Intrinsic and extrinsic labeling for studies of manganese absorption in humans

A dual-radioisotope method was used to simultaneously study whole-body manganese retention from a chicken liver based meal intrinsically labeled with ⁵⁴Mn and extrinsically labeled with ⁵²Mn. Manganese retention was monitored in a sensitive whole-body counter during approximately 30 d in six young adult women. Both radioisotopes were retained to a similar degree and excreted at identical rates. Retention at d 5 was 14.4 ± 10.3 and 14.0 ± 9.9% while retention at d 10 was 5.0 ± 3.1 and 5.0 ± 3.0% (X̄ ± SD) for ⁵⁴Mn and ⁵²Mn, respectively. From these results we conclude that the intrinsic and extrinsic Mn isotopes did form a common pool before absorption. The results can therefore be regarded as a direct validation of the use of extrinsic labeling for studies of Mn retention for estimating Mn absorption in man.