Abstract： Objective To investigate the effect of postconditioning with propofol on Toll-like receptor 4 (TLR4) expression in the lung tissue in lipopolysaccharide (LPS)-induced acute lung injury (ALI) rats.Methods Thirty Sprague-Dawley (SD) rats were randomly assigned to control group,ALI group,and propofol postconditioned group (each n =10 ).The model of ALI was reproduced by intravenous injection of LPS (8 mg/kg for 30 minutes ) into the rats,equivalent normal saline was injected into the rats of control group.The rats were postconditioned with propofol injected intravenously by 20 mg/kg bolus dose and then continuously by 40 mg· kg-1· h-1 with a constant speed for 1 hour.The rats were sacrificed 6 hours after drug injection.Lung wet/dry weight ( W/D ) ratio and lung permeability index ( LPI ) was taken.Tumor necrosis factor- α ( TNF-α ) level in bronchoalveolar lavage fluid (BALF) was detected using enzyme linked immunosorbent assay (ELISA) method and TLR4 mRNA expression in lung tissue was assessed by reverse transcription-polymerase chain reaction (RT-PCR).Results The lung W/D ratio,LPI,TLR4 mRNA and TNF-α (ng/L) in BALF were all increased in ALI group compared with control group [lung W/D ratio:5.30 -± 0.28 vs.4.21 ±0.14,LPI ( × 10-3):8.7 ± 2.2 vs.3.3 ± 2.0,TLR4 mRNA:2.451 ± 0.028 vs.0.998 ± 0.021,TNF-α:643.46 ± 62.31 vs.120.43 ± 12.65,all P＜0.05].The above indexes were significantly reduced in the propofol group than those in the ALI group [lung W/D ratio:4.68 ± 0.19 vs.5.30 ± 0.28,LPI ( × 10-3):5.8 ± 2.0 vs.8.7 ± 2.2,TLR4 mRNA:1.126 ±0.025 vs.2.451 ± 0.028,TNF-α:290.53 ± 32.01 vs.643.46 ± 62.31,all P＜0.05],but still higher than those in control group ( all P＜0.05 ).Conclusion Postconditioning with propofol may alleviate ALI via reducing TLR4 mRNA expression,and inhibit the waterfall-like inflammatory reaction.