Molybdenum is a trace element essential to life. Nevertheless, little information is available on its metabolism in humans. A methodology based on stable isotope administration that combines compartmental analysis, simultaneous use of two tracers, and proton nuclear activation (PNA) is presented. A four-compartment metabolic model was adopted. The compartments are stomach, small intestine, transfer compartment, and unquantified tissue pool. The employment of two different stable isotopes of the element under investigation as tracers was made possible by PNA. Optimization of the technique for molybdenum determination in plasma led to the choice of 95Mo and 96Mo as tracers. Their concentrations in plasma can be determined measuring the disintegration gamma lines of the corresponding technetium radioisotopes produced via (p,n) reaction. In the adopted experimental conditions, a minimum detectable concentration of 2 ng isotope/ml plasma was attained. A kinetics study was performed on two healthy volunteers. To both subjects one tracer was orally administered, and the other intravenously injected. Venous blood samples were withdrawn at different postinjection times and the concentrations for both isotopes determined. The model parameters describing molybdenum kinetics were obtained for the two individuals. Total absorbed fraction was found to be 0.84 +/- 0.03 and 0.86 +/- 0.07, respectively.
The biokinetics of ruthenium after oral and intravenous administration has been investigated in two human subjects using the stable isotope 101Ru as a tracer. Tracer concentrations in blood plasma have been determined using activation analysis with protons. The results presented here prove that the stable tracer technique is a valuable tool for obtaining relevant information about the biokinetics of ruthenium in humans. From these pilot studies, it may be argued that the clearance of systemic ruthenium from plasma is significantly slower than the predictions of the biokinetic model currently recommended by the International Commission on Radiological Protection (ICRP). The experimental data for the orally administered tracer, which reflect the gastrointestinal absorption process, differ from the curve derived from the ICRP model, suggesting that the uptake into the systemic circulation may be lower than predicted. On the basis of these preliminary data, investigations on a larger number of subjects with improvements in the experimental design are scheduled.
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