The Effects of Vitamin A and Citral on Epithelial Differentiation in vitro 1. The Chick Tracheal Epithelium
In many animals the tracheal epithelium is one of the first tissues to respond to deficiency of vitamin A. Mori (1922a, b) in a careful study of the histological changes in vitamin A deficient rats, showed that the secretion of mucus from the tracheal epithelium and many other mucous membranes and glands was reduced, and that the secretory epithelia were gradually replaced by thicker, drier, keratinized membranes. Similar changes have been demonstrated in many other vitamin A deficient animals, including chickens (Beach, 1923; Seifried, 1930; Jungherr, 1943). Though vitamin A deficiency appears to have relatively little effect on skin and other epithelia that are normally keratinized, these epithelia change with high concentrations of vitamin A. When the vitamin was applied locally to the skin of rats (Sabella, Bern & Kahn, 1951) or administered orally in very large doses (Studer & Frey, 1949), the skin failed to keratinize normally, while the immature, non-keratinized cells proliferated rapidly and formed a thick epithelium.