Objective To observe the changes in the lung aquaporin 1 (AQP1) expression in adrenaline-induced pulmonary edema(PE),and the effect of Methylprednisolone (MP) on its expression.Methods Fifty Wister rats of 1-month old were randomly divided into 5 groups (10 rats in each group):control,adrenaline PE,MP A,MP B,and MP C groups,respectively.Control group animals were treated with 0.27 mL 9 g/L saline;PE group was given 2.7 mg/kg adrenaline (1 ∶ 1 000) by intraperitoneal injection;MP A,MP B and MP C groups rats were intraperitoneally injected 10 mg/kg,20 mg/kg,and 30 mg/kg MP intraperitoneally immediately after intraperitoneal injection of adrenaline,respectively.The morphology changes in the lungs were observed with HE staining,and lung wet/dry weight (W/D) was measured.The levels of AQP1 mRNA,AQP1 protein,and AQP1 distribution in the lung tissues were detected by using real time-polymerase chain reaction,Western blot,and immunohistochemical method.Results (1)PE group exhibited a faster breathing rate,and double lung volume increased significantly;there was a visible hemorrhagic distribution in the lung surface and cross section,endotracheal filled with white or pink foam liquid.(2) The W/D of rats in PE group was higher than that of the control group (6.50 ± 0.53 vs.4.59 ± 0.36,P ＜ 0.05).(3) Pathological grading of PE group (3.80 ± 0.42) increased significantly compared with that of the MP A group (3.30 ± 0.48),MP B group (2.30 ± 0.68) and MP C group (1.20 ± 0.42),and there were significant differences (all P ＜ 0.05).(4) Immunohistochemistry showed that the expression of AQP1 in PE group (1.20 ± 0.79) was reduced compared with that of the control group (4.20 ± 1.03),and there were significant differences (all P ＜ 0.05).(5) The levels of AQP1 mRNA and AQP1 protein (0.12 ± 0.43 and 0.20 ± 0.04) were significantly lower than those of the control group (0.90 ± 0.32 and 0.60 ± 0.15),and there were significant differences (all P ＜ 0.05);compared with PE group,AQP1 mRNA and AQP1 protein of each group with MP treatment showed the highest values (MP A group:0.17 ±0.06 and 0.32 ±0.04,MP B group:0.39 ±0.13 and 0.37-±0.09,MP C group:0.61 ±0.21 and 0.44 ± 0.07) (all P ＜ 0.05).Conclusion The expression of AQP1 reduced in adrenaline-induced PE rats.MP could improve the expression of AQP1,and significantly ameliorate the PE and bleeding.