Inhibition of inducible nitric oxide synthase ameliorates endotoxin-induced gut mucosal barrier dysfunction in rats

The permeability of intestinal epithelial monolayers increases after exposure to nitric oxide. The aim of this study was to investigate the role of excessive NO production on intestinal barrier function in rats injected with lipopolysaccharide (LPS).

Rats were injected with saline or LPS (5 mg/ kg). Bacterial translocation to mesenteric lymph nodes, liver, and spleen was assessed 24 hours after LPS injection. Mucosal permeability was determined by loading fluorescein-labeled dextran (mol wt, 4000 daltons) into an intestinal segment and measuring its appearance in plasma. Intestinal mucosal mitochondrial respiration was assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide.

Intestinal tissue from LPS-challenged rats showed upregulation of inducible NO synthase (iNOS) messenger RNA expression and subsequent up-regulation of iNOS enzymatic activity. Plasma concentrations of nitrite plus nitrate (NO2-/NO3-) were increased for at least 24 hours after injection of LPS. Treatment with the selective iNOS inhibitor, aminoguanidine, inhibited iNOS enzymatic activity and overproduction of NO2-/NO3-. LPS-induced bacterial translocation was reduced by aminoguanidine. LPS-induced intestinal hyperpermeability was ameliorated by both aminoguanidine and another selective iNOS inhibitor, S-methylisothiourea. LPS depressed intestinal mucosal mitochondrial function, and this effect was ameliorated by aminoguanidine.

Overproduction of NO may contribute to intestinal barrier dysfunction in LPS challenged rats, possibly by interfering with mitochondrial oxidative metabolism.