Human Growth Hormone Secretion in Responses to Cold and Heat

Abstract

Secretion of growth hormone (hGH) in response to cold and heat has been studied in normal adult subjects aged 21 to 38 years (2 males and 4 females) exposed to 4°C for 1 or 2 h. Body temperature decreased to less than 34°C in all cases. The serum level of Cortisol increased from 18.4 to 23.8 μg/100 ml in one subject, but changed little in the others. FFA increased progressively to 113%, 136%, 226%, and 268% of the initial value in four of the subjects. Levels of hGH did not change or decrease during cooling, but increased from less than 1.1 ng/ml to more than 4.2 ng/ml (7.48 ± 4.13 ng/ml) on rewarming. Figure 1 shows a typical pattern of hGH secretion during and after cold exposure. An insulin tolerance test at a dose of 0.05 U/kg of body weight was performed on the two male subjects during cold exposure. hGH values reached maxima of 32 and 7 ng/ml in the two subjects. Two female subjects were given 20 mg of propranolol orally and then exposed to cold air for 1 h. FFA changed little throughout the test. Levels of hGH did not increase during cooling, but increased from 1.7 and 2.2 to 9.5 and 6.8 ng/ml, respectively, on rewarming. There were no significant changes in hGH levels in control subjects held at room temoerature (Okada et al., 1970).

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