Creatine Metabolism in Hyperthyroidism. ∗

Abstract

Summary

Hyperthyroidism was induced in rats by thyroxine injections and by feeding of desiccated thyroid. Normal and hyperthyroid rats were injected with glycine-1-C¹⁴ and incorporation of the isotope into glycocyamine and creatine was determined. In other experiments normal and hyperthyroid rats were injected with creatine-1-C¹⁴ and its incorporation into skeletal muscle and heart creatine was determined. Hyperthyroidism resulted in an increased creatinuria, and increased heart weight and a decreased heart creatine concentration. Hyperthyroidism led to increased incorporation of glycine into liver creatine and to decreased incorporation into skeletal muscle and heart creatine. It is concluded that the creatinuria of hyperthyroidism is the result of a block in incorporation of creatine into skeletal muscle and cardiac muscle.