This study is to explore the actions of nitric oxide(NO)and inducible nitric oxide synthase(iNOS)onendotoxin(lipopolysaccharide,LPS)induced rat acute lung injury(ALI)and effect of Rhubarb onthem.LPS was injected into the sublingual vein of male Wistar rats to prepare ALI animal models.Therats were divided into 4 groups:LPS,control,Rhubarb,and dexamethasone.Macroscopic andhistopathological examinations of the lung specimens were performed and the biological indexes oflung,including wet weight/dry weight,the rate of neutrophils and protein content in the pulmonaryalveolar lavage fluid,pulmonary vascular permeability and pulmonary alveolar permeability wereobserved.In the mean time,the contents of serum NO and the activities of lung tissue homogenateiNOS were measured.The results showed that in the LPS group,the injury and celluar infiltration inthe pulmonary stroma and alveoli were more prominent than that in the control group.Lung wetweight/dry weight,the rate of neutrophils,protein content,pulmonary alveolar permeability,pulmonary vascular permeability were significantly increased(P<0.01);NO and iNOS were alsomarkedly elevated(P<0.01).In the groups of dexamethasone and Rhubarb,the histopathologicalchanges were significantly milder,and all the above biological indexes of lung injury and the contentsof NO and the activities of iNOS were correspondingly decreased(P<0.05).The above datademonstrate that NO and iNOS play an important role in the onset of ALI;dexamethasone andRhubarb interfering treatment can ameliorate lung injury and decrease the concentrations of NO andthe activities of iNOS,showing that through inhibiting the levels of NO and the activities of iNOS,these2 agents exert protective effect on ALI induced LPS. This study is to explore the actions of nitric oxide (NO) and inducible nitric oxide synthase (iNOS) onendotoxin (lipopolysaccharide, LPS) induced rat acute lung injury (ALI) and effect of Rhubarb on them.LPS was injected into the sublingual vein of male Wistar rats to prepare ALI animal models.The rats were divided into 4 groups:LPS,control,Rhubarb,and dexamethasone.Macroscopic andhistopathological examinations of the lung specimens were performed and the biological indexes oflung, including wet weight/dry weight, the rate of neutrophils And protein content in the pulmonaryalveolar lavage fluid, pulmonary vascular permeability and pulmonary alveolar permeability wereobserved.In the mean time,the contents of serum NO and the activities of lung tissue homogenateiNOS were measured.The results showed that in the LPS group,the injury and Celluar infiltration inthe pulmonary stroma and alveoli were more prominent than that in the control group.Lung wetweight/dry weight,the rate of neutrophils,protein con Tent,pulmonary alveolar permeability,pulmonary vascular permeability were significantly increased(P<0.01);NO and iNOS were alsomarkedly elevated(P<0.01).In the groups of dexamethasone and Rhubarb,the histopathologicalchanges were significantly milder,and all the above biological indexes Of lung injury and the contentsof NO and the activities of iNOS were correspondingly decreased(P<0.05).The above datademonstrate that NO and iNOS play an important role in the onset of ALI;dexamethasone andRhubarb interfering treatment can ameliorate lung injury and decrease the concentrations Of NO andthe activities of iNOS,showing that through inhibiting the levels of NO and the activities of iNOS,these2 agents impact protective effect on ALI induced LPS.