Study For Postconditioning In Type 2 Diabetic Rats

The incidence of acute myocardial infarction has been increasing year by year. Reperfusion is the best effective treatment method in the treatment of acute myocardial infarction. Injury brought by reperfusion lead to apoptosis and necrosis of myocytes increasing and myocardial infarct size enlarged, arhythmia, heart function corruption. If reperfusion injury is reduced, the prognosis of myocardial infarction will be improved.The phenomenon of ischemic postconditioning first described in 2003 by Vinten-Johansen's group, in which brief intermittent repetitive interruptions to reperfusion at the onset of reperfusion after a prolonged period of ischemia reduced myocardial injury.Diabetes is the main risk factors of coronary artery disease. The mortality rate of acute myocardial infarction patient with diabetes patients higher than negative diabetes patients. Therefore, the study of ischemic postconditioning under diabetic state is absolutely necessary and significant. However, it is a pity that the mechanisms of ischemic preconditioning under diabetic state is not clear. So far there are few studies related to ischemic postconditioning under diabetic state.This study will first establish the animal model of type 2 diabetes with high fat forage and streptozocin (STZ) intraperitoneal injection (ip), then mimic ischemic/reperfusion and ischemic postconditioning using the isolated buffer-perfused rat heart model. Accordingly, our aims in this study study were to evaluate the cardioprotection of postconditioning in an isolated buffer- perfused normal rat heart and diabetes rat heart model.Method1,Establishment of the animal model of type 2 diabetesAdult male rats were bulided hyperlipidemia and insulin resistance model after they are raised by high fat forage for one month. The rats were given 40mg/kg streptozocin (STZ) through intraperitoneal injection.2,Langendorff isolated rat heart model of ischemic reperfusion and postconditioningRat hearts were rapidly excised, mounted on a Langendorff system, and perfused with a Krebs-Henseleit buffer from aortic root. All hearts were subjected to 30 min of global ischemia and 60 min of reperfusion. Postconditioning protocol is that after the 30 min ischemia, the hearts immediately underwent a protocol of six cycles of 10 s reperfusion and 10 s global ischemia, then the reperfution continue.3,Assessment of myocardial injuryUsing 8-channel polygraph the hemodynamic parameters were monitored, including heart rate (HR), left ventricular systolic pressure (LVSP) maximal rise rate of left ventricular pressure (+dP/dtmax).Myocardial damage was estimated by measuring LDH and CK from coronary flow. At the end of 60 minutes of reperfusion, hearts were perfused with 2, 3, 5-triphenyltetrazolium chloride (TTC) for infarct size calculation, and other hearts for immunohisto -chemical staining.Result1,Glucose of diabetes group is higher than control group (p<0.01) in the seventh day after STZ intraperitoneal injection. The glucose come up to the standard of the animal model of type 2 diabetes.2,Hemodynamic parameters in IPOST group recovered higher than that in I/R group after 30 min reperfusion; LDH,CK in IPOST group released fewer than in I/R group, postconditioning reduced infarct size compared with I/R group (29.50% VS 37.35%) (p<0.05). Postconditioning increased significant phosphorylation of Akt compared with I/R group. When the AKT inhibitor Wortmannin was given for the first 15 minutes of reperfusion, the postconditioning-induced cardioprotectione was abolished.3,Hemodynamic parameters in diabetes IPOST group have no difference with in diabetes I/R group after 30 min reperfusion; LDH,CK in diabetes IPOST group released no difference with in diabetes I/R group, postconditioning did not reduced infarct size compared with I/R group (50.12% VS 45.65% (p>0.05). Postconditioning does not increased phosphorylationof Akt compared with diabetes I/R group . When the AKT inhibitor Wortmannin was given for the first 15 minutes of reperfusion, there are no diference.Conclusion1,Ischemic postconditioning protected the myocardium in normal isolated perfused rat hearts. Ischemic postconditioning significantly reduced infarct size and LDH, CK released, and improved hemodynamic parameters and phosphorylation of Akt.Wortmannin can abolished the postconditioning induced cardioprotection, and reduced phosphorylation of Akt. we showed that cardioprotection was mediated via the PI3K-Akt prosurvival signaling cascade.2,Ischemic postconditioning did not protected the myocardium in type 2 diabetes isolated perfused rat hearts. Ischemic postconditioning did not reduced infarct size and LDH, CK released, and improved hemodynamic parameters and phosphorylationof Akt. Ischemic postconditioning actived AKT insufficiently in diabetes group. In conclusion, postconditioning did not protected the diabetic heart which may be due to insufficient Akt activation.