The effects of age on mucosal morphology and epithelial cell production in rat small intestine.

Six groups of male Wistar rats were used, with mean weights of 29, 63, 97, 161, 249 and 399 g. Pieces of small intestine from three sites were examined after staining in bulk with the Feulgen reaction. Crypt/villus ratio (the number of crypts per villus) rose with age at all three sites, Villus height and crypt depth were measured on microdissected specimens. Villi in the proximal intestine were always taller than those distally. Proximal villi increased in height in successively older rats, except in the oldest group. Villi at the two distal sites tended to be tall in the youngest group of rats, but suffered a temporary reduction in height in the next two age groups. Crypt depth increased markedly within the first three age groups, and more slowly thereafter. Colchicine-metaphase accumulation rate was estimated from counts on microdissected intact crypts. The rate was low in the youngest group (8 cells/crypt/hour) but about 30 cells/crypt/hour in all other groups. After the changes during the early phase of rapid growth, no marked changes were seen during later life. The significance of these findings is discussed.