| Objective:To investigate the effect of mild therapeutic hypothermia(MTH) at 34℃ on myocardial ischemia-reperfusion injury(MIRI) in young and aged isolated rat hearts; to explore the role of age on MTH at 34℃ against MIRI in isolated rat hearts. Methods:Seventy-two healthy male Sprague-Dawley rats(provided by the Experimental Animal Science Department of Nanchang University), including the Young rats(4-6 mouths, 280-350 g) and aged rats(18-20 mouths, 400-600 g). The rats of same age were randomly divided into three groups: control group(C group); hypothermia group(H group); the L-NAME( NO synthase inhibitor) group(L group), 12 cases in each group. C group, with normothermia during ischemia for 30 min and reperfusion for 120 min throughout the study; H group, with MTH at 34 ℃ during reperfusion period; L group, which was similarly treated to the reperfusion with the addition of L-NAME during reperfusion. Then record the index including the level of heart rate( HR)、left ventricular developed pressure(LVDP)、dp/dtmax and dp/dtmin at the time point of baseline, 30 min before ischemia(T0); reperfusion 15 min(T1),30 min(T2),60 min(T3),120 min(T4)。Myocardial infarction sizes were evaluated by triphenyltetrazolium chloride staining(TTC) after the end of reperfusion. In addition, the content of adenosine triphosphate(ATP), superoxide dismutase(SOD) and malondialdehyde(MDA) in infarctional myocardium were determined. Result:1. Hemodynamic parameters(1) The comparisons between different age groups under the same procedure①At the end of baseline 30 min:The HR、LVDP、dp/dtmax and dp/dtmin in the youg group were higher than the corresponding aged group(P<0.05).②At the end of the 120 min reperfusion:The recovery rate of LVDP、dp/dtmax and dp/dtmin in C group, H group, L group of both youg group and aged group, there were no significant differences(P>0.05).(2) The comparisons between different treatments within each age group①Young group: at the time of T0, HR, LVDP, dp/dtmax and dp/dtmin in C group, H group and L group were not different(P>0.05); compared with T0, HR was decreased at the time of T1, T2, T3, T4 in H group; at the time of T1, T2, T3, T4, compared with C group, HR was decreased in H group, while there were no differences between C group and L group(P>0.05).②Aged group: at the time of T0, HR, LVDP, dp/dtmax and dp/dtmin in C group, H group and L group were not different(P>0.05); compared with T0, HR was decreased at the time of T2, T3, T4 in H group; at the time of T2, T3, T4, compared with C group, HR was decreased in H group, while there were no differences between C group and L group(P>0.05).2. The content of ATP(1) The comparisons between different age groups under the same procedureCompared with aged rats, the ATP content of myocardial sectoins in C group, H group and L group were significantly higher in young rats(P> 0.05).(2) The comparisons between different treatments within each age groupCompared with C group, the ATP content was increased in H group(P<0.05); compared with H group, the ATP content was decreased in L group(P<0.05); there were no significant differences between group C and group L(P>0.05).3. The activity of SOD and the concentration of MDA(1) The comparisons between different age groups under the same procedureCompared with aged rats, the SOD content of myocardial sections in C group, H group and L group were significantly higher in young rats(P> 0.05), while the MDA concentration is lower in young group(P <0.05).(2) The comparisons between different treatments within each age groupCompared with C group, the SOD content was increased in H group, while the MDA concentration was decreased(P<0.05); compared with H group, the SOD content was decreased in L group, while the MDA concentration was increased(P<0.05); there were no significant differences between C group and L group(P>0.05).4. Myocardial infarction size(1) The comparisons between different age groups under the same procedureCompared with aged rats, the myocardial infarct size in myocardial sections in C group, H group and L group were significantly higher in young rats(P> 0.05).(2) The comparisons between different treatments within each age groupCompared with C group, the myocardial infarct size was decreased in H group(P <0.05); compared with H group, the myocardial infarct size was increased in L group(P<0.05); there were no significant differences between C group and L group(P> 0.05). Conclusion:1. MTH at 34℃ protects young and aged isolated rat hearts against MIRI,which may through reducing the ATP consumption, increasing the activity of SOD, reducing the production of MDA and decreasing myocardial infarct size;2. There are differences in the protective effect of MTH at 34℃ between young and aged isolated rat hearts, which may be caused by age.3. NOS inhibitor L-NAME can reverse MTH at 34℃ against MIRI in young and aged isolated rat hearts, especially in elderly rats. |
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