Combined Effect of X-rays and N-Ethyl-N-Nitrosourea at Threshold Dose on The Induction of Thymic Lymphomas in B6C3F1 Mice

Abstract

Radiation carcinogenesis in human is considered as a result of the combined effect of radiation and environment factor. The aims of current study are both to demonstrate the dose-response relationship for the combined treatment of radiation and chemical carcinogens (ENU) at low doses and to elucidate the underlying mechanism. The data in progress showed that the dose-response curve for radiation-induced TLs (0.2, 0.4, 0.8, 1.0, 1.2, 1.6, and 2.0Gy a week × 4 times) was sigmoidal with threshold dose at 0.8Gy, and that for ENU-induced TLs (50, 100, 200, and 400ppm, drinking for 4 weeks) was linear with threshold dose at 100ppm. Combined-treatment of both agents at the threshold dose increased the incidence of TLs synergistically. The treatment in the sequence of X-rays (1.0Gy) - ENU (100ppm) induced TLs at higher incidence than the reverse sequence of ENU - X-rays. The frequency of loss of heterozygousity was much reduced in the TLs induced by combined treatments compared with X-ray-induced one. [J Radiat Res 44:398-399 (2003)]