The influence of thyroxine on oxygen consumption of tissues from the frog Rana pipiens

Sixteen leopard frogs received daily injections of Na- l-thyroxine (2.0 μg/10 g body weight) for 5 days; and 18 control animals received daily injections of the vehicle. During the period of treatment, all frogs were maintained at a constant temperature of 25°C. At the end of the fifth day, metabolism of liver slices and of skeletal muscle was determined at 25°C by differential respirometry. The mean oxygen uptake of liver samples from hyperthyroid frogs was higher than that of liver preparations from control animals. Additionally, liver tissue from female frogs exhibited a higher mean rate of metabolism than preparations from males, irrespective of treatment. Preparations of skeletal muscle did not survive well during experimentation. The data indicate that increased metabolism of intact, hyperthyroid frogs is attributable to a direct response of peripheral tissues to circulating hormone, and lend support to the concept that the thyroid glands of adult anurans exercise important control over intermediary metabolism.