The effects of prolonged exposure to lowered ambient temperature on thyroid activity in mature female rats.

The effects of prolonged exposure to lowered ambient temperature (18-19 degrees C) for 6 weeks, on thyroid function, were studied in mature female rats. Exposure to cold resulted in a significant rise in serum thyrotrophin level but a fall in serum thyroxine. Radioactive iodine uptake by the thyroid gland was also depressed. Rectal temperature was reduced following cold exposure. Histological examination of the thyroid gland was suggestive of reduced glandular activity. Thus prolonged exposure to lowered ambient temperature leads to a reduction in thyroid gland activity which is accompanied by a lower body temperature.