Changes in colonic mucins of germfree rats in response to the introduction of a "normal" rat microbial flora. Rat colonic mucin.

In order to determine the influence of bacterial colonization on amount and composition of colonic mucins, germfree male AS/Ztm rats were colonized with a rat specific intestinal flora for different times (2, 7, 14, 21, 28, 35, 120 days). The amount of colonic mucins was determined by gel filtration on Sepharose CL-4B; the relative amount of acidic mucins was calculated after ion exchange chromatography. In addition, cecal weight and dry matter of feces were monitored. While germfree and SPF rats revealed similar amounts of colonic mucins (7.0 vs. 7.2 mg mucin/300 g body weight), the initial phase of association was characterized by considerably decreasing values. After four weeks of association, the total amount of colonic mucins had almost equalized in the two groups. The amount of acidic mucins, having decreased during the first three weeks of colonization, rendered values comparable to the SPF mucins after four months of adaptation. Cecomegaly in germfree rats disappeared within the first two days, while solidification of the intestinal content occurred within four months. Mucin losses during initial phase of association are attributed 1. to the disappearance of the cecal mucin pool, and 2. to the mucin degrading activity of some bacterial strains known to be present in the intestinal flora. Further development is conducted by a stimulation of mucin secretion, described to follow the colonization. The initially increased secretion of neutral mucins is attributed to a pronounced release of immature mucin glycoproteins, while the shift to more acidic mucins is considered to result from stimulated secretion as well as from a selective bacterial degradation of neutral mucin components.

Acidification of the colonic mucins following polyvalent colonization of the germ-free rat.

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 moieties 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.