| Low temperature can decrease the oxygen consumption and the utilization of high-energy phosphate. Hypothermia has been used in medical treatments such as heart surgery, living tissue preservation and brain injury salvage. Deep hypothermia below 30 centigrade has been fully investigated, and now the research interests were turning to mild hypothermia. Mild hypothermia refers to the temperature between 32 to 35 , which has been proved safe and easy implemented. Does mild hypothermia have protective effect for acute myocardial infarction (AMI)?The present research had investigated the effect of mild hypothermia for AMI in the rabbits at the early stage. The experiments were divided into three protocols. Firstly, we investigated the protective effect of mild hypothermia on permanent coronary occlusion. Twenty-two rabbits were assigned into two groups: the mild hypothermia group (MHG) and the control group. A left thoracotomy was performed and the pericardium was opened to expose the heart. The anterior descending coronary was occluded for 3 hours. The MHG body temperature was dropped below 35 after occluded for 30 min by putting ice bags around the rabbits, while the control group was kept above 38 . Core temperatures were measured with thermistor. The myocardial area at risk and the infarct area were determined with Evans blue dye and triphenyl tetrazolium chloride (TTC). The results suggested that blood gas and blood routine data hadno difference between the two groups. The total elevated amplitude of ST segment in chest leads V1, V3 and V5 in MHG were lower than that in the control group (22.8 18.7mV vs. 34.7 19.3mV; P=0.090). After 3 hours coronary occlusion, the changes of serum CK-MB activities in MHG were significantly lower than the control (2672.1 909.1 vs.4192.7 1960.9 U/L; P=0.047). Myocardial infarct size as a percentage of the ischemic risk zone (31.3 7.6% vs. 47.9 6.6%; P<0.001) and of the left ventricle size (6.5 1.3% vs. 11.3 3.7 %; P<0.001) of MHG were smaller than the control group. Pathology study by microscope showed there was obvious red blood cell infiltration and tissue edema at the ischemic myocardial in the control group, which of them were slight in MHG. We also measured the changes of serum level of cardiovascular active factors such as endothelin-1, calaitonin gene related peptide, C-type natriutetic peptide and adrenomedullin. The results showed that the adrenomedullin level was significantly dropped after 3 hours coronary occlusion. Secondly, we investigated the protective effect of mild hypothermia on transient coronary occlusion. Fourteen rabbits were assigned into MHG and control group. The anterior descending coronary was occluded for 45 min followed by a 2 hours reperfusion. The results showed that the total elevated amplitude of ST segment in chest leads V1, V3 and V5 in MHG were lower than that in the control (25.8 8.5mV vs.37.7 6.5mV; P=0.021). The changes of serum CK-MB activities in MHG were significantly lower than the control (2646.9 1227.3 U/L vs.4787.8 1934.2 U/L; P=0.045) . The weight of infarct myocardium of the mild hypothermia group were lower than the control (0.23 0.05g vs. 0.42 0.16g; P=0.020), and the myocardial infarct size of MHG as a percentage of the risk zone (21.4 4.4%vs. 35.7 6.6%; P=0.001) and of the left ventricle size (4.1 1.0% vs. 7.1 2.7%; P=0.029) were smaller than the control group. Finally,we studied the effect for AMI by combining mild hypothermia and ischemic preconditioning. Fourteen rabbits underwent twice 5 min coronary occlusion 10 min reperfusion preconditioning, and then followed a 45 min coronary occlusion and a 120 min reperfusion. Like the second part of the study, the total elevated amplitude of ST segment in chest leads and the changes of serum CK-MB activities in MHG were lower than the control, but the differences had no statistics meaning (P>0. 05). Myocardial infarct size of MHG as a percentage of the risk zone and the left ventricle size also were smaller than the control group (P<0. 05).Conc... |
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