P32 Distribution and Excretion in Rats Fed Vitamin D-free and Low Phosphorus Diets

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Abstract
In this study a comparison has been made of the deposition and turnover of orally and intramuscularly administered P32 in the blood, liver, kidney, muscle and femur of growing rats maintained on diets that were (1) adequate, (2) adequate but lacking in vitamin D, and (3) low in phosphorus; total phosphorus was determined in the above tissues, and radioautographs were made of the femurs of rats of the three dietary groups. Essentially no difference was demonstrated by isotope or total phosphorus data between the two groups of rats receiving adequate phosphorus; that is, the absence of vitamin D was without any observed effect in the presence of an optimum calcium-to-phosphorus ratio. On the other hand, the rats of the low phosphorus group deposited more P32 in their soft tissues than the rats of the two groups fed adequate phosphorus diets, but less in the femur, as indicated by both Geiger counting and radioautographs; total phosphorus values indicated depletion in the femurs but not in the soft tissues. The rats on the low phosphorus diet excreted about the same percentage of isotope in the feces as those on the adequate phosphorus rations, after both oral and parenteral dosage, but showed a marked decrease in the amount excreted in the urine, indicating a considerable capacity in this respect to conserve phosphorus when the intake of this mineral is inadequate. Total phosphorus excretion in the feces of the low phosphorus diet rats was approximately one-ninth that of the adequate phosphorus groups. The radioautographs demonstrated only slight deposition of P32 in the proximal end of the femur of the low phosphorus group as compared with the femurs of the rats receiving adequate phosphorus.