Morphological and autoradiographic studies of cleft palate induced in rat embryos by maternal hypervitaminosis A

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Abstract
Oral administration of 60,000 international units of vitamin A acetate to pregnant rats for 3 consecutive days beginning on either day 9 or 10 of pregnancy resulted in more than 80 per cent, of their embryos developing cleft palate. The initiation of palatine shelf movement in normal control embryos was associated with an aggregation of preosteoblastic tissue on the medial aspect of the vertically oriented shelves at the junction of their anterior two-thirds and posterior one-third. Delay in the movement of palatine shelves from the vertical to the horizontal position was not observed in a major percentage of the vitamin A treated embryos. In many vitamin A treated embryos a considerably lesser amount of mesenchymal tissue was contributed by the maxillary processes to form the palatine shelves. A process of heterotopic chondrogenesis was detected within the preosteoblastic tissues of maxillae and palatine shelves as early as day 15 and by day 17 had replaced a major portion of the maxillary bone. On the basis of the methods employed, more S35 was fixed by the tissues of treated embryos than by those of normal controls prior to the time of palatal closure.

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