Prenatal multicarcinogenesis by ethylnitrosourea in mice.

The Role of prenatal age, sex, and the maternal background upon the incidence, multiplicity, and spectrum of tumors induced by ethylnitrosourea has been studied in the offspring of reciprocal hybrids of the same genotype. The first generation (F1) offspring of C57BL/6J X C3HeB/FeJ and the reciprocal hybrids were observed throughout their life-span for tumor development following single i.p. injections of ethylnitrosourea (60 microng/g) given to pregnant mothers at 12, 14, 16, or 18 days of gestation. Animals exposed to ethylnitrosourea survived on the average for only 90 weeks. They developed by that age tumors in lungs, livers, ovaries, nervous system, and forestomach. Control mice killed at 90 weeks were essentially free of tumors. The fetal age at the time of administration of the carcinogen was one of the most significant modulators of tumor development in lung, liver, ovaries, and nervous system. The sex of the animals influenced the rate of development of liver tumors, whereas maternal background affected the multiplicity of lung tumors.