Squamous metaplasia of the tracheal epithelium in organ culture. I. Effects of hydrocortisone and beta-retinyl acetate.

Organ cultures of hamster trachea were incubated for periods of as long as 16 weeks in chemically defined medium containing hydrocortisone sodium succinate or the vitamin A analog, β-retinyl acetate. Medium from replicate cultures was assayed weekly for acid phosphatase activity, and representative tissues were harvested after pulse labeling with [³H]thymidine. Explants maintained in medium containing hydrocortisone showed basal cell proliferation, squamous metaplasia, and extensive keratinization, whereas those in medium containing β-retinyl acetate exhibited a proliferative ciliated epithelium that gradually became hypoplastic after 8 weeks in vitro. Simultaneous addition of these agents in equal concentrations resulted in an epithelium which appeared dedifferentiated. Acid phosphatase activity in cultures containing hydrocortisone was elevated. In contrast, release of the enzyme was inhibited when β-retinyl acetate was added to culture medium. Results indicate that hydrocortisone and β-retinyl acetate act in a competitive fashion on differentiation of the basal cell.