The Pituitary-Thyroid Response to Low Environmental Temperature

Abstract

This chapter discusses the pituitary–thyroid response to cold: the cold response starts as an open-loop reaction with the following elements: the central nervous system (CNS), pituitary gland, and thyroid gland. After longer periods of cold exposure, thyroid function is controlled by the hormonal negative feedback system between pituitary thyroid stimulating hormone (TSH) secretion and thyroid function, with only a minor modulatory influence of the hypothalamus. The available evidence indicates that this two-phase concept of the thyroidal cold response is highly likely. The timing and the interweaving of the two mechanisms (and phases) of the thyroidal response to cold are still uncertain. On the other hand, a body of data obtained for the greater part after longer periods of cold exposure indicates that the cold response may be due to the following chain of events: increased gastrointestinal loss of triiodothyronine (TH) in the cold, a tendency of the blood level of TH to fall, stimulation of TSH secretion by way of the well-known negative feedback between the secretion of TH and TSH, and increased TH secretion.