Morphine alleviates myocardial ischemia/reperfusion injury in rats by inhibiting TLR4/NF-κB signaling pathway

OBJECTIVE: The aim of this study was to investigate the effect of morphine on myocardial ischemia/reperfusion (I/R) injury in rats and its underlying mechanism, thereby providing a reference for the prevention and treatment of myocardial I/R injury in clinical practice. MATERIALS AND METHODS: A total of 60 male Sprague-Dawley (SD) rats were randomly divided into 3 groups, including: Sham group (n=20), I/R group (n=20) and I/R + morphine group (n=20) using a random number table. The left anterior descending coronary artery (LAD) of rat was ligated and re-canalized, and the I/R model was established in rats. Rats in I/R + sevoflurane (SEV) group were pretreated with 2.5% SEV. Infarction area of heart in each group was detected using triphenyltetrazolium chloride (TTC) test. Ejection fraction % (EF%) and fraction shortening % (FS%) were determined by echocardiography. Hematoxylin-eosin (HE) staining assay was performed to detect the morphological changes of cardiac myocardial cells in each group. Meanwhile, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) staining was adopted to detect the apoptosis of myocardial cells and fibroblasts. In addition, the expression levels of toll-like receptor 4 (TLR4) and p65 in heart samples of rats in each group were measured via immuno-histochemical staining. Finally. the influence of morphine on TLR4/nuclear factor kappa-light-chainenhancer of activated B cells (NF-kappa B) signaling pathway was detected using Western blotting. RESULTS: Morphine significantly alleviated I/R-induced cardiac dysfunction in rats. whereas significantly increased EF% and FS% (p<0.05). In addition, morphine evidently inhibited myocardial infarction caused by I/R injury. Meanwhile, it reduced the infarction area from [(59.61 +/- 3.41) %] to [(26.67 +/- 3.62) %] (p<0.05). The results of HE staining showed that compared with I/R group, I/R + morphine group exhibited remarkably tidier cardiac myofilament, less degradation and necrosis. as well as significantly relieved cellular edema. Immuno-histochemical staining results revealed that morphine overtly reversed decreased expressions of TLR4 and p65 induced by I/R in rats (p<0.05). Furthermore, Western blotting found that morphine significantly inhibited the protein expressions of TLR4 and phosphorylated p65. CONCLUSIONS: Morphine clearly alleviates I/R-induced myocardial injury in rats. The possible mechanism may be associated with the inhibition on TLR4/NF-kappa B signaling pathway.