Metabolism of 241Am citrate relative to age

Animal age has a marked influence on the metabolism of a number of radionuclides, although few data are available for 241Am. Therefore its deposition and retention were determined at intervals after intravenous injection in adult and weanling and intracardial injection in newborn rats. Doses of 1 and 10 μCi/kg body weight were used; no dose-related effect on deposition or retention were found. The adult liver contained about half of the dose at one day postinjection and the weanling and newborn livers 10 and 18%, respectively. The rate of loss, however, was more rapid in the adult resulting in 16,7 and 12% remaining at 14 days in the adult, weanling and newborn livers respectively. Femoral deposition was highest in the weanlings and lowest in the newborns, presumably reflecting the relative rates of active mineralization occuring at these ages. The ratio of the concentrations, skull:femur at one day was one for newborns, 0.5 for weanlings and 0.7 for adults. Since little 241Am was lost from the skeleton and minimal growth of the skull occured, the ratio had increased for all ages by 14 days because of growth of the femur. There was little effect of age on the fraction of the dose deposited in other tissues