All trans retinoic acid interfering with palatal development. Scanning electron microscopical and light microscopical observations on embryonic rat palate

Diverse studies on retinoic acid teratogenesis, during the recent years, indicate that the drug's analogues target on diverse cell population during differentiation in mammals. During an extended teratological protocol concerning retinoic acid influence in diverse embryonic tissue differentiation in experimental animals we studied all-trans-retinoic acid's influence on palatal development in the white rat embryo. For this purpose, six groups of white rat embryos were studied: Group 1 was treated with 100 mg/kilogram of body weight (k.b.w.) on gestational days (g.d.) 10th and 11th, Group 2 was treated with 100 mg all-trans-retinoic acid/k.b.w. on g.d. 11.5, Group 3 was treated with 50 mg all-trans retinoic acid/k.b.w. on g.d. 10th, 11th and 12th, Group 4 was treated with 50 mg all-trans-retinoic acid/k.b.w. on g.d. 11th and 12th, Group 5 was treated with 20 mg all-trans-retinoic acid/k.b.w. on g.d. 7.5, 8.5, 9.5, 10.5 and 11.5, Group 6 remained untreated. Embryonic heads aged 20 days were observed by light microscopy and scanning electron microscopy. In all treated groups clefts and malformations concerning the differentiation of palatal cell populations were observed. All our findings were compared with normal palatal morphology of untreated "control" embryos. Among the malformations, median clefts were observed, extended along only a part of the primary and all the secondary palate for group 2, the primary and secondary palate for groups 1, 3 and 5 while on group 4, an irregularity of the median palatal raphe and rugae were combined with a median incomplete cleft extended between the primary and secondary palate. Our results are discussed in relation with the international literature results.