The effect of heating and central cooling on serum TSH, GH, and norepinephrine in resting normal man.
Level 4 - case-series / case-control
Small non-randomized physiological intervention study (pre-post challenge)
PubMed 6858704 · doi:10.1111/j.1748-1716.1983.tb07176.x
What was done
Ten healthy resting males underwent central cooling (induced by ice ingestion while immersed in water temperature chosen to elicit only minor cutaneous thermal reflexes) and exterior heating. Researchers measured serum concentrations of thyrotropin (TSH), thyroid hormones, growth hormone (GH), and plasma norepinephrine.
What was found
TSH and thyroid hormones did not change during cooling or heating. Cooling induced virtually complete suppression of GH secretion, whereas heating caused a pronounced increase in GH secretion (including without prior cooling). Plasma norepinephrine rose by a factor of 2.5 during cooling and 1.7 during heating. Absolute baseline and post-intervention concentrations were not provided in the abstract.
Why it matters
The findings demonstrate that the human pituitary-thyroid axis does not participate in acute thermoregulation, unlike in some smaller mammals, while external thermal stress substantially modulates growth hormone and sympathetic tone.
Limits
The sample size was very small (n=10) and restricted to males. The abstract does not report baseline hormone values, exact temperatures, variability, or formal statistical significance metrics.
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