Relationship between changes in serum thyrotropin and total and lipoprotein cholesterol with prolonged Antarctic residence.

Antarctic residence (AR) is associated with a 50% increase in the thyrotropin (TSH) response to TSH-releasing hormone (TRH) and an expanded triiodothyronine (T3) distribution volume and extravascular hormone pool, collectively called the polar T3 syndrome. To investigate the possible biologic significance of this syndrome, we studied the relationship between nonstimulated TSH and serum lipid profiles in nine subjects, once while in California and monthly during 9 months of AR. We measured serum levels of TSH, total thyroxine (TT4), free T4 (FT4), total T3 (TT3), free T3 (FT3), thyroid-binding globulin (TBG), total cholesterol (T-CHOL), high-density lipoprotein cholesterol (HDL-C), triglyceride (TG), dietary cholesterol (D-CHOL), dietary fat (D-FAT), and dietary kilocalories at each month. The paired mean monthly change from baseline was used to determine significance. The group's mean levels of TSH (approximately 30%), TBG (approximately 16%), T-CHOL (approximately 4%), HDL-C (approximately 10%), and D-CHOL (approximately 19%) increased with AR (P < .05). Small but significant decreases (P < .05) were observed in the mean changes of TT4 (approximately 8%), FT4 (approximately 6%), and TT3 (approximately 6%). FT3, D-FAT, dietary kilocalories, body weight, TG, and the calculated low-density lipoprotein (LDL-C) were unchanged with AR. A significant rate of change (P < .05) during AR was also calculated from the slope of a fitted logarithmic function for TSH (0.96 +/- 0.31 mU.L-1 x mo-1), TBG (61.19 +/- 12.29 nmol.L-1 x mo-1), TT3 (0.09 +/- 0.04 nmol.L-1 x mo-1), TT4/TBG (-0.06 +/- 0.01/mo), TT3/TBG (-8.49 +/- 1.98 x 10(-4)/mo), and TG (-0.33 +/- 0.15 mmol.L-1 x mo-1).(ABSTRACT TRUNCATED AT 250 WORDS)