1. Self-filling blind loops of jejunum were constructed in three groups of rats; in the first, blind loops were created without further manipulation; in the second the bile was diverted permanently into the lower ileum below the blind loop, whereas in a third neomycin was added to the drinking water throughout the experiment. Two weeks after the creation of the blind loops, they were used for structural and functional studies.

2. Morphometric and microdissection techniques demonstrated that the surface area of the individual villi of the mucosa of ‘ordinary’ blind loops had increased fourfold in comparison with corresponding control jejunum, whereas the increase was only twofold in rats with bile diversion or in the series treated with neomycin. There were proportional increases in crypt length and mitotic activity of the crypts in all three series, which suggest that the alterations in the mucosa were due to hyperplasia in both villus and crypt compartments.

3. Sucrase, succinate dehydrogenase, alkaline phosphatase and non-specific esterase activities, determined biochemically or histochemically, were reduced in the mucosae of all blind loops, though the changes were most pronounced in the ‘ordinary’ blind loops. The accumulation of l-phenylalanine by mucosal slices in vitro was depressed, although the decrease was less marked in the series treated with neomycin.

4. These results suggest that both bacteria and deconjugated bile acids play a role in the development of the hyperplastic changes of the blind-loop mucosa, but that another factor might also be involved: as a possible candidate, stasis of the intestinal contents was considered.

5. To test this hypothesis, loops of rat colon were transposed into the jejunum. Above the transposed loop, the jejunal mucosa developed hyperplasia of both villus and crypt compartments, with a reduction in its ability to accumulate l-phenylalanine. It is argued that these changes, probably caused by stasis of the intestinal contents, are triggered off by the dilatation of the gut, which may also be implicated in the mucosal alterations in blind loops.

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