Effect Of Hydromorphone Postconditioning On Cardiac Electrophysiology And Its Mechanism Investigation In Ischaemia And Reperfusion Of Isolated Rat Hearts

Objectives:To observe the effect of hydromorphone post-conditioning on reperfusion arrhythmia（RA）and monophasic action potential（MAP）in ischemia and reperfusion of isolated rat hearts and investigate the relevant mechanisms.Methods:Forty healthy adult male Sprague-Dawley（SD）rats weighting 280-360 g were randomly assigned to five groups after successful preparation of the Langendroff isolated heart perfusion model（n=8）:control group（C group）,ischemia/reperfusion group（IR group）,IR+hydromorphone group（HM group）,IR+hydromorphone+azimilide（Ik channel antagonist）group（HA group）and IR+hydromorphone+naltridole（δ-opioid receptors antagonist）group（HN group）.Each group was infused with 37℃K-H solution for 20 min to maintain stabilization,and then the perfusion suspended for 60 minutes of global ischemia,followed by 60 minutes of reperfusion except C group.During the period of reperfusion,the HM,HA and HN groups were reperfused first with 4.1ng/ml hydromorphone K-H solution or with 4.1ng/ml hydromorphone+3μM azimilide K-H solution or with 4.1ng/ml hydromorphone+5μM naltridole K-H solution for 10 min followed by 50 min reperfusion with K-H solution.The heart rate（HR）,the d V/dtmax of phase 0(V_max),monophasic action potential amplitude（MAPA）and both 50%and90%monophasic action potential durations(MAPD₅₀0 and MAPD₉₀)of three myocardial layers[endocardium（Endo）,mid-myocardium（Mid）and epicardium（Epi）],and the transmural dispersion of repolarization（TDR）were recorded at the time of stabilization 20 min（T₀）,and the time of reperfusion 10,25,40,60 minutes（T₁,T₂,T₃,T₄）.The resuscitation time of HR and arrhythmia was also determined during the reperfusion period.The content of ATP in cardiomyocytes was detected by colorimetry.HE staining was used to observe the changes of ventricular myocytes.The expression and distribution of Akt and Cx43 in cardiomyocytes was detected by immunohistochemical（IHC）staining and western blot.Results:When compared to C group,the HR decreased in the HA group at T1-2 and HN group at T2-4（P<0.05）.With the exception of C group,the RA was dominated by PVBs with different degrees of atrioventricular blocks（AVBs）,lasting about 10 min during the early period of reperfusion.The resuscitation times of HR and the early reperfusion arrhythmia（RA）duration of the HM and HN groups were significantly shorter than those of observed in the IR and HA groups（P<0.05）,however,the whole RA duration amongst the HN,IR and HA groups was not statistically significant（P>0.05）.When compared to C group,the MAPA and V_maxax of three myocardial layers were decreased,the MAPD₅₀and MAPD₉₀ of the three myocardial layers（particularly Endo）were significantly extended at T₁ in other four groups（P<0.05）.Compared with IR group,the increase of MAPD₅₀ and MAPD₉₀ of the Endo was suppressed in the HM group at T₁ but accelerated in the HA group at T_1-3 and HN group at T_1-4（P<0.05）,the TDR decreased in the HM group at T₁、₄ and HN group at T₁,but increased in the HN group at T_3-4（P<0.05）.When compared to C group,the morphologic changes of ventricular myocytes were detected,the content of ATP and the expression of Cx43 in cardiomyocytes were decreased in other four groups（P<0.05）.Compared with IR group,the pathological changes of ventricular myocytes and the decreased of myocardial ATP were alleviated,the expression and distribution of Cx43 and Akt in cardiomyocytes was significantly increased in the HM group（P<0.05）,but using theδ-opioid receptors antagonist naltridole and Ik channel antagonist azimilide can bolished some above effects of hydormorphine postcondtioning to varying degree.Conclusions:Myocardial ischemia reperfusion injury can extend the repolarization duration,increase the repolarization heterogeneity,change the morphology of myocardium,decrease energy storage and the expression of Cx43 in the myocardium.But hydromorphone postconditioning can alleviate the above changes,maintain the electrical stability of ischemia-reperfusion myocardium leads to decrease the incidence of RA.The mechanism of which may be related to the activation ofδ-opioid receptors regulate Ik channel function disorder,and alleviate the down-regulated expression and the disorder of Cx43 by activating Akt signal pathway in isolated rat hearts.