¡¾Abstract¡¿ AIM: To investigate the effect of 4ª²aminosalicylic acid (4ª²ASA) on trinitrobenzene sulfonic acid (TNBS) ª²induced colitis in rats and to clarify the related mechanism. METHODS: Colitis was induced in female SD rats by rectal administration of TNBS resolved in ethanol. The colitis rats were treated with 4ª²ASAª²Na with doses of 100 and 200 mg/kg respectively for 2 weeks. 5ª²aminosalicylic acid (5ª²ASA) and normal saline were used as control groups. The colonic inflammation including macroscopic and histological changes and myeloperoxidase (MPO) activity was evaluated. Superoxide dismutase (SOD) activity and malondialdehyde (MDA) level in colonic mucosa were detected by biochemical methods. The expressions of interleukinª²1¦Â (ILª²1¦Â) and tumor necrosis factorª²¦Á (TNFª²¦Á) mRNAs in colonic mucosa were determined by a reverse transcription polymerase chain reaction (RTª²PCR) method. RESULTS: Compared with TNBS control group, the macroscopic and histological scores and MPO activity in 4ª²ASA treated groups were decreased (P<0.05), SOD activity was increased (P<0.05), and the level of MDA in colonic mucosa was reduced significantly (P<0.05). The expressions of ILª²1¦Â and TNFª²¦Á mRNAs in colonic mucosa were also decreased significantly (P<0.05). The intracolonic administration with 4ª²ASA had no more therapeutic effect than topical treatment with 5ª²ASA. CONCLUSION: The topical treatment with 4ª²ASA can significantly attenuate the colonic damage in TNBSª²induced colitis in rats and it may be related to the antioxidant mechanism and the inhibition of the expression of proª²inflammatory cytokines including ILª²1¦Â and TNFª²¦Á. ......