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

Abstract

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.