Embryopathic action of N-nitrosomethylurea in the pregnant mouse manifest for three generations

A high incidence of tumour bearing animals (T.B.A.) occurred in the 3 generations of mice descended from dams exposed to N.M.U. on the 18th day of gestation (20 mg/Kg/ip). In the first generation, T.B.A.s (p less than 0.001 binomial analysis) were detected early and were due largely to reticuloses in males and females. In the second generation, T.B.A.s were again in increased number and involved young mice; females were particularly affected by reticuloses, 9 had these neoplasms compared with 2 in the controls. In the 3rd generation, the number of tumour bearing females was double that in the concurrent controls. Offspring from treated dams had a significantly increased incidence of reticuloses, in the first generation this amounted to p less than 0.05 (binomial analysis) and in the second to (p less than 0.01). A high incidence of mortality persisted for 3 generations. In the first, 18 per cent died by 80 weeks compared with 7 per cent of the controls; this difference was significant (p less than 0.05). In the second generation, 15 per cent died compared with 10 per cent of the controls. Sixteen per cent of the third generation also died, white the control incidence remained at 10 per cent.