The high sensitivity of the rabbit to the teratogenic effects of 13-cis-retinoic acid (isotretinoin) is a consequence of prolonged exposure of the embryo to 13-cis-retinoic acid and 13-cis-4-oxo-retinoic acid, and not of isomerization to all-trans-retinoic acid. - Tzimas,G.; Bürgin,H.; Collins,MD.; Hummler,H.; Nau,H. (Arch Toxicol, 1994)