Interactions of sleep and clonidine on daytime prolactin secretion in humans

The suppressive roles of adrenergic stimulation and rapid eye movement (REM) sleep on human prolactin (PRL) secretion are controversial. We examined the effects of sleep, clonidine (an alpha 2-adrenergic agonist), and their interaction on PRL secretion. Two groups of normal men (nine each) were studied in two morning sessions. Each group received either placebo or clonidine in both sessions. Subjects remained awake in the first session and in the next session they were asked to sleep for 3 h after the test dose was given. Blood samples were drawn at 30-min intervals and polysomnographic recordings were obtained at each session. PRL concentrations remained at baseline and no clonidine effect was detected while awake. PRL concentrations increased in placebo and clonidine groups during sleep. Despite significant suppression of REM sleep in the clonidine group, no differences were detected between the placebo and clonidine groups in peak PRL or mean PRL concentrations during the study. Also, no significant difference was detected in comparing PRL responses during non-REM sleep in both groups. The results suggest that alpha 2-adrenergic stimulation does not have a significant role in modulating human PRL secretion during sleep.