X irradiation and sister chromatid exchange in cultured human lymphocytes

Sister chromatid exchange (SCE) frequency was not increased in G0 lymphocytes following irradiation up to 400 rads. Lymphocytes irradiation after 42 or 60 hours of culture showed a dose-dependent increases in exchange frequency at 100 and 200 rads. SCE was not increased in cells irradiated in G2 (68.5 hours). Lymphocytes maintained in a 5-Bromodeoxyuridine (BrdUrd) free medium and irradiated 42 hours after culture initiation showed an increase in SCE if BrdUrd was added immediately after irradiation, but no increase was found if there was a 5 hour holding period to the additional of BrdUrd. The effect on induced SCE frequency of heightened radiosensitivity due to increased amounts of BrdUrd was also investigated. When the BrdUrd concentration was increased form 10 micrograms/ml, the percent increase in X-ray-induced SCE was lower at 50 micrograms/ml. In addition, increased BrdUrd concentration only slightly increased the sensitivity of the SCE technique to irradiation doses of 50 rads.