Radio-adaptive response: characterization of a cytogenetic repair induced by low-level ionizing radiation in cultured Chinese hamster cells.

Pretreatment with low doses of beta-rays from incorporated tritiated thymidine ([3H]dThd) or of Co-60 gamma-rays (1 or 5 cGy) rendered actively growing Chinese hamster V79 cells more resistant to the induction of micronuclei or sister-chromatid exchanges (SCEs) by a subsequent high dose of gamma-rays (1 Gy). This adaptive response to ionizing radiation (radio-adaptive response) can be induced by an optimal range of low doses of 3H beta-rays, but not by much lower or higher adapting doses. Full expression of the adaptive response induced by the exposure to low doses of 60Co gamma-rays occurred 4 h after the adapting dose. The cells pre-exposed to low doses of gamma-rays showed cross-resistance to challenge doses of gamma-rays themselves and also of mitomycin C (MMC) and near ultraviolet light (UV-B, 313 nm), but not to those of ethyl methanesulfonate (EMS) or cis-platinum (II) diammine dichloride (cisplatin) for SCE induction. These results suggest that the radio-adaptive response mechanistically couples to the repair network which copes with chromatin lesions induced by MMC and UV-B.