Effect of dietary zinc on 65-ZN absorption and turnover in rats

Abstract

The effect of zinc intake on retention, absorption, and biological half-life of 65-Zn was investigated using whole body counting after the carrier-free radioisotope was administered intragastrically or intramuscularly to 7-week old male rats. When animals consumed 7.8, 11.7, 16.0, 20.8, 36.8, 80.2, or 149.1 mg Zn/kg diet for 3 weeks before and 4 weeks after 65-Zn administration, the biological half-life and the retention of gavaged or injected 65-Zn were curvilinearly related to the dietary zinc concentration. Absorption was similarly affected, except that absorption was nearly 100 per cent at the two lowest levels of intake. Zinc concentrations in bone and serum were unaffected except in animals fed 7.8 mg Zn/kg diet. When zinc intakes varied only 4 days before 65-Zn administration, retention of injected 65-Zn and absorption were less affected. Animals fed 11.5 rather than 85.0 mg Zn/kg beginning 7 to 8 hours after 65-Zn administration, had greater retention of gavaged or injected 65-Zn; absorption and biological half-life of 65-Zn were also greater. Thus, retention of dietary zinc by the body depended on recent and subsequent zinc intake, with recent intake affecting mainly absorption, and subsequent intake affecting mainly excretion. Adjustments in absorption and excretion occurred within days, and were highly coordinated when zinc intakes exceeded the requirement.