Functional activity and expression of inducible nitric oxide synthase (iNOS) in muscle of the isolated distal colon of mdx mice

The inducible isoform of nitric oxide (NO) synthase (iNOS), expressed in endothelium, epithelium, and inflammatory cells, produces a large amount of NO. Previous studies on mouse intestine indicate that a muscular iNOS may have a role in the storage of intraluminal content. In this study we investigated the presence and function of iNOS in the colonic smooth muscle cells of 2- and 12-month-old dystrophic (mdx) mice. By using an in vitro isovolumic technique, and immunohistochemical and Western blot analysis, we demonstrated that iNOS is expressed and active in the smooth muscle cells of normal mouse and defective in young adult (2-month-old) mdx mice. Therefore, an altered activity of the muscle iNOS might explain the motility disorders observed in the colon of mdx mice and, from a clinical point of view, the impairment of intestinal function in dystrophic patients.