Role of hyperthyroidism in increased thermogenesis in the cold-acclimated Syrian hamster

The oxygen consumption of cold-acclimated Syrian hamsters (measured in pentobarbital-anaesthetized animals) was 59% greater than that of warm-acclimated hamsters. Upon return of the cold-acclimated hamsters to 24 degrees C, the elevated metabolic rate declined slowly, with half-life of approximately 1 day. The increase correlated well with our previous finding of a four-fold increase in serum 3,5,3'-triiodothyronine concentration in cold-acclimated hamsters and the slow decline in concentration of this hormone during deacclimation. Daily administration of T3 (for 7 days) to warm-acclimated hamsters at 24 degrees C resulted in a similar increase in oxygen consumption that persisted 1 day after the last injection and had disappeared by 7 days after the last injection. We conclude that the high concentration of serum triiodothyronine in the cold-acclimated hamster exerts a thermogenic effect that probably contributes to thermoregulatory thermogenesis in the cold.