Mild Hypothermia On Myocardium During Acute Ischemia-Reperfusion And Its Potential Mechanism In Anesthetized Rabbits

Objective:To investigate the effect of mild hypothermia on myocardium during ischemia-reperfusion and its mechanism in anesthetized rabbits.methods: 32 rabbits were randomly divided into five groups: I :shame operated group(SC),n=6; II :control group(ischemia reperfusion,I/R),n=7; III :physical hypothermia group(PH),n=6; IV chlorpromazine group (CH) , n=6; V: CH+PH, n=7 The rabbits in II ~V were undergone 30min of occlusion on LADs and 2h of reperfusion.The physical hypothermia in III and V was induced by padding one slight ice-bag under the rabbits and setting another six ice-bags at the axilla,groin and the sides of abdomen 30min before occlusion and constituted 30min.Chlorpromazine in IV and V was injected slowly(2.5mg/kg) 30min before occlusion.The body temperature and the level of HR,LVSP and ± dp/dt_max were monitored at the time of baseline,30min before occlusion,occusion,30min after occlusion,30min after reperfusion, 60min after reperfusion, 90min after reperfusion and 120min after reperfusion.The content of ATP,LD,FFA,SOD and MDA in infarctional myocardium or(and) in blood were determined. In addition ,the myocardial infarction size was determined by means of double-dyed(Evens and TTC)and the change of myocardial ultralstructure was examined by transmission electron microscope.Resultas:l.Body temperature in every group tended to downward after the start of the experiment and at the end there was no rabbits whose body temperature was below 32°C.the baseline body temprature was not different in all groups(p>0.05), but in every timepoint after temprature-dropped,the level of body temprature in III and V were lower than that of I, II and IV (p<0.05). 2. The baseline levels of HR,LVSP and ± dp/dtmax were not different in all groups(p>0.05),but in every timepoint after temprature-dropped,the level of these hemodynamic parameters in III and V were lower than that of I,II and IV(p<0.05).3. The infact size of III,IV and V was less than that of II by 35.0%,16.8% and 45.9% respectively(23.2±2.1% vs 35.7 + 3.7%,29.5 + 1.9% vs 35.7 + 3.7%,19.3 + 1.6% vs 35.7 + 3.7%,p<0.05),also the infact size of V is semaller than that of III and IV(19.3±1.6% vs 23.2 + 2.1%,p<0.05).4. The content ATP in myocardium of III and V is significantly higher than that of II (3.76 + 0.39 vs 1.51+0.08 u mol ? g"',3.80 + 0.32 vsl.51 +0.08 u mol ? g"1, p<0.05) .5. The content LD,FFA and MDA in myocardium and in blood of III, IV and V is significantly lower than that of II (p<0.05),and the level of SOD in myocardium and blood of III,IV and V is higher than that of II (p<0.05).6. The electron microscope finding of myocardial ultrastructure damage in III and V were less severe than that of II.Conclussion: 1. Our findings show that mild hypothermia can decrease infarction size,alleviate myocardial ultrastructure damage, at the same time it makes the cardiac function meet the body's need at a lower level, and the mechanism possiblely include delaying myocardial energy depletion,decreasing harmful metabolism outcomes such as LD and FFA,reducing oxygeon depletion and anti-oxdization.2. The better effect in PH+CH may be due to the action of chlorpromazine itself such as improving metabolism and anti-oxdization during ischemia-reperfusion.