Effect of dietary phosphorus supplementation on the uptake of radioactive strontium in rats.

I . After feeding radioactive markers 85Sr and 45Ca for 10 days to weanling and adult rats receiving basal diets all of which contained adequate calcium and phosphorus to support normal growth, the skeletal retention of the markers was compared with that in litter-mates receiving seven different P compounds as dietary supplements so that the P intake was increased z to 3& times. 2. In weanling rats a dietarysupplement of KH,PO, decreased the skeletal retention of 85Sr by some 30 % without affecting the retention of 45Ca. In adults on this supplement, the skelctal retention of compared with controls on the same basal diet. 3 . When the supplement contained Ca as well as P the reduction in skeletal retention of 85Sr in young and adult rats was greater than when no Ca was present in the supplement. 4. It is concluded that there was no experimental evidence to show that supplements of P which also contained Ca induced any Ca deficiency in the rats. j. In rats receiving P supplements which also contained Ca, the ratio of the skeletal retention of 85Sr, experimental to controls, was 0.45 for weanling rats and 0.52 in adults, 34 weeks old. These ratios were not significantly different for any of the seven supplements used. 6 . From comparisons with previous experiments, it is concluded that supplementation with Ca plus P is more promising as a remedial measure for decreasing the uptake of radioactive Sr from the diet than supplementation with Ca alone. was reduced by over 40