No adaptive response of Chinese hamster ovary cells to low doses of ionizing radiation.

Chinese hamster ovary (CHO) cells that had been exposed to very low doses of ionizing radiation from incorporated tritiated thymidine or X-rays were shown not to be more resistant to the induction of chromatid aberrations by a subsequent higher dose of ionizing radiation than previously untreated cells. The adaptive response to ionizing radiation was absent both in cells challenged with high doses of X-rays (1.25 Gy) and in cells post-treated with thermal neutrons (0.5-1 x 10(12) n/cm2). In agreement with these observations in CHO cells we were unable to demonstrate an adaptive response to X-rays also in human lymphocytes from five different donors.