CONSTITUTIVE EXPRESSION OF INDUCIBLE NITRIC-OXIDE SYNTHASE IN THE MOUSE ILEAL MUCOSA

It has been demonstrated previously that the inducible isoform of nitr ic oxide synthase (iNOS) is present throughout the intestinal tract in various inflammatory disease processes. Here we demonstrate that iNOS mRNA is present in the ileum but not in the jejunum or colon of norma l mice. By Western blot analysis, iNOS protein is also detected in nor mal ileum, but not in the normal jejunum. However, by 3 h postinjectio n of 0.5 mg/kg lipopolysaccharide (LPS), iNOS mRNA is also detectable in the jejunum and colon. The enzyme message and protein, localized im munohistochemically by in situ hybridization and iNOS expression, is n ormally restricted to the villus epithelial cells. The iNOS mRNA was a lso present in the ilea of mice with defined intestinal flora (anaerob es only), germ-free mice, nude mice, and to a lesser extent in mice wi th severe combined immunodeficiency. These results suggest that the co nstitutive presence of iNOS in ileal epithelium indicates a role for t his enzyme in maintaining intestinal homeostasis.