NOCTURNAL WAKEFULNESS INHIBITS GROWTH-HORMONE (GH)-RELEASING HORMONE-INDUCED GH SECRETION

Recent studies have suggested that spontaneous release of GH as well a s GH secretion stimulated by exogenous GHRH are influenced by central nervous mechanisms that regulate sleep and wakefulness. Here, the effe ct of nocturnal wakefulness on GH secretion stimulated by iv administr ation of GHRH was examined in two experiments in healthy men. On all n ights, GHRH (1 mu g/kg BW) was injected after the subjects had slept f or about 2.5 h to minimize interference of endogenous release of GH du ring early sleep with the response to exogenous GHRH. Both experiments included a control condition to assess GH secretory responses to GHRH during undisturbed sleep and an experimental condition to assess the effect of wakefulness. In the control conditions, subjects slept throu ghout the night, and GHRH was administered 170 min after sleep onset. In the experimental condition of Exp I (n = 10), subjects were awakene d 150 min after sleep onset and stayed awake. GHRH was given 20 min af ter awakening. In the experimental condition of Exp II (n = 8), subjec ts mere awakened 30 min after GHRH treatment, which was administered 1 70 min after sleep onset. GHRH administrations during sleep fell into epochs of stage 2 sleep or rapid eye movement sleep. GH secretion and sleep characteristics before GHRH administrations were comparable for experimental and control conditions of both experiments. GH secretory responses were inhibited when the subject was awake at the time of GHR H administration compared to GH responses during undisturbed sleep. Aw akening the subject 30 min after GHRH administration abruptly interrup ted the initiated GH secretory response. The results demonstrate a pro found inhibitory effect of nocturnal awakenings on GHRH-induced GH sec retion. They indicate that the GH secretory response to GHRH is strong ly determined by central nervous system sleep-wake activity.