KINETIC-MODEL OF MOLYBDENUM METABOLISM DEVELOPED FROM DUAL STABLE-ISOTOPE EXCRETION IN MEN CONSUMING A LOW MOLYBDENUM DIET

The aim of this study was to develop a compartmental model of molybden um metabolism based on stable isotope excretion patterns. Molybdenum ( Mo) is an essential trace element in humans, with an estimated safe an d adequate daily dietary intake (ESADDI) of 75-250 mu g Mo/d. Four adu lt men were fed low molybdenum diets, 22 mu g Mo/d, for a period of 10 2 d. Mo-97 and Mo-100 stable isotopes, in intravenous and oral doses, respectively, were administered at selected intervals. The resulting 6 -d cumulative urinary and fecal isotope excretion data were used to mo del molybdenum metabolism using SAAM/CONSAM software. A kinetic model, including gastrointestinal (GI), plasma, slow-turnover tissue and fas t-turnover tissue compartments, accurately simulated the observed patt ern of urinary and fecal excretion for both stable isotopes in all fou r subjects. Residence time for molybdenum in the GI tract was estimate d at 1.7 +/- 0.4 d. Predicted residence time for plasma molybdenum was 22 +/- 4 min, whereas slow-turnover tissue (possibly hepatic) retenti on averaged 58 +/- 16 d. The model thus permitted estimation of kineti c parameters for molybdenum metabolism in tissues not readily accessib le or measurable in humans.