Functional and structural characteristics of the rat intestinal mucosa following ileo-jejunal transposition.

The transformation of the rat ileal mucosa following interposition into the jejunum has been examined with respect to its functional and structural characteristics. Morphometric studies show that there is an increase in the size of the villi and crypts in the same proportions, such that the structures become longer than those of normal jejunal mucosa. There is no change in villus width or epithelial cell height and no evidence of mucosal damage. In agreement with these observations, there is an increase in the amount of DNA per unit weight mucosa in the transposed ileum. L-phenylalanine accumulation in vitro by transposed loops is reduced to the level of the control jejunum, whereas beta-methyl-D-glucose uptake is unchanged. Biochemical and histochemical determinations of various enzyme activities reveal that the levels in the transposed mucosa are much lower than in the controls. The results show that although certain features of the transposed ileum resemble those of the normal jejunum, this does not apply to all characteristics. It is argued that the ileal mucosa retains its normal functional properties, but undergoes hyperplastic changes, possibly as a result of contact with chyme that is richer in nutritive material, resulting in the establishment of a more immature cell population with a global reduction in enzyme levels and transport capacities.