Aging and intestinal polyamine metabolism in the rat.

Hyperproliferation and delayed expression of enzyme activity occur in small intestinal enterocytes of aging rats, and starvation and refeeding result in impaired control of these processes. Since altered polyamine metabolism may accompany changes in enterocyte proliferation, we studied the effects of nutrient manipulation upon cell numbers, ornithine decarboxylase (ODC) activity and polyamine content in jejunum and ileum of 4- to 5- and 26- to 27-month Fischer rats. In both groups, cell numbers fell during starvation and and increased during refeeding. Crypt cell hyperplasia was found in aging animals. Jejunal putrescine, spermine and spermidine content were greater in older rats, fell during starvation, and rose during refeeding. Ileal ODC activity was 66% greater in the aging rats, but jejunal ODC activity was modestly increased in young animals. Intestinal polyamine content correlates with proliferative changes and polyamine metabolism responds appropriately to nutrient manipulation during aging. Dissociation of ODC activity and polyamine content in aging jejunum probably occurred because enterocyte differentiation was delayed. Investigation of intestinal polyamine metabolism may be useful in elucidating deranged proliferative activities found in the intestine of aging rodents.