Direct exposure of postimplantation mouse embryos to 5-bromodeoxyuridine in vitro and its effect on subsequent chondrogenesis in the limbs.

As maternally administered 5-bromodeoxyuridine (BudR) is very quickly degraded by the liver, a combination of whole embryo culture and organ culture techniques was adopted to expose postimplantation mouse embryos to the analog and to study the effects of long-term embryos were exposed to increasing concentrations of BudR for 12 or 24 h. Forelimbs of the treated embryos were then organ-cultured in drug-free medium and the extent of cartilage development in the explants examined. Exposure of embryos to 50-150 mug/ml of BudR for 24 h resulted in significant inhibition of chondrogenesis in the subsequent limb cultures and the effect was related to dose. After treatment with 150 mug/ml of the drug, the forelimbs of the early 11-day embryos (somite stage 26-29) showed an almost complete lack of cartilage, while the limbs of mid-11 th-day embryos (somite stage 32-34) were not nearly as sensitive and exhibited about 50% reduction in the amount of cartilage development. We conclude that if embryos in which the limb development is at a very early stage of development are exposed to BudR, the future course of limb differentiation is permanently and irreversibly damaged, resulting in a partial or even complete suppression of chondrogenesis in the organ. As both the dose and perhaps also the duration of treatment were critical, we suggest that the rather low frequency of reported limb malformations after in vivo injection of teratological doses of BudR may be due to only a small amount of the chemical reaching the embryos.