The Effect Of JAK-STAT Pathway On Myocardial Ischemic Post-conditioning In Rabbit Hearts

Objective:After GAO, a domestic scholar, introduced the concept of Hypoxic Postconditioning(HP) in 1999,many labs, include domestic and overseas, carried out further research and introduced the concept of Ischemic postconditioning(IPO) on this groundwork. The means of this concept is that we can decrease arrhythmic,improve heart function,diminute infarct size and reduce cadiocyte apoptosis by performing a circle of temporal ischemic/reperfusion before myocardial reperfusion in hearts. This method is different from ischemic preconditioning(IPC) that it was first introduced by Murry in 1986. The episode was carried out between the postischemic and reperfusion. Because of the unpredict ischemic in clinical, the use of IPC is limited. On the contrary, IPO can be controlled by the doctor in clinical. So the use of IPO is more perspective. But the mechanism of IPO has no accepted conclusion .In this study, we explored the effect of JAK-STAT pathway on myocardial ischemic postconditioning in vivo model of rabbit heart.Methods:40 rabbits (either sex ,weighting 2.5-3.0kg) were randomly divided into four groups. After anaesthesia, to lie on the back, head and four limbs was fixed, electrocardiogram was linked to four limbs, to cut open the neck skin, to expose air hose and cut the air tube like falled'T', intubation tube was linked to breathing machine. Cutted the breast bone, ecarteur was fixed on it. We cutted pericardium and inserted arterial puncture needle that it was connected with pressure transmitter of monitor to left ventricular apex. Group 1(ischemic/reperfusion, I/R n=10):Exposed LAD, used 1# silk suture ligated LAD on the upper 1/3 of it, let the line through a little rubber tube, interrupted the flow of LAD(the mark is ST segment raised).After 30 min occlusion, reperfusion for 120 min. Group 2(ischemic postconditioning, IPO,n=10): Interruption the flow of LAD, After 30 min occlusion, reperfusion for 30s ,reocclusion 30s, repeat it 3 times, reperfusion for 120min.Group 3(AG490+DMSO+IPO, n=10):After 10min of occlusion of LAD, give tyrosine inhibitor AG490(1g/kg),the other work was same to group 2.Group 4(DMSO+IPO, n=10): After 10min of occlusion of LAD, give DMSO,the other work was same to group 2.Take the time before occlusion 10 min as starting point . Recorded electrocardiogram and left ventricle pressur per 10 min in the procedure of ischemic/reperfusion. Collected 2ml blood as a sample at the specified time every groups. The samples randomly divided into two groups at the same time. CPK(creatine phosphatekinase, CPK)was detected in One group, ANP(Atrial natriuretic peptide, ANP) was detected in the other. After experiment was completed, the rabbits were executed. Remove the heart of rabbit, all hearts of every group were divided into two parts, observed the pathological changes and detected the apoptosis on the myocardium obtained on the ischemic region in one part; in the other, infarct size was measured through TTC staining method.Results:1.The change of CPK and ANPCPK was increased on 3th,12th, 18th time point in every groups(P<0.01).The level of CPK in group 2 and group 4 was significant decrease compared to group 1 (P<0.01). There were no significant difference between group 1 and group 3(P>0.05).ANP was increased on 3th time point in every groups,and keep on the same level on the 12th,18th time point in group 2 and group 4. There were significant difference between group 1 and group 2 on the 12th,18th time point (P<0.05),but there were no significant difference between group 1 and group 3(P>0.05)2.The change of electrocardiographicWe detected arrhythmia(atrial premature beats APB, ventricular premature beat VPB, ventricular tachycardia VT, ventricular fibrillation VF) in group 1 after reperfusion. The epoch of arrhythmia was mostly on 1-15 min after reperfusion. The ST segment obviously depression on 1-20min after reperfusion. Along with the reperfusion, ST segment was slowly raised and keeped a high level in the end of reperfusion; Q wave appear too. The tendency of this change was significant. The change of electrocardiogram of group 2 and group 4 was not significant. The incidence of arrhythmia keep a lower level, ST segment`s change was not significant, and without Q wave.3. The change of heart functional parameter±dp/dt max is an important index to reflect left ventricle contractile function and diastolic function. It has a bad heart function if±dp/dt max approach to zero. The heart function in group 1 was downtrend compared with group 2.this change was due to the IPO. In group 3, The heart function was downtrend.4. The change of heart cell morphologyThe cell tissue structure has been in disorder, cardiac muscle fibers keep sparseness and without sequence, cell has been Severity edema in group 1and group 3.The pathology change of cell of group 2 and group 4 abatement obviously, cardiac muscle fibers line up in order, slightly sparseness, cell edema was abatement obviously.5. The change of heart infarct sizeThe infarct size of group 2 and group 4 was less than group1 , the difference was significant(P<0.01). There was no significant difference between group 1and group 3(P>0.05).6.The apoptosis of cadiocyteThe cadiocyte apoptosis of group1 and group 3 was higher than the cadiocyte apoptosis of group2 and group 4. The apoptosis cell always cluster in group1 and group 3.We did not found this phenomenon in group2 and group 4.The statistical results show that the contrast between group 1 and group 2 was significant(P<0.01); there was no significant contras between group 1 and group 3 (P>0.05); it was the same manner between group 2 and group 4(P>0.05).Conclusion:1.IPO can reduce the release of CPK, the incidence of arrhythmia , necrosis and apoptosis of cell; decrease the heart infarct size; improve the heart function.2.The JAK-STAT pathway participate the protection me- chanism of IPO.3.In IPO, The JAK-STAT pathway educe the myocardial preservation through increasing the express of ANP.