Influence of the colonic contents on the structure and function of the rat jejunal mucosa

Segments of rat jejunum were transposed into the ascending colon and were examined structurally and functionally 3 weeks later in order to explore the influence of the colonic contents on the jejunal mucosa. The transposed segments revealed longer crypts, wider villi, larger epithelial cells, and thicker muscular layers than those of the control jejunum. The villus height was variable, some animals possessing longer villi and some shorter ones. Quantitative histochemistry of the epithelia of transposed segments disclosed large reductions in the leucine-aminopeptidase, succinic dehydrogenase, and nonspecific esterase activities of the individual epithelial cells. Sucrase activity of the mucosa was concomitantly reduced. The uptake of phenylalanine by rings of transposed intestine was much lower than in control jejunum. The results are interpreted in terms of a hyper-regenerative transformation of the mucosa of the transposed segments, induced primarily by deleterious factors present in the colonic contents.