M. Anlauf et al., Localization of xenin-immunoreactive cells in the duodenal mucosa of humans and various mammals, J HIST CYTO, 48(12), 2000, pp. 1617-1626
Xenin is a 25-amino-acid peptide extractable from mammalian tissue. This pe
ptide is biologically active. It stimulates exocrine pancreatic secretion a
nd intestinal motility and inhibits gastric secretion of acid and food inta
ke. Xenin circulates in the human plasma after meals. In this study, the ce
llular origin of xenin in the gastro-entero-pancreatic system of humans, Rh
esus monkeys, and dogs was investigated by immunohistochemistry and immunoe
lectron microscopy. Sequence-specific antibodies against xenin detected spe
cific endocrine cells in the duodenal and jejunal mucosa of all three speci
es. These xenin-immunoreactive cells were distinct from enterochromaffin, s
omatostatin, motilin, cholecystokinin, neurotensin, and secretin cells, and
comprised 8.8% of the chromogranin A-positive cells in the dog duodenum an
d 4.6% of the chromogranin A-positive cells in human duodenum. In all three
species, co-localization of xenin was found with a subpopulation of gastri
c inhibitory polypeptide (GIP)-immunoreactive cells. Immunoelectron microsc
opy in the canine duodenal mucosa demonstrated accumulation of gold particl
es in round, homogeneous, and osmiophilic secretory granules with a closely
adhering membrane of 187 +/- 19 nm diameter (mean +/- SEM). This cell type
was found to be identical to the previously described canine CIP cell. Imm
unocytochemical expression of the peptide xenin in a subpopulation of chrom
ogranin A-positive cells as wetI as the localization of xenin immunoreactiv
ity in ultrastructurally characterized secretory granules permitted the ide
ntification of a novel endocrine cell type as the cellular source of circul
ating xenin.