Elevation in Serum Thyroglobulin during Prolonged Antarctic Residence: Effect of Thyroxine Supplement in the Polar 3,5,3′-Triiodothyronine Syndrome

Abstract

Extended Antarctic residence (AR) is associated with an increase in serum TSH, a decrease in free T(4), and an increase in T(3) production and clearance. It is not clear whether these adaptations reflect changes in clearance alone or whether intrinsic thyroidal synthetic activity also changes. Thyroglobulin (Tg) secretion is an independent marker of intrinsic thyroid activity whose kinetics are independent of those of T(3) and T(4). In this study we examined changes in Tg levels in healthy subjects before and during AR and their responses to thyroid supplementation to help determine whether alterations in thyroid activity, and not just kinetics of clearance, underlie the changes seen with the polar T(3) syndrome. In cohort 1, we compared measurements of TSH and Tg in 12 subjects before deployment and monthly for 11 months during AR. In cohort 2, we compared the same measurements in 12 subjects monthly for 11 months of AR. Subjects were randomized to receive either placebo or levothyroxine in cohort 1 for 7 months and in cohort 2 for 11 months. Tg increased over baseline during the first 4 months of AR by 17.0 +/- 4.6% and after 7 more months by 31.7 +/- 4.3% over baseline in the placebo group of both cohorts (P < 0.0002). When L-T(4) was taken, Tg returned to a value not different from baseline (4.5 +/- 3.9%). The percent changes from baseline in serum TSH and Tg during AR were highly correlated (P < 0.00003) in the placebo group for both cohorts. The rise in Tg with TSH and the reduction in Tg with L-T(4) provide evidence of target tissue response to TSH and further confirm the TSH rise as physiologically significant. The results also suggest that the adaptive changes in thyroid hormone economy with AR reflect TSH-dependent changes in thyroid synthetic activity, which may help explain a portion of the increases in T(3) production found with AR.

Different adaptations of Chinese winter-over expeditioners during prolonged Antarctic and sub-Antarctic residence

“…*P < 0.05, Great Wall Station versus Zhongshan Station Palinkas et al 2007a;Levy et al 2013), FT4 of the Zhongshan Station crew decreased during the austral winter. Concurrently, TSH levels increased gradually until return to China, where they became statistically significant, suggesting the presence of Polar T3 Syndrome (Sawhney et al 1995;Do et al 2004). The declining levels of FT3 and FT4 prompt the hypothalamic-pituitary-thyroid (HPT) axis to produce more TSH to stimulate the increased availability of these two hormones.…”

Psychological Hibernation in Antarctica

“…Secondly, studies have shown cold-related changes in thyroid function in Antarctica, referred to as the polar triiodothyronine (T3) syndrome, characterized by an increase in serum TSH, a decrease in free T4, and an increase in T3 production and clearance. These changes have typically been associated with decreased mood and cognitive impairment ( Do et al, 2004 ; Chen et al, 2016 ). Thirdly, research across different confined and isolated contexts have suggested that psychological resilience is linked to the relative passage of time, and that a decrease tends to occur around the third quarter of the stay independent of the actual duration, as the participants realize that the mission is only half complete ( Bechtel and Berning, 1991 ).…”

Influence of Chronic Exposure to Cold Environment on Thyroid Gland Function in Rabbits

“…Increases in serum TSH levels have also been observed in infants and young children during surgical hypothermia [ 15 ] . Some studies have shown prolonged arctic residence leads the increase in TSH to be associated with an increase in thyroglobulin and T3 [ 16 ] . In addition, cold exposure in animals leads to enhanced thyroid hormonal secretion, degradation, and excretion.…”