Myogenic NOS and endogenous NO production are defective in colon from dystrophic (mdx) mice.

The aim of the present study was to evaluate whether alterations in the distribution and/or function of nitric oxide synthase (NOS) could be involved in the development of the spontaneous mechanical tone observed in colon from dystrophic ( mdx) mice. By recording the intraluminal pressure of isolated colon from normal mice, we showed that Nω-nitro- l-arginine methyl ester (l-NAME) increased the tone, even in the presence of tetrodotoxin. The effect was prevented by l-arginine, nifedipine, or Ca2+-free solution. In colon from mdx mice, l-NAME was ineffective. Immunohistochemistry revealed that the presence and distribution of neuronal (nNOS), endothelial, and inducible NOS isoforms in smooth…