Effects of thyroid hormones and cold acclimation on the energy metabolism of the striped hamster (Cricetulus barabensis)

To examine the effects of low ambient temperature and thyroid hormones on the energy metabolism of the striped hamster (Cricetulus barabensis), adult male striped hamsters were kept at 30 degrees C, or acclimated to 5 degrees C, for 4weeks. During this time, hamsters were treated with a synthetic thyroxine, levothyroxine sodium (LTS), the antithyroid drug methimazole, or saline solution (control). Hamster's food intake, basal metabolic rate (BMR), non-shivering thermogenesis (NST), thyroid hormones, body fat content, mitochondrial state-4 respiration, cytochrome c oxidase, and uncoupling protein 1 (UCP1) gene expression in brown adipose tissue (BAT), were measured. Both acclimation to 5 degrees C and LTS increased serum levels of triiodothyronine, which was associated with increased food and energy intake and BMR. Interestingly, although acclimation to 5 degrees C also increased NST and UCP1 gene expression in BAT, and decreased body fat content, these changes were not induced by LTS treatment. Finally, exposure to 5 degrees C reduced the effects of LTS on energy intake and expenditure in specific metabolic markers and organs. Together, these data illustrate that ambient temperature and thyroid hormones can have both independent, and interactive, effects on the metabolic changes in striped hamsters induced by cold acclimation.