Metabolic response to thyroxine in the newborn pig

The oxygen consumption rate (ml O2/kg/min), the pulse rate, respiratory frequency and body temperatures were measured after a single subcutaneous injection of thyroxine (80 micrograms/kg) or adrenaline (200 micrograms/kg) in unfasted pigs aged 1--11 days. Thyroxine produced a metabolic response after a latent period and potentiated the metabolic action of adrenaline. As reported in the literature, the existence of an immediate metabolic response to thyroxine was not evidenced. The obtained results support the view that in the newborn pig the physiological rise in metabolism which leads to metabolic stability might be caused by thyroxine, whose free fraction and highest level in the blood occurs shortly after birth. Potentiation of adrenaline action by thyroxine can contribute to this process.