Life-Shortening and Carcinogenesis in Mice Irradiated Neonatally with X Rays

The characteristics of life-shortening and carcinogenesis were investigated in x-irradiated neonatal B6WFr mice. Animals were irradiated with 24 hr after birth and allowed to complete their normal life span. Mean life span was shortened linearly with doses at a rate of 9.1% per 100 R for females and 9.8% for males. The spectrum of neoplastic diseases was apparently modulated by x irradiation, showing neonatal B6WFr mice to be highly susceptible to the induction of thymic lymphoma, liver tumor, and pituitary tumor. The dose-response relationship for thymice lymphoma could be described by a linear-quadratic model, and linearity could be rejected. Thymic lymphoma developed after a short latent period, resulting in death between 100 and 450 days of age. Liver and pituitary tumors increased with increasing dose up to 400 R and decreased thereafter. The latent period for liver tumor development was apparently shortened with increasing doses. Pituitary tumor developed in excess only in females after a long latent period.