Abstract
The effects of cold-adaptation, rewarming and heat exposure were studied in euthyroid and hypothyroid male rats. Pituitary and serum TSH concentrations were measured. Thyroid function was assessed by weight, histology, 131I uptake, serum TSH and PBI values. Net pituitary TSH synthesis, the calculated TSH secretion rate (SR) and the response to challenge with propylthiouracil (PTU) were obtained. There was no evidence of increased TSH secretion in cold-adapted rats. In some experiments the serum TSH level, the PBI and net TSH synthesis were decreased. When cold-adapted rats were rewarmed, the PBI increased briefly, the serum and pituitary TSH remained unchanged or increased, and net TSH synthesis and the SR remained unchanged. Exposure to heat caused an increase in pituitary TSH and sometimes in serum TSH and the elevated net TSH synthesis observed in hypothyroid rats and the TSH SR in hypothyroid rats were not inhibited. These observations support the current opinion that an increase in thyroid activity i...
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