Phylogenetic aspects of the occurrence and distribution of secretogranin II immunoreactivity in lower vertebrate gut.

A novel monoclonal antibody raised against bovine secretogranin II (Sg II) was used in immunohistochemical studies on amphibian (Rana esculenta), reptilian (Podarcis sicula) and avian (Gallus gallus) gut. Sg II immunoreactivity was detected in epithelial and nervous elements. Cells immunoreactive for Sg II were examined by double immunostainings to determine whether they might also co-store certain previously known bioactive amine/peptide substances. Almost all the endocrine cells immunoreactive for bombesin, substance P, neurotensin, gastrin/cholecystokinin, neuropeptide tyrosine (NPY) and calcitonin gene-related peptide as well as some of those immunostained for serotonin, histamine, and polypeptide tyrosine tyrosine (PYY) also contained Sg II. Sg II-immunoreactive cells varied in number and distribution according to regions of the gut and animal species. The number of Sg II immunoreactive granules notably varied not only according to cell type, but also within the same cell population. Many histamine-, calcitonin gene-related peptide (CGRP)-, substance P-, PYY-, and neurotensin-immunoreactive neurons also contained Sg II. These were mostly situated in the myenteric plexus; their distribution pattern varied among the three species. These findings show that, despite being well conserved during phylogeny, Sg II has a heterogeneous distribution.