Cadmium teratogenesis in the chick: Period of vulnerability using the early chick culture method, and prevention by divalent cations

Cadmium (Cd) is teratogenic in chick embryos following treatment in ovo or in shell-less culture. We investigated the ability of other divalent cations (Mn, Ni, Se, Mg and Ca) to influence the effects of Cd. As the proposed mechanism of protection of these ions is prevention of Cd influx by blocking or competing for Ca channels, we also assessed verapamil, a Ca-channel blocker. We used a new, completely ex ovo method, explanting the embryos onto an agar–albumen substrate (0.6% agar diluted 1:1 with thin albumen) to which test substances were added. Following 48–96 h incubation, chicks were explanted onto medium containing 7.5 μM Cd acetate or equimolar sodium acetate. Morphology and somite numbers were assessed at explantation, and again following 24 h incubation on the culture media. In addition, 60-h embryos were explanted onto media containing various concentrations of the aforementioned agents, alone or in combination with 7.5 μM Cd. Chicks were vulnerable to Cd teratogenesis between Hamburger–Hamilton stages 13 and 18. Co-treatment with Se, Mn and Ni prevented malformation at 2×, 50× and 100× the molar dose of Cd, respectively. Ca, Mg and verapamil failed to protect. These results indicate that some, but not all, divalent cations protect against Cd malformation, but the mechanism of rescue remains unresolved.