Atrophy of villi with hypertrophy and hyperplasia of Paneth cells in isolated (thiry-Vella) ileal loops in rabbits. Light-microscopic studies.

Thiry-Vella loops in rabbit ileum were prepared by a new technique and were studied 18 hr to 49 days postisolation. The loops became grossly shortened after 14 days. Histologically, some shortening and blunting of villi was detectable as early as 4 days postisolation, and with prolonged isolation the changes became marked. Reduction in epithelial cell height and in brush border thickness were noted, and goblet cells were increased somewhat in size and prominence. Yet there was only slightly increased chronic inflammation in the mucosa and acute inflammation was uncommon, suggesting that mucosal injury was minimal. Furthermore, mean epithelial mitotic indices for the crypts did not rise and were generally reduced. Striking hyperplasia and hypertrophy of Paneth cells associated with mitotic figures in Paneth cells accompanied the atrophic changes in the villi. Reimplantation of loops into the bowel 3 weeks after isolation led to complete reversal of all changes, including hyperplasia of Paneth cells. On the other hand, regular perfusion of loops with a solution containing a large variety of nutrient substances failed to reverse the mucosal changes. It was concluded that atrophy of villi in isolated ileum of the rabbit occurred mainly because one or more substances contained in the chyme are needed to maintain normal mucosal architecture. These substances probably help regulate epithelial cell turnover and may well be endogenous in origin. Loss of substances in the chyme after loop isolation may also have led to Paneth cell hyperplasia. Alternatively, the Paneth cell changes and atrophy of villi might have been related in a cause and effect way.