Cardioprotective Effects Of Limbs Ischemic Postconditioning By Different Strength And Time In Rabbits

Coronary heart disease(CHD)is one of the major diseases,which hazards to the human health now. Revascularization is an important method of treatment. In recent years, with the widespread application of thrombolysis, coronary artery interventional therapy, and coronary artery bypass grafting surgery, myocardial ischemia reperfusion injury (IR) is payed extensive attention because of lowering treatment effect. Therefore, it has important clinical value that seeking effective treatment measures to reduce reperfusion injury.Since Murry and colleagues firstly defined the concept of ischemic preconditioning (IP), a number of studies have been confirmed that both the direct myocardial ischemic preconditioning and the remote ischemic preconditioning can reduce myocardial ischemia-reperfusion injury, but the application of ischemic preconditioning has been greatly limited, because the clinical ischemic events are unpredictable. Since Zhao and other scholars pointed out the conception of ischemic postconditioning and confirmed that it has a similar protective effect compared with ischemic preconditioning, people began to research this treatment approach in a variety of animal models.The ischemic postconditioning includes direct myocardial ischemic postconditioning and remote ischemic postconditioning, but compared with the direct myocardial ischemic postconditioning, the application of remote ischemic postconditioning can avoid the further myocardial invasive injury. Now, the research about remote ischemic postconditioning has been developed from the brain, kidney and other important organs to a safe, simple organization such as the skeletal muscle. Otherwise, studies have shown that limb ischemic postconditioning can significantly protect the myocardium from ischemia reperfusion injury, but there is no report about the cardioprotective effects of limb ischemic postconditioning by different strength and in different time windows now, and it is not yet known that the better limb ischemic postconditioning protocol.In generally, compared with the heart, brain, kidney and other organs, the skeletal muscle tolerance to ischemia and hypoxia is more intensive. In addition, some studies have shown that ischemia postconditioning must be executed during early reperfusion, or it will lose cardioprotective effects. Of course, the time window of postconditioning may be different according to different tissues and organs. So it is unknown whether different time window and ischemic strength performed on sketetal muscle can cause different cardioprotective effects in remote ischemic postconditioning.Objective:To observe different protective effects of limbs ischemic postconditioning by different strength and time windows in rabbits. And the better protocol of limb ischemia postconditioning is tried to be found in order to supply some experimental evidence for research and implementation of limb ischemia postconditioning.Methods:42 healthy New Zealand rabbits were randomly divided into 7 groups:1) Sham: nothing to do.2) CONT (Control): 45 minutes LCX occlusion (ischemia) followed by 120 minutes of coronary artery reperfusion; the external iliac artery (EIA) was isolated but not occluded.3) 6M-DSP (6min-delayed skeletal muscle postconditioning): the EIA was occluded for 5 minutes and reperfused by release of the artery clamp 1 minute, 1 circle at 45 minutes of coronary artery ischemia.4) 1M-DSP (1min-delayed skeletal muscle postconditioning): the EIA was occluded for 5 minutes and reperfused by release of the artery clamp 1 minute, 1 circle at 40 minutes of coronary artery ischemia.5) SP (Skeletal muscle postconditioning): the EIA was occluded for 5 minutes and reperfused by release of the artery clamp 1 minute, 1 circle at 39 minutes of coronary artery ischemia.6) SSP (Strengthen skeletal muscle postconditioning): the EIA was occluded for 5 minutes and reperfused by release of the artery clamp 1 minute, 2 circles at 33 minutes of coronary artery ischemia.7) WSP (Weakened skeletal muscle postconditioning): the