Histogenesis of benzo(a)pyrene-induced lesions in tracheal explants.

Cytokinetic and histogenic alterations associated with the development of benzo(a)-pyrene (BP) induced epidermoid metaplasia were studied in tracheal explants derived from normal hamsters. Treatment of the explants with BP induced hyperplasia in both the basal and mucous cells. The hyperplasia of the basal cells persisted throughout the duration of the experiment whereas the hyperplasia of the mucous cells subsided between 7 and 10 days after treatment. This was accompanied by stimulation of ciliated cell differentiation and aberrant ciliogenesis which was not limited to the surface cells since some basal cells were observed differentiating into ciliated cells. Subsequently, the differentiation of basal cells into mucous cells was inhibited. Instead, the basal cells differentiated into metaplastic cells. With the progression of the lesions, the mucociliary surface layer was sloughed into the lumen due to the population pressure from the underlying actively proliferating metaplastic cells and their subsequent epidermoid differentiation. Approximately 50% of the explants exhibited focal areas of squamous metaplasia at 7 days after the treatment and extensive epidermoid metaplasia was present in approximately 90% of the explants at 10 days. These results support the hypothesis that BP induced epidermoid metaplasia of tracheal explants originates from the basal cells.