Experiments showed that some carcinogenic nitroso-compounds (alkylnitrosoanilines and alkyl-nitrosoureas) induced different malformations in rat embryos when applied at stages of organogenesis. However, the parallelism between carcinogenic and teratogenic activity was not always observed. Potent carcinogens failing to produce malformations were polycyclic hydrocarbons and symmetrical dialkylnitrosamines. In experiments with 1,2,5,6-dibenzanthracene, urethan and ethylnitrosourea the sensitivity of the embryonic tissues to carcinogenic effect of these substances is evident. Organotropism of oncogenic substances, as observed in the adult animal, is generally also demonstrable after application during prenatal life. Rats in 17 subsequent generations showed alterations in sensitivity to the action of 6-methylthiouracil which induces thyroid tumours. Factors are analyzed which might determine the embryotoxic, teratogenic and blastomogenic reactions of the embryo and the risk of blastomogenesis due to prenatal action of carcinogenic substances. © 1968 Springer-Verlag.
