Pancreatic and extrapancreatic galanin release during sympathetic neural activation

To address the hypothesis that the neutropeptide, galanin, functions as a sympathetic neurotransmitter in the endocrine pancreas, we sought to determine if galanin is released from pancreatic sympathetic nerves during their direct electrical stimulation in halothane-anesthetized dogs. During bilateral thoracic splanchnic nerve stimulation (BTSNS), both peripheral arterial and pancreatic venous levels of galanin-like immunoreactivity (GLIR) increased (delta at 10 min = +92 +/- 31 and +88 +/- 25 fmol/ml, respectively). Systemic infusions of synthetic galanin demonstrated that 1) the increment of arterial GLIR observed during BTSNS was sufficient to modestly restrain basal insulin secretion and 2) only 25% of any given increment of arterial GLIR appears in the pancreatic vein, suggesting that the pancreas extracts galanin, as it does other neurotransmitters. By use of 75% for pancreatic extraction of circulating galanin, it was calculated that pancreatic galanin spillover (output) increased by 410 +/- 110 fmol/min during BTSNS. To reinforce the conclusion that pancreatic sympathetic nerves release galanin, GLIR spillover was next measured during direct local stimulation of the pancreatic sympathetic input produced by electrical stimulation of the mixed autonomic pancreatic nerves (MPNS) in the presence of the ganglionic blocker, hexamethonium. During this local pancreatic sympathetic nerve stimulation, arterial GLIR remained unchanged, but pancreatic venous GLIR increased by 123 +/- 34 fmol/ml. Thus pancreatic GLIR spillover increased by 420 +/- 110 fmol/min during MPNS in the presence of hexamethonium. We conclude that galanin is released from both pancreatic and extrapancreatic sources during sympathetic neural activation in dogs.