Sister Chromatid Exchanges in Human Lymphocytes Exposed to Ionizing Radiation during G 0

Several authors have reported small, but statistically significant, increases in sister chromatid exchanges (SCEs) in mammalian cells exposed to low-LET radiation during culture in the presence of (/sup 3/H)-thymidine or bromodeoxyuiridine (BUdR). To determine whether ionizing radiation also induces lesions in the unsubstituted DNA of G/sub 0/ lymphocytes that lead to SCEs in second division metaphases, we exposed human lymphocytes to 150 or 300 /sup 60/Co-..gamma.. radiation prior to culture in the presence of phytohemagglutinin and BUdR. Increased frequencies of SCEs were not observed in the irradiated cultures, either in second division metaphases having ring and dicentric chromosomes or those that did not have detectable chromosome aberrations. these findings suggest that increased frequencies of SCEs would not be observed in cultured lymphocytes from persons with in vivo exposures to radiation, and raise questions regarding the efficacy of ionizing radiation in inducing long-lived lesions in native DNA that can subsequently be expressed as SCEs.