The influence of acclimation temperature on the metabolic response of frog tissue to thyroxine administered in vivo

Abstract

Leopard frogs ( Rana pipiens complex) were given daily injections of Na- l-thyroxine (2.0 μg/10 g body wt) in the dorsal lymph sac, while control animals were given daily injections of equivalent volumes of the alkaline vehicle. Half of the animals were acclimated in darkness at a constant temperature of 15°, whereas the remaining frogs were acclimated in darkness at 25°. At the end of 5.5 days of treatment, the frogs were sacrificed; and oxygen consumption of liver tissue from each animal was measured by differential respirometry at the temperature to which the donor was acclimated. Oxygen consumption of liver tissue from hyperthyroid frogs acclimated at 25° was 21% higher than it was in preparations from control animals acclimated at the same temperature. However, oxygen uptake by liver preparations from hyperthyroid frogs acclimated at 15° did not differ significantly from control levels. Thus, in anuran amphibians—as in reptilian ectotherms—temperature seems to govern the metabolic response of tissues to thyroid hormones.