Role of inducible nitric oxide synthase in trinitrobenzene sulphonic acid induced colitis in mice

Background-Studies using inhibitors of nitric oxide synthase (NOS) to date are inconclusive regarding the role of inducible NOS (iNOS) in intestinal i nflammation. Aims-(1) To examine the role of iNOS in the development of chronic intestin al inflammation; (2) to identify the cellular source(s) of iNOS, Methods-Colitis. was induced by an intrarectal instillation of trinitrobenz ene sulphonic acid (TNBS, 60 mg/ml, 30% ethanol), in wild type (control) or iNOS deficient mice. Mice were studied over II days; the colons were score d for injury and granulocyte infiltration was quantified. Blood to lumen le akage of Cr-51-EDTA was measured as a quantitative index of mucosal damage. Results-At 24 and 72 hours, iNOS deficient mice had significantly increased macroscopic inflammation compared with wild type mice. Granulocyte infiltr ation increased significantly at 24 hours and remained elevated in iNOS def icient mice at 72 hours, but, significantly decreased in controls. However, by seven days post-TNBS macroscopic damage, microscopic histology, granulo cyte infiltration, and mucosal permeability did not differ between wild typ e and iNOS deficient mice. A four- to fivefold increase in iNOS mRNA was ob served in wild type mice at 72 hours and seven days post-TNBS and was absen t in iNOS deficient mice. Immunohistochemistry techniques showed that iNOS expression was predominantly localised in neutrophils, with some staining a lso in macrophages. Conclusions-These results suggest that leucocyte derived iNOS ameliorates t he early phase, but does not impact on the chronic phase of TNBS induced co litis despite the presence of iNOS.