Gastrin releasing peptide (GRP) is known to stimulate pancreatic enzym
e and islet hormone secretion. In the present immunohistochemical stud
y, 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 nume
rous nerve fibers diffusely distributed to the exocrine pancreas, but
was not seen in intrapancreatic nerve cells of normal pancreatic speci
mens examined. Nerve fibers and terminals with GRP-LI were found in ab
undance around pancreatic acini and capillaries, with moderate density
around ductules and in the walls of arterioles, and a few were seen i
n islets. This distribution pattern was quite similar to that of vasoa
ctive intestinal polypeptide (VIP)-LI nerve fibers. The study, using t
he antibody elution method, strongly suggests the co-localization of G
RP- and VIP-LIs within a part of VIP-containing nerve fibers. In the c
hronic pancreatitis specimens, neurons with GRP-LI were frequently fou
nd, and >90% of intrapancreatic nerve cells were VIP-immunoreactive. I
mmunostainings for GRP and for VIP on serial adjacent sections of intr
apancreatic ganglia from chronic pancreatitis specimens suggested the
co-localization of the two immunoreactivities in >70% of intrapancreat
ic neurons. The present findings may provide a morphological basis for
neurotransmitter and/or neuromodulator roles of GRP in the human panc
reas.