ABSTRACT
AIM To study protective effect of [D-Ala~2, D-Leu~5]-enkephalin (DADLE) against hydrogen peroxide (H_2O_2) induced myocardial cell injury and its possible mechanisms. METHODS Myocardial cells were isolated from neonatal rats and cultured for 48 h. Then the cells were randomly assigned into normal control, H_2O_2（200 μmol·L~(-1)）, H_2O_2+DADLE(1 μmol·L~(-1)), H_2O_2+DADLE +naltrindole(10 μmol·L~(-1)) and H_2O_2+DADLE +U0126(10 nmol·L~(-1)) groups and cultured for another 48 h.[~3H]TdR incorporation assay and flow cytometry were used to measure the cell proliferation and apoptosis rate. The lactate dehydrogenase (LDH) activities in culture supernatant measured by using LDH activity kit. The superoxide dismutase (SOD) activity and malondialdehyde (MDA) content in cells were measured with xanthine oxidase method and color reaction of thiobarbituric acid, respectively. The expressions of extracellular signal-regulated kinase (ERK) and phosphorylated-ERK (p-ERK) were observed with Western blot. RESULTS ① Compared with normal control group, the incorporation of [~3H]TdR in myocardial cells of H_2O_2 group was significantly lower, apoptosis rate was higher, LDH activity and MDA content in cells were higher, while SOD activity in cells was lower. In addition, the ratio of IA_( p-ERK) /IA_( ERK) was decreased. ② Compared with H_2O_2 group, the incorporation of ［3H］TdR in H_2O_2+DADLE group was significantly higher, apoptosis rate was lower, LDH activity and MDA content in cells decreased, while SOD activity increased significantly. The ratio of IA_( p-ERK) /IA_( ERK) was increased. ③ δ-Opioid receptor antagonist naltrindole and ERK antagonist U0126 inhibited this effect of DADLE on the above index changes induced by H_2O_2. CONCLUSION The δ-opioid receptor has protective effect against H_2O_2-induced myocardial cell injury, and its possible mechanism may be related to its promotion of antioxide capacity and ERK phosphorylation.
