Transplacental passage of label after administration of [3H]retinoic acid (vitamin A acid) to pregnant mice

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Abstract
To determine whether there is transplacental passage of retinoic acid (vitamin A acid) or its metabolites levels of radioactivity were measured in embryos after administration to 12th‐day pregnant ICR/DUB mice of nonteratogenic or teratogenic quantities of [3H]retinoic acid. After the former treatment radioactivity was demonstrable in embryos, placentas, and visceral yolk sacs (VYS) at 1 h after treatment. Expressed in terms of radioactivity per unit protein content, embryos at 1 h had about one‐third as much radioactivity as maternal livers. The placentas had maximum radioactivity at 2 h, whereas embryos and VYS accumulated maximum levels by 6 h after treatment. At 6 h the level in embryos was twice that in placentas. After teratogenic treatment placentas and embryos attained peak levels of radioactivity at 6 and 12 h later, respectively. Again, embryos at peak level contained 2‐3 times as much radioactivity as placentas or VYS. The amount of retinoic acid, metabolites, or both, in embryos after the teratogenic treatment, calculated on the basis of specific activity of the injected label, was 26 times greater than after nonteratogenic treatment; the amount in maternal liver was 75 times greater. The results support previous evidence that the teratogenic effects of retinoic acid are associated with raised levels of retinoic acid, its metabolites, or both, in embryos.