Immunoreactivities for chromogranin A and B, and secretogranin II in the guinea pig entero-endocrine system: cellular distributions and intercellular heterogeneities.

The family of the chromogranin/secretogranin proteins consists of three major subtypes: chromogranin A (CgA), chromogranin B (CgB) and secretogranin II (SgII). These proteins are present in various endocrine cells and organs. Using immunohistochemistry on serial semithin sections, we have investigated ten endocrine cell types of the guinea pig gastro-intestinal tract for their content of chromogranin/secretogranin proteins. The gastrin cell was the only cell type containing immunoreactivities for all three chromogranin subtypes. The majority of entero-endocrine cells showed immunoreactivities for CgA and SgII. Somatostatin cells lacked immunoreactivities for any of the chromogranins. Moreover, the densities of the corresponding immunoreactivities varied among the different endocrine cell types or even among endocrine cells of a given population. Aminergic endocrine cells (e.g., enterochromaffin and enterochromaffin-like cells) regularly exhibited strong immunoreactivities for CgA but failed to react for SgII. In peptidergic endocrine cells, the immunoreactivities for both CgA and SgII ranged from dense to faint. This was also true for CgB in gastrin cells. Hence, only CgA and SgII can be considered as regular constituents of entero-endocrine cells. The intercellular differences in immunoreactivities for all three chromogranin subtypes indicate that every endocrine cell has its own composition of chromogranin/secretogranin proteins. This may be due to differences in the regulation of biosynthesis or processing of the chromogranins in individual endocrine cells; this in turn might be related to the functional states of endocrine cells.