Micromorphology of the placenta of rats reared on marginal vitamin-A-deficient diet.

Abstract

This study describes some effects of marginal vitamin A deficiency on the light-microscopic morphology of the placentas of rats. The placentas obtained were from rat dams reared on a basal vitamin-A-deficient diet supplemented with retinyl ester and other dams reared on the same basal diet supplemented with retinoic acid. These supplements are forms of vitamin A. The placentas at the 14th and 17th days of gestation were examined histologically. All placentas were associated with viable, apparently healthy fetuses and showed no signs of necrosis. Placentas at these ages were selected because a marked decrease in the number of viable fetuses occurs following the 14th day in the dams maintained on the retinoic-acid-supplemented diet. The placentas from these two groups were essentially similar in their histological appearance. However, differences were noted in the general proportions and topographic relations of the cells (trophospongial and glycogen cells) in the central region of the junctional zone and the inner tro-phoblast cells of the labyrinthine zone. These differences are probably related to the rate of cellular differentiation and the facilitation of the metaplastic changes of the (1) parenchymal cells to glycogen cells of the junctional zone and (2) inner trophoblast cells of the labyrinthine zone. This is consistent with the known role of vitamin A in the development and differentiation of epithelial cells. The change in the rate in the differentiation of the inner trophoblast cells is probably a crucial event and can account for the inability of the placenta of many marginal vitamin-A-deficient rat dams to carry fetuses to term.