Potent effects of human galanin in man: growth hormone secretion and vagal blockade

Human galanin (hGAL) is a 30-amino acid neurohormone that has recently been shown to differ significantly from porcine and rat GAL. We investigated the endocrine and cardiovascular effects of hGAL in eight male volunteers. On three separate occasions, each received a 90-min infusion of saline, low dose (33 pmol/kg.min) and high (132 pmol/kg.min) dose hGAL, combined with an iv glucose bolus (to assess effects on insulin and GH release). hGAL was undetectable, 1.4 +/- 0.2 nmol/L, and 3.7 +/- 0.5 nmol/L during control, low dose, and high dose studies, respectively. The half-life of hGAL was 3.5 +/- 0.5 min. GH levels rose significantly in both studies (vs. control) and were not suppressed by hyperglycemia [low dose area under the curve (AUC), 1827 +/- 348 micrograms/min.L (P < 0.05); peak, 19.5 +/- 5.3 micrograms/L; high dose AUC, 1896 +/- 401 micrograms/min.L (P < 0.005); peak, 28.0 +/- 7.5 micrograms/L]. PRL levels rose significantly with the high dose study only (AUC, 12.8 +/- 1.1 micrograms/min.L; P < 0.01). FSH, LH, and catecholamine levels were unchanged. Glucose-stimulated insulin release was not inhibited. There was a dose-dependent increase in pulse rate and a profound decrease in sinus arrhythmia, but no change in blood pressure. These cardiovascular effects have not been reported with studies in humans using GAL of other species. We conclude that hGAL may play an important role in man in modulating GH secretion and cardiac vagal tone, but not insulin release.