Cb. Verchere et al., EVIDENCE THAT GALANIN IS A PARASYMPATHETIC, RATHER THAN A SYMPATHETIC, NEUROTRANSMITTER IN THE BABOON PANCREAS, Regulatory peptides, 67(2), 1996, pp. 93-101
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.