Neurons containing gastrin releasing peptide-like immunoreactivity in the human pancreas

Gastrin releasing peptide (GRP) is known to stimulate pancreatic enzyme and islet hormone secretion. In the present immunohistochemical study, the localization and distribution of GRP-like immunoreactivity were investigated in the human pancreas using two antisera with different specificities. GRP-like immunoreactivity (GRP-LI) was observed in numerous nerve fibers diffusely distributed to the exocrine pancreas, but was not seen in intrapancreatic nerve cells of normal pancreatic specimens examined. Nerve fibers and terminals with GRP-LI were found in abundance around pancreatic acini and capillaries, with moderate density around ductules and in the walls of arterioles, and a few were seen in islets. This distribution pattern was quite similar to that of vasoactive intestinal polypeptide (VIP)-LI nerve fibers. The study, using the antibody elution method, strongly suggests the co-localization of GRP- and VIP-LIs within a part of VIP-containing nerve fibers. In the chronic pancreatitis specimens, neurons with GRP-LI were frequently found, and > 90% of intrapancreatic nerve cells were VIP-immunoreactive. Immunostainings for GRP and for VIP on serial adjacent sections of intrapancreatic ganglia from chronic pancreatitis specimens suggested the co-localization of the two immunoreactivities in > 70% of intrapancreatic neurons. The present findings may provide a morphological basis for neurotransmitter and/or neuromodulator roles of GRP in the human pancreas.