Influences of partial REM sleep deprivation and awakenings on nocturnal cortisol release.

Decreasing endogenous plasma cortisol levels during rapid eye movement (REM) sleep have been recently reported, suggesting a diminished or absent secretory activity of the adrenals during this period. On the other hand, episodes of light sleep (Stage 1) and intermittent wakefulness have been found to be associated with increasing plasma cortisol levels. The present experiments in 10 adult men were designed to examine whether or not REM sleep inhibits adrenocortical activity and if short periods of wakefulness increase nocturnal cortisol release. Somnopolygraphic recordings were obtained from each subject under three experimental sleep conditions: a baseline night, an REM deprivation night in which the subject's sleep was disturbed contingent upon the occurrence of REM, and a control night in which sleep was disturbed both during REM deprivation and non-REM (NREM) epochs, i.e., mostly during Stage 2 sleep. This last condition was introduced to distinguish the effects of REM deprivation from those of arousals that may per se act as stressful stimuli for cortisol release. Contrary to expectation, we found that both REM sleep deprivation and arousals in NREM epochs reduced rather than enhanced mean plasma cortisol levels as compared with baseline conditions. These findings do not support the hypothesis of an inhibitory effect of REM sleep on cortisol secretion, though present data do not refute this hypothesis. The awakenings, or the light sleep subsequent to sleep disturbance, appear to have no stimulatory effect on adrenocortical secretion. Awakenings during sleep at night may even reflect the activity of mechanisms inhibiting sleep-related increases in plasma cortisol concentration.