Djungarian hamsters (Phodopus sungorus) live in a seasonally changing environment.
To cope with harsh winter conditions they undergo multiple changes in behaviour and
physiology including spontaneous daily torpor, a state of hypometabolism and hypothermia.
Thyroid hormones play a key role in regulation of seasonal as well as acute changes
in metabolism. In our study we investigated effects of thyroid hormone manipulation
on the spontaneous torpor response. Thyroid hormone levels were increased by giving
T4, T3 or decreased by methimazole via drinking water. Body temperature was recorded
during the entire experiment and gene expression was analysed by qPCR in hypothalamus,
brown adipose tissue (BAT) and muscle. High or low serum T3 levels had reciprocal
effects on torpor bout frequency and duration as well as body temperature during torpor
bouts and active periods, food intake and body weight. Gene expression of type 2 deiodinase
(dio2) involved in T3 activation indicated a tissue specific response to treatment.
Torpor per se affected dio2 expression irrespective of treatment or tissue, suggesting
down regulation of T3 production during hypometabolism. Uncoupling proteins, target
genes of T3 that are involved in thermoregulation, were affected by treatment and
torpor. Taken together our data indicate a strong effect of thyroid hormones on torpor.
Understanding sites and mechanisms of thyroid hormone action in naturally occurring
torpor will help to understand general regulatory mechanisms of metabolism and thermoregulation.
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© 2015 Published by Elsevier Inc.