Pituitary and autonomic responses to cold exposures in man

Abstract

This review presents hormonal responses to various cold exposures and their calorigenic effects in man and some animals. Previous studies in rats have shown that cold exposures activate the hypothalamic-pituitary-thyroid axis. Increased thyroid hormone concentrations lead to heat production via general stimulation of metabolism (obligatory thermogenesis) and possibly via activation of thyroid hormone receptors and uncoupling protein 1 (UCP 1) and deiodinase enzyme genes in the brown adipose tissue (BAT). In human subjects long-term cold exposures do not seem to activate the pituitary-thyroid axis, but rather accelerate the elimination of triiodothyronine (T3), leading to low serum concentrations of free T3 hormone. In corollary to this a hypothyreotic condition with increased serum thyroid-stimulating hormone and impaired mood and cognitive performance can be observed after long-term cold exposures such as wintering. During cold exposures the sympathetic nerve system is activated and noradrenaline is released to blood circulation and to BAT, where it leads to production of cAMP, lipolysis and free fatty acids. Free fatty acids open the mitochondrial proton channel protein in BAT. Protons enter the mitochondria and inhibit ATP synthesis (uncoupling). By this way energy is transformed into heat (facultatory or adaptive thermogenesis). In adult human subjects the amount of BAT is small and adaptive thermogenesis (non-shivering thermogenesis) has a smaller role. UCP 1 with other uncoupling proteins may have other functions in the control of body weight, sugar balance and formation of reactive oxygen species.

Psychoneuroendocrine effects of combined thyroxine and triiodothyronine versus tyrosine during prolonged Antarctic residence

“…The placebo group also experienced significant declines in the level of plasma catecholamines (E and NE) in the summer. This is also in agreement with previous studies in the Antarctic (35), and may indicate a pattern of cold acclimation where the initial increase in catecholamines in response to cold exposure eventually returns to baseline (36,37). Patterns of mood and cognitive performance in this study were consistent with some (38,39), documenting an absence of significant decrements of cognitive performance and a seasonal pattern of decrements in mood (21,40,41).…”

Effect of Cold Acclimation on Antioxidant Status in Cold Acclimated Skaters

“…Additionally, an increase in ROS production may occur during and after exercise by an increase of oxygen uptake, increase of catecholamine levels (Cohen and Heikkila, 1974) acid lactic production (Marzatico et al, 1997), elevated rate of hemoglobin autoxidation (Misra and Fridovich, 1972) and hyperthermia (Salo et al, 1991). However, adult human subjects the amount of BAT is small and adaptive thermogenesis (nonshivering thermogenesis) has a smaller role (Leppaluoto et al, 2005). Therefore, a direct linkage between the free radical generation and these physiological and biochemical alterations in cold acclimated subjects has not been fully established (Ji et al, 1992).…”

Effects of whole-body cryotherapy on serum mediators of inflammation and serum muscle enzymes in athletes

“…The mechanism underlying the decrease in muscle enzyme levels is unknown. The normal response of the human body to cold exposure is accelerated elimination of triiodothyronine (T3) and activation of the sympathetic nerve system, which increases the release of noradrenaline in the blood (Leppä luoto et al, 2005). The augmented T3 catabolism is not accompanied by activation of the pituitary-thyroid axis during long-term cold exposure, but rather by a hypothyroid-like status (Leppä luoto et al, 2005).…”