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Relationship of ⁶⁵Zn Absorption Kinetics to Intestinal Metallothionein in Rats: Effects of Zinc Depletion and Fasting¹

Food Science and Human Nutrition Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611

Intestinal ⁶⁵Zn transport and metallothionein levels were examined in rats fed zinc-adequate and zinc-deficient diets and in rats subjected to an overnight fast. ⁶⁵Zn uptake by intestines perfused with 1.5 µM ⁶⁵Zn was greater in both zinc-deficient and fasted groups than in the control group. Mucosal retention of ⁶⁵Zn was also greater in the zinc-deficient group but not in the fasted group. The greater ⁶⁵Zn uptake in the fasted group was associated with a compartment that readily released ⁶⁵Zn back into the lumen. Kinetic analysis of the rate of ⁶⁵Zn transfer to the vascular space (absorption) showed that ⁶⁵Zn absorption involved approximately 3% of mucosal ⁶⁵Zn in a 40-min perfusion period. The half-life (t) of this mucosal ⁶⁵Zn rapid transport pool corresponded directly to changes in intestinal metallothionein levels. Both metallothionein and t were higher in the fasted group and lower in the zinc-deficient group than in controls. While the rate of ⁶⁵Zn transport from this rapid transport pool decreased with increasing metallothionein level, the predicted pool size increased when the metallothionein level was elevated by fasting. These results indicate that the rate of zinc absorption is inversely related to intestinal metallothionein levels, but the portion of mucosal ⁶⁵Zn available for absorption is directly related to intestinal metallothionein.

KEY WORDS: • zinc • intestine • absorption • kinetics • metallothionein

¹ This research was supported by National Institutes of Health Grant No. DK 31127 from the National Institute of Diabetes and Digestive and Kidney Diseases and by Boston Family Endowment funds.

² Present address: Food and Drug Administration, Division of Nutrition, Washington, DC 20204.

³ To whom reprint requests and correspondence should be addressed.

Manuscript received 4 May 1987. Revision accepted 16 December 1987.