Inhalation of methane preserves the epithelial barrier during ischemia and reperfusion in the rat small intestine.

BACKGROUND: Methane is part of the gaseous environment of the intestinal lumen. The purpose of this study was to elucidate the bioactivity of exogenous methane on the intestinal barrier function in an antigen-independent model of acute inflammation. METHODS: Anesthetized rats underwent sham operation or 45-min occlusion of the superior mesenteric artery. A normoxic methane (2.2%)-air mixture was inhaled for 15 min at the end of ischemia and at the beginning of a 60-min or 180-min reperfusion. The integrity of the epithelial barrier of the ileum was assessed by determining the lumen-to-blood clearance of fluorescent dextran, while microvascular permeability changes were detected by the Evans blue technique. Tissue levels of superoxide, nitrotyrosine, myeloperoxidase, and endothelin-1 were measured, the superficial mucosal damage was visualized and quantified, and the serosal microcirculation and mesenteric flow was recorded. Erythrocyte deformability and aggregation were tested in vitro. RESULTS: Reperfusion significantly increased epithelial permeability, worsened macro- and microcirculation, increased the production of proinflammatory mediators, and resulted in a rapid loss of the epithelium. Exogenous normoxic methane inhalation maintained the superficial mucosal structure, decreased epithelial permeability, and improved local microcirculation, with a decrease in reactive oxygen and nitrogen species generation. Both the deformability and aggregation of erythrocytes improved with incubation of methane. CONCLUSION: Normoxic methane decreases the signs of oxidative and nitrosative stress, improves tissue microcirculation, and thus appears to modulate the ischemia-reperfusion-induced epithelial permeability changes. These findings suggest that the administration of exogenous methane may be a useful strategy for maintaining the integrity of the mucosa sustaining an oxido-reductive attack.

N-methyl-D-aspartate receptor antagonist therapy suppresses colon motility and inflammatory activation six days after the onset of experimental colitis in rats.

We set out to investigate the time-dependent colon motility and inflammatory changes in a rodent model of 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis in order to estimate the efficacy of N-methyl-D-aspartate (NMDA) receptor antagonist therapy administered 6 day after the acute inflammatory event. Anaesthetized Sprague-Dawley rats were randomized to control (n=6) or colitis groups (n=18). The endogenous NMDA receptor antagonist kynurenic acid (n=6) or the synthetic analog SZR-72 (n=6) was administered 6 day after TNBS induction. Large bowel motility parameters, macrohaemodynamics and serosal microcirculatory changes were recorded; the severity of colonic damage was monitored by using in vivo confocal laser endomicroscopy. Nitrite/nitrate and nitrotyrosine levels, and xanthine oxidoreductase and myeloperoxidase activities were determined on colon biopsies; plasma levels of TNF-α and IL-6 were compared with those under control and 1-day colitis (n=6) conditions. TNBS induction elevated the tissue inflammatory enzyme activities, proinflammatory cytokine release, and nitrite/nitrate and nitrotyrosine formation. The microscopic vascular and mucosal lesions were accompanied by significant increases in serosal microcirculation and frequent intestinal movements 6 day after colitis. The NMDA receptor antagonist treatments significantly decreased the signs of inflammatory activation and the levels of nitric oxide end-products, normalized the microcirculation and the rate of bowel movements in both NMDA receptor antagonist-treated colitis groups. Blockade of the enteric NMDA receptors 6 day after colitis induction concurrently influenced NO production-linked nitrosative stress and colon dysmotility and may therefore offer a possibility via which to inhibit the progression of inflammatory changes in the later phase of TNBS colitis.