The circannual variations of thyroid activity in the woodchuck (Marmota monax)

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1. 1. The I-131 uptake by the thyroid gland of the woodchuck (Marmota monax) shows relatively low levels of uptake during the early summer and early fall months. Uptake levels are at their greatest level during the winter months when the animal is in hibernation and just prior to arousal. 2. 2. Thyroxine serum levels indicate that the thyroid gland is actively secreting this hormone and circulating it in the blood stream. The serum thyroid binding globulin which carries this hormone is also found in increased levels at this time. 3. 3. These results appear to indicate an in vivo demonstration of the uncoupling of oxidative phosphorylation by thyroxine during a period which the animals' metabolic reaction are at a minimum. It is thought that the uncoupling is essential to produce heat for winter survival. © 1973.

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Comparative Biochemistry and Physiology -- Part A: Physiology