Objective and design: To investigate the severity and duration of colitis induced by two different doses of 2,4,6-trinitrobenzenesulfonic acid (TNBS) and the changes in mast cell number in acute infl ammation and in the recovery process of colitis. Methods: Colitis was induced in rats by an enema of TNBS (10 or 30 mg) in 25 % ethanol. Macroscopic and histologic changes of the colon, colon weight and mast cell counts were examined at various times (7, 30 and 60 days) after colitis induction. Results: TNBS induced a colonic damage which was doserelated for both severity and time necessary to complete recovery. On day 7 after colitis induction 10 mg TNBS induced macroscopic and microscopic alterations of colonic architecture that completely resolved at day 60. By contrast, 30 mg TNBS induced massive necrosis, thickening of the colon, severe histologic changes that were only partially reversed after two months. Mast cell number in the submucosa and muscularis propria decreased signifi cantly in the acute phase of infl ammation (7 days) and slowly increased thereafter, reaching a maximum level (up to about 5-fold) at day 60 after both doses of TNBS. Conclusions: Present data confi rm the ability of TNBS to induce in rats damage to the colon that was dose-dependent for severity and duration. Moreover, these data unravel a different role of mast cells in TNBS-induced colitis: an early degranulation in the acute phase of infl ammation and a subsequent accumulation of mast cells in the late phase of the disease, associated with tissue repair.
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