Article Text
Abstract
BACKGROUND AND AIMS Luminal nitric oxide (NO) is greatly increased in the colon of patients with collagenous and ulcerative colitis. To define the source and consequence of enhanced NO production we have studied expression of NO synthase (NOS) isoforms and nitrotyrosine in mucosal biopsies from these patients. In addition, effects on colonic fluid transfer caused by manipulating the substrate of NOS were studied in patients with collagenous colitis.
PATIENTS Eight patients with collagenous colitis, nine with active ulcerative colitis, and 10 with uninflamed bowel were included.
METHODS Expression of NOS isoforms was quantified by western blotting. Inducible NOS (iNOS) and nitrotyrosine were localised by immunohistochemistry. Modulation of NOS activity by topicalN G-monomethyl-l-arginine (l-NMMA) or l-arginine was assessed during perfusion of whole colon. Plasma and perfusate nitrite/nitrate (NOx) was measured by Griess' reaction.
RESULTS Both in collagenous and ulcerative colitis, expression of iNOS was 102–103 higher (p<0.001) than in uninflamed bowel and localised primarily to the epithelium. Endothelial NOS was evenly expressed in all groups while neuronal NOS was undetectable. Nitrotyrosine was markedly expressed in active ulcerative colitis but rarely detected in collagenous colitis and never in uninflamed bowel. In collagenous colitis, the output of NOx was markedly increased compared with uninflamed bowel (283 (58)v <37 nmol/min; p<0.01) and fluid was net secreted. l-NMMA reduced the output of NOx by 13–66% (95% confidence intervals) and secretion of fluid by 25–109% whereas l-arginine increased the output of NOx by 3–39% and secretion of fluid by 15–93%.
CONCLUSIONS In collagenous colitis, as opposed to ulcerative colitis, upregulation of iNOS occurs in the absence of nitrotyrosine formation and mucosal damage. Excess generation of NO may be the primary cause of diarrhoea in this condition.
- colitis
- ulcerative colitis
- collagenous colitis
- inflammatory bowel diseases
- large intestine
- nitric oxide
- nitric oxide synthase
Abbreviations used in this paper
- cNOS
- constitutive nitric oxide synthase
- EDTA
- ethylene diamine tetra-acetic acid
- eNOS
- endothelial nitric oxide synthase
- GAPDH
- glyceraldehyde 3-phosphate dehydrogenase
- IgG
- immunoglobulin G
- iNOS
- inducible nitric oxide synthase
- l-NMMA
- NG-monomethyl-l-arginine
- nNOS
- neuronal nitric oxide synthase
- NO
- nitric oxide
- NOS
- nitric oxide synthase
- NOx
- nitrite/nitrate
- PBS
- phosphate buffered saline