Thyroid status and noradrenaline-induced regulatory thermogenesis in heat acclimated rats

Adjustments of the obligatory and regulatory thermogenesis upon heat acclimation (34 degrees C) and perchlorate treatment were observed in male rats. Resting oxygen consumption measured at neutral temperature was reduced, with respect to control, by 23, 27, and 34% in heat acclimated, perchlorate treated, and heat acclimated-perchlorate treated rats, respectively. Administration of 0.4 mg NA/kg increased oxygen consumption by 40, 30, 5 and 1% above resting level in control, heat acclimated, perchlorate treated, and heat acclimated-perchlorate treated rats, respectively. Whereas significant interaction was found between the effects of thyroid hormones and acclimation temperature on obligatory thermogenesis, the interaction of these factors on regulatory thermogenesis was not statistically significant. Still, hypothyroidism may be considered a thermoregulatory advantage during chronic heat exposure.