Effects of pure 2,4‐dichlorophenoxyacetic acid on cultured rat embryos

dichlorophenoxyacetic acid (2,4- D), a plant growth regulator, has been used worldwide as a herbicide. Previously we evaluated the prenatal devel- opmental effects of 2,4-D by feeding it to pregnant rats and found that it is maternally toxic and embryolethal, and it induces urogenital malformations in rat fetuses. In the study presented here, we investigated the effects of pure 2,4-D on rat embryos in whole embryo culture. Rat embryos on day 9.5 of gestation were cultured for 48 h at several concentration levels with pure 2,4-D (50-500 m g/mL). 2,4-D caused a concentration-related increase in the incidence of each malformation. Signifi- cant decreases in the number of somites were observed at a concentration of 100 m g/mL or more. At the concen- tration of 100 m g/mL, there was normal yolk sac circula- tion. This result suggests that 2,4-D has a detrimental effect on somite development and directly damages developing embryos.