Mucosal histology, crypt cell proliferation and brush border
enzymes were measured in rats with varying degrees of
jejunoileal bypass, in order to compare the effect of systemic and
luminal factors on adaptive growth and differentiation (brush border
enzymes) in small intestinal epithelium. Eighty five percent
jejunoileal bypass caused a functional short gut; in intestine remaining in continuity there were significant increases in segmental weight, villus area and crypt depth, compared with
sham operated controls and 25%
jejunoileal bypass rats. Despite villus cell
hyperplasia in 85% bypass rats, mucosal
sucrase and
alkaline phosphatase fell in jejunum and remained low in ileum, while
leucine amino
peptidase rose in ileum. There was a significant fall in villus area (p less than 0.01) and crypt cell production (p less than 0.001) in self emptying loops of 25% bypass rats not exposed to
luminal contents compared with control segments of
sham operated rats. In contrast, self emptying loops of 85% bypass rats were not atrophied despite the much greater distance from
luminal nutrients; the villus area (p less than 0.01) and crypt cell production (p less than 0.005) were higher than in 25% bypass rats, and at least as great as in
sham operated rats. These results indicate that adaptive
hyperplasia has a variable effect on expression of brush border
enzymes which might reflect villus cell immaturity. The atrophic effect of diversion of
luminal contents can be counteracted by systemic
growth factors released as part of the adaptive response; thus systemic
growth factors are not dependent on a permissive effect of
luminal contents.