CPAA for studying biokinetics with stable isotopes : a preliminary investigation on zirconium metabolism in animals

In order to estimate gut absorption by determining tracer concentration in plasma, a technique baled on the administration of two stable isotopes of the same element was combined with proton activation analysis. The optimization for the determination of Zr isotopes in biological samples is presented together with the results of a preliminary study on Zr biokinetics in animals. (p,n) reactions on 90Zr and 96Zr resulted the most convenient. The obtained minimum detectable quantities are 3 and 2 ng/ml plasma, respectively, for 90Zr and 96Zr. Zr plasma clearance and Zr response to a simple oral test were studied separately in different subjects by using the natural Zr solution. The data analysis was performed measuring the concentration of 90Zr to obtain indication on the time behavior and fractional level of Zr appearance in plasma depending on the administration routes. Two rabbits were intravenously injected 50 μg 90Zr and a third rabbit was orally given 2.5 mg of 90Zr. Concentration in plasma samples of intravenously and orally given Zr isotopes are reported, as a function of lime after administration. The injected tracer concentration relative to the first two rabbits were fitted simultaneously to obtain clearance parameters. Zr intestinal absorption is evaluated to be less than 0.2%. The work confirms that proton activation is a powerful tool for biokinetic studies with stable isotopes.