GALANIN ABOLISHES THE INHIBITORY EFFECT OF CHOLINERGIC BLOCKADE ON GROWTH HORMONE-RELEASING HORMONE-INDUCED SECRETION OF GROWTH HORMONE IN MAN

In five healthy normal male volunteers, pretreatment with the cholinergic muscarinic antagonist pirenze-pine (30 mg i.v.) almost abolished the growth hormone(GH) response to a maximal dose (120 pg i.v.) of growth hormone-releasing hormone (GHRH) (GH response at 40 min 5.6 \m=+-\1.3 mU/l with GHRH and pirenzepine vs 40.8 \m=+-\5.3mU/l with GHRH alone, P <0.02). Con-comitant i.v. infusion of galanin (40 pmol/kg/min) with pirenzepine not only restored but significantly potentiated the GH response to GHRH (GH at 40 min 72.2 \m=+-\10.5 mU/l, P <0.001 vs GHRH and pirenzepine, P <0.02 vs GHRH alone). Previous studies have pro-posed that cholinergic pathways control GH release via somatostatin and this study suggests that galan-in may act by modulating hypothalamic somatostatin-ergic tone either directly or, possibly, by facilitating cholinergic neurotransmission