The Changes And Intervention Study Of NADPH Oxidase In Rat Ventricular Tissue After Myocardial Infarction

Objective: To explore the changes of NADPH oxidase in the rat ventricular tissue after myocardial infarction, and the intervention study on the NADPH oxidase with apocynin.Methods: Using male SD rats, MI group was made by ligation of anterior descending coronary artery, the sham group underwent the same procedure without coronary artery ligation, the animals with MI or sham group were assigned randomly to intragastrically receive apocynin (15 mg/kg/day) or saline respectively on the second day after operation for 5 weeks. Echocardiogram were used before the operation and on the 6th week after the operation respectively. On the 6th week after the operation, the rats were killed and the hearts were removed. The concentration of O2- and the activity of NADPH oxidase were measured by the method of absorption photometry, and the expression level of gp91phox mRNA was detected with RT-PCR, and the correlations between the concentration of O2- and the activity of the NADPH oxidase, and the expression level of the gp91phox mRNA were respectively calculated.Results:1. The concentration of O2- in the MI group[(83200±7582)RLU/mg protein] increased significantly compared to the sham group [(50300±3416)RLU/mg protein](P<0.01). The concentration of O2- in the MI+apocynin group[(53300±5517)RLU/mg protein] decreased significantly compared to the MI group(P<0.05). There were no significant differences between the MI+apocynin group, the sham+apocynin group and the sham group (P=0.45, 0.41).2. The activity of NADPH oxidase in the MI group [(4.77±0.46)RLU/mg protein] increased significantly compared to the sham group[(3.38±0.35)RLU/mg protein](P<0.01). The activity of the NADPH oxidase in the MI+apocynin group[(3.62±0.32)RLU/mg protein] decreased significantly compared to the MI group(P<0.05). There were no significant differences between the MI+apocynin group, the sham+apocynin group and the sham group(P= 0.27, 0.37).3. The expression level of gp91phox mRNA in the MI group [0.69±0.06]increased significantly compared to the sham group[0.46±0.07](P<0.01). The expression level of gp91phox mRNA in the MI+apocynin group[0.49±0.06] decreased significantly compared to the MI group(P<0.05). There were no significant differences between the MI+apocynin group, the sham+apocynin group and the sham group(P=0.54, 0.64).4. The concentration of O2- positively correlated to the activity of the NADPH oxidase(R=0.73,P<0.01), and the expression level of the gp91phox mRNA(R=0.80,P<0.01).Conclusions: 1. The concentration of O2-, the activity of the NADPH oxidase and the expression level of gp91phox mRNA in the MI group increase significantly. There are positive correlations between the concentration of O2- and the activity of NADPH oxidase, and between the concentration of O2- and the expression level of gp91phox mRNA. These indicate that the NADPH oxidase system is actived after myocardial infarction.2. The apocynin decreases the production of O2- by inhibiting the activity of NADPH oxidase and the expression level of gp91phox mRNA. This suggests that apocynin as a NADPH oxidase inhibitor could significantly attenuate the level of oxidase stress after myocardial infarction.