Cardioprotective Effects Of Emulsified Isoflurane Postconditioning Against Ischemia Reperfusion Injury In Rabbit Heart And Its Mechanisms

Objective Emulsified isoflurane is a new lipid-based formulation of the volatile anesthetic that permits intravenous administration. Prior investigations have demonstrated the feasibility and safety of induction of anesthsia with intravenous emulsified isoflurane. It has been reported that emulsified isoflurane administered intravenous provides similar myocardial protection against ischemia reperfusion injury as inhaled isoflurane in an in vivo rabbit model,but we do not know whether emulsified isoflurane administration during early reperfusion would mimic ischemic postconditioning. The purpose of this study was to investigate the effect of emulsified isoflurane postconditioning against ischemia reperfusion injury in rabbit heart and its mechanisms.Methods Male New Zealand white rabbits weighing 2.5～3.0 kg underwent 30 min ischemia followed by 180 min reperfusion and ischemia reperfuion injury were elicited by occlusion and open of left anterior descending coronary artery (LAD). The study contained three parts: First, to investigate the effect of emulsified isoflurane postconditioning on ischemia reperfusion injury heart in rabbits, 38 rabbits were randomly assigned to control group (CON, n = 8), ischemia postconditioning group (IPO, n = 8), 0.5 MAC emulsified isoflurane postconditioning group (LEPO, n = 7), 1.0 MAC emulsified isoflurane postconditioning group (HEPO, n = 8), intralipid group (INT, n = 7). CON received 2 ml 0.9% normal saline 5 min before reperfusion, IPO received three cycles of postconditioning ischemia (20 s) during early reperfusion after 30 min coronary artery occlusion, 4～6 ml of 8 % emulsified isoflurane as a bolus and then at a rate of 4～6 ml·kg-1·h-1 via an ear vein to maintain an end-tidal concentration 0.64 (1.0 MAC=1.28% in rabbits) administered for 3 min before and 2 min after reperfusion(LEPO); 8～10 ml of 8 % emulsified isoflurane as a bolus and then at a rate of 6～8 ml·kg-1·h-1 via an ear vein to maintain an end-tidal concentration 1.28 administered for 3 min before and 2 min after reperfusion(HEPO); 30% intralipid intravenous 9 ml bolus and then 7 ml·kg-1·h-1 for 3 min before and 2 min after reperfusion(INT). Second, to investigate the role of mitochondrial ATP-sensitive K+ (KATP) channel in cardioprotective effects of emulsified isoflurane postconditioning, additional groups of rabbits received the combination of HEPO and the nonselective KATP channel antagonist glibenclamide (GLI +HEPO,n=8) or the selective mitochondrial KATP channel antagonist 5-hydroxydecanoate (5-HD+ HEPO, n=7). Glibenclamide was dissolved in 2 ml of dimethylsulfoxide and administered as an intravenous injection 5 min before reperfusion(GLI, n=7),5-HD was dissolved in 2 ml of 0.9% normal saline and administered 5 min before reperfusion(5-HD, n=8), and group DMSO(n=8) received 2 ml of dimethylsulfoxide 5 min before reperfusion. Third, to investigate the effects of emulsified isoflurane postconditioning on cardiomyocyte apoptosis, rabbits were randomly divided into 4 groups(n=5):Sham, CON, HEPO and INT. Hemodynamic parameters were recorded during experiment. Infarct size(IS), as a percentage of the area at risk(AAR), was determined by 2,3,5-triphenyltetrazolium staining(TTC), the activities of serum creatine kinase(CK) and lactate dehydrogenase(LDH) were measured, and apoptosis of cardiomyocytes was assessed by method of terminal deoxynucleotidyl transferase biotin-dUTP nickend labeling (TUNEL). Expression of Bcl-2 and Bax was determined by immunohistochemical method at the end of 180 min reperfusion. Results Compared to CON group, the IS/AAR and serum CK, LDH activities of IPO and HEPO group were declined significantly (P <0.05). There were no significant difference among CON, LEPO, INT, GLI+HEPO, 5-HD+HEPO, GLI, 5-HD and DMSO group in IS/AAR and activities of CK and LDH (P >0.05). Compared to HEPO group, the IS/AAR and serum CK, LDH activities of GLI+HEPO and 5-HD+HEPO group were raised significantly (P <0.05). Compared to Sham group, apoptotic index (AI), expression of Bcl-2 and Bax increased significantly(P <0.05). Compared to CON group, apoptotic index (AI) and expression of Bax declined significantly(P <0.05), and expression of Bcl-2 increased significantly in HEPO (P<0.05).Conclusion 1.0 MAC emulsified isoflurane mimics the cardioprotective effect of ischemic postconditioning in rabbit hearts in vivo.Mitochondrial KATP channel activation is involved in the protective effects of emulsified isoflurane postconditioning. Moreover, Emulsified isoflurane postconditioning can effectively protect myocardium against ischemia reperfusion injury by up-rugulating Bcl-2 protein expression and down-regulating Bax protein expression.