A methodology for biokinetic studies using stable isotopes: results of repeated molybdenum investigations on a healthy volunteer.

A method for biokinetic studies in humans using stable isotopes is presented. The technique is based on double tracer administration and on proton activation as the analytical method. As an application, the results of investigations on molybdenum metabolism in humans are reported. The contents of 95Mo and 96Mo in biological samples were determined by inducing (p,n) reactions and by analysing the gamma-rays emitted by the radioactive products. The minimum detectable quantity was 2 ng/mL plasma for both Mo isotopes. Four investigations on molybdenum metabolism were performed on a healthy volunteer subject in the course of 3 yr. Two absorption studies with different amounts of tracers in aqueous solution were performed by giving 96Mo orally and 95Mo intravenously. Two investigations were performed with single oral administration of 96Mo in aqueous solution and of a 96Mo solution mixed with an infant formula respectively. The stability with time of the biokinetic parameters was tested. The fractional absorption values measured in this volunteer were 0.84, 0.98 and 0.95 for three studies with Mo in HCl and 0.51 for a single study with Mo administered in an infant formula, these data are discussed.