Endocrine Responses to Heat and Cold Stress

Abstract

Summary. This review focuses on the endocrine responses to thermal stimuli during passive heat or cold exposure, with particular reference to the relation of these responses to the changes in the body core temperature (Teare). Mild to moderate hyperthermia (<1°C rise in Teare) induces the release of growth hormone and prolactin (PRL). Moderate hypothermia (la_2°C fall in Teore) suppresses PRL release. A positive correlation between plasma PRL and Teare suggests some role for PRL in thermoregulation. Hypothermia activates the hypothalamo-pituitary-thyroid (HPT) axis and releases thyrotropin-releasing hormone, thyroid-stimulating hormone (TSH), and thyroid hormones and increases the metabolic rate. Enhancement of extrathyroidal production of triiodothyronine (T3) from thyroxine (T4) may precede the TSH response to cold. Both severe hyperthermia and hypothermia (1°_3°C changes in Teare) activate the hypothalamo-pituitary-adrenal (HPA) axis and the sympathetic nervous system, resulting in release of corticotropin-releasing factor, adrenocorticotropic hormone, cortisol, and norepinephrine. The responses in the HPT axis and the HPA axis are not apparent in humans, as they are in rats, probably owing to the larger body mass of humans. Hyperthermia stimulates the renin-angiotensin-aldosterone system and the release of arginine vasopressin (AVP) and atrial natriuretic peptide, but this might be due to nonthermal factors. Diuresis due to suppression of AVP release is induced by cold. Gonadal response to thermal stimuli is possibly suppressive. The hormonal responses induced by thermal stress are mostly dependent on the change in Teare in humans; in small animals they are also dependent on the change in skin temperature. I ntrod uctionBody core temperature (Teare) may increase during physical exercise and passive heating (while sauna bathing, with head-out water immersion, and exposure to hot environments); it decreases during cold exposure. Changes in Teare induce various endocrine responses to maintain homeostasis of the body. Recently, local and whole-body hyperthermia therapy for cancer and some benign diseases and induced hypothermia treatment to protect the important organs from hypoxic damage have been developed and widely utilized. On these occasions, the endocrine responses induced by the changes in Teare should be considered. Hormonal responses and their relation to the immune system during exercise in the heat and passive hyperthermia have been reviewed [1][2][3], but little attention has been paid to the relation of endocrine responses to the change in Teare. Body heating and cooling paradigms may include concurrent psychological stress. This review focuses on the endocrine responses to thermal stimuli during passive heating and cooling, with particular reference to their relation to changes in Teare. The study was undertaken to elucidate the thermal influence alone, excluding the influence of non thermal stress. Growth HormoneThere have been many consistent findings that hyperthermia induces a rapid rise in ci...

Balneotherapy, Immune System, and Stress Response: A Hormetic Strategy?

“…Hyperthermia-induced activation of the HPA axis and SNS has been reported mostly in healthy subjects undergoing plain hydrotherapy or sauna baths [ 64 , 65 ]. This activation was manifested by increased circulating concentrations of ACTH [ 66 , 67 ], cortisol [ 66 , 68 ], growth hormone (GH) [ 68 , 69 ], prolactin [ 70 , 71 ], β-endorphins [ 66 , 71 , 72 ], and noradrenaline (NA) [ 67 , 69 , 70 , 73 ].…”

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Molecular biomarkers for assessing the heat-adapted phenotype: a narrative scoping review

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