On the effects of human galanin in man.
Human galanin was recently isolated and sequenced and was found to differ from porcine galanin, hitherto used for studies in humans, in several important respects. We therefore synthesized and purified human galanin and infused it i.v. at a rate of 74 pmol.kg-1.min-1 into six healthy volunteers for 60 min during a hyperglycaemic clamp. The clamp was achieved by i.v. infusion of glucose at a rate which in a control experiment had been demonstrated to maintain the plasma glucose level at 12-13 mmol/l for 90 min. Galanin concentrations reached a plateau of approximately 1500 pmol/l throughout the infusion as opposed to pre-infusion and control levels of 20-30 pmol/l. The glucose levels obtained in the two experiments were indistinguishable. Plasma levels of C-peptide and insulin increased significantly in both experiments and the dynamic concentration curves were almost identical. Glucagon concentrations in plasma decreased significantly and similarly. Growth hormone levels, however, increased eight-fold during galanin infusions. Galanin was eliminated from plasma with a half-life of 3.7 +/- 0.4 min, similar to that of porcine galanin. It is concluded that human galanin powerfully stimulates growth hormone secretion in man, but has no effect on pancreatic endocrine secretion or glucose metabolism in the concentrations obtained in this study.