Distribution of a novel peptide in the anterior pituitary, gastric pyloric gland, and pancreatic islets of rat.

We used Western blot and immunohistochemical methods to investigate the biochemical characteristics and cellular distribution of a novel peptide (peptide 23) that was previously shown to be released from anterior pituitary cells of rat in response to growth hormone-releasing hormone. In the pituitary, peptide 23 isolated from intact cells had an Mr of 31,000, whereas that released into culture medium had an Mr of 16,000. Pancreatic islets contained a 19 KD form of the peptide. Immunohistochemically, peptide 23 in the rat pituitary gland was localized in a subpopulation of somatotropes. In pancreatic islets, the peptide was found by triple immunofluorescence labeling to be present in both insulin- and somatostatin-containing cells. In the gastrointestinal tract, peptide 23 was found only in a subpopulation of endocrine cells in the pyloric glands. This subpopulation of cells was found to be entirely separate from those containing either serotonin or somatostatin, and may represent one of the other known or as yet biochemically uncharacterized cell types in this gland. The results suggest that in response to secretagogues in vitro, an altered form of the peptide is secreted from pituitary cells and that an intracellular form of peptide 23 is expressed in some but not all somatotropes, a large proportion of islet cells, and a distinct population of pyloric cells.