Postnatal Growth and Differentiation of the Salivary Gland

In order to determine the postnatal proliferation potential of the salivary gland cells, we labeled the rat submandibular gland with Brdu (5-bromo-2-deoxyuridine). We detected cells in the proliferation cycle and examined populational changes of cell types during a period of 98 days after birth. BrdU labeling was observed in all segments of the gland: ductal, terminal tubule, myoepithelial and acinar cells. Acinar cells, ductal cells, and myoepithelial cells, characterized by S-100 protein positive cytoplasm, increased in number, and their final population reached approximately 60 and 30.9%, respectively. In contrast, terminal tubule cells, which could clearly be identified by their Masson's trichrome positive granules, occupied 43% of the whole gland at birth, decreased in ratio and disappeared at day 41. The results suggest that the salivary constituent cells with specific functions duplicate in their own locations through the postnatal growth of salivary glands, and that in the salivary gland there is no proliferating zone in which some reserve cells serve as multiple cell types. Based on these results, we have added discussion on oncogenetic pathways of salivary tumors