Retinoids and Control of Epithelial Differentiation and Keratin Biosynthesis in Hamster Trachea

This chapter describes the methodologies utilized in the assessment of the morphological and biochemical alterations that occur during vitamin A deficiency in the hamster tracheal epithelium. The tracheal epithelium is of the pseudostratified type—that is, all its cells are in contact with the basement membrane. The epithelial tracheal surface fulfills its function of clearing foreign particles by virtue of the movement of the cilia. These, in turn, are aided in their motion by the presence of the mucus secreted by the goblet cells. Mechanical or chemical injury causes focal replacement of the mucociliary epithelium by a squamous metaplastic phenotype. Eventual reestablishment of the mucociliary epithelium after injury takes place gradually. In animals lacking vitamin A, a similar process of loss of the mucociliary epithelium and squamoid metaplasia is also observed. Retinoids at very low concentrations permit the regeneration of the normal mucociliary phenotype in vivo as well as in organ and cell culture. The morphological changes arising from deficiency of vitamin A are usually assessed at the midpoint of the tracheas. This is in part because the larynx is normally squamoid and keratinized.