Embryotoxicity induced by diethylstilbestrol in vitro1

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Abstract
The embryotoxic potential of diethylstilbestrol (DES) was examined in a whole embryo culture system containing a P‐450–dependent bioactivating system. Sprague‐Dawley rat embryos were explanted on day 10 and cultured for 24 hours. Concentration‐dependent effects of DES on embryonic growth parameters, viability, and embryotoxicity were observed. Concentrations of DES greater than 0.26 mM (final concentration) produced 100% embryolethality, while those below 0.15 mM were without significant effects. At a final concentration of 0.19 mM, DES produced only a slight increase in embryolethality. The same concentration elicited a marked increase in observed embryotoxicity, including prosencephalic hypoplasia, incomplete axial rotation, and open neural tubes. In addition, reductions in embryonic length, somite number, and protein and DNA content were observed. An exogenous P‐450–dependent hepatic biotransforming (catechol‐generating) system failed to alter either the incidence of observed toxic effects or measured growth parameters. Likewise, exposure of cultured embryos to 20% carbon monoxide (CO) failed to reduce DES‐induced embryotoxicity, indicating a lack of participation of an endogenous P‐450‐dependent embryonic bioactivating system. Arachidonic acid (0.20 mM) and/or indomethacin (0.50 mM) also had no observable effect on DES‐induced embryotoxicity, suggesting that prostaglandin synthase was not involved in the embryotoxic activity of DES, as has been proposed to explain its carcinogenic effect. The antioxidants N‐acetylcysteine (1.14 mM) and α‐tocopherol (0.08 mM) failed to protect against DES‐induced embryotoxicity, while the antiestrogen tamoxifen (up to 0.85 mM) actually enhanced this effect of DES in culture. The DES analogs Z,Z‐dienestrol (DIES, 0.10 mM) and hexestrol (HES, 0.48 mM) were both embryotoxic in vitro. The presence of an exogenous P‐450‐dependent hepatic biotransforming system appeared to protect against HES‐induced embryolethality but had little effect upon DIES‐induced embryotoxicity. The results were consistent with a direct effect of DES independent of either estrogenicity or exogenously generated metabolites.