Effects of growth hormone-releasing peptide-6 on the nocturnal secretion of GH, ACTH and cortisol and on the sleep EEG in man: role of routes of administration

This study investigated the effects of GHRP-6 on nocturnal hormone secretion and sleep architecture, comparing different routes of administration (intravenous and intranasal) in healthy male volunteers. The research used polysomnography combined with serial hormone measurements throughout the night to simultaneously capture neuroendocrine and sleep effects.

Intranasal GHRP-6 administration promoted a significant increase in GH concentration throughout the night, without the acute peaks observed with the intravenous route. There was also a trend toward increased ACTH in the first half of the night, consistent with GHRP-6 action on the hypothalamic-pituitary-adrenal axis, although cortisol levels did not show clinically relevant changes.

Regarding sleep architecture, intranasal GHRP-6 produced an increase in stage 2 NREM sleep in the second half of the night, without deleterious effects on slow-wave sleep (stage 3/4) or REM sleep. These findings suggest that GHRP-6 can modulate sleep without compromising its deeper restorative phases.

The authors concluded that the intranasal route of GHRP-6 offers a distinct pharmacological profile from the intravenous route, with more sustained release and more gradual neuroendocrine effects. These data are relevant for understanding the interaction between the somatotropic system and sleep regulation, and for the development of intranasal formulations of GH secretagogues.