title: Dose-rate effectiveness for unstable-type chromosome aberrations detected in mice after continuous irradiation with low-dose-rate gamma rays.
abstract: Chronological changes in the chromosome aberration rates of splenocytes from specific-pathogen-free (SPF) mice after continuous and long-term exposure to low-dose-rate gamma rays were studied. Incidences of dicentrics plus centric rings (Dic+Rc), detected by conventional Giemsa staining, and dicentric chromosomes, detected by fluorescence in situ hybridization (Dic by FISH) using a centromere probe, showed an essentially linear increase up to a total accumulated dose of 8000 mGy after irradiation for about 400 days at a low dose rate of 20 mGy/day. For comparison, acute high-dose-rate and medium-dose-rate irradiation were performed. The values of the alpha coefficients in the linear regression lines for these unstable-type aberrations decreased as the dose rates were lowered from medium dose rates (200 and 400 mGy/day) to low dose rates (1 and 20 mGy/day). The dose and dose-rate effectiveness factor (DDREF), estimated by the ratio of calculated incidences using the best-fit regression lines at a high dose rate (890 mGy/min) and low dose rate (20 mGy/day), was 4.5 for Dic by FISH and 5.2 for Dic+Rc, respectively, at the same dose of 100 mGy, while different DDREFs were obtained for different accumulated doses. This is the first study to provide information regarding the effects of long-term exposure to low-dose-rate radiation on chromosomes.
authors.affiliation: Department of Radiobiology, Institute for Environmental Sciences, Hacchazawa 2-121, Takahoko, Rokkasho, Kamikita, Aomori 039-3213, Japan. kmtanaka@ies.or.jp
authors.forename: Kimio
authors.initials: K
authors.lastname: Tanaka
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kohda
authors.forename: Kenichi
authors.initials: K
authors.lastname: Satoh
authors.forename: Takuo
authors.initials: T
authors.lastname: Toyokawa
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Ichinohe
authors.forename: Megu
authors.initials: M
authors.lastname: Ohtaki
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Oghiso
mesh_terms: D000375:Aging / Q000235:genetics; D000818:Animals; D001399:Azure Stains; D043171:Chromosomal Instability / Q000528:radiation effects*; D004260:DNA Repair / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005720:Gamma Rays / Q000009:adverse effects*; D017404:In Situ Hybridization, Fluorescence; D051379:Mice; D011829:Radiation Dosage; D013997:Time Factors
chemical_list: D001399:Azure Stains