The influence of thyroxine and acclimation temperature on glycogen reserves of the frog Rana pipiens

Leopard frogs were given daily injections of Na-l-thyroxine (2.0 mug/10 g body weight) for seven days, and control animals were given daily injections of the vehicle. During the period of treatment, half of the frogs were acclimated, in darkness and without food, at a constant temperature of 15 degrees C, whereas the remainder of the animals were acclimated at 25 degrees C. At the end of the seventh day, the frogs were killed by decapitation, and the glycogen concentration in samples of liver tissue and skeletal muscle was determined spectrophotometrically. Total hepatic glycogen of each frog subsequently was calculated from data on glycogen concentration and liver weight. Treatment of leopard frogs with thyroxine had no apparent effect on hepatic glycogen reserves of animals acclimated at 15 degrees C, but there was a striking reduction in glycogen content of livers from hyperthyroid frogs held at 25 degrees C. Mobilization of hepatic glycogen in thyroxine-treated animals held at 25 degrees C presumably was secondary to a general stimulation of oxidative metabolism. Treatment with thyroxine had no effect on the concentration of glycogen in skeletal muscle of leopard frogs held at either of the acclimation temperatures used in this study.