Characteristics of the limb malformations induced by maternal exposure to cadmium in the mouse.

Single doses of 2,3,4,6,8,10, and 15 mg/kg of cadmium chloride were administered (SC) to groups of MF1 mice on one of days 7 to 12 of gestation. Fetuses collected on day 18 were observed for limb malformations, and alizarin red-S stained skeletons were examined for their skeletal bases. Ectrodactyly, postaxial polydactyly, syndactyly, brachydactyly, adactyly, phocomelia, meromelia, and malrotation of the limbs were detected in a significant number of fetuses. Days 7 to 10 were greatly susceptible for induction of these malformations. Postaxial ectrodactyly was more frequent in the forepaws, and sidedness was not significant. Preaxial ectrodactyly preferentially affected the left hindpaws in the 9th-day treatment group. Postaxial polydactyly was predominently right sided and mostly involved the forepaws. Day 8 was particularly susceptible for induction of adactyly. Malrotation of the limbs together with edema and caudal narrowing resulted in a 'penguin-like' appearance. Ossification of the long bones, the carpals, tarsals, and phalanges were affected. Even those limbs that were not externally malformed had skeletal dysgenesis. Limb buds examined histologically at midgestation showed scanty and poorly organized mesenchyme, extensive elaboration of marginal sinsus, reduced thickness of the apical ectodermal ridge (AER), and discontinuous basement membrane. It is speculated that such histologic alterations at early stages of development could have contributed to the defective morphogenesis of limbs in this animal model.