Abstract: Objective: To investigate the protective effects of tetramethylpyrazine(TMP) on the acute lung injury induced(ALI) by lipopolysaccharide(LPS) in rats.Methods: All rats were randomly into the control group,LPS group,TMP Ⅰ group(injected with 40 mg/kg) and TMP Ⅱ group(injected with 80 mg/kg)(6 rats each group).The twenty-four ALI model Wistar rats were established by injecting 1 mg/kg of LPS into abdominal cavity,and dripping 3 mg/kg of LPS into trachea after 16 hours.The rats were sacrificed,fixed with 4% paraformaldehyde and treated with pathology at 3 hours after treatment with tetramethylpyrazine.The wet/dry weight ratio of lung and levels of MPO and MDA in lung tissues were measured.The protein expressions of RhoA and ROCK2,and mRNA expression of ROCK2 in lung tissues were detected using western-blot and RT-PCR,respectively.Results: Compared with the control group,the pathological section showed that the pulmonary interstitial edema,alveolar cavity bleeding,inflammatory cells exudate,wet/dry weight ratio of lung,MPO activity and MDA content increased significantly in LPS group(P<0.01),the protein expressions of RhoA and ROCK2,and mRNA expression of ROCK2 were also increased in LPS group(P<0.01).The wet/dry weight ratio of lung,MPO activity,MDA content and indexes of RhoA and ROCK2 in TMP Ⅰ group and TMP Ⅱ group were significantly less than those in LPS group(P<0.05 to P<0.01),but their differences between TMPⅠ group and TMP Ⅱ group were not statistical significance(P>0.05).Conclusions: Tetramethylpyrazine can protect against the acute lung injury induced by LPS in rats.