The influence of diets and gut microflora on lectin binding patterns of intestinal mucins in rats

The mechanisms responsible for the biosynthesis, storage, secretion, or degradation of intestinal mucins are still unclear. Little is known about the carbohydrate composition of mucins in response to changes in the intestinal lumen, so lectin histochemical techniques were used to study the alterations in glycoconjugate synthesis of mucins in rats under different diets and microfloras.

Nine-week-old germ-free and conventional rats were given either a purified diet of finely powdered ingredients, including cellulose as a source of fiber, or a more coarsely ground commercial diet of natural ingredients containing crude fiber of cereal origin. To mimic the human situation more closely, a group of rats born germ-free, inoculated with a suspension of human feces, and fed a purified diet were used as an experimental model.

In rats fed a commercial diet, the surface goblet cells in the small intestine were more intensely labeled with N-acetyl-glucosamine and sialic acid-linked D-galactose-specific lectins than in rats fed the purified diet. A similar increased staining with a N-acetylgalactosamine-specific lectin was observed in the large intestine of rats fed a commercial diet. The microbial flora modified the crypt-surface glycosylation of fucosyl and sialic acid residues in the large intestine. The human flora specifically altered the goblet cell glycoconjugates in the surface epithelium.

The significant changes in goblet cell glycoconjugates reflect the adaptation of the intestinal mucosa to different diets and microbial populations. An overall reduction in sialic acid-linked D-galactose residues in conventional rats and a loss of crypt-to-surface gradient of fucosyl expression in the large intestine of human flora rats are likely to be due to differing strains of glycosidases in the two microflora.