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

Abstract

ABSTRACT In five healthy normal male volunteers, pretreatment with the cholinergic muscarinic antagonist pirenzepine (30 mg i.v.) almost abolished the growth hormone (GH) response to a maximal dose (120 μg i.v.) of growth hormone-releasing hormone (GHRH) (GH response at 40 min 5.6 ± 1.3 mU/l with GHRH and pirenzepine vs 40.8 ± 5.3 mU/l with GHRH alone, P <0.02). Concomitant 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 ± 10.5 mU/l, P <0.001 vs GHRH and pirenzepine, P <0.02 vs GHRH alone). Previous studies have proposed that cholinergic pathways control GH release via samatostatin and this study suggests that galanin may act by modulating hypothalamic somatostatinergic tone either directly or, possibly, by facilitating cholinergic neurotransmission.