Serum 3,5,3'-triiodothyronine and 3,3',5'-triiodothyronine concentrations during acute heat load

Yoram Epstein, Raphael Udassin, Joseph Sack*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


To determine the changes in thyroid hormone metabolism during short periods of exposure to heat, 30 euthyroid healthy male volunteers (aged 23-40 yr) were placed in a climatic chamber for 2 h (35 C, 50% relative humidity). The subjects were at complete rest during the first hour and performed light work (40 watts) during the second hour. Blood samples for T4, T3, and rT3 were drawn at 0, 60, and 120 min. Rectal temperature and heart rate were monitored continuously. No significant changes in T4, T3, rT3, rectal temperature, or heart rate were observed after the first hour (basal levels, 8.5 ± 0.3 μg/dl, 160 ± 5 ng/dl, 14.5 ± 2.5 ng/dl, 37.2 ± 0.1 C, and 78 ± 8 beats/min, respectively; mean ± SEM). During the second hour, a significant rise in body temperature was recorded (38.5 ±0.1 C), accompanied by a significant decrease in mean serum T3 concentration and a rise in mean serum rT3 concentration. T4 concentration remained unchanged. Our findings suggest that, parallel to the elevation in body temperature, there is a shift in the conversion of T4 to the noncalorigenic rT3 metabolite rather than to T3.

Original languageEnglish
Pages (from-to)677-678
Number of pages2
JournalJournal of Clinical Endocrinology and Metabolism
Issue number5
StatePublished - Nov 1979
Externally publishedYes


Dive into the research topics of 'Serum 3,5,3'-triiodothyronine and 3,3',5'-triiodothyronine concentrations during acute heat load'. Together they form a unique fingerprint.

Cite this