Reciprocal changes in serum concentrations of triiodothyronine and reverse triiodothyronine between summer and winter in normal adult men.

Abstract

Serum concentrations of thyroxine (T4), 3, 5, 3'-triiodothyronine (T3), 3, 3', 5'-triiodothyronine (reverse T3, rT3), thyronine-binding globulin (TBG), thyroid stimulating hormone (TSH) and cortisol in summer and in winter were compared in carefully selected normal adult men (aged 30-49 yr); 107 people from Sapporo (58 in summer and 49 in winter) and 15 hospital workers.A modest but significantly higher serum T3 concentration was recorded in winter than in summer, while T4, TSH, TBG and cortisol levels were similar in both seasons. Serum rT3 concentration in the Sapporo subjects was slightly higher in summer than in winter but difference was not statistically significant.However, a paired analysis of rT3 concentration in the hospital workers had significantly higher levels in summer than in winter, showed a significant rise in the rT3 to T3 ratio in summer compared to winter. These results were not likely to be due to changes in TBG, cortisol and hematocrit values. The present findings and our previous report on a similar TSH response to thyrotropin-releasing hormone in summer and in winter, indicate that the changes in thyroid hormone metabolism rather than in thyroidal secretion would, at least partly, be responsible for the reciprocal alteration in T3 and rT3 concentrations.

Alterations in the Hypothalamic‐pituitary‐thyroid Axis After Prolonged Residence in Antarctica

“…They concluded that this indirectly reflected an increased serum level of T4. However, in contrast to this and in agreement with our data, other investigators have shown no change in serum T4 in euthyroid or hypothyroid subjects during seasonal exposure (Konno, 1980;Konno & Morikawa, 1982). In a continuously high altitude and cold exposed mountaineering group, Mordes et al. (1 983) demonstrated higher levels of serum total T4, free T4 and free T4 index compared to control vaiues.…”

Normal thyrotrophin response to intravenous thyrotrophin releasing hormone administration: the best index of optimal L-thyroxine therapy in primary hypothyroidism

“…This discrepancy in TSH regulation between the previous reports and our study may be because the adequacy of therapy was established by normal TSH response to TRH administration in this study rather than normalization of basal TSH alone. This finding is consistent with previous reports of lack of seasonal variation in TSH response to TRH administration in normal subjects (Konno, 1978;Konno, 1980).…”

Seasonal variations in TSH serum levels in athyreotic patients under L‐thyroxine replacement monotherapy

“…In our study, we observed steady TSH and thyroid hormone values in euthyroid subjects during different months of the year. Even after comparing the coldest (December to March) to the hottest (June to September) months of the year, no significant change in TSH and thyroid hormone median values was observed except for a small increase in FT3 values (+2.9%, P <.01, Table ) during winter, an observation already reported in other temperate climate areas . Whether this is the consequence of increased thyroid gland T3 production or increased peripheral T4 to T3 conversion during the cold season is not clear …”