Species differences between rats and mice in the teratogenic action of ethylenethiourea: in vivo/in vitro tests and teratogenic activity of sera using an embryonic cell differentiation system.

In vivo/in vitro studies on rats showed that ethylenethiourea inhibited the differentiation of midbrain cells more severely than that of limb bud cells. In in vitro studies using midbrain cell cultures, ethylenethiourea concentrations inhibited the production of differentiated foci by 50% in mouse cells, a rate 11-fold higher than that in rat cells. Differentiation of rat midbrain cells was also inhibited by the serum samples prepared from rats or mice dosed with up to 200 mg/kg of ethylenethiourea. However, differentiation of mouse cells was not inhibited by these animal serum samples. The concentration of ethylenethiourea in rat sera was only 2-fold higher than that in mice sera at 2 hr after dosing with 200 mg/kg. Therefore, the different sensitivity of the midbrains of these two species may be one reason that ethylenethiourea is teratogenic in rats but not in mice.