Role of nitric oxide synthase inhibitor in experimental colitis induced by 2,4,6-trinitrobenzene sulphonic acid in rats.

1. The present study was designed to investigate the role of nitric oxide (NO) in modulating 2,4,6-trinitrobenzene sulphonic acid (TNBS)-induced colitis in rats. 2. Damage scores and NO synthase (NOS) activity were measured. 3. The damage scores and NOS activity reached a peak on the 4th day after administration of TNBS solution (day 0), thereafter gradually decreasing, and were significantly higher than in the group treated with saline throughout the experimental period. 4. Subsequently, we divided the stage of colitis into two groups, one from day 0 to day 3 after induction of colitis, and the other from day 4 onwards. We evaluated the effects of the NOS inhibitor N(G)-monomethyl-L-arginine (L-NMMA), on TNBS-hapten-induced colitis and colonic mucosal blood flow. Two different methods of L-NMMA administration, from day 0 to day 3, and from day 4 onwards, were undertaken. 5. The damage score in the early L-NMMA treatment group was significantly higher than in the group without L-NMMA on day 14. In contrast, the damage score in the late L-NMMA treatment group was not significantly different from the group without L-NMMA. Colonic mucosal blood flow in the early L-NMMA treatment group was not significantly different from that in the late L-NMMA treatment group. 6. These data suggest that NO is important for inhibiting inflammation during the early stages.