Late effects of fetal mice x-irradiated at middle or late intrauterine stage

Mice of F1 hybrids of (C57BL/6xWHT) strains were exposed in utero to 200 R of X-rays at 12 or 16 approximately 18 days post coitum. Mice of both sexes were allowed to liver through their life span, and the induction of tumors, growth retardation, and induction of degenerative diseases were examined. A significant enhancement of lung, pituitary gland, and ovary tumorigenesis was observed in mice irradiated at the late intrauterine stage. Also, incidence of liver and skin tumors was increased slightly in this group, whereas thymic lymphomas were not induced. Persistent growth retardation, several congenital malformation, and amyloid degeneration were found in mice irradiated at the middle intrauterine stage. However, no increases incidence of tumors was seen in this group. Moreover, incidnece of lymphoreticular tissue tumors, lung tumors, and leiomyosarcomas of uterus was significantly decreased by irradiation at the middle intrauterine stage from the unirradiated control and the late intrauterine irradiated group.