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The Time Course of Adaptation of Intestinal Nutrient Uptake in Mice Is Independent of Age^1,2,

Department of Physiology, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey 07103-2714

Slow adaptive responses are typical of aged animals. The pace of intestinal adaptation is relatively rapid in young mice but is not known in aged mice. In this study, we determined the time course of adaptation of intestinal nutrient uptake to abrupt and substantial changes in levels of dietary nutrients in young and aged mice. Mice (24-mo-old and 6- to 7-mo-old, controls) were fed a no carbohydrate, high protein diet for 7 d and then were switched to a high carbohydrate, low protein diet for 0, 1, 2, 3 and 5 d. Body weights, feeding rates, intestinal weights and lengths were all independent of diet. Within 1 d after the switch in diet, glucose and fructose uptakes increased in young and aged mice. In both age groups, alanine and aspartate uptakes decreased significantly, whereas proline, leucine and lysine uptakes were independent of diet. In both age groups, total intestinal absorptive capacity for glucose and fructose increased overnight by about 70 and 200%, respectively. Previous studies linked time course of adaptation to rates of enterocyte proliferation. Rates of enterocyte turnover and migration along the crypt/villus axis of proximal, middle and distal small intestine were independent of age. Thus, the time course of intestinal adaptation in aged mice remains largely unchanged from that in young mice, probably because rates of enterocyte proliferation seem independent of age.

KEY WORDS: • amino acids • sugars • mice • cell lifetime • aging

¹ Supported by the American Federation for Aging Research and NIH grant AG11403. Research in the laboratory was also supported by a grant from the Office of Sea Grant, Department of Commerce, NA36-RG0505 (R/F-58).

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ To whom correspondence should be addressed.

Manuscript received 17 October 1994. Revision accepted 14 February 1995.