Induction of squamous metaplasia (vitamin A deficiency) and hypersecretory activity in tracheal organ cultures.

Maintenance of rat tracheal organ cultures in various nutritional environments was studied. In Waymouth's 752/1 defined, vitamin A-free medium the mucociliary epithelium, at the site of the original mucosa, changed to a highly active keratinizing squamous epithelium. Epithelial cells that migrated from the original mucosa and covered the underside of the tracheal explants developed into keratinizing squamous epithelium with in a few days. These transitions were accompanied by high rates of DNA synthesis as revealed by 3H-thymidine incorporation into the explants. Addition of 10 per cent horse serum to the Waymouth's medium completely inhibited squanous metaplasia. In this medium, the actively secreting mucociliary epithelium of the original mucosa slowly became quiescent, and the undergrowth epithelium usually remained undifferentiated. These explants maintained a lower level of DNA synthesis. When vitamin A (all trans retinol) was added to the serum-supplemented medium, 0.2 and 2.0 mug. per ml. induced hypersecretory activity in the original mucosa. Addition of 2.0 mug. per ml. also stimulated cellular hyperplasia and mitoses. A concentration of 20 mug. of vitamin A per milliliter of medium was toxic. It is concluded that a spectrum of epithelial cell types normally found in the tracheal mucosa in vivo can be induced and maintained in tracheal organ cultures in vitro by selection of the appropriate nutritional environment.