| In recent years, coronary heart disease with the rising incidence has become a hazard to human health, and in many countries myocardial infarction is to become the first cause of death. Coronary thrombolytic therapy, percutaneous coronary intervention and coronary artery bypass surgery has been widely used in clinical, but no matter what kind of treatment can cause myocardial reperfusion injury. These injuries include myocardial systolic dysfunction, reperfusion arrhythmia, permeability change of myocardial cell membrane etc, which directly affects the treatment. Therefore, searching for the active and effective treatment to reduce myocardial ischemia-reperfusion injury has important clinical significance.In 1986, Murry, who first proposed the concept of ischemic preconditioning, namely, myocardium has a strong tolerance if in one or more short-term myocardial ischemia and reperfusion , then in a long- time ischemia-reperfusion. Subsequently, a large number of experiments show that Preconditioning has a protective effect. However, in clinical, the time of myocardial ischemia is unpredictable, so that,the clinical application of Preconditioning is greatly limited. Later, Zhao et al proposed the concept of ischemic postconditioning in the study of Myocardial ischemia -reperfusion. In early reperfusion, repeated coronary occlusion and recanalization can significantly reduce reperfusion injury. In a study of variety animal models such as dogs, pigs, rabbits et al,ischemic postconditioning was confirmed to have protective effect on the heart. Subsequently, different organs such as brain, liver, kidney, skeletal muscle in the different species of animal, have also been shown to have different degrees of protection. In 2005, Faraz, Kerendy et al found that myocardial reperfusion given before renal ischemia and reperfusion in the mouse model, can reduce the levels of creatine kinase in the myocardial tissue, reduce the myocardial infarct size. Therefore,remote ischemic postconditioning has a cardioprotective effect, and confirmed the role of adenosine receptor activation. The study of remote ischemic postconditioning of myocardial from the liver, kidney, brain and other vital organs developed to the one of skeletal muscle. Remote ischemic postconditioning of skeletal muscle is simple, safe, convenient. Studies have confirmed that the ischemia-reperfusion of the skeletal muscle on the protective effect of the necrosis of myocardial of mice. But it is not clear whether it has the same protective effect on myocardial necrosis and myocardial apoptosis on rabbits.Objective:To investigate the role of rabbit skeletal muscle ischemia reperfusion on myocardial necrosis and apoptosis .Methods:36 healthy New Zealand rabbits were randomly divided into 3 groups:1) Sham: Only thoracotomy exposed the heart, threading at the midpoint at left ventricular branch of the left coronary artery , no ligation.2) I/R (Ischemia-Reperfution): 45 minutes of LCX occlusion (ischemia) followed by 120 minutes of coronary artery reperfusion; the external iliac artery (EIA) was isolated but not occluded.3) RPostC(Remote ischemic postconditioning)the EIAs were occluded for 5 minutes and reperfused by release of the artery clamp 1 minute, 1 circle at 39 minutes of coronary artery ischemia.The model of ischemia reperfusion was produced by regular occlusion and reperfusion of left ventricular branch of the left coronary artery. The skeletal muscle ischemia-reperfusion model was produced by regular occlusion and reperfusion of the external iliac arteries. Myocardial ischemia and myocardial infracted area was determinded using area calculation and weight measurement methods by Evans blue (Evans) and TTC double staining. Myocardial cell apoptosis was determinded by Tunel method. The protein expression of casepase3,Bcl-2 and Bax was determined by immunohistochemistry.Results:1 Hemodynamic parameters in three groups:1.1 HemodynamicsThe hemodynamic paramenters included heart rate (HR) and mean arterial blood pressure (MAP). The heart rates(HR, bpm) and mean arterial pressure (MAP, mmHg) were not different statistically beteewn every groups before 45min ischemia and 60min or 120min reperfusion.But the heart rate (HR, bpm) of three groups at different time points was decreased throughout the experiment. Mean arterial pressure (MAP, mmHg) was also found to have overall downward trend. Mean arterial blood pressure had a rising trend at the beginning of reperfusion, but the changes had no significant difference(P> 0.05). And it recovered to the level before ischemia at the end of 120min of reperfusion.1.2 Baseline dataIn the experiment, the body weight (G), left ventricular mass (LV) and ischemic area of left ventricle caused by ligation beteewn every group had no significant difference (P> 0.05).2 Myocardial ischemia and infarction2.1 The comparison of the ischemic areas among the three groups.Myocardial ischemia size was expressed by area ratio (area at risk/left ventricle, IZ/LVs) and weight ratio (weight of area at risk/left ventricle, IZ/LVg).The extent of ischemic (IZ / LVg, IZ / LVs) of ischemia control group (I / R) and remote ischemic postconditioning group (RPostC) had no statistically difference(P> 0.05).2.2 The comparision of the infarction areas in the 3 groups.Myocardial infarcted size was expressed by area ratio (NZ/IZs) and weight ratio (NZ/IZg). Compared with the I/R group, myocardial infarcted size of RPostC was significantly reduced: (I/R : NZ/IZg 35.9%±6.3% NZ/IZs 32.7%±6.8% vs RPostC:NZ/IZg 19.4%±5.6%,NZ/IZs 17.11%±7.74%,P<0.05).3 Creatine kinase (CK) and Lactate Dehydrogenase (LDH) observation:3.1 Changes of serum creatine kinase (CK):CK in 3 groups before ischemia had no significally different (P> 0.05). In the late reperfusion, compared with I / R group, CK of RpostC was significantly reduced ( RpostC: 3997±865U / L vs I/R:6885±1202U / L, P <0.05).3.2 Changes of Lactate Dehydrogenase(LDH):LDH baseline in every group had no significant difference (P> 0.05). At the end of reperfusion,compared with the sham group, LDH of the I / R group and RPostC was significantly increased(I/R:324±89U/LvsSham:180±47U/L; RpostC:294±95U/LvsSham:180±47U/L, P<0.05), but RPostC group and I / R groups had no significally difference(P> 0.05).4 Tunel test results: In the Sham group there was only a small amount of myocardialtissue apoptosis, but in the ischemia-reperfusion group there are a large number of apoptotic cells in ischemic area(apoptotic index (35.81±1.10)%) . The apoptosis index of RPostC (21.79±1.07)%, which was significantly lower than I/R group (P<0.05).5 Caspase-3 protein test resultsCompared with the sham group (4.57%±1.72%), the index of Caspase-3 of ischemia-reperfusion group (39%±2.43%) was significantly increased, (P<0.05), and RPostC group of positive cell index (25.03%±1.16%). Compared with the ischemia-reperfusion group was significantly reduced (P<0.05).6 Bcl-2 and Bax expressionCompared with the Sham group, the Bax protein expression index and the Bcl-2 protein expression index of I/R group and RpostC group was increased, Bax/Bcl-2 ratio of RpostC group was decreased, while in the I/R group, Bax/Bcl-2 ratio was increased. Compared with the I/R group, the Bax protein expression index and the ratio of Bax/Bcl-2 of RPostC goup was significantly reduced, Bcl-2 expression was significantly higher, the differences were statistically significant (P <0.05).Conclusions:1.The study found that early reperfusion in rabbits'external iliac arteries given by a short ischemia and reperfusion could reduce myocardial reperfusion injury.2.The study found that limb ischemic postconditioning could significantly reduce the myocardial ischemia reperfusion injury manifested as it could significantly reduce myocardial apoptosis.
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