EVIDENCE AGAINST A ROLE FOR THE GROWTH HORMONE-RELEASING PEPTIDE AXISIN HUMAN SLOW-WAVE SLEEP REGULATION

A complex interrelationship exists between sleep and somatotropic acti vity. In humans, intravenous injections of growth hormone-releasing ho rmone (GHRH) given during sleep consistently stimulate slow-wave (SW) sleep, particularly when given in the latter part of the night. In the present study, the possible somnogenic effects induced under similar conditions by GH-releasing peptide (GHRP) were investigated in seven y oung healthy men. Bolus intravenous injections of GHRP-2 (1 mu g/kg bo dy wt) or saline, in randomized order, were given after 60 s of the th ird rapid-eye-movement period. All GHRP injections were immediately fo llowed by transient prolactin elevations and by GH pulses of a magnitu de within or around the upper limit of the physiological range. Except for a nonsignificant tendency to increased amounts of wakefulness dur ing the 1st h after the injection, no effects of GHRP-2 administration on sleep were detected. There was in particular no enhancement of SW sleep. Thus, in contrast to GHRH, late-night single injections of GHRP -2 at a dosage resulting in similar GH elevations have no stimulatory effects on SW sleep. The present data provide evidence against the inv olvement of the GHRP axis in human SW sleep regulation.