The effect of heating and central cooling on serum TSH, GH, and norepinephrine in resting normal man

The effects of central cooling and exterior heating on serum concentrations of thyrotropin (TSH), growth hormone (GH), and norepinephrine were studied in 10 normal males under resting conditions. Cooling was induced by ingestion of ice while the subjects were immersed in water of a temperature prone to elicit only minor cutaneous thermal reflexes. TSH and thyroid hormones changed neither during cooling nor during heating. Cooling induced a virtually complete suppression of GH-secretion whereas heating had the opposite effect: pronounced increase, also without previous cooling. Plasma norepinephrine rose by a factor of 2.5 and 1.7 during cooling and heating, respectively. It is concluded that the pituitary-thyroid system does not take part in short-term thermoregulation in man--as opposed to the situation in some smaller mammals. The mechanisms and the physiological role of the GH-responses to cooling and heating are as yet unknown, but the latter stimulus is an advantageous tool in clinical and pathophysiological studies of pituitary function as it is both safe and convenient.