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.

Objective To evaluate the role of activation of astrocytes in the spinal cord in myocardial ischemia-reperfusion (I/R) injury in rats.Methods Eighteen healthy adult male Sprague-Dawley rats,in which intrathecal catheters were successfully implanted,weighing 250-300 g,were divided into 3 groups (n =6 each) using a random number table method:sham operation group (group Sham),myocardial I/R group (group I/R) and an astrocyte inhibitor fluorocitrate group (group I/R+FC).Myocardial ischemia was induced by 30 min occlusion of left anterior descending branch of coronary artery followed by 120 min reperfusion in chloral hydrate-anesthetized rats.Fluorocitrate 10 μl (1 nmol) was intrathecally infused at a constant rate starting from 30 min before ischemia in group I/R+ FC.Arrhythmia was scored according to the results of electrocardiography during I/R.Arterial blood samples were collected at 120 min of reperfusion to determine the serum cardiac troponin Ⅰ (cTnⅠ) concentration by chemiluminescence assay.The animals were then sacrificed,myocardial specimens were taken for measurement of the infarct size,and T2-6 segments of the spinal cord were harvested for determination of the expression of glial fibrillary acidic protein (GFAP) (by Western blot).Results Compared with group Sham,the serum cTnⅠ concentration,arrhythmia score,and myocardial infarct size were significantly increased,and the expression of GFAP was up-regulated in I/R and I/R+FC groups (P＜0.05).Compared with group I/R,the serum cTnⅠ concentration,arrhythmia score,and myocardial infarct size were significantly decreased,and the expression of GFAP was down-regulated in group I/R+FC (P＜0.05).Conclusion The activation of astrocytes in spinal cord is involved in myocardial I/R injury in rats.