Prenatal development of the palatine gland of rats

The present study aimed to elucidate the prenatal development of the rat palatine gland. Parasagittal 5 μm thick serial sections made from Wistar rats at embryonic days (E) 17 to 22 were stained with haematoxylin-eosin (HE), Alcian blue-Kernechtrot or immunohistochemistry for 5-bromo-2′-deoxyuridine (BrdU) as a marker of proliferating cells. Additionally, three-dimensional images of developing glandular parenchyma were reconstructed from serial HE sections with a personal computer. At E 17, several thickenings of the palatal epithelium had appeared which thereafter became the epithelial cords. Branching and lumenization commenced at E 20, and immature acini were observed at E 21. Three-dimensional reconstruction showed that the proximal part of the epithelial cord differentiated into the duct, and the distal part of the epithelial cord differentiated into the acinus. In immunohistochemical staining, there were many BrdU-positive cells in the epithelial cords including thickenings of the palatal epithelium, ducts, and acini. The BrdU labeling index of the cells of the epithelial cord was the highest (statistically significant) of the three in the primitive palatine gland. In conclusion, during the development of the rat palatine gland, epithelial cords with very high proliferative activity arise from the palatal epithelium, and then the proximal part of the epithelial cord differentiates into the duct, and the distal part of the epithelial cord differentiates into the acinus. Proliferation of these glandular parenchyma contributes to the growth of the developing palatine gland.