Small bowel morphology and epithelial proliferation in intravenously alimented rabbits.

Intravenous (IV) alimentation of experimental animals has been associated with an attenuation of the small bowel mucosa. To determine whether alterations in epithelial renewal accompany the morphological changes, we studied cell proliferation as well as the light and electron microscopic appearance of the small bowel in intravenously and orally alimented rabbits. After 10 days of either IV or oral alimentation, 3H-thymidine was given intravenously to all animals to label proliferating cells, and 1 hour later sections of duodenum, upper jejunum, and distal ileum were taken for autoradiography and light and electron microscopy. IV alimentation was accompanied by significant reductions in epithelial cell proliferation and mucosal thickness in the proximal small bowel. The density of goblet cells was greater in the duodenum and jejunum, but less in the ileum, of intravenously alimented rabbits than in corresponding areas of the oral controls. Furthermore, ultrastructural changes in the villous absorptive cells of intravenously alimented rabbits, such as lengthened microvilli and increased numbers of multivesicular bodies, suggested that epithelial migration also may be slowed during IV alimentation.