Adaptive changes of intestinal enzymes to nutritional intake in the aging rat.

We previously have shown that aging alters the expression of several intestinal enzymes during cell migration from the crypt base to the villus tip. The activities of many mucosal enzymes are dramatically altered by starvation and refeeding. We compared the effects of starvation and refeeding on the activities of selected intestinal enzymes in young and aging Fischer 344 rats. Gut mass fell during starvation and rose during refeeding to a similar extent in both groups. Sucrase and maltase specific activities in control aging rats were lower than in young controls and, during starvation, enzyme activities declined at approximately similar rates in both groups. Total duodenal enzyme activities fell by about two-thirds in young animals and by greater than 80% in aged animals. Alkaline phosphatase and adenosine deaminase activities also were lower in aging than young animals. During refeeding, enzyme activities rose more in aging rats than in the young. In fact, the specific activities of sucrase and maltase in aging rats refed for 1 day exceeded the values found in fed aging controls. The adaptive responses of duodenal enzymes exceeded those in the jejunum. In conclusion, the aging intestine responds appropriately to starvation and refeeding. However, the fluctuations in brush-border enzyme activities are much greater in aging than in young rats. Such alterations may be an important influence of aging on gut differentiation and might have an adverse impact upon nutritional maintenance in aging animals.