The metabolic response to thyroxine of lizards maintained in a thermal gradient

Abstract

Groups of adult lizards, Sceloporus cyanogenys, were maintained in a thermal gradient, temperature range 12°–60°C. One group received daily injections of thyroxine, a second group daily injections of thiourea, the third group as controls received saline. One week of thyroxine treatment increased oxygen consumption, whereas thiourea caused a decrease. Such an increase and decrease were noted for 3 weeks at which time the animals were sacrificed and the oxygen consumption of liver, kidney, and brain tissue was measured. Thyroxine was found to increase and thiourea to decrease oxygen consumption of each tissue. Groups of newborn lizards were observed to respond to thyroxine with an increase in oxygen consumption when maintained at a constant 32°C or in a gradient, but not at a constant 16°C. Metabolic response at a constant 32°C was somewhat greater than in the gradient. These data suggest that a rise in oxygen consumption can occur as the result of the in vivo administration of thyroxine to lizards maintained in a thermal gradient.