NALOXONE AND METERGOLINE EFFECTS ON GROWTH-HORMONE RESPONSE TO GAMMA-HYDROXYBUTYRIC ACID

Gamma-hydroxybutyric acid (GHB) has been recently used in alcohol deto xification, but conflicting data are available concerning the central mechanism of action of this GABA catabolite. GHB ability to stimulate growth hormone (GH) secretion has been reported. Our previous studies revealed the ability of flumazenil (a benzodiazepine antagonist) to co unteract GHB effects on GH secretion. Other hypotheses, including an o pioid or serotonergic role of GHB, have been considered. In the presen t study we investigated GH responses to GHB with or without naloxone ( an opiate receptor antagonist) or metergoline (a serotonin receptor an tagonist) pretreatment. This study included 10 male healthy volunteers (aged 24.3 +/- 2.9 years) who were submitted to four tests in random order: (A) oral GHB administration; CB) oral GHB and i.v. naloxone adm inistration; (C) oral GHB and oral metergoline administration; and (D) oral placebo and i.v. saline administration. Blood samples for GH ass ay were collected during the three tests at -15, 0, 15, 30, 45, 60 and 90 min. GHB induced a significant increase in GH plasma levels; nalox one pretreatment did not antagonize GHB action on GH secretion; meterg oline significantly decreased GH response to GHB (p < 0.05). No change s were obtained with placebo and saline administration. The opioid sys tem does not seem to be involved in GHB effects on GH-secreting pituit ary cells; GHB effects on the serotonergic system influencing GH secre tion, on the other hand, cannot be excluded.