Tumors in two generations of mice in different environmental conditions.

The influence of environmental carcinogens on the developing embryo has been investigated using SWA mice as models and 1-ethyl-1-nitrosourea (ENU) as the carcinogen. The percentage of tumor development among the F1 generations of siblings delivered and nursed by mothers treated with ENU was higher than that of the F1 generations of siblings delivered of treated mothers but nursed by untreated foster mothers. The presence of multople tumors was also more frequent in this group compared to the siblings which were exposed only transplacentally to ENU. The second generations also developed malignant tumors. Two successive generations of siblings which were delivered of untreated mothers but nursed by foster mothers treated with ENU on the 12th day of pregnancy, showed a higher percentage of tumors when compared to the control group. This result is of great significance as the siblings were not exposed to the carcinogen transplacentally, and the foster mothers were treated with only a single dose of ENU long before the lactating period, namely, on the 12th day of pregnancy.