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Grupos de ratos Wistar e cães Beagle foram submetidos a dietas com dopagem de urânio, iniciando-se no desmame do animal e prolongando-se até sua maturidade. O conteúdo de urânio em ossos foi determinado por duas técnicas nucleares: nêutron-fissão e análise por ativação neutrônica, obtendo-se microdistribuição e conteúdos totais, respectivamente. O conteúdo total de U em ossos de ratos, em função da quantidade ingerida (medida em ppm de U na ração), exigiu um comportamento tendendo à saturação para doses de urânio na vizinhança de 20 ppm, sendo verificado também ser este o limiar toxicológico do U em ratos. Observou-se uma alteração do regime de saturação para outro, linear crescente, em dosagens superiores a 20 ppm. Esta ocorrência foi discutida em termos de uma provável falência renal de origem toxicológica. A microdistribuição de U em seções transversais do colo femoral de Beagles mostrou que, contrariamente ao que ocorre em situações de ingestão aguda e única, esse radionuclídeo distribui-se igualmente tanto no córtex quanto na medula óssea. Vários \"hot spots\" de U foram observados na região próxima ao endósteo. Foi desenvolvido um modelo biocinético para descrever a acumulação do U em função do tempo, e esse modelo foi validado vis-a-vis dados obtidos neste trabalho com ossos de Beagles. Com isso obteve-se, por extrapolação, que a saturação óssea de U ocorreria num período igual ou superior a 8 anos. Doses internas e microdoses foram acumuladas para a região da medula óssea, e as possíveis consequências radiobiológicas foram discutidas, tomando-se como exemplo ilustrativo a recente questão do urânio depletado disperso, via operações militares, nas regiões do Golfo Pérsico e Balcans. / Groups of Wistar rats and Beagle dogs were submitted to uranium doped diets, starting in the post-weaning period and extending till maturity. The uranium content in bones was determined by means of two techniques: neutron-fission and neutron activation analysis, to obtain microdistributions and total contents, respectively. The total content of U in bones of Wistar rats, as a function of the ingested amount (measured in terms of ppm of U in the food), showed a trend toward saturation for U dosages around 20 ppm, which also represents the toxicological threshold of U in Wistar rats, as verified in this work. Is was also observed, at dosages higher than 20 ppm, a change of the saturation regime into another linearly increasing. This fact was discussed in terms of a possible toxicologically originated renal failure. The U microdistribution in transverse sections of Beagle femoral shafts, showed that this radionuclide is equally distributed all along the cortex and marrow, which is at variance with experimental situations of single and acute dosages. Several U hot spots were observed at locations near to the endosteo. Is was developed a biokinetical model to describe accumulation as a function of time, and this model was validated by a comparison with data for Beagle bones obtained in this work. We came to the conclusion, by extrapolation of the model, that the U saturation in bone would take place after a period equal or higher to 8 years. Internal and microdoses imparted to the central bone marrow were calculated, and the possible radiobiological consequences were discussed, where the recent issue of depleted uranium dispersed in the environment, by means of military operations in the Gulf and Balkans regions, was used as a working example.

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