Expression of inducible nitric oxide synthase and effects of L-arginine on colonic nitric oxide production and fluid transport in patients with minimal colitis

摘要

Objective. Some patients with idiopathic, chronic diarrhoea have minimal, non-specific colonic inflammation. As nitric oxide (NO) acts as a secretagogue in the colon, we studied the expression of inducible NO synthase (iNOS) in mucosal biopsies and the effects of NOS stimulation on colonic transfer of fluid and output of NO in patients with "minimal colitis".Material and methods. Twelve patients with idiopathic, chronic diarrhoea and "minimal colitis" and 6 healthy volunteers were included in the study. Expression of iNOS in colonic mucosal biopsies was quantified by Western blot analysis and localized by immunohistochemistry. The effects of topical L-arginine or placebo on colonic net fluid transfer and nitriteitrate (NO(x)) output were assessed during "steady state" perfusion of the whole colon. Concentrations of NO(x) were measured by Griess' assay.Results. The expression of iNOS was increased 10-fold (p<0.01) in patients with "minimal colitis" compared with that in healthy volunteers and localized to the colonic epithelium. Colonic absorption of fluid was impaired (mean (SEM) 1.5 (0.2) versus 3.0 (0.2) ml/min, p<0.001) and the output of NO(x) was increased (47 (4) nmol/min versus <37 nmol/min, p<0.05) in patients with "minimal colitis" compared with that in healthy volunteers. Luminal L-arginine (20 mM) reduced colonic absorption of fluid in both groups (95% confidence intervals (CIs) 21-50% in patients with "minimal colitis" versus 4-18% in healthy volunteers), but an increase in NO(x) output was detectable only in the group of patients (8-106%). In time control experiments, colonic net transfer rates of fluid and outputs of NO(x) were unaffected by placebo.Conclusions. In patients with idiopathic, chronic diarrhoea and histopathological evidence of minimal colitis epithelial expression of iNOS and mucosal production of NO is enhanced. It could be speculated that NO in excess contributes to the diarrhoea observed in "minimal colitis".