The Deposition of the Rare Earths in Bone

Abstract

Since both yttrium and a number of other rare earths are concentrated nonuniformly in bone, their exact site of deposition and chronological behavior are of radiobiological interest inasmuch as they permit the observation of radiation effects after partial irradiation of the skeleton. Although there is adequate evidence to show that the alkaline earths are taken up in areas of bone formation in the process of calcification, there exist contradictory explanations of the deposition of the rare earths in bone. Hamilton (1) and Durbin et al. (2) in their studies on the metabolism of the lanthanons describe autoradiographs of bone sections showing concentrations of the isotopes beneath the periosteum, the endosteum, and the epiphyseal plate. They interpret them to demonstrate an affinity between these elements and the uncalcified osteoid matrix of bone protein. Copp et al. (3) compared the deposition of strontium and yttrium in the bone of normal and rachitic rats and found that yttrium retention, unlike strontium, is unaffected by age or rickets, and they came to the same conclusion as Hamilton. Their evidence, however, was not conclusive, because only two fractions of bone were considered as possible sites of deposition of the elements, the mineral and the organic, and the argument was rather that the rare earths did not behave like calcium and therefore were not taken up by the inorganic fraction during mineralization, but must be in the organic fraction. Work carried out at Oxford (4) was designed to illustrate the deposition in the skeleton of yttrium, the product of Sr90 decay, and the autoradiographic results showed yttrium to be deposited in areas of bone resorption and not in the osteoid matrix.