Interactions between the Pituitary, Thyroid and Adrenal Cortex during Acute Exposure to Cold or to Electric Shocks in the Rat

Abstract

In intact rats acclimated to 25 ± 1°C, acute exposure to cold resulted in simultaneous stimulation of TSH and ACTH secretion. The plasma TSH response to cold was identical at temperatures varying from + 14 to -10°C, whereas the adrenocortical response increased proportionally to the severity of cold. Acute stimulation of ACTH secretion by exposure to a stressful situation (electrical shocks) did not alter the TSH response to cold. Conversely, acute blockade of the pituitary-adrenocortical response by dexamethasone treatment did not enhance the TSH response to cold. Chronic stimulation of ACTH secretion resulting from adrenalectomy did not interfere with the TSH response during subsequent exposure to cold. However, a reduced adrenocortical response to cold was observed during chronic hypersecretion of TSH resulting from previous thyroidectomy. These findings do not support the hypothesis of an inverse relationship between TSH and ACTH secretions during acute cold exposure, but rather suggest that these secretions are independent.

Cold Stress and Corticotropin-Releasing Hormone Induced Changes in Messenger Ribonucleic Acid for the α₁-Subunit of the L-Type Ca²⁺ Channel in the Rat Anterior Pituitary and Enriched Populations of Corticotropes

“…For example, CS causes increases in both plasma ACTH and TSH. However, plasma TSH levels move in a direction opposite to that of plasma ACTH following many other stresses, including RS [36, 37, 38]. Alternatively, NS and RS may have evoked transient changes in α 1C mRNA levels that were not evident at the times examined.…”

A New Perspective on Regulation of Pituitary Plasticity: The Network of SOX2-Positive Cells May Coordinate Responses to Challenge

“…A hierarchy of cell regulation within the pituitary is suggested by aspects of axes crosstalk. In end-organ ablation studies in rats, it has been shown that thyroidectomy decreases the corticotroph response to stress in adrenalectomized rats ( 68 ), while concurrent adrenalectomy and gonadectomy results in a delayed gonadotroph response compared with gonadectomy alone ( 69 , 70 ). Further analysis of gonadectomized and adrenalectomized animals reveals a hormone-negative cell population that preferentially proliferates to generate corticotrophs rather than gonadotrophs if both organs are ablated ( 71 ).…”

A Novel Endogenous Corticotropin Release Inhibiting Factor

“…In response to most forms of acute stress, plasma ACTH levels increase, whereas TSH levels decrease. 64–67 Cold stress is unique in that it results in activation of thyrothrophs, 68 in addition to the corticotrophs, leading to increased TSH levels. 65,67,69 This increase in TSH could be due to increased hypothalamic stimulation, since TRH and TRH mRNA are also increased.…”

“…64–67 Cold stress is unique in that it results in activation of thyrothrophs, 68 in addition to the corticotrophs, leading to increased TSH levels. 65,67,69 This increase in TSH could be due to increased hypothalamic stimulation, since TRH and TRH mRNA are also increased. 70 Interestingly, although plasma ACTH levels are usually increased in response to cold stress, 71–73 no significant differences in hypothalamic CRH and pituitary POMC mRNA levels are seen in response to cold, in contrast to many other stressors.…”