Amino acid and peptide absorption in bypassed jejunum following jejunoileal bypass in rats.

The intestinal digestive and absorptive function of the excluded jejunum was evaluated 6 and 12 weeks after jejunoileal bypass in rats. Brush border and cytosol aminopeptidase activities as well as mucosal sucrase activity were measured in self-emptying excluded jejunal segments following bypass surgery. In addition, following in vivo perfusion of equimolar amounts of amino acid (L-leucine) and dipeptide (L-leucyl-L-leucine) solutions through bypassed jejunal segments, the uptake of L-leucine was determined. Mucosal weight, protein, and DNA content were reduced in the bypass segment reflecting jejunal mucosal cell hypoplasia. Hydrolytic activities for all enzymes (including the subcellular fractions of the aminopeptidase activities) and absorption rates from both the free amino acid and peptide solutions were reduced in bypassed jejunal segments. When expressed on the basis of mucosal DNA content, however, no changes were observed. This study indicates that the functional alterations in the excluded jejunum after bypass are due to the reduced mucosal cell content of this segment.