Cell proliferation, differentiation and transformation in the rat submandibular gland during early postnatal growth. A quantitative and morphological study.

The development of the submandibular gland of the rat was studied between days 2 and 55 of the postpartum. Besides confirming previous ultrastructural findings wer observed at the electron microscope that the architecturally complex terminal tubules, proacinar, acinar and striated duct cells retained mitosis the major ultrastructural features they exhibited in interphase. The ultrastructure of cells that were in the S period of the proliferative cycle was evaluated in high resolution autoradiographs from rats injected with thymidine-H3. All cell types were thus studied and no obvious cytoarchitectural modifications could be detected in these cells preparing for dividion. We obtained ultrastructural evidence that between days 20 and 30 some terminal tubule cells undergo transformation into acinar cells. The intercalated duct cells showed the highest rate of proliferation and the lowest daily increment in number. This suggests that cells from the intercalated ducts migrate to the neighboring morphological compartments. Quantitative data on the rate of cell proliferation and accumulation in the straited duct indicated that cells from the intercalcated ducts should differentiate into straited duct cells. Differentiation of intercalated duct cells into the terminal tubule cells was observed with the electron microscope.