Nighttime plasma cortisol secretion and EEG sleep--are they associated?

Since the initial rise in plasma cortisol during sleep usually occurs near the second period of rapid eye movement (REM) sleep, a more precise association between the initial cortisol rise and electroencephalographic (EEG) sleep was examined in 22 normal control subjects. Our results indicate that the length of the total non-REM sleep period between the first and second REM period including awake time was significantly correlated to the cortisol rise time. However, the timing of the initial cortisol rise was not significantly related to the overall plasma cortisol levels during the night. But the second non-REM sleep period (minus awake time) is inversely related to overall cortisol levels during the night.