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Journal of Nutrition Vol. 109 No. 7 July 1979, pp. 1258-1264
Copyright © 1979 by American Society for Nutrition
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Zinc Absorption in the Rat Determined by Radioisotope Dilution1

Gary W. Evans, Elaine C. Johnson and Phyllis E. Johnson

United States Department of Agriculture, Science and Education Administration, Human Nutrition Laboratory, Grand Forks, North Dakota 58201

Zinc absorption in rats was examined by use of an isotope dilution technique. Young rats and mature rats fed varying levels of dietary zinc were injected intramuscularly with 65Zn. Nine days later, a zinc balance study was begun and continued for 5 days. The rats were then decapitated and the intestines and kidneys were removed and analyzed for zinc and 65Zn content. The feces were analyzed for zinc and 65Zn content and the specific activities of the intestines and kidneys were used to compute the contribution of endogenous zinc to total daily zinc excretion and thus calculate the true daily absorption of zinc. The zinc concentration of the intestines and kidneys did not differ significantly among groups but the specific radioactivity in these organs decreased as dietary zinc intake increased. Endogenous zinc excretion was greatest in mature rats and young rats fed the highest level of dietary zinc. Mature rats actually absorbed as much or more zinc than young rats fed the same dietary level of zinc. The results demonstrate that zinc homeostasis in rats is maintained by zinc secretion from the intestine rather than by regulation of zinc absorption.

KEY WORDS: • zinc • absorption • excretion • homeostasis

1 Supported in part by the USDA Cooperative Agreement No. 12-14-3001-294.

Manuscript received 27 November 1978.




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