Previous studies have reported that small and large intestinal crypt hyperplasia and hyperproliferation occur in senescent rats about 27 mo of age. We have studied duodenal and ileal architecture in ad libitum chow-fed rats and have demonstrated that the increase in duodenal crypt depth and crypt hyperplasia do not develop throughout the life span, but become apparent at 21 and 27 mo of age. These crypt hyperplastic features occur without a change in duodenal villus cell number. Ileal villus cellularity increased throughout the life span, suggesting exposure to a gradually increasing luminal nutrient load. Diet restriction to 60% of the ad libitum feeding rate prolonged the life span of animals from 27 to greater than 33 mo and prevented both the duodenal hyperplasia and the increase in ileal villus cell numbers to the age of 27 mo. Thirty-three-month diet-restricted rats did show evidence of duodenal crypt hyperplasia. We conclude that proximal intestinal hyperplasia is a phenomenon that develops in advanced age, but that ileal villus cellularity increases throughout the ad libitum-fed rodent life span. Diet restriction dramatically retards these intestinal changes that are seen with ad libitum feeding and provides an experimental model for the study of age-related cellular changes of the rodent gastrointestinal tract.
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