Morphologic changes in intestinal mucosa with urinary contact--effects of urine or disuse?

To evaluate the morphological changes induced in bypassed ileal and colonic segments and the influence of the urine on the mucosal histology.

In a rat model, an isolated ileocolonic segment was used for construction of an ileocolocystoplasty or an exteriorized blind loop. Sham-operated animals were used for control.

In ileal mucosa, villi and microvilli were better preserved when exposed to urine than when deprived of contact with luminal content. Numerical reduction of microvilli was found in colonic mucosa deprived of luminal content. In colonic mucosa exposed to urine some areas were denuded of microvilli and showed blebs. Findings of intact tight junctions in all specimens implied that an important morphological requirement of maintained epithelial barrier function is present in mucosa deprived of normal luminal stimulation and also after contact with urine. The intracellular ultrastructural changes in both colon and ileum were similar in the 2 groups. However, there were more solitary ribosomes lying free in the mucosa exposed to urine, indicating depressed or arrested protein synthesis.

Mucosa in contact with urine seems to maintain surface characteristics better than mucosa deprived of luminal stimulation, indicating that factors present in the urine may be important for the epithelial cell physiology. Certain intracellular changes were found more often in mucosa exposed to urine, but there were no major differences. The changes noticed may indicate enterocyte adaptation to a new physiologic environment.