Influence of thyroid hormone on glycogen metabolism in rat liver.

The livers removed from thyroidectomized and L-T4 supplemented rats were rapidly frozen by Freon-12 chilled with liquid nitrogen, and concentrations of metabolites which affect glycogen synthetase and phosphorylase were determined. Serum and liver glycose levels were not changed in any thyroid functioning. But liver G6P and ATP were increased by thyroidectomy and decreased by L-T4 supplement, while cAMP was increased by the hormone supplement. The "enzyme activity" ratio of glycogen synthetase a to phosphorylase a was increased by thyroidectomy and decreased by L-T4 supplement. The most intimate correlation was observed between the "enzyme activity" ratio and the ratio of the "energy charge" ratio of cAMP among other indices calculated from changes in the metabolite concentrations in the various thyroid functioning. The change in the substrate levels brought about by thyroidectomy and L-T4 supplement appeared to modulate both the enzyme activities which in turn regulate the glycogen metabolism.