This study investigates the short-term effects of pulsatile cortisol administrations upon sleep electroencephalogram (EEG) and spontaneous release of growth hormone (GH) in humans. Ten young healthy male volunteers received intravenous injections of either placebo or cortisol every 60 min between 17.00 hours and 06.00 hours (1 mg kg-1 BW with a loading dose of 20% starting at 17.00 hours, followed by a dose of 6% every hour until 06.00 hours). The amount of rapid eye-movement (REM) sleep was significantly reduced (placebo: 19.9 +/- 1.8; cortisol: 12.2 +/- 1.5%; P <0.05), whereas the time spent in slow-wave sleep (SWS) was significantly increased (placebo: 9.4 +/- 1.6; cortisol: 13.9 +/- 1.9%; P <0.05). The SWS-promoting effect was most prominent during the first hours of sleep, but tended to persist also during the second half of the night. The pulsatile cortisol administration augmented the total amount of plasma GH concentrations (mean area under the time course curve, AUC, placebo: 3.2 +/- 0.5; cortisol: 4.4 +/- 0.6 [ng x 1000 x ml min-1]; P <0.05) due to an increase of GH release before sleep onset, and during the second half of the night, while the GH surge at sleep onset remained unchanged. Our data are in accordance with the hypotheses that cortisol-induced changes of both sleep-EEG and GH secretion involve a common mechanism that includes activation of the hypothalamic-somatotrophic (growth hormone releasing hormone-growth hormone) system.
