The pre-epithelial mucus layer (PML) and epithelial mucins were studied by mucin histochemistry in 10 microns-thick celloidinstabilized cryostat sections in the proximal and distal colon of conventional and germ-free rats aged 120 and 350 days. No continuous PML was found in the proximal colon. A continuous mucus blanket, of fairly homogenous thickness, was observed in the distal colon, where the PML-thickness was 40 +/- 24 microns at 120 days of age and 44 +/- 22 microns at 350 days of age in conventional rats, and 25 +/- 17 microns (120 days) and 22 +/- 10 microns (350 days) in germ-free rats. The stainability of the PML by periodic acid-Schiff and Alcian Blue at pH 2.5 and 1.0 was stronger in conventional rats than in germ-free rats, indicating higher concentrations of mucosubstances and of acid and sulphated mucins, respectively. The PML of the conventional rat distal colon showed a stratified structure of up to eight sublayers. In the distal colon of germ-free rats, the whole gut wall thickness was reduced 47% compared to the conventional rat (germ-free; 185 +/- 73 microns, conventional: 350 +/- 115 microns). No stratification of the PML was observed. The presence of intestinal microflora obviously had a strong influence on the thickness, compactness, mucin content, mucin composition and structure of the pre-epithelial mucus layer.
Colonic mucins of germ-free (GF) and conventional rats (CV) were compared. After isolation by gel filtration on Sepharose CL-4B and purification by density gradient centrifugation, the content of isolated colonic mucins was estimated by determination of PAS positive carbohydrates. Purified mucins were subjected to carbohydrate and amino acid analysis and separated into mucin subclasses by ion exchange chromatography.While the total amount of colonic mucins was not statistically different in GF and CV animals, analysis of carbohydrate composition demonstrated an increased amount of sialic acid in CV rat mucin. This was in accordance with results of ion exchange chromatography, revealing a significant higher amount of negative charged mucin subclasses in CV mucin, compared to the germ-free counterpart. The results of amino acid analysis were similar in both groups.The compositional differences in carbohydrate moities are attributed to modulations by the intestinal flora. A selective bacterial degradation of the neutral mucin subclasses and modifications in the mucin composition due to a stimulated synthesis are discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.