Effect of aging upon small intestinal structure in the Fischer rat.

The dimensions and composition of the small intestine were studied in fed aged (27 month) and young adult (4 to 5 months) male Fischer rats maintained under barrier-reared, controlled conditions. In the proximal intestine (duodenum and jejunum) of aged rats there was no reduction in mucosal mass, protein, or deoxyribose nucleic acid, and the villus epithelium had similar dimensions and cell number as in young rats. The ileum of old rats had a 20% larger villus epithelium than those of young rats, suggesting that the function of the proximal intestine in aged rats might be impaired. In the proximal intestine of old rats, the proliferative zone was expanded, crypt depth and cell number were approximately 20% greater than in young rats. Because previous studies have shown no effect of aging upon epithelial cell migration in proximal intestine and villus height in young and old animals was not different, decreased survival of newly formed crypt epithelial cells is likely. These observations must be taken into account in the analysis of nutritional requirements and intestinal function.