Objective:To investigate the role of Caveolin (Cav-3)/extracellular signal-regulated kinase (ERK) signaling pathway in reduction of myocardial ischemia-reperfusion (I/R) injury by morphine preconditioning in rats with chronic heart failure.Methods:Clean-grade healthy adult male Sprague-Dawley rats, weighing 200-250 g, were used in this study.Chronic heart failure was induced by ligating the left anterior descending coronary artery for 6 weeks.Thirty-six Langendorff-perfused hearts with chronic heart failure were divided into 4 groups ( n=9 each) by a random number table method: myocardial I/R group (group IR), morphine preconditioning group (group MP), morphine preconditioning plus methyl-β-cyclodextrin group (group MP+ MβCD), and methyl-β-cyclodextrin group (group MβCD). Global myocardial I/R was induced by 30 min ischemia followed by 120 min reperfusion.In group MP, after 15 min of equilibration, hearts were subjected to 3 cycles of 5 min perfusion with K-H solution containing 1 μmol/L morphine for preconditioning followed by 5 min perfusion with K-H solution, 30 min in total, and after the end of treatment, hearts were subjected to 30 min ischemia followed by 120 min reperfusion.In group MP+ MβCD, hearts were perfused with K-H solution containing 200 μmol/L methyl-β-cyclodextrin at 10 min before preconditioning with morphine, and the other treatments were similar to those previously described in group MP.In group MβCD, hearts were perfused with K-H solution containing 200 μmol/L methyl-β-cyclodextrin at 40 min before ischemia, and the other treatments were similar to those previously described in group IR.At the end of 15 min of equilibration (T 0) and 5 and 10 min of reperfusion (T 1, 2), coronary outflow was collected for determination of actate dehydrogenase (LDH) activity by chemical colorimetry.Myocardial infarct size (IS) and area at risk (AAR) were measured, and IS/AAR was calculated at the end of 120 min reperfusion.Myocardial tissues of left ventricle were taken to detect the expression of Cav-3, ERK1/2 and phosphorylated ERK1/2 (p-ERK1/2) by Western blot, and p-ERK1/2/ERK1/2 ratio was calculated. Results:Compared with group IR, IS, IS/AAR and LDH activity in coronary outflow were significantly decreased, the expression of Cav-3 was up-regulated, and p-ERK1/2/ERK1/2 ratio was increased in group MP ( P<0.05). Compared with group MP, IS, IS/AAR and LDH activity in coronary outflow were significantly increased, the expression of Cav-3 was down-regulated, and p-ERK1/2/ERK1/2 ratio was decreased in group MP+ MβCD ( P<0.05). Conclusions:The mechanism by which morphine preconditioning reduces I/R injury may be related to activation of Cav-3/ERK signaling pathway in rats with chronic heart failure.