| Objective:To study the protection of noninvasive delayed limb ischemicpreconditioning (NDLIP)against myocardial ischemia reperfusion (I/R)injuryin streptozotocin(STZ)-induced diabetic rats.Method:Healthy male Wistar rats were administered once intravenousinjection of STZ solution at a dose of 45 mg/kg,to induce acute diabetes mellitus.Then the diabetic rats were assigned randomly into four groups.(1)Shamgroup (n=13):rats were threaded a silk suture under the left coronary arteryanterior descending (LAD)and laid up throughout the experiment.(2)I/Rgroup (n=24):rats were subjected to 30 min LAD occlusion of the left coronaryartery anterior descending (LAD)followed by 120 min of reperfusion.(3)earlymyocardial ischemic preconditioning (EMIP)group (n=24):rats weresubjected to three episodes of 5 rain LAD occlusion followed by 5 minreperfusion before 30 min ischemia and 120 min reperfusion.(4)NDLIP group(n=24):rats were subjected to three episodes of 5 min ischemia of left hind limbfollowed by 5 min reperfusion daily for three consecutive days to induce NDLIP.On the forth day,30 min ischemia followed by 120 min reperfusion of LADwas performed.Delayed protective effects of NDLIP were evaluated accordingto the changes of ECG,injury and death of myocardial cell,myocardial antioxidativeability,blood vessel endothelial function,function of fibrinolysis and myocardialenergy.Heart rate (HR),mean arterial blood pressure (MAP)and ECG during 30min ischemia and 120 min reperfusion were monitored.Myocardial infarct size wasdetermined based on 2,3,5-triphenyltetrazolium chloride staining.Myocardialapoptosis was detected using the TUNEL method.Expressions ofapoptosis-associated protein Fas and FasL were measured by the real-timequantitative PCR and by Western blotting Blotting technique.Changes of myocardialmorphology were observed after by HE staining.Activities of myocardial tissuemyeloperoxidase (MPO),total-superoxide dismutase (T-SOD),manganese-superoxide dismutase (Mn-SOD),glutathione peroxidase (GSH-PX)andxanthine oxidase (XOD),content of myocardial malonaldehyde (MDA)and concentration of nitric oxide (NO)in serum were detected by spectrophotometer.Activity of creatine kinase-MB type isoenzyme (CK-MB)in serum was determinedby immunological inhibition method.Serum concentrations of cardiac troponin I(cTnI),endothelin-1 (ET-1),tissue plasminogen activator (t-PA)and plasminogenactivator inhibitor-1 (PAI-1)were detected by ELISA method.Mn-SOD mRNA wasmeasured by reverse transcription-PCR method.The contents of ATP,ADP,AMP inmyocardium were detected by HPLC assay,and then the total adenine nucleotide andenergy charge potential were calculated.Results:1.Effects of NDLIP on changes of cardiac physiological functioninduced by myocardial I/R injuryCompared with I/R group,the extent of ST-segment was degraded(P＜0.01),onsets of ventricular premature contraction (VPC)and ventriculartachycardia (VT)were delayed (P＜0.05 or P＜0.01),durations of them wereshortened (P＜0.01;P＜0.05),incidences of VT and ventricular fibrillation (VF)were decreased (P＜0.05;P＜0.01;P＜0.01)in EMIP group and NDLIP group.Changes of MAP and HR caused by I/R injury were not influenced by NDLIP2.Effects of NDLIP on myocardial cell injury and necrosis induced bymyocardial I/R injuryCompared with I/R group,the amplitude of increase in the activity ofCK-MB and serum content of cTnI were reduced (P＜0.01;P＜0.05 and P＜0.01)at the end of reperfusion,myocardial infarct size was diminished (P＜0.01),activity of MPO was attenuated (P＜0.05),and the injury of myocardialmorphous was improved in EMIP group and NDLIP group.The protection of NDLIPwas as effective as that of EMIP3.Effects of NDLIP on myocardial cell apoptosis induced by myocardial I/RinjuryCompared with I/R group,apoptosis of cadiocytes was decreased (P＜0.01),expression of Fas and FasL were lessened (P＜0.01or P＜0.05)in EMIP groupand