Induction of Congenital Malformations in Mice by Paternal Methylnitrosourea Treatment

ABSTRACTA single dose of methylnitrosourea (MNU, 25–100 mg/kg) was injected intraperitoneally into ICR strain male mice. The males were mated to untreated females of the same strain on days 1–21 and 64–80 after the treatment. On day 18 of pregnancy, the fetuses were examined for external and skeletal abnormalities. MNU treatment of paternal germ cells caused significant increases in the incidence of abnormal fetuses over the control level. The induction rate per live fetus per unit dose in mg/kg by treating spermatogonial stem cells was estimated to be 3.0 × 10−4, which is quite similar to the rate previously estimated for the same endpoint at the same germ cell stage with the fractionated doses of MNU (daily doses at 5–25 mg/kg for 5 days). Cleft palate and dwarfism were the most frequent external abnormalities in the MNU‐treated and the control series. Malformed ribs was the most frequent skeletal abnormality in the treated series. It was concluded that congenital malformations induced after treating male mice with a single dose of MNU were quantitatively and qualitatively similar to those induced after treating male mice with the fractionated doses of MNU.