Stimulation of adrenal glucocorticoid secretion in man by raising the body temperature.

1. Plasma cortisol and corticosterone concentrations increased significantly in eleven resting, unacclimatized subjects after 2 hr exposure to an ambient temperature of 46 degrees C dry bulb, 36 degrees C wet bulb and in two subjects investigated by controlled elevation of body temperature in a hyperthermia test-bed.2. In the same experiments the urinary excretion of 17-hydroxycorticosteroids (17-OHCS) estimated as the 11-oxy and 11-deoxy fractions did not differ significantly in hot and in control conditions.3. Following an initial fall in plasma cortisol concentration during the first hour of heat exposure, cortisol levels increased in the second hour when body temperatures exceeded a ;critical' level of 38.3 degrees C. Two acclimatized subjects did not attain this body temperature even after 2 hr heating and showed no increase in plasma glucocorticoid levels.4. Sweat collected in arm bags, or by suction, in controlled hyperthermia experiments contained negligible amounts of cortisol (0.34-1.70 mug/100 ml. sweat).5. Changes in plasma cortisol specific activity after intravenous injection of 1,2[(3)H]cortisol indicated that the raised plasma concentration was brought about by increased adrenal secretion, though this was accompanied by more rapid removal of cortisol from the circulation in hot conditions. Excretion of tritium by the kidney was not significantly altered. It was not possible to determine whether changes in liver function contributed to the elevation of the plasma cortisol level but it was found that a larger proportion of cortisol was oxidized to cortisone, or to a metabolite closely resembling cortisone, in the heat.