RESUMO
Data are presented on the whole-body retention of 133Ba (half-life 10.74 y), over periods of up to 13 y after injection into six healthy male volunteers aged 25-81, and on their levels of biochemical markers for bone turnover. The results are relevant to propositions underlying the ICRP's current (Publication 67) and former (Publication 20) models of alkaline earth metabolism. The tracer was predominantly skeletal within weeks of the injection, as predicted in the current model. The mean retention accorded satisfactorily throughout with predictions based on the current model, but this accord does not necessarily validate the model, for two reasons. First, parameter values attributed to barium were influenced by data emerging during the early years of this study. Second, bone resorption rates in these subjects, as indicated by urinary markers, appear insufficient to explain the long-term reductions in skeletal retention which, in the present model, arise exclusively through this mechanism.
Assuntos
Radioisótopos de Bário/farmacocinética , Adulto , Idoso , Idoso de 80 Anos ou mais , Fosfatase Alcalina/sangue , Fosfatase Alcalina/urina , Aminoácidos/sangue , Aminoácidos/urina , Radioisótopos de Bário/administração & dosagem , Densidade Óssea , Osso e Ossos/metabolismo , Colágeno/sangue , Colágeno/urina , Colágeno Tipo I/sangue , Colágeno Tipo I/urina , Fracionamento da Dose de Radiação , Humanos , Masculino , Pessoa de Meia-Idade , Osteocalcina/sangue , Osteocalcina/urina , Peptídeos/sangue , Peptídeos/urina , Distribuição TecidualRESUMO
Data are presented on the early metabolism and long-term retention of 133Ba (half-life 10.74 y) injected into six healthy male volunteers at ages 25-81 y. The tracer appeared to be mainly skeletal within several days, much earlier than predicted by the ICRP's model of alkaline earth metabolism. Excretion was mainly fecal, the relative fecal:urinary clearance up to 14 d ranging from 6 to 15 in the six subjects. The whole-body retention at 50 d (mean 8%, range 4.5 to 12%) was similar to that inferred from published data on the retention of injected Ra in man (mean 7%, range 3-13%). For about 1 y thereafter, the retention of Ba could be represented by simple power functions of time, with the rate of loss correlating with the excretory plasma clearance rate inferred over the first 4 d. In the subject aged 81 y, the pattern differed from that established following an earlier injection at age 60, but the differences were not necessarily related to advancing age.
