Zinc-65 Absorption and Turnover in Rats

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Abstract
Zinc-65 as chloride or glycine complex was administered to growing rats receiving a practical diet in 6 experiments. A rapid fecal excretion of Zn65 occurred following administration via feed or gavage. Increased dietary calcium significantly increased (P < 0.01) the initial rate of Zn65 loss following oral administration and consistently and significantly decreased the percentage remaining in the body longer than 2 days. Conversely, body loss of injected Zn65 decreased significantly (P < 0.01) with increased calcium. Comparison of retention curves at 100 to 250 hours post-administration for injected and dietary or gavage-administered Zn65 and their extrapolation to zero time allowed the determination of the percentage of radiozinc absorbed. Calcium significantly decreased (P < 0.01) the percentage of Zn65 absorption and increased the biological half-life (decreased turnover) of Zn65 beyond 100 hours post-administration. Calcium did not affect body weight. The results are explained by a decreased absorption of stable and radiozinc with increased dietary calcium. Calcium also significantly increased (P < 0.01) carcass Zn65 in the femur and decreased it in liver, kidney and muscle at 28 days post-administration.