Peptide YY: a neuropeptide in the gut. Immunocytochemical and immunochemical evidence.

Peptide YY immunoreactivity was detected in neuronal elements in the upper digestive tract of the rat, cat, ferret and pig by immunocytochemistry and radioimmunoassay combined with high-performance liquid chromatography. The two peptide YY antisera used do not recognize the related peptides neuropeptide Y and pancreatic polypeptide. In the rat peptide YY-immunoreactive nerve fibres were virtually restricted to the stomach smooth muscle of the minor curvature where they were numerous. Peptide YY-immunoreactive nerve cell bodies occurred in small ganglia on the serosal surface of the minor curvature. In the cat and ferret peptide YY-immunoreactive nerve fibres occurred in the circular smooth muscle layer of both the minor and major curvatures of the stomach and also in the upper small intestine; such fibres were numerous also in myenteric ganglia in these regions. In the pig, they were few but had roughly the same distribution as in the cat and ferret, except that they were quite numerous in thick muscle bundles close to the oesophagogastric junction. The presence of peptide YY-immunoreactive nerve cell bodies within the myenteric ganglia along the upper digestive tract of cat, ferret and pig, and in serosal ganglia of the rat stomach, indicates that at least some of the peptide YY-immunoreactive fibres demonstrated originate in or close to the gut wall. Double-staining experiments revealed that virtually all peptide YY-containing neurons and nerve fibres were distinct from those storing neuropeptide Y. Peptide YY-immunoreactive endocrine cells were encountered not only in the lower intestines but also in the stomach of the four species studied. In the antrum such cells were numerous and constituted a subpopulation of the gastrin-containing cells. In the oxyntic mucosa they were few and contained somatostatin. Radioimmunoassay revealed peptide YY-like peptides in gastric mucosa and smooth muscle from the upper digestive tract of all four species examined. The results of high-performance liquid chromatography suggest that the peptide YY-like material in the upper digestive tract is distinct from neuropeptide Y and pancreatic polypeptide and identical with authentic peptide YY except in the antral mucosa where only a small proportion of the peptide YY-immunoreactive material eluted like authentic peptide YY.