Toxic effects of chemicals on mouse post-blastocyst development--a trial to establish a testing system for...

We established a new testing system to assess embryotoxic chemicals using cultured preimplantation mouse embryos. Randomly bred Crj:CD-1 (ICR) mice were used. Late blastocysts collected on Day 4 of pregnancy (plug day:Day 1) were exposed for 24 hrs. to various chemicals at varying concentrations. Morphological embryonic development, structural chromosome aberrations and sister chromatid exchanges (SCEs) were examined as the parameters of embryotoxicity. Treated embryos were then transferred to pseudopregnant foster mice for the evaluation of in vivo development. Of the morphological developmental endpoints in vitro, the formation of two-layer ICMs (inner cell masses) was the most sensitive to the toxicity of chemicals, followed by ICMs and trophoblast outgrowth. Threshold limit values were confirmed regarding morphological growth. However, exposure of embryos to lower concentrations than threshold enhanced the frequency of chromosome aberrations and SCEs. Transfer of embryos treated with the lower concentration of 4-nitroquinoline 1-oxide induced not only fetal wastage but also developmental retardation. 4-nitroquinoline 1-oxide was the most embryotoxic in mouse blastocysts, followed in order by mitomycin C, bleomycin, methylmercuric chloride, diethylstilbestrol, mercuric chloride and ochratoxin-A. This new testing system appears to be a sensitive method of measuring the direct effects of toxic chemicals which yields results in a short term.