Comparison of the effects of retinol and retinoic acid on postimplantation rat embryos in vitro

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Abstract
Rat embryos were explanted on day 8 or 9 of pregnancy and cultured for up to 48 hours in serum containing added retinol (vitamin A), retinoic acid (vitamin A acid), or absolute ethanol. They were examined morphologically and their protein content determined. Retinoic acid was more teratogenic and growthretarding than retinol. Electron microscopy of embryos cultured for 30 minutes or one hour revealed that both forms of vitamin A brought about similar ultrastructural effects on the embryonic cells; however, the abnormally large intracellular lipid droplets observed in a previous study following exposure to retinol in vitro and retinyl palmitate in vivo were not observed in embryos exposed to retinoic acid. It is possible that the differential teratogenicity may be due to the inability of the embryonic cells to convert and store retinoic acid in a less teratogenic form.