维生素A及其衍生物——类视黄物质(retinoids),为分泌性上皮的生长、分化及维持其正常功能所必需。缺乏维生素A的动物,其呼吸道、唾液腺、胰腺、前列腺等的具纤毛并能分泌粘液的上皮可转化为一种多层的角化上皮。此种改变可通过补充类视黄物质而得以预防或逆转。其作用机理尚未弄清。但似乎它是与一些受体相互作用,作用方式与多肽激素相仿。类视黄物质对上皮细胞的作用究竟是直接的,抑或以上皮之下的基质为间介,尚未明瞭。如同在血清中已发现的另一种与视黄醇结合的蛋白质一样,在细胞中也初 Vitamin A and its derivatives, retinoids, are essential for the growth and differentiation of secretory epithelium and to maintain its normal function. In animals lacking vitamin A, epithelium with ciliated and mucus secreting in respiratory tract, salivary glands, pancreas, prostate, etc., can be converted into a multi-layered keratinized epithelium. This change can be prevented or reversed by supplementing the retinoid substance. Its mechanism of action has not yet been clarified. But it seems that it interacts with some receptors and acts like peptide hormones. The effect of retinoids on epithelial cells is either direct or inferential. Like another retinol-binding protein found in serum, it is also present in cells.