Cortisol Secretion Is Inhibited during Sleep in Normal Man*

Abstract

In order to test the hypothesis that cortisol secretion is inhibited during sleep, six healthy young men (ages 18–24) were studied in a 4-day protocol. A baseline nocturnal sleep period was followed by one night's total sleep deprivation, then sleep at 180° phase shift, and then return to a normal nocturnal sleep episode (SP-3). Plasma cortisol concentrations were measured every 20 min (obtained by an indwelling venous catheter), rectal temperature was measured every minute, and sleep was polygraphically defined. During the first 4 h of sustained sleep, cortisol secretion was decreased even when sleep occurred during a time when the subject was usually awake; conversely, it was elevated if awake at the usual daily time of sleeping. This was not the case for the last 4 h of sleep. Body temperature was also decreased but during each entire 7-to8-h sleep period. Meals produced only a small brief rise of cortisol and produced no change in body temperature. Stage 4 sleep was increased during the 180° inverted sleep episode and decreased during SP-3. REM sleep however was increased during SP-3. A reciprocal relationship was found between REM and stages 3 and 4 for the second, third, and fourth, and sixth h of sleep for SP-3. These results demonstrate the inhibitory effect of the behavioral complex of sleeping on cortisol secretion superimposed on its endogenous circadian and ultradian rhythm. These neuro-physiological events may be used to entrain and time the period and phase of biological rhythms in relation to shift work, sleep deprivation, and transmeridian jet travel.