Serum thyroxine and triiodothyronine responses to cold in man

Abstract

Total serum thyroxine (T4) and triiodothyronine (T3) concentrations became measurable only recently. This chapter presents an experiment that was done to examine the serum thyroxine and triiodothyronine responses to cold in man. In the experiment, four volunteers stayed in the cold room for four days. Average room temperature was 6–6°C. Serial blood samples were taken before the experiment, at 0, 6, 12, 24, 48, 72, and 96 hours during the cold. Further samples were taken two and six days after the cold exposure. T4 was estimated by a competitive protein binding method using thyroxine-binding globulin (TBG) and T3 by a radioimmunoassay in unextracted serum, using 8-analino-l-naphthalene sulfonic acid, to block TBG. There were significant increases during the cold in the levels of total serum T4, T3 concentrations, and the free thyroxine index (FT4I). There were also significant decreases in these parameters from the cold to the postexposure period.