Biokinetic studies in humans with stable isotopes as tracers. Part 2: Uptake of molybdenum from aqueous solutions and labelled foodstuffs.

Molybdenum (Mo) has been identified as an essential trace mental for humans. The present study was aimed at the assessment of data on intestinal Mo absorption from aqueous solutions and from foodstuffs in humans applying the methodology for intrinsic labelling described in Part 1. The intestinal absorption of Mo was investigated by means of a double tracer method in 3 healthy volunteers on a total of 15 occasions. When administered as aqueous solution, almost complete uptake of Mo was observed up to doses of 1 mg and only a slight decrease for higher doses. But addition of black tea reduces the absorbed fraction by about a factor of ten. Studying Mo absorption from food, intrinsically labelled cress showed a reduced uptake as compared to extrinsically labelled cress and aqueous solutions. Even less Mo was absorbed from an extrinsically labelled composite meal. The data obtained demonstrate a pattern of intestinal Mo absorption which is different from that of other essential trace metals, e.g., Fe or Co.

Biokinetic studies in humans with stable isotopes as tracers. Part 1: A methodology for incorporation of trace metals into vegetables.

The metabolism and biokinetics of trace metals in humans can be successfully studied employing stable isotopes of the investigated elements as tracers. For the estimation of the bioavailability and the intestinal absorption from solid food, materials are required which have been intrinsically labelled with the chosen stable tracer, since the use of an extrinsic label may lead to erroneous results. Here a technique for producing intrinsically labelled vegetables is presented and optimized with regard to molybdenum, gadolinium and ruthenium, elements of interest in the field of radiation protection and/or nutrition. These feasibility studies were aimed to determine the most favourable conditions for the production of vegetables containing the selected tracers in amounts high enough to enable successful biokinetic studies in humans. In this optimization study the natural elements were used instead of the more expensive stable isotopes. Mo is readily absorbed both into cress (Lepidium sativum) and into french beans (Phaseolus vulg. var. nanus). Gd uptake into cress is moderate, while Ru may be easily and successfully incorporated only into sprouts of mung beans (Vigna radiata).

Internal biokinetic behaviour of molybdenum in humans studied with stable isotopes as tracers.

Although molybdenum is considered to be an essential trace metal for humans, the knowledge about its metabolism is rather limited. The present study was aimed at the assessment of biokinetics following intravenous injection of trace amounts of 95Mo or 96Mo into five healthy volunteers. In a total of 11 investigations, the plasma clearance up to eight hours and the urinary excretion for at least three days after the injection were evaluated. The tracer concentrations were determined by proton nuclear activation analysis in blood plasma and by thermal ionization mass spectrometry in urine samples respectively. In all subjects, the plasma clearance is much faster than expected from the literature. The data obtained for the plasma clearance of the tracer can reasonably be fitted by a two exponential equation. The half times of the fast component range between 4 and 70 minutes and for the slow component between 3 and 30 hours. The urinary excretion of the injected tracer seems also to be faster than expected and the fractions lost are higher for larger doses administered. For the smallest dose given, 34% of the injected tracer were excreted within one day whereas for the four times larger dose about 60% were lost. These findings on urinary excretion are in agreement with recently published results.