Galanin: a novel pancreatic neuropeptide.

Immunofluorescent staining for galanin in canine pancreatic tissue was performed together with an evaluation of the effects of synthetic galanin on pancreatic output of glucagon, somatostatin, and insulin in pentobarbital-anesthetized dogs. A dense network of galaninlike immunoreactive nerve fibers was visualized in association with the islets of Langerhans and occasional galanin immunoreactive fibers were seen to course through the exocrine parenchyma of dog pancreas. During intravenous infusion of synthetic porcine galanin (25 pmol X kg-1 X min-1) pancreatic glucagon output rapidly doubled, and the output of both somatostatin and insulin decreased by 70%. Because arterial and pancreatic venous catecholamine levels remained unchanged, the effects on hormone secretion were not secondary to activation of the sympathetic nervous system. The direct pancreatic action of galanin was confirmed by infusing a peripherally ineffective dose of galanin (0.25 pmol X kg-1 X min-1) into the pancreatic artery, which also stimulated glucagon (+90%) and suppressed somatostatin (-50%) and insulin (-70%) release. The presence of galaninlike immunoreactive neurons in dog islets, together with the direct action of galanin on pancreatic hormone release, suggest that this recently discovered peptide could serve as an important neuromodulator of endocrine pancreatic function.