Chromogranins in mammalian GEP endocrine cells: their distribution and interrelations with co-stored amines and peptides.

Chromogranins (Cg) are large acidic proteins, co-stored with amines or peptides in the secretory granules of a wide variety of paraneurons. By immunohistochemistry performed on serial semithin sections, the distribution of Cg in the gastroenteropancreatic (GEP) system was analyzed in the endocrine pancreas of 10 mammalian species and in enteroendocrine cells of 6 species. Of the Cg families, CgA is primarily localized in GEP endocrine cells. CgA was regularly present in amine containing cells (EC and EC-like cells). In 11 other endocrine cell types, CgA-immunoreactivities showed inter-species and intra-species variations in their distribution or in the intensity of staining. However, no endocrine cell type lacked CgA-immunoreactivities in all species investigated. Findings from extended studies indicate that CgA is involved in the intracellular storage of resident amines, and in the storage of newly formed amines after exogenous application of the corresponding precursors. Finally, densitometric findings on possible reciprocal relationships between CgA- and peptide-immunoreactivities suggest that CgA also participates in the intragranular storage of peptide hormones in certain GEP endocrine cells.