Cell population growth in the rat parotid gland during postnatal development.

The growth kinetics of different cell populations in the rat parotid was studied. The evolution of the frequency and absolute number of each cell type was determined morphometrically by a particle-counting method and the evolution of the [(3)H]thymidine labeling indices of the same cell types was determined by autoradiography. The data obtained for the evolution of cell number in each gland compartment, i.e. acini, intercalated ducts, striated ducts and stroma, were adjusted by exponential equations, permitting estimation of the effective cell accumulation rate in the compartment for each population, i.e. the mean population duplication time (T(D)). In addition, the cell production rate in each gland compartment was determined using the mean labeling index for the period studied and a mathematical estimation of the mean cell generation time (T(G)), assuming an exponential growth pattern for the acinar, intercalated duct and striated duct populations during the period from 5 to 20 days of postnatal development. Analysis of the relation between effective cell accumulation (T(D)) and presumed cell production (labeling index and T(G)) for each intralobular parenchymal compartment of the rat parotid during this period suggests that the proliferative activity of the acinar cell population was sufficient to guarantee marked growth of its compartment and provided cells that presumably dedifferentiated into intercalated duct cells, whereas cells produced in the intercalated duct compartment migrated to, and differentiated into, cells of the striated duct compartment.