The Deposition of Uranium in Bone* I. Animal Studies

Studies of the distribution of uranium in animal tissues (1, 2) have shown that a large proportion of the injected dose accumulates initially in the bone and kidney. 40 days after injection, however, bone is the only tissue which has retained significant quantities of the metal (2). Because of the importance of bone as a storage site for uranium, more specific information has been obtained concerning the factors which influence the deposition of uranium in bone in the animal. One of the problems presented by the previous work concerned the differences in the skeletal distribution of uranium which occurred between the sexes. The bones of male rats consistently accumulated greater quantities of uranium than those of females. All of these rats weighed 200 gm. At this weight, the male rats averaged 9 weeks in age, the females 16 weeks. Were these differences related to age or sex? Recent studies with radioactive phosphorus (3) have emphasized the importance of the relative vascularity of bone in determining the rate and, as a result, the amount of deposition of minerals in bone. This suggested that the differences observed in young male and adult female rats resulted from variation in the relative vascularity of the skeleton with age. To test this hypothesis, normal male and female rats of various ages and rats in a state of severe rickets were injected with uranium and their bones analyzed. An analysis of the content of uranium in different types of bone structures as represented by skull, vertebra, and long bone was also made. Epiphysis, metaphysis, and diaphysis from rabbits, and periosteum from a dog were examined for purposes of comparison. A study of the uptake of radiophosphate in different parts of the skeleton supplemented the experiments with uranium.