Some results and prospects of transplacental carcinogenesis studies.

Analysis of literary data and the author's findings have shown that the transplacental action of most of the compounds tested in experiments on rats manifested itself by a neurotropic carcinogenic effect. A marked neurotropism in transplacental carcinogenesis in rats is characteristic even for such drugs (e.g. dimethylbenzathracene) that have never induced neurogenic neoplasms in adult animals. To elucidate the relationship between teratogenesis and carcinogenesis the peculiarities of tumor development in brain against the background of malformations induced by combined transplacental treatment by methylnitrosourea (MNU) and ethylnitrosourea (ENU) in rats have been studied. Tumorigenesis was sharply inhibited by administration of ENU (on the 13th day) prior to MNU treatment (on the 15th day). There is reason to believe that the cytotoxic effect of MNU for microephaly results in the death of a considerable part of the cell population already transformed by ENU. In a special series of experiments characteristics of the permeability of polycyclic aromatic hydrocarbons through the placenta in rats have been specified.