Interaction between mercuric chloride and zinc in rat whole-embryo culture

Ten-day-old rat embryos were cultured in rat serum for 24 or 28 hr in the presence of mercuric chloride and zinc chloride alone or together, at concentrations ranging from 15 to 35 mum and 7 to 220 mum, respectively. At the end of the culture period, embryos were observed microscopically for growth parameters and malformations, and examined biochemically for protein and DNA contents. The effects of HgCl(2) on growth and development were related to concentration. Yolk-sac diameter, and head length, number of somites, protein and DNA contents were significantly reduced at 20 and 25 mum-HgCl(2), respectively. Viability decreased at 30 mum-HgCl(2), and malformations appeared at 20 mum-HgCl(2). These mainly consisted of lateral dilatation of prosencephale, swollen mandibular arches, protrusion of the allantois and the extremity of the caudal neural tube from the yolk-sac, turning failure, poor or absent yolk-sac circulation and open cranial neural folds. Embryos exposed to ZnCl(2) developed normally at all doses tested. Addition of ZnCl(2) to the culture medium at concentrations of up to 220 mum, simultaneously or 4 hr before the addition of 25 mum-HgCl(2), failed to ameliorate HgCl(2)-induced teratogenicity. It is concluded that zinc has no influence on the effects induced by HgCl(2) in the whole-embryo culture system.