Zinc Absorption, Intraluminal Zinc and Intestinal Metallothionein Levels in Zinc-Deficient and Zinc-Replete Rodents

Abstract

Zinc absorption, endogenous luminal zinc and intestinal metallothionein were examined in rats and mice fed zinc-deficient and zinc-replete diets for 5–7 days. Small intestinal luminal washings from undosed rodents fed the replete diet contained 18- to 20-fold more zinc than those from zinc-deficient animals. Isotope dilution by this endogenous zinc could account for apparent differences between the groups in absorption of ⁶⁵Zn from oral doses of 0.1–0.2 µmol ⁶⁵Zn. With larger (1–2 µmol) oral doses of ⁶⁵Zn in mice, no difference between the dietary groups was found, although zinc-deficient rats still absorbed more zinc than zinc-replete controls. In mice, zinc absorption from perfused duodenum, jejunum and ileum also was not increased by zinc deficiency. With oral doses, food generally lowered zinc absorption where endogenous or exogenous zinc was present in the gastrointestinal tract; food in perfusates lowered uptake more than transfer. Polarographically determined metallothionein was highest in duodenum of mice. It was lowered by feeding the deficient diet for 5 days without an increase in zinc absorption. It was concluded that zinc absorption is homeostatically increased by zinc deficiency in rats but not in mice and that intestinal metallothionein levels do not affect zinc absorption in mice.