plus mild hypothermia on ischemia-reperfusion injury to isolated rat hearts

Objective To investigate the protective effects of isoflurane preconditioning plus mild hypothermia on isolated rat hearts against ischemia-reperfusion (I/R) injury. Methods Fifty male SD rats weighing 250-300 g were randomly divided into 5 groups ( n = 10 each): group Ⅰ control (group C); group Ⅱ I/R; group Ⅲ isoflurane preconditioning (group P); group Ⅳ mild hypothermia (group M) and group Ⅴ isoflurane preconditioning + mild hypothermia (group PM). The animals were anesthetized with intraperitoneal pentobarbital 40 mg/kg. The hearts were immediately removed and perfused with Krebs-Hensleit (K-H) solution aerated with 95% O2 and 5% CO2 at 10 kPa via aorta at 37℃ in a Langendorff apparatus. The hearts were made globally ischemic for 30 min followed by 60 min reperfusion in group Ⅱ-Ⅴ. In group P and PM the hearts were perfused with K-H solution saturated with 1.0% isoflurane for 15 min followed by 15 min washout before ischemia.In group M and PM the hearts were made ischemic at 31 ℃ and perfused at 37℃. LVEDP, LVSP, dp/dtmax,dp/dtmm and HR were measured after equilibration (baseline), immediately before ischemia, and at 30 and 60 min reperfusion. The infarct size and cytochrome C level in cytoplasm and mitochondria of myocytes were measured.Motochondrial ultrastructure was examined using electron microscope. Results Cardiac function was significantly better, the infarct size significantly smaller, the cytochrome C level in cytoplasm significantly lower, while the cytochrome C level in mitochondria of myocytes significantly higher in group Ⅲ-Ⅴ than in group Ⅱ and in group Ⅴ than in group Ⅲ. The cytochrome C level in cytoplasm was significantly lower, while the cytochrome C level in mitochondria of myocytes significantly higher in group Ⅴ than in group Ⅳ. Less damage to mitochondria was observed in group PM than in group I/R, P and M. Conclusion Isoflurane preconditioning combined with mild hypothermia provides better protection against myocardial I/R injury by attenuating the release of cytochrome C from mitochrondria. Key words: Isoflurane; Ischemic preconditioning; Hypothermia, induced; Myocardial reperfusion injury