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ObjectiveTo investigate the effects of oxidative stress on diaphragma and its mechanism, and to explore the beneficial effect of N-acetylcysteine （NAC） .Methods45 SD male rats were randomly divided into control group, COPD model group and N-acetylcysteine （NAC） group. In COPD group the COPD rat model was established by passive smoking and intra-tracheal instillation of lipopolys- accharide （LPS）. In NAC group, established the COPD rat model like the COPD group,meanwhile all the rats were orally instilled by NAC（50mg/100g）. In Control group, all the rats were nosmoking, all the others （LPS、NAC） were replaced by the same volume saline solution. All rats were killed in the 30th day.Departed and weighted the diaphragma. Observed the change of lung tissues under light microscope, while observe the change of diaphragma under light microscope and Electron microscopy respectively. The effects of treatment were tested by measuring MDA by thiobarbituric acid （TBA） method, SOD by xanthine oxidase assay, apoptotic index of diaphragmatic cells by TUNEL method.The expression of ubiquitin was assessed by immunohistochemistry method, then analysed the average gray value by the CIAS systems.Results1. After establishing the models, the copd group appeared generally abnormal, the NAC group rats performed similar to the copd group rats, but to be a less degree.2. As the Pathology shown, in COPD group lung tissue of rats presented emphysema and bronchial inflammatory infiltrated,structural changed etc, while those in NAC group rats showed less changed. In COPD group, the fiber structu -re of diaphragm was damaged seriously, atrophy, disorder, ruptured etc; the ultrastructure of diaphragm was also damaged, mitochondria hyperplasia, a great quantity vacuoles among mitochondria, and chromatin of nucleuses was condensed, while all above in NAC group displayed a much more improvement.3. The weight of diaphragm in COPD group were significantly lower than those both in the control and NAC group（P<0.01）: 0.73g±0.05, 0.85g±0.02, 0.80g±0.03 respectively.4. The content of MDA in COPD group were significantly higher than those both in the control and NAC group（P<0.01） : （4.38±0.47）μmol·g-1, （3.10±0.24）μmol·g-1, （3.62±0.42）μmol·g-1 respectively; while the activity of SOD were significantly lower than those in the control and NAC group （P<0.01）: （154.20±20.05） ng·g-1, （198.67±13.71）ng·g-1, （174.37±15.59） ng·g-1 respectively.5. Compare to the control group ,the expression of ubiquitin was higher in COPD group, and the average gray value was significantly lower （155.49±6.39 vs 170.41±5.75,P<0.01）, while compare to COPD group, the expression of ubiquitin was lower in NAC group, and the average gray value was significantly higher （167.20±7.60 vs 155.49±6.39,P<0.01）.6. The AI of diaphragmatic cell in COPD group were significantly higher than those both in the control and NAC group （P<0.01） : 28.27±2.52, 5.37±0.94, 15.00±2.07 respectively.Conclusions1. Oxidative stress in copd rats’diaphragmatic can increase the expression of ubiquitin and the apoptosis index of rat diaphragmatic musclecell, both of these can damage structure, cause diaphragm atrophy.2. N-acetylcysteine can reduce oxidative stress level, decrease the expression of ubiquitin and the opoptosis index of diaphragmatic muscle cell in rat model of COPD, thus protect diaphragm from atrophy.
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