Influence of time and cell cycle phase on radiation-induced chromosome lesions.

Human lymphocytes were irradiated with gamma-rays every hour from 7 to 1 h before harvesting. BrdU was added to the cultures immediately after irradiation to estimate the cell cycle phase by studying replication band patterns for each analysed metaphase. The average number of lesions has been observed to be more related to the time elapsed between irradiation and harvesting than to the cell phase. However, the types of lesions i.e. chromatid, chromosome breaks and chromatid exchanges are closely dependent on the phase. Cells irradiated 2 h before harvesting exhibit 3 and 6 times more lesions than those irradiated 3 and 7 h before harvesting respectively. This high sensitivity of cells, 2 h before harvesting, is observed for cells irradiated during late S as well as during G2 phase.