Objective:To investigate the mechanism of urokinase on inflammatory substances and thrombomodulin (TM) in deep vein thrombosis (DVT) rats.Methods:A rat model of deep vein thrombosis was established. Thirty rats were randomly divided into sham group, DVT group and UK (urokinase) group. The rat model of deep venous thrombosis was established in DVT group and UK group. One day after operation, urokinase (20 000 U/kg) was injected into caudal vein in UK group once a day for 14 days; Sham group and DVT group were given the same volume of normal saline. The wet weight and the ratio of wet weight/length of thrombus were compared among the three groups; HE staining was used to detect the pathological changes of thrombus in the three groups; The plasma inflammatory factors interleukin-8 (IL-8) and tumor necrosis factor α (TNF-α) were detected by enzyme-linked immunosorbent assay (ELISA). The mRNA expression of TM in the three groups was detected by real-time fluorescence quantitativepolymerase chain reaction (qRT-PCR).Results:Compared with sham group, thrombosis was found in DVT group. The wet weight and wet weight/length ratio of thrombus in DVT group were significantly higher than those in sham group ( P<0.05); After urokinase intervention, the wet weight of thrombus in UK group was significantly lower than that in DVT group, and the wet weight/length ratio of thrombus was also significantly lower than that in DVT group ( P<0.05). Compared with sham group, DVT group had obvious thrombosis, granulation tissue covered around the tissue, obvious adhesion between blood vessels and tube wall, a large number of inflammatory cell infiltration around venous tissue and obvious destruction of valve structure; After urokinase intervention, the thrombus tissue of UK group was significantly improved. Compared with sham group, the concentration of IL-8 , TNF-α and sTM in DVT group were significantly increased ( P<0.05). After urokinase intervention, the IL-8, TNF-α and sTM concentration in UK group were significantly lower than those in DVT group ( P<0.05). qRT-PCR results showed that TM mRNA expression in DVT group was significantly higher than that in sham group ( P<0.05). The TM mRNA expression in UK group was significantly lower than that in DVT group ( P<0.05). Conclusions:Urokinase can inhibit the inflammatory factors and the expression of thrombomodulin in DVT.