Adrenocorticotropin-like and alpha-melanotropin-like peptides in a subpopulation of human gastrin cell granules: bioassay, immunoassay, and immunocytochemical evidence.

Adrenocorticotropin (ACTH)-like and alpha-melanotropin (alpha-MSH)-like peptides have been localized to a subpopulation of cytoplasmic (secretory) granules of human antropyloric gastric cells and of fetal and neoplastic gastrin cells. These granules also store gastrin and belong to the electron-dense variety of gastrin cell granules. Gastrin cells also contain granules of low to medium electron density; these store only gastrin and do not react with ACTH or alpha-MSH antisera. The alpha-MSH immunoreactive peptide was shown also to display alpha-MSH bioactivity by a combined immunosorbent-bioassay technique. This peptide cochromatographs with synthetic alpha-MSH in several systems and is not detected in oxyntic mucosa or in gastric muscle wall. As in the pituitary intermediate lobe, the alpha-MSH-like peptide may be formed by cleavage of ACTH-like peptides also in gastrin cells. These data provide additional evidence for local formation of ACTH/alpha-MSH-related peptides in gastrin cells and suggest a heterogenous peptide make-up of endocrine cell granules.