RESUMO
In vivo and in vitro effects of L-T3, L-T4, estradiol, corticosterone, epinephrine and norepinephrine were studied on the rate of liver and muscle tissue respiration in B. melanostictus during hibernation and active phase under natural climatic conditions. Thyroid hormones were found to be calorigenic only during the active phase. Estradiol stimulated the respiratory rate directly during hibernation and indirectly during the active phase. Adrenal hormones invariably increased the respiratory rate of the tissues in all the experiments. On the basis of the present findings it can be concluded that the sensitivity of the tissues to various hormones is altered during the active phase and hibernation. The calorigenic action of thyroid hormones seems to be associated with activity-linked energy demand. Direct stimulation of tissue respiration by estradiol during hibernation may be of great adaptative significance. Due to their temperature-independent calorigenic action, adrenal hormones may be considered as emergency hormones for the regulation of the oxidative metabolism in the toad.