Effects of Thyroxine Upon Strontium and Calcium Metabolism of Embryonic Bone Grownin Vitro

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Abstract
Embryonic chick bone was cultured in a synthetic medium for periods up to 7 days to determine the effect of levels of 0.05 to 5.0 μg thyroxine per 100 ml medium upon the uptake and removal of Sr85 and Ca45 from bone. Thyroxine generally caused a decrease in the bone content of Sr85 and Ca45, reduced growth and reduced selection against strontium. Serum in the medium seemed to eliminate the effect of thyroxine. The reduced content of Sr85 and Ca45 due to thyroxine was evident in bone cultured at 37 C but not at 30 C. The removal of radionuclides from labeled bones was decreased by the presence of thyroxine. The results have been interpreted to mean that thyroxine could increase the conversion of labile bone Sr85 and Ca45 into the nonlabile fraction and reduce its reconversion back to the labile form.