The Turnover of Calcium and Strontium in the Skeletons of Growing Rats on High-strontium Diets

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Abstract
The deposition of strontium in the skeletons of rats of three different age-groups has been investigated. The rats were fed for 21 days on special diets differing from a commercial rat-diet only in that equimolar substitutions of strontium for calcium were made. At the end of the feeding period there was an approximate equilibrium between the calcium and strontium in the diet and the calcium and strontium in bone. On diets in which the strontium to calcium ratio was small, the overall discrimination (bone to diet) varied from 0·27–0·33, indicating a preferential deposition of calcium rather than strontium in bone. This discrimination decreased slightly with increasing age. It is postulated that equilibration of bone calcium and strontium with dietary calcium and strontium takes place only in a labile fraction of the skeleton which is computed to be 23 per cent of the bone calcium in young rats and 6 per cent in adults. This labile fraction is shown to be composed of about equal parts of pre-formed but still labile bone and new bone laid down over the feeding period (growth). The implications of these results on the deposition of strontium-90 in the skeleton are discussed.