The role of the thyroid in the temperature acclimation of the oxidative metabolism in the frog Rana temporaria

Abstract

The oxygen consumption of skeletal muscle was significantly lower in winter frogs acclimated for 1 and 2 weeks to 24°C than in the frogs acclimated to 10°C. This effect was not found in summer frogs. The succinic dehydrogenase activity in muscle homogenates and the activity of the thyroid, as judged from the histological picture (relative height of the epithelium), were also decreased by warm acclimation in the winter but not in the summer. Repeated daily epinephrine (adrenaline) injections to frogs kept at 25°C caused an increase in the thyroid activity and in the succinic dehydrogenase activity of skeletal and heart muscle homogenates, similar to that induced by cold acclimation. Injections of 5-hydroxytryptamine (5-HT) did not affect the thyroid or the succinic dehydrogenase activity of the muscle homogenates significantly, but caused a slight increase in the succinic dehydrogenase activity of the liver homogenates. The thyroid apparently participates in the mediation of the compensatory changes in oxidative metabolism during temperature acclimation. The control of the thyroid in the acclimation process may occur either directly by catecholamines, or by TSH, the release of which may be affected by the neurochemical changes found during temperature acclimation.