The occurrence of tumours in F1, F2 and F3 descendants of bd rats exposed to N-nitrosomethylurea during pregnancy.

N-nitrosomethylurea (NMU) was administered once IP at a dose of 20 mg/kg to BD female rats on the 18th day of pregnancy. The first generation descendants (F1) were mated to produce a second generation (F2), which were then mated to produce a third generation (F3). While F1 rats were exposed directly to NMU during intrauterine life, it can be reasonably excluded that F2 and F3 descendants were exposed to NMU or its metabolites. F2 and F3 rats received no other treatment and untreated rats served as controls. Kidney and nervous-tissue tumours were observed in F1 descendants and, with a lower incidence, in F2 descendants. In F3 rats, tumours of nervous tissue, but not of kidneys, were observed. These results confirm previous observations that exposure to a carcinogen during prenatal life results in an increased cancer risk which may persist for more than one generation.