Low muscle and liver glycogen contents in dogs treated with thyroid hormones.

Muscle biopsies for glycogen determinations were taken from dogs before (controls) and after prolonged treatment with thyroid hormones (T4 or T3). The glycogen content in quadriceps femoris was measured before exercise, immediately after its cessation, and during 24h of post-exercise recovery. The effect of thyroxine treatment on the liver glycogen content both at rest and following physical effort was also studied. A marked decrease in the muscle glycogen content determined at rest was found both in T4 and T3-treated dogs in comparison with controls. Physical exercise diminished the muscle glycogen store to similar values in control and thyroid hormone-treated dogs, but the rate of the muscle glycogen utilization during exercise was lower in the latter. The rate of the post-exercise muscle glycogen synthesis was considerably inhibited in thyroid hormone-treated dogs, but 1 hr glucose infusion, applied immediately after cessation of exercise, accelerated the rate of glycogen re-synthesis, so it was close to that in controls without infusion. Thyroxine treatment also affected the liver glycogen store. Both at rest and after physical exercise significantly lower liver glycogen contents were found in T4-treated dogs than in controls.