Cell division of alveolar macrophages in rat lung following exposure to NO2

The purpose of this research was to study cell division of alveolar macrophages following exposure of rats to NO(2). Dividing cells were labeled with (3)H-TdR and studied for 12 hours after labeling. The kinetics of cell division were determined from a curve constructed from the percent of labeled mitotic figures. Dividing alveolar macrophages were localized in alveoli near the openings of terminal bronchioles. There were no morphologic differences observed between labeled and unlabeled macrophages. Estimates of the durations of the various phases of the cell cycle gave approximate values of: G(2), 1 hour; t(2), 1.8 hour; M, 2.8 hours; and S, 5.8 hours. This evidence, combined with that of others, is compatible with an interpretation for alveolar cell renewal in which marrow-derived cells enter the alveoli and become macrophages. While in the alveoli, the cells may divide and thus increase their numbers. Eventually the macrophages are extruded from the alveoli. Alveolar macrophages were classified as a dividing, transient renewing cell population.