Nocturnal ghrelin levels--relationship to sleep EEG, the levels of growth hormone, ACTH and cortisol--and gender differences

Ghrelin, an endogenous ligand of the growth hormone (GH) secretagogue receptor, stimulates sleep, appetite and weight gain as well as the secretion of GH, adrenocorticotropic hormone (ACTH), cortisol in humans and rodents. The interaction between nocturnal ghrelin levels, sleep EEG and the secretion of these hormones was not investigated systematically so far. Furthermore conflicting data exist on gender differences in nocturnal ghrelin secretion. We examined simultaneously sleep EEG and the nocturnal levels of ghrelin, GH, ACTH and cortisol in young and middle-aged normal human subjects (eight males, eight females). A significant interaction between gender and the course of ghrelin concentration was observed to the interval between 20:00 and 23:00 hours. In males a continuous increase of ghrelin levels before sleep onset was found. In females, however, a rise of ghrelin during the night was missed. We found a trend suggesting a lower time spent in stage I sleep in subjects with high nocturnal ghrelin levels. Other systematic interactions between plasma ghrelin, sleep EEG and other hormones were not found. No peak in plasma ghrelin levels resembling the GH surge was observed. We suggest that under naturalistic conditions plasma ghrelin levels show no distinct interaction with sleep.