NDLIP group.The anti-apoptosis protection of NDLIP was as effective as that ofEMIP 4.Effects of NDLIP on myocardial antioxidative activity after myocardial I/RinjuryCompared with I/R group,activities of T-SOD (P＜0.01),Mn-SOD(P＜0.01)and GSH-PX (P＜0.01)were augmented,expression of Mn-SODmRNA was increased (P＜0.01),activity of XOD (P＜0.01)and content of MDA(P＜0.01)were decreased in EMIP group and NDLIP group.The antioxidativeprotection of NDLIP was as effective as that of EMIP.5.Effects of NDLIP on blood vessel endothelial function before and aftermyocardial I/R injuryBefore 30 min ischemia,serum concentration of NO was increased inEMIP group and NDLIP group compared with I/R group (P＜0.05),ratio ofET-1 and NO was decreased (P＜0.05).After 120 min reperfusion,the increasein content of ET-1 was reduced (P＜0.01),the concentration of NO waspreserved (P＜0.05 and P＜0.01),the increase in ET-1/NO was diminished(P＜0.01)in EMIP group and NDLIP group.The protection of NDLIP onendothelial function was as effective as that of EMIP.6.Effects of NDLIP on fibrinolytic factors before and after myocardial I/RinjuryBefore 30 min ischemia,there were no significant differences on serumconcentrations of t-PA and PAI-1 among the three groups.At the end ofreperfusion,the increase in concentration of serum PAI-1 was decreased inEMIP group and NDLIP group compared with I/R group (P＜0.05),while nostatistical change in the content of t-PA was observed among the groups.7.Effects of NDLIP on the level of myocardial energy after I/R injuryCompared with I/R group,the levels of ATP(P＜0.01),ADP (P＜0.01 andP＜0.05,respectively),AMP(P＜0.05)and TAN(P＜0.01)in myocardium wereelevated in EMIP group and NDLIP group.As a result,the ECP wassignificantly increased in the two groups (P＜0.05).No significant deferencein the content of AMP was observed among the groups.Conclusion:1.NDLIP decreased the extent of ST-segment increase induced by I/R injury,delayed onsets and shortened durations of VPC and VT,and decreasesthe incidence of severe ventricular arrhythmia during ischemia.The effect ofNDLIP on anti-ventricular arrhythmias was similar to that of EMIP in diabeticmyocardium.Changes of MAP and HR caused by I/R injury were not influenced byNDLIP.2.NDLIP decreased the release of myocardial CK-MB and cTnI anddiminished myocardial infarct size and improved myocardial morphology afterI/R injury.The protective effect of NDLIP against cell injury and necrosis wasas effective as that of EMIP in diabetic myocardium.The decline in activity ofMPO may contribute to the protection.3.NDLIP decreased the apoptotic index and down regulated expression ofapoptotic proteins Fas and FasL to the extent of that by EMIP in diabeticmyocardium suffered from I/R injury,which may be one of the mechanisms ofdelayed myocardial protection of NDLIP contributed to the decrease ofmyocardial infarct size.4.NDLIP enhanced myocardial antioxidative function after I/R injury todecrease peroxidative injury to the extent of EMIP in diabetic myocardium.5.NDLIP increased the basic serum concentration of NO,which made thebalance between ET-1 and NO shift toward NO.Preservation of NO,declinein serum elevation of ET-1 and maintainance of balance between ET-1 and NOinduced by NDLIP after I/R injury in diabetic myocardium indicated animprovement in endothelial function,which reached to the extent of that byEMIP6.NDLIP exhibited no effect on the serum contents of both t-PA andPAI-1 in basic condition and that of t-PA after I/R injury,but it decreased theelevation in serum PAI-1 to the extent of EMIP,which may be one of themechanisms of delayed myocardial protection of NDLIP,and did no change inserum t-PA induced by I/R injury in diabetic myocardium.7.NDLIP increased the contents of ATP,ADP and TAN and raised theECP in diabetic myocardium after I/R injury,which reached to the extent ofthat by EMIP...
|
PDF Full Text Request