Effect of Phosphate on Serum Strontium

The effect of phosphate on serum strontium and hence serum calcium is described. A possible mechanism of action is proposed. Organ distribution data in rats at different time intervals after iv injection of strontium and strontium with excess phosphate are presented. Studies show that, unlike the control animals, phosphate-treated animals had an initial large trapping of radiostrontium in liver, followed by its release into the circulation. Initial bone radioactivity was less in the phosphate-treated group than in the other. Within a 4-hr period, bone activity of the former gradually approached that of the latter. We propose that initial high activity in the liver was due to formation of strontium phosphate colloid and its removal by liver RE cells. This also explains the low initial activity in bone, as well as the lowering of serum strontium (or calcium), following phosphate therapy. The similarity of bone ⁸⁵Sr content in the two groups after 4 hr demonstrates the transitoriness of the altered body distribution of strontium and/ or calcium which follows phosphate load.