Responses of anterior pituitary hormones to heat exposure.

To determine anterior pituitary response to mild hyperthermia, plasma GH, ACTH, PRL and TSH were measured every 10 min in five subjects exposed to hot air (120 min, 50 C, 20 mbar) in a climatic chamber. Mean rectal temperatures increases of 0,8 C and mean sweat losses of 760 g were observed. GH levels increased from 4.4 +/- 0.4 ng/ml to 22.0 +/- 7.0 ng/ml (mean +/- SE) and reached maximum 80 min after the beginning of heat exposure and then declined before the end of the heat stress. These peak levels varied widely with the individual, whereas no significant changes in ACTH, PRL and TSH levels were observed during the exposure period. These results suggest that the mechanisms regulating GH secretion are more sensitive to an acute heat exposure than those of the other pituitary hormones studied.