Effects of retinoic acid on morula-stage embryo development in mice.

BACKGROUND In a previous study, we investigated the short-term effects of in utero retinoic acid (RA) exposure on early development at the cleavage stage before implantation to understand the possible roles of RA in blastocyst formation. We designed the present study to investigate the long-term effects of RA exposure on pre-implantation embryos in vivo and in vitro. METHOD To evaluate late pre-implantation exposure to RA, pregnant female mice were fed peanut oil with 50 mg/kg RA by oral gavage in the late afternoon of day 2 and early morning of day 3 of gestation. Mice were sacrificed on day 8. The number and morphology of embryos were recorded. The morula-stage embryos were treated with different doses of t-RA for 1 day and were cultured for the following 7 days in vitro. The post-implantation development in vitro was evaluated. RESULTS The in vivo study showed that the rate of blastocyst implantation was not significantly different (9.2 vs 10.2 per mouse) and the rate of post-implantation embryo resorption was significantly higher in retinoic acid treated mice than in controls (35% vs 0%). RA was administered to morula-stage embryos at levels of 0, 0.001 micro, 0.1 micro, or 10 micro M throughout in vitro culture. For embryos that continued to develop following implantation, the development stages were delayed when assessed in 7-day culture. The percentage of embryos in the later stages of development changed depending on the dose of retinoic acid used. CONCLUSION These findings document, for the first time, that RA exerts adverse effects on morula-stage embryos during the early stage of development.