Neural, pituitary, and mammary tumors in Sprague-Dawley rats treated with X irradiation to the head and N-Ethyl-N-nitrosourea (ENU) during the early postnatal period: a statistical study of tumor incidence and survival.

To study the late effects of early postnatal treatment with N-ethyl-N-nitrosourea (ENU) preceded by X irradiation to the head, 226 neonatal CD rats were divided into six groups which received the following treatment: (1) 500-rad X irradiation to the head on the third postnatal day (pnd); (2) injection ip with 30 mg/kg ENU on the fourth pnd; (3) injection ip with 30 mg/kg ENU on the seventh pnd; (4) a combination of 500-rad X irradiation to the head on the third pnd, followed by ip 30 mg/kg ENU on the fourth pnd; (5) a combination of 500-rad X irradiation to the head on the third pnd, followed by ip 30 mg/kg ENU on the seventh pnd; and (6) untreated controls. The results indicate that (1) X irradiation to the head alone significantly extended the life span of females compared to that of control females, and did not affect survival of males; (2) X irradiation did not influence the latent period or mortality from neurogenic tumors when ENU was given 1 or 3 days afterward; (3) ENU itself was a factor in shortening latent periods for mammary tumors; (4) X irradiation alone did not increase the incidence of mammary tumors, and revealed no protective effect on the ENU-induced mammary carcinogenesis; (5) X irradiation increased the prevalence of pituitary tumors in the females; (6) no enhancement of pituitary tumors by ENU was observed: and (7) there was a statistically significant association of pituitary and mammary tumors in females.