EIA was occluded for 3 minutes and reperfused by release of the artery clamp 1minute, 1 circle at 41 minutes of coronary artery ischemia.Acute ischemia reperfusion model was induced by 45 minutes occlusion on left circumflex coronary artery (LCX) and 2 hours reperfusion in all anesthetized open-chest rabbits except the Sham, the coronary occlusion and reperfusion was assessed by changes of ECG and cardiac muscle color. Limb ischemia was induced by external iliac artery occlusion and reperfusion through artery clamp. The distal arterial pulse disappearance was the sign for external iliac artery occlusion. Blood serum creatine kinase (CK) activity and lactate dehydrogenase (LDH) activity were measured at baseline,the end of ischemia, after 1 hour and 2 hours of reperfusion respectively. The extent of myocardial infarction was assessed by triphenyltetrazolium (TTC) staining and expressed by area ratio (area necrotic/area at risk, AN/AARs) and weight ratio (weight of area necrotic/area at risk, AN/AARg).Results:1 General date and hemodynamic observation:1.1 About hemodynamics including heart rate (HR) and mean arterial blood pressure (MAP), there were also no significant difference in each group and different periods(P>0.05).1.2 About the observation indicators of weight of animal(G), left ventricular(LV) and area at risk(AAR), there were no significant difference among all groups(P>0.05). 2 Myocardial ischemia and infarct size observation:2.1 Myocardial ischemia size was expressed by area ratio (area at risk/left ventricle, AAR/LVs) and weight ratio (weight of area at risk/left ventricle, AAR/LVg).There was no significant difference about myocardial ischemia size observation among CON,6M-DSP,1M-DSP,SP,SSP,WSP six groups(P>0.05).2.2 Myocardial infarct size was expressed by area ratio (area necrotic/area at risk, AN/AARs) and weight ratio (weight of area necrotic/area at risk, AN/AARg).Compared with the CONT, myocardial infarct size of 1M-DSP was significantly reduced:( CON:AN/AARg 36.06%±5.74%,AN/AARs 33.46%±7.20% vs 1M-DSP:AN/AARg 20.80%±5.30%,AN/AARs 19.18%±4.53%,P<0.05).Compared with the CONT, myocardial infarct size of SP was significantly reduced: (CON:AN/AARg 36.06%±5.74%,AN/AARs 33.46%±7.20% vs SP : AN/AARg 18.04%±5.84%,AN/AARs 18.81%±8.83%,P<0.05);Compared with the CONT, myocardial infarct size of SSP was also significantly reduced: (CON:AN/AARg 36.06%±5.74%,AN/AARs 33.46%±7.20% vs SSP : AN/AARg 18.62%±6.25%,AN/AARs 17.11%±7.74%,P<0.05);There was no significant difference in 1M-DSP,SP,SSP three groups (P>0.05).Otherwise, Compared with the CONT, myocardial infarct size was not significantly reduced by 6M-DSP and WSP (P>0.05).3 Creatine kinase (CK) and lactate dehydrogenase (LDH) observation:The reduction of CK was similar to the trend of myocardial infarct size. CK activity at the end of 2 hours reperfusion: CONT 6885±1202 U/L VS Sham 1785±490 U/L,1M-DSP 4023±1017 U/L,SP 3848±1135 U/L, SSP 3997±865U/L(P<0.05). There was no significant reduction of LDH activity (P>0.05).Conclusions:1 The study found that limb ischemic postconditioning could significantly reduce the myocardial ischemia reperfusion injury manifested as it could significantly reduce the value of CK and diminish the myocardial infarct size, compared with the CONT.2 The study found that the limb ischemia strength of 5minI/1minR×1cycle could significantly reduce the myocardial ischemia reperfusion injury in rabbits. The double cycle did not produce a stronger cardioprotective effect, but the weakened limb ischemia strength of 3minI/1minR×1cycle lost the cardioprotective effects.3 The study found that the protective time window of reducing myocardial ischemia reperfusion injury was in the early reperfusion. For the limb ischemic postconditioning of rabbits, we should achieve limb ischemic postconditioning before myocardial reperfusion 1 minute. If we delayed 1 minute, limb ischemic postconditioning was achieved at the same time with myocardial reperfusion, there were still significantly cardioprotective effects, despite the downward trend. If we delayed 5 minutes again, the cardioprotective effects were lost.