Previous studies have demonstrated that the specific activities of several proximal small intestinal mucosal enzymes fall in the aging rat. This reduction was due to a delay in the full expression of activity of these enzymes during epithelial cell transit from the crypt onto the intestinal villus. We now show in the ad libitum fed Fischer 344 rat that jejunal sucrase, maltase, and alkaline phosphatase specific activities do not fall gradually throughout the life span, but are reduced during senesence. Caloric restriction to 60% of ad libitum intake (DR) abolishes or delays this fall in enzyme activity. Jejunal mucosal immunoprecipitable sucrase-isomaltase (S-I) content also falls with age, but sucrase specific activity per molecule of S-I is less in the older ad libitum fed (approximately 45) than in the DR rats (approximately 60). Jejunal lactase activity falls gradually throughout the life span of ad libitum and DR rats, but lactase activity consistently was higher in DR animals. These observations indicate that DR alters the age-related changes in the activity of several enzymes in the rapidly replicating gut mucosa.
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