cigarette smoke/ethanol-induced limb defects in mouse embryos

we have produced a spectrum of limb defects in developing mouse embryos by exposing the mother to smoke from cigarettes with different nicotine concentrations, ethanol, and a combination of ethanol and cigarette smoke. the critical time of exposure was determined to be during day 10 of gestation (vaginal plug=day 0). this time is prior to the critical events which occur between the apical ectodermal ridge and the developing limb mesenchyme. when pregnant animals were exposed to smoke from two high-nicotine cigarettes (at 10:30 a.m. and ii :30 a.m. on day 10), no limb defects were observed. if ethanol was given (0.015 mg/g 25% i.p. in two doses on the morning of day 10) one percent of offspring showed a limb defect. by contrast, exposure to a combination of cigarette smoke and ethanol resulted in 43% (44/102) of newborns developing both fore - and hindlimb defects. birth weight was reduced by about 33% in animals carrying the defects. when mesenchyme cells beneath the limb apical ectodermal ridge were examined two days after teratogen exposure, striking changes in cell shape and size were evident. in as much as the incidence of mesenchymal changes in the limb buds seen on day 12 parallels the incidence of malformations seen in newborns, we postulate that anomalous limb development is secondary to the events occurring in the limb mesenchyme. we conclude that critical stages of development occur in the limb buds, and therefore certain teratogens or combinations of teratogenic agents may interfere with their normal development.