After the discovery that the two vitamin A related drugs - Accutane (registered trademark) and Tigason (registered trademark) - are human teratogens, the question has arisen if vitamin A (retinol) itself is also teratogenic if ingested as an oral supplement. Information gathered until the year 1986 from at least seven published and eleven unpublished case reports indicate the occurrence of major malformations in infants if daily intake of vitamin A during pregnancy was 25,000 IU or more. There are no epidemiological studies to provide corroborative data, but several good animal models are available. Our aim is to understand the biological basis (i.e., mechanism) of vitamin A-induced teratogenicity in an animal model (mouse) by studying the underlying cellular and subcellular events in susceptible and embryonic tissues. Previous studies under this project have provided evidence that a) formation of retinoic acid from retinol is the first step in this mechanism and that b) there are certain specific structural requirements in the retinoid molecule that enhance or lower its teratogenic activity. Our specific aims are first to attempt an identification of the likeliest active natural metabolite or metabolites of retinol/retinoic acid by means of whole animal and tissue culture bioassays established previously. Radiochemical and HPLC methodologies will be used in this attempt, and synthetic retinoid compounds will be included in the analyses. Second, select variably-active retinoids from ongoing studies and use them to compare their ability to localize and interact with cellular and nuclear components in the embryonic target tissues. Cell fractionation, density gradient centrifugation, SDS/polyacrylamide gel electrophoresis, and HPLC will supplement other methods to seek the role of nuclear retinoid receptor(s) in vitamin A-induced teratogenic response. This research will bring us closer to a proposal that the physiologic and pharmacologic effects of vitamin A have a common basis.