Interspecies comparison of lung clearance using monodisperse terbium oxide particles

Preliminary results are reported of measurements on human subjects, monkeys, dogs and rats following inhalation of 1.0 μm monodisperse ¹⁶⁰Tb-labelled terbium oxide particles. Lung retention at 6 months ranged from about 0.1 of the initial alveolar deposit (IAD) in man, monkey and dog to 0.03 in rats. Most of the ¹⁶⁰Tb cleared from the lungs was dissolved and absorbed by blood and accumulated at systemic sites, with skeleton, and to a lesser extent liver, being shown as the principle organs of accumulation in the animal species. Neglecting fast particle clearance into faeces during the first days after inhalation, ¹⁶⁰Tb was mainly excreted and accumulated in the urine (0.1 IAD). The results from this study, with metabolic data obtained from intravenously injected terbium, will be used with recently developed biokinetic models to derive the kinetics of absorption from the lungs to blood of these particles and the particle transport to the GI tract for each species. The biokinetics of each of the animal species will be compared with those determined for the human.