EVIDENCE THAT GALANIN IS A PARASYMPATHETIC, RATHER THAN A SYMPATHETIC, NEUROTRANSMITTER IN THE BABOON PANCREAS

To determine whether galanin is a pancreatic sympathetic neurotransmit ter regulating insulin secretion in the baboon, as it is in the dog, w e evaluated galanin for inhibitory effects on insulin secretion in con scious baboons, determined if baboon pancreatic islets are innervated by galaninergic fibers using immunohistochemistry, and measured galani n content in the major sympathetic ganglion supplying the pancreas. Su rprisingly, infusion of galanin (1 mu g/kg per min) had no effect on a rginine-stimulated secretion of either insulin (71 +/- 14 vs. 88 +/- 1 7 mu U/ml; P = NS) or glucagon (104 +/- 12 vs. 94 +/- 9 pg/ml; P = NS) . By contrast, growth hormone secretion was markedly increased during galanin infusion. In the baboon celiac ganglion, no galanin immunoreac tivity was detectable in sympathetic neuronal cell bodies by immunosta ining and their content of galanin-like immunoreactivity, determined b y radioimmunoassay, was only 3% of that in dog celiac ganglion (5.2 +/ - 0.8 vs. 158 +/- 13 pmol/g; P < 0.001). By contrast, galanin immunore activity was observed in many nerve fibers in the baboon exocrine panc reas and occasionally in baboon pancreatic islets. Moreover, galanin c ontent of the baboon pancreas was similar to that of dog (8.7 +/- 1.5 vs. 5.5 +/- 1.2 pmol/g; P = NS). The finding of galanin immunoreactivi ty in many neuronal cell bodies in baboon intrapancreatic ganglia sugg ests a parasympathetic source for these galaninergic fibers in the bab oon. Together these data demonstrate that galanin is likely to be a pa rasympathetic neurotransmitter in the baboon pancreas, without major e ffects on insulin or glucagon secretion.