Abstract
We have reported that translocations and dicentric chromosomes were increased almost linearly up to a total accumulated dose of 8000 mGy, in female C3H mice continuously irradiated by gamma-ray in SPF condition at a low-dose-rate (LDR) of 20 mGy/22h/day (0.91 mGy/h) from the age of 8 weeks.
Translocations in human lymphocytes induced by high-dose-rate (HDR) irradiation persist for a long time without elimination, on the while dicentric chromosomes decrease to about 50% at 3 years after irradiation. In similar, dicentric chromosomes decrease to background level at 112 days after HDR-X-ray irradiation in mice.
In present experiment, mice were kept for up to 400 days, after the LDR-irradiation for 200 days (total dose is 4,000 mGy), and chromosome aberration rates were examined periodically. Translocations and dicentric chromosomes were slowly decreased up to 200 days after the LDR-irradiation. Frequencies of dicentric chromosome were still higher than that of age-matched non-irradiated control mice, which was different from HDR-irradiation. The slight reduction of dicentric chromosomes after LDR-irradiation was not only caused by life span of splenic lymphocytes, but also by turn-over of splenic lymphocytes supplied from immature stages in bone marrow or other organs. The persistence of lymphocytes with dicentric chromosomes for more than 200 days after LDR-irradiation without rapid reduction might be closely related to the increase of dicentric chromosomes almost linearly depending on accumulated dose during the continuous LDR-irradiation. This study was performed under contact with Aomori Prefecture Government, Japan.
