Study On Mechanism Of Dexmedetomidine Preconditioning Alleviating Myocardial Ischemia/Reperfusion Injury In Rats Through Inhibition Of Endoplasmic Reticulum Stress

Part one:Dexmedetomidine preconditioning alleviates myocardial ischemia/reperfusion injury in rats through inhibition of endoplasmic reticulum stress via ?2-ARObjective To investigate whether dexmedetomidine preconditioning could alleviate myocardial ischemia/reperfusion injury in rats through inhibition of endoplasmic reticulum stress via ?2-AR.Methods Seventy-five male rats,weighing 230-270g,were divided randomly into five groups(n=15 for each group):sham operation(group Sham),group I/R,group Dex+I/R,group Yoh+I/R and group Yoh+Dex+I/R.MI/RI model was established by occlusion of left anterior descending coronary artery(LAD)for 30min followed by 6h reperfusion.Dexmedetomidine(6 ?g·kg-1·h-1 for 10min,followed by 0.7?g·kg-1·h-1 for 15 min)was infused via the right jugular vein.Yoh(Yohimbine)is the antagonist of a2-adrenergic receptor,was infused via the jugular vein(lmg·kg-1 for 5min,0.5mg·kg-1·h-1 for 20min).The ischemic and infracted region size was measured by Evans blue and 2,3,5-triphenyl tetrazolium chloride(TTC)double staining.The mRNA level of endoplasmic reticulum stress related molecules GRP78,CHOP and inflammatory factors IL-1?,IL-6 were detected by real-time quantitative PCR(RT-qPCR).Western blotting was adopted to detect relative protein expression of GRP78,p-PERK,CHOP and cleaved caspase 3.HE staining was adopted to evaluate myocardial pathological damage.The apoptosis rate of cardiomyocytes was detected by TUNEL(DAB)staining.The concentration of serum cTnI was detected by ELISA.Results Compared with group Sham,the infract size in group I/R was significantly increased(P<0.05),the mRNA level of GRP78,CHOP,IL-1?,IL-6 and the protein level of GRP78,p-PERK,CHOP and cleaved caspase 3,myocardial pathological damage,the apoptosis rate of cardiomyocytes,the level of cTnI in group I/R was obviously enhanced(P<0.05).Compared with Group I/R,the above related factors in group Dex+I/R were significantly declined(P<0.05).Compared with group Dex+I/R,those parameters above were significantly enhanced in group Yoh+Dex+I/R(P<0.05).Conclusions Dexmedetomidine preconditioning could alleviate myocardial ischemia/reperfusion injury in rats by reducing apoptosis and inflammation.These effects may depend on inhibiting endoplasmic reticulum stress through activating a2-AR.Part two:Dexmedetomidine preconditioning alleviates myocardial ischemia/reperfusion injury in rats through inhibition of PERK/CHOP pathwayObjective To determine whether dexmedetomidine preconditioning alleviates myocardial ischemia/reperfusion injury in rats through inhibition of PERK/CHOP pathway.Methods Seventy-five male rats,weighing 230-270g,were randomly divided into five groups(n=15 for each group):sham operation(group Sham),group I/R,group Dex+I/R,group CCT+I/R and group CCT+Dex+I/R.MI/RI model and the administration of dexmedetomidine was the same as Part one.CCT(CCT020312)was the selective PERK agonist,and was injected intraperitoneally(2mg·kg-1)one hour before operation.The ischemic and infracted region size was measured by Evans blue and TTC double staining.The mRNA level of endoplasmic reticulum stress related molecules GRP78,CHOP and inflammatory factors IL-1?,IL-6 were detected by real-time quantitative PCR(RT-qPCR).Western blotting was adopted to detect relative protein expression of GRP78,p-PERK,CHOP and cleaved caspase 3.HE staining was adopted to evaluate myocardial pathological damage.The apoptosis rate of cardiomyocytes was detected by TUNEL(DAB)staining.The concentration of serum cTnI was detected by ELISA.Results Compared with group Sham,the infract size in group I/R was significantly increased(P<0.05),the mRNA level of GRP78,CHOP,IL-1?,IL-6 and the protein level of GRP78,p-PERK,CHOP and cleaved caspase 3,myocardial pathological damage,the apoptosis rate of cardiomyocytes,the level of cTnI in group I/R was obviously enhanced(P<0.05).Compared with group I/R,the above factors in group Dex+I/R were significantly declined(P<0.05).Compared with group I/R,the mRNA and protein level of GRP78 in group CCT+I/R were of no significant difference(P>0.05)and the other parameters were significantly increased(P<0.05).Compared with group Dex+I/R,the mRNA and protein level of GRP78 in group CCT+Dex+I/R were of no significant difference(P>0.05)and the other parameters were significantly increased(P<0.05).Conclusion Dexmedetomidine preconditioning may alleviate myocardial ischemia/reperfusion injury through inhibition of PERK/CHOP pathway.