Abstract:
［Abstract］  ObjectiveTo investigate the protective effects of different doses of methylprednisolone(MP) on HCLinduced acute lung injury in rats. MethodsA total of 48 male SD rats were divided randomly into four groups according to the random number table method:model group, control group, smalldose MP group and highdose MP group. Each group included 12 rats. The model group were injected with hydrochloric acid(pH=18, 2 mL/kg) by the endotracheal intubation, and the control group were injected with equal volume of normal saline by the endotracheal intubation. The smalldose MP group and highdose MP group were intraperitoneally injected with 5 mg/kg and 40 mg/kg MP after duplicating model. Four hours after duplicating model, the pathological changes of lung tissue were observed under light microscope. The lung wet/dry ratio(W/D) was calculated. Protein concentration, PMN% in bronchoalveloar lavage fluid and the expression of  Na+K+ATPase α1  isoforms mRNA in lung tissues were measured.  ResultsIn the control group, the lung tissue structure was clear, the alveolar septum was uniform, and there was no fibrin exudation and neutrophil infiltration in the alveolar. Model group showed the bronchial epithelial cells, alveolar cavity, a large number of fibrin exudation and edema fluid formation. Compared with model group, there were different degrees of improvement of the lung tissue pathologic characteristics in the smalldose MP group and highdose MP group.  In model group，smalldose MP group and highdose MP group, W/D，protein concentration and PMN% in BALF were significantly increased， the Na+K+ATPase α1  isoforms mRNA expressions were significantly lower. and the protein concentrations in BALF in smalldose MP group and highdose MP group were significantly decreased, compared with control group. The difference was statistically significant (P＜001). ConclusionMP can significantly improve lung injury degree of hydrochloric acidinduced acute lung injure model of rats. Smalldose MP has more advantage on lung protection than highdose MP on acute lung injury of rats.

Key words: acute lung injury, methylprednisolone, hydrochloric acid, rats