In order to investigate the effect of abnormality in dietary calcium and phosphorus content on the excretion of radioactive strontium, albino rats, about 2 months old, were maintained on diets low in phosphorus (P, 0.187%), low in calcium (Ca, 0.011%), and low in phosphorus and calcium (P, 0.189%, Ca, 0.015%), and on a normal control diet (P, 0.582%, Ca, 0.601%). The rats were injected subcutaneously with radioactive strontium and then treated with dihydrotachysterol given orally.
In addition to the metabolism of radiostrontium, calcium and phosphorus metabolism were examined. In the groups of low calcium diet and of low phosphorus and calcium diet, rate of radiostrontium excretion was not markedly changed, though calcium balance had become negative and the amount of calcium in carcasses was reduced. On the other hand, greatly enhanced excretion of radiostrontium, mainly into urine, was observed in the group of low phosphorus diet, which was merely slightly low in the amount of phosphorus as compared with the severely deficient diet reported effective to activate radiostrontium excretion by Copp,
et al. In the low-phosphorus group no decrease of carcass calcium was observed, though slight decrease in calcium retention was found. Therefore, it is evident that normal bone structure was not markedly injured in this group.
Active excretion of radiostrontium in the group of low phosphorus diet seems to be related to increased activity of urinary excretion of calcium and to active absorption of calcium in the intestines. Skeletal disturbance in low calcium and in low calcium and phosphorus diets fail to decrease radiostrontium accumulation into the skeleton. Dihydrotachysterol did not have any significant effect on radioactive strontium excretion.
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