Galanin was infused intravenously in 8 healthy volunteers at a dose of 40 pmol/kg.min for 1 h to investigate the pharmacologic effects of this peptide on postprandial gastrointestinal motility and gut peptide release in humans. Galanin strongly inhibited gastrointestinal motility. Gastric emptying was significantly delayed, with the time taken to empty 50% of the gastric contents increasing from 59.0 +/- 4.8 min (control infusion) to 99.3 +/- 4.7 min (galanin infusion). Mouth-to-cecum transit time increased from 67.5 +/- 6.9 to 126.3 +/- 18.5 min. Galanin potently suppressed the initial postprandial rise in plasma concentrations of glucose, insulin, peptide tyrosine tyrosine, neurotensin, enteroglucagon, pancreatic glucagon, somatostatin, and pancreatic polypeptide, but did not change gastric inhibitory polypeptide, motilin, peptide histidine methionine, and gastrin concentrations compared with control. The results indicate that an infusion of galanin has potent effects on the gastrointestinal tract in humans. The changes in motor activity in particular suggest that the local galaninergic innervation could have an important physiologic role in the control of human gastrointestinal propulsive motor activity.