Immediate and delayed effects of vincristine administered during early postimplantation stages of murine embryogenesis

Vincristine was given to pregnant mice on day 7 1/2 of pregnancy and the teratogenic effects of this treatment were assessed 2 and 3 days thereafter. Most of the embryos in litters removed on day 9 1/2 of pregnancy (2 days after treatment) were morphologically normal, whereas on day 10 1/2 most embryos were either developmentally retarded by the treatment or malformed. The morphologically 'normal' embryos removed on day 9 1/2 of pregnancy were cultured in vitro for 24 hr. During this procedure more than 50% of them showed growth retardation or abnormal development. These data indicate that exposure of early postimplantation embryos to vincristine has an immediate teratogenic and embryocidal action, and also a delayed effect which becomes apparent only several days after exposure and following an ostensibly 'normal' period of embryonic development.