Developmental changes of sugar residues and secretory protein in mucous cells of the early postnatal rat parotid gland

Mucous cells have been identified in the terminal portions of the early pos tnatal parotid gland in human and rat, although mature parotid gland acini are composed of serous cells or seromucous cells. Previously, Ikeda et al, demonstrated that mucous cells are present in the rat parotid gland on days 1 to 8 after birth and that the secretory granules within these mucous cel ls share some histochemical characteristics with mature serous cells. Howev er, it is still not clear whether the mucous cells change into serous cells as the gland develops. The purpose of this study was to determine whether the mucous cells that appear in the early postnatal rat parotid gland chang e into serous cells. Parotid glands were obtained from male or female Wistar rats (aged 0-14 day s and adults). Fixed tissue sections were reacted with soybean agglutinin ( SBA) and wheat germ agglutinin (WGA) to detect glycoconjugates, or were sta ined using an anti-neonatal submandibular gland protein B1 (SMG-B1) antibod y to identify serous acinar cells. The sections were observed by transmissi on electron microscopy. Electron microscopy revealed that cells with characteristics intermediate b etween those of mucous and serous cells (transitional cells) appeared aroun d day 8 and that the nuclei of these cells did not show chromatin condensat ion, a characteristic of apoptotic cells. Lectin histochemistry showed that the mucous cells had the same sugar residues as the serous cells, which ap peared after day 10. Immunohistochemistry with an anti-SMG-B1 antibody gave a positive reaction not only in the cells with highly electron-dense granu les but also in the electron-dense cores of bipartite or tripartite granule s in the transitional cells. Cells with morphological characteristics intermediate between those of muco us and serous cells (transitional cells) appearing in the early postnatal r at parotid gland begin to produce B1-immunoreactive protein common to serou s acinar cells during development of the gland. Anat Rec 255:155-161, 1999. (C) 1999 Wiley-Liss, Inc.