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."