Role of μ opioid receptor in morphine preconditioning-induced reduction of myocardial ischemia-reperfusion injury in rats with chronic heart failure: an in vitro experiment / 中华麻醉学杂志

ABSTRACT

Objective To evaluate the role of μ opioid receptor in morphine preconditioning-induced reduction of myocardial ischemia-reperfusion (I/R) injury in rats with chronic heart failure.Methods Adult male Sprague-Dawley rats,weighing 170-230 g,in which chronic heart failure was induced by injecting doxorubicin via the tail vein,were studied.The rats were sacrificed and their hearts were excised and perfused in a Langendorff apparatus with K-H solution saturated with 95％ O2-5％ CO2 at 37 ℃.Forty isolated rat hearts with I/R injury were randomly divided into 4 groups (n=10 each)group I/R,morphine preconditioning group (group MP),μ opioid receptor antagonist CTOP plus morphine preconditioning group (group CTOP+MP) and CTOP group.Myocardial I/R was induced by occlusion of the left coronary artery for 30 min followed by 120 min of reperfusion.In group MP,the hearts were perfused with K-H solution for 15 min,with K-H solution containing 1 μmol/L morphine for 5 min and with K-H solution for 5 min,3 cycles in total,and then the model of myocardial I/R was established.The hearts were perfused with K-H solution containing 1 μmol/L CTOP starting from 10 min before morphine preconditioning until 5 min of ischemia in group CTOP + MP.The hearts were perfused with K-H solution containing 1 μmol/L CTOP starting from 40 min before ischemia until 5 min of ischemia in group CTOP.The coronary effluent was collected at 15 min of equilibration (baseline) and 5 and 10 min of reperfusion to detect the activity of lactate dehydrogenase (LDH).Myocardial infarct size (IS) and the area at risk (AAR) were measured by 2,3,5-triphenyl-tetrazolium staining,and IS/AAR percentage was calculated.The expression of Bcl-2 and Bax mRNA was determined using uantitative real-time polymerase chain reaction,and the ratio of Bcl-2/Bax was calculated.Results Compared with group I/R,the IS and IS/AAR percentage were significantly decreased,the activity of LDH in coronary effluent was decreased,the expression of Bax mRNA was downregulated,the expression of Bcl-2 mRNA was up-regulated,and the Bcl-2/Bax ratio was increased in group MP (P＜0.05),and no significant change was found in the IS or IS/AAR percentage in CTOP and CTOP+ MP groups (P＞0.05).Compared with group MP,the IS and IS/AAR percentage were significantly increased,the activity of LDH in coronary effluent was increased,the expression of Bax mRNA was up-regulated,the expression of Bcl-2 mRNA was down-regulated,and the Bcl-2/Bax ratio was decreased in group CTOP+MP (P＜0.05).Conclusion The mechanism by which morphine preconditioning reduces myocardial I/R injury may be related to activating μ opioid receptors and thus maintaining the balance between Bcl2 and Bax gene expression in the rats with chronic heart failure.