Hypothermic general cold adaptation induced by local cold acclimation.

To study relationships between local cold adaptation of the lower limbs and general cold adaptation, eight subjects were submitted both to a cold foot test (CFT, 5 degrees C water immersion, 5 min) and to a whole-body standard cold air test (SCAT, 1 degree C, 2 h, nude at rest) before and after a local cold acclimation (LCA) of the lower limbs effected by repeated cold water immersions. The LCA induced a local cold adaptation confirmed by higher skin temperatures of the lower limbs during CFT and a hypothermic insulative general cold adaptation (decreased rectal temperature and mean skin temperature P < 0.05) without a change either in metabolic heat production or in lower limb skin temperatures during SCAT after LCA. It was concluded that local cold adaptation was related to the habituation process confirmed by decreased plasma concentrations of noradrenaline (NA) during LCA (P < 0.05). However, the hypothermic insulative general cold adaptation was unrelated either to local cold adaptation or to the habituation process, because an increased NA during SCAT after LCA (P < 0.05) was observed but was rather related to a "T3 polar syndrome" occurring during LCA.

Thyroid hormone changes in a cold air environment after local cold acclimation.

Serum thyroid hormones (TH) and internal temperatures were investigated in 8 euthyroid men during a general standard cold air test (SCAT) (dry bulb temperature = 1 degree C, 2 h, nude, at rest) performed both before and after a local cold acclimation. Serum total thyroxin (TT4), total triiodothyronine (TT3), free thyroxin (FT4), free triiodothyronine (FT3), and thyrotropin (TSH) were studied during the SCT. The TH values were corrected following the plasmatic volume reduction (delta PV) calculated with Dill and Costill's formula. During SCAT, delta PV reached -9 to -11% (P < 0.05) without any effect of local cold acclimation. Slight TH changes were observed according to delta PV: TT4, TT3, and TSH increased during SCAT (P < 0.05) only before correction. FT4 and FT3 did not vary before correction but increased after correction (P < 0.05). After acclimation, a slightly decreased TT3 was observed both before and after correction (-18% and -11.7%, respectively; P < 0.05). Decreased internal temperatures after local cold acclimation suggested a hypothermic general cold adaptation. It was concluded that TH changes during SCAT differed if correction due to delta PV was applied and that the slight decrease in TT3 observed after local cold acclimation could suggest the presence of a "T3 polar syndrome."

[Induction of a "triiodothyronine polar syndrome" in man under laboratory conditions]. / Induction d'un "syndrome polaire de la tri-iodothyronine" en laboratoire chez l'homme.

To precise the thyroid hormonal changes (TH) during an acute cold exposure, 8 subjects were subjected to a cold air test (2 h, 1 degrees C nude, at rest) in a climatic chamber before and after a local cold acclimation. After cold acclimation the thyroid hormonal changes could suggest the presence of a "T3 polar syndrome" in laboratory conditions. This syndrome was up to now described only after a stay in natural cold environment.