Results from previous experiments have indicated tha persistence of an increased cancer risk in subsequent generations following prenatal exposure to a chemical carcinogen. In the present experiment, the possible role of prezygotic events in determined cancer risk was investigated in the progeny of male rats treated with ethylnitrosourea (ENU) before mating with untreated females. Eight BDVI male rats were given a single i.p. dose of 80 mg/kg bw ENU and each rat was then caged at weeks 1, 2, 3 and 4 after treatment with three untreated females. Fertility was lower and preweaning mortality higher in the experimental group, as compared to controls, particularly at the 4th-week mating. Survival rates after weaning were similar in the progeny of treated males and controls, as was the total incidence of tumours. However, analysis of tumour incidence at the various organ sites showed an increased incidence of neurogenic tumours in the progeny of ENU-treated males, as compared to that of controls.

A single dose of 40 mg/kg of N-nitrosoethylurea (ENU) was administered to BDVI rats on the 16th day of pregnancy. The first generation descendants (F1) were mated on a brother-to-sister system to produce a second generation (F2) which was then mated to produce a third generation. A high incidence of nervous tissue tumors and a few kidney tumours were observed in F1 descendants. A few nervous tissue tumours were observed in F3 but not in F2 descendants. These results partially confirm previous observations obtained with 7,12-dimethylbenz(a)anthracene in mice and nitrosomethylurea in rats and indicate that prenatal exposure to a chemical carcinogen may result in an increased cancer risk which can persist for more than one generation.

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Vinylidene chloride (VDC) monomer dissolved in olive oil was given orally to female BD IV rats (150 mg/kg body weight) on the 17th day of gestation. Their offspring were treated weekly with 50 mg/kg body weight VDC by stomach tube from the time of weaning for life span. Liver and meningeal tumours were more frequently observed in treated than in untreated animals, but the total number of tumour-bearing animals was not significantly different between treated and untreated animals. Chloroprene (CP) monomer dissolved in olive oil was given orally to female BD IV rats (100 mg/kg body weight) on the 17th day of gestation and their offspring were treated weekly with 50 mg/kg body weight by stomach tube from the time of weaning for life span. Total incidence of tumours was similar in treated and untreated animals. The data presented provide limited evidence of the carcinogenicity of VDC and no evidence of the carcinogenicity of CP when given by the oral route to rats.