Effect to cholecalciferol and 1,25-Dihydroxycholecalciferol on the intestinal absorption of zinc in the chick.

The effect of cholecalciferol on the intestinal absorption of 65Zn was assessed in zinc-deficient and zinc-replete rachitic chicks, using the in situ ligated loop techniques. Cholecalciferol did not significantly affect 65Zn absorption in either group, although the synthesis of the intestinal calcium-binding protein (CaBP) in both groups was similar. In an analogous study, 1,25-dihydroxycholecalciferol increased 47Ca absorption and induced the synthesis of CaBP but exerted on effect on 65Zn absorption in zinc-deficient rachitic chicks. When fed a diet adequate in cholecalciferol, more CaBP was present in the intestine of the zinc-adequate group than in the zinc-deficient group, possibly due to the greater rate of growth and therefore the greater need for calcium by the former group. These results suggest that cholecalciferol and its most active metabolite do not directly affect zinc absorption and, by inference, that the vitamin D-dependent transport mechanism is not involved in zinc homeostasis, or in the interaction between calcium and zinc.