Growth hormone release in man induced by galanin, a new hypothalamic peptide

Galanin, a 29-aminoacid neuropeptide, was infused for 60 min into healthy volunteers at 7.8 pmol/kg/min (n = 4) or 33.2 pmol/kg/min (n = 6). During the infusion there was no change in heart rate or blood pressure and the only symptoms were a transitory bitter taste and slight hypersalivation. Plasma growth hormone levels rose during the high-dose galanin infusion from 2.8 +/- 0.8 mU/l to a mean peak of 48.5 +/- 19.8 mU/l; prolactin levels rose from 176 +/- 33 mU/l to 274 +/- 33 mU/l. A significant rise in growth hormone also occurred with the low-dose infusion (2.5 +/- 1.1 mU/l to a mean peak of 23.5 +/- 6.6 mU/l). There was no change in cortisol, thyroid-stimulating hormone, follicle-stimulating hormone, or luteinising hormone at either dose. 20 min after the start of the infusion a 25 g glucose bolus was given intravenously. Galanin reduced glucose clearance without significantly affecting plasma insulin concentrations. Pancreatic polypeptide levels were suppressed by the galanin infusion but levels of glucagon and gastric inhibitory peptide were unchanged.