Excess dietary zinc decreases tissue alpha-tocopherol in chicks

Experiments were conducted to determine the basis of the reduction in tissue alpha-tocopherol concentrations by excess dietary zinc (Zn) in chicks fed purified diets. These reductions were preceded by elevations in the Zn concentrations of plasma and pancreas, and in the amylase activity of plasma and by reductions of exportable enzymes of the pancreas. Chicks fed similar levels of Zn as supplements to a non-purified diet showed no such impairments in either exocrine pancreatic function or tissue alpha-tocopherol concentrations. Depression of feed intake and subsequent changes of concentrations of tissue lipid components by excess dietary Zn accounted for only a minor portion of the reduction of tissue alpha-tocopherol concentrations. Tissue alpha-tocopherol concentrations were moderately correlated with tissue lipid concentrations. The rate of appearance of radioactivity from an oral dose of all-rac-alpha-tocopherol-[3,4-3H]2 in plasma was reduced by 64% by addition of 500 mg Zn/kg to the purified diet for 2 wk. These results indicate that impaired enteric absorption and/or transport of vitamin E as a consequence of Zn-induced pancreatic insufficiency is a major cause of reduced tissue concentrations of alpha-tocopherol produced by excess dietary Zn.