Squamous metaplasia in organ cultures of vitamin A-deficient hamster trachea: cytokinetic and ultrastructural alterations.

Cytokinetic and morphologic studies were performed to elucidate the origin of epidermoid metaplasia in organ cultures of tracheas derived from vitamin A-deficient Syrian golden hamsters. Focal areas of squamous metaplasia were observed 2 days after explantation, and extensive epidermoid metaplasia and cornification were present in approximately 89% of the explants at day 10. During the first 2 days, both basal and mucous cells proliferated actively. By day 3, the total mucous cell [3H]thymidine labeling index (LI) had declined and remained at very low levels during the remaining culture period. The basal cell LI also declined from its higher level, but it remained at relatively higher levels than those of the mucous cells between days 3 and 9 after culture. In the lesions, labeled cells were generally confined to the basal layer, and the LI was about thirtyfold greater than the total basal cell LI. As the lesions progressed, the surface layer containing the mucous and ciliated cells was exfoliated as a result of population pressure from the underlying actively proliferating basal cells and subsequent epidermoid differentiation of the daughter cells. These data support the hypothesis that epidermoid metaplasia of tracheobronchial epithelium caused by vitamin A deficiency originates from the generative or basal cells.