Effect of Vitamin D on 65Zn Absorption, Distribution and Turnover in Rats

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Abstract
Experiments were designed to study the effect of dietary vitamin D on the absorption, distribution and turnover of 65Zn in growing rats. In the first experiment, whole-animal retention of oral 65Zn by rats fed zinc-supplemented, but not zinc-deficient, diets was slightly (0.1 > P > 0.05) increased by continuous supplementation with vitamin D. Retention of injected 65Zn was not similarly enhanced, suggesting a possible effect on 65Zn absorption. In the second experiment 65Zn absorption and turnover were determined by more detailed analysis of whole-animal 65Zn retention patterns, and the distribution of oral and injected 65Zn at 60 hours postadministration was examined. The effect of vitamin D on uptake of oral 65Zn was most pronounced when the vitamin was suddenly added to the diet of previously vitamin D-deficient rats. At 60 hours skeletal, but not soft tissue, uptake of either oral or injected 65Zn was significantly increased by the supplementation of vitamin D to vitamin D-deficient rats. However, skeletal specific activity (% 65Zn per g) was increased by vitamin D only with the orally administered 65Zn. An explanation consistent with all data is that the increased absorption of dietary zinc attributed to vitamin D probably results, not from a direct effect of the vitamin, but from a homeostatic response to the increased need for zinc which accompanies enhanced skeletal growth and calcification.