Development of the ectopia cordis induced by hydrocortisone administration

Our previous study on the development of thorax in chick embryos revealed that mechanical disturbance of the so-called membrana reuniens causes the development of the ectopia cordis (EC). To assess whether membrana reuniens disturbance was really essential for EC development, we employed hydrocortisone, a teratogen known to produce a high incidence of EC. The incidence of EC after the hydrocortisone intraamniotic application on the 4th embryonic day reached 84,8%. It was found that although in the whole course of EC development the membrana reuniens appeared very thin, it nevertheless remained continuous. The morphology of the membrana reuniens in embryos with fully developed EC, studied in classical serial histological sections, was similar to that of the amniotic membrane. Flow cytometry analysis of the cell cycle revealed that EC induced by hydrocortisone administration was associated with a significantly lowered proliferation activity of the prospective body-wall mesenchyme involved in the closure of the anterior wall of thorax. The probable mechanism of EC development is suggested.