Objective To test the effects of TNF-α inhibitor Etanercept on myocardial ischemia/ reperfusion (MI/R) injury in posttraumatic mice,and explore related mechanisms.Methods Traumatic mouse model was established with Noble-Collip drum.Five days after trauma,Notch1 was knocked down by intramyocardial injection of Notch1 small interfering RNAs (siRNA) or scrambled siRNA (20 μg).Seven days after trauma,mice were subjected to MI/R (30 minutes ischemia followed by reperfusion).Sham operation was similarly performed without coronary artery ligation.Ten minutes before reperfusion,mice received Etanercept (8 mg/kg,i.p.).ELISA was used to detect plasma levels of TNF-α and troponin I (cTnI) and myocardial nitrotyrosine content.Twenty-four hours after reperfusion,left ventricular ejection fraction (LVEF) was measured by echocardiography.Infarct size was determined by Evans blue/2,3,5-triphenyl tetrazolium chloride (TTC) double staining.Cardiac caspase-3 activity was detected using a caspase-3 kit.Myocardial TNF-α and Notchl intracellular domains (Notch1 ICD) expressions were determined by Western blot.Chemiluminescence was used to assess myocardial superoxide anion content.Results (1) Compared to vehicle group,Etanercept treatment significantly reduced cTnl content,infarct size and caspase-3 activity (all P ＜0.01),while obviously increased LVEF (P ＜0.01).(2) Etanercept treatment also significantly reduced plasma and myocardial TNF-α contents (P ＜ 0.01),whereas markedly increased myocardial Notch1 ICD content (P ＜0.05).(3) Compared to scrambled siRNA group,Notch1 deficiency significantly increased cTnI content,infarct size and caspase-3 activity (P ＜ 0.05),whereas obviously reduced LVEF (P ＜ 0.05).(4) Etanercept significantly reduced myocardial superoxide anion and nitrotyrosine content (P ＜ 0.01),which was reversed by downregulation of Notch1 (P ＜ 0.05).Conclusions TNF-α inhibitor Etanercept can alleviate MI/R injury after trauma by reducing myocardial oxidative/nitrative stress via activating Notch1 signaling pathway.