Studies of vitamin A‐induced teratogenesis: Effects on embryonic mesenchyme and epithelium, and on incorporation of H3‐thymidine

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Abstract
Some aspects of tissue differentiation were studied in 13‐day rat embryos after vitamin A treatment of their mothers on days 10, 11, and 12 of gestation. Severely affected embryos showed extensive growth retardation. Inhibition of cell proliferation, assumed from a decreased rate of H3‐thymidine uptake, was found in the liver, loose mesenchyme of the cephalic region, posterior region of the palatine shelves, trigeminal nucleus, and in some areas of the skin. Other tissues investigated showed no inhibition.Development of the face in these embryos was characterized by the appearance of defects in the mesoderm of the maxillary process and in the oral epithelium. It is suggested that palatal and dental abnormalities of vitamin A‐treated embryos arise because of some initial changes in the epithelium, which subsequently lead to a disrupted epithelial‐mesodermal relation in this region, so essential for normal development.Some physicochemical properties of vitamin A, such as its high surface activity and its effect on membrane permeability, enable it to have widespread effects. Information about the importance of these phenomena in the developing embryo must await further elucidation of the mechanism of action of vitamin A in biological organisms in general.