[Repair of chromosomal aberrations in a human peripheral blood lymphocyte system after single and split-dose...

Whole human peripheral blood was exposed either acutely to 125 or 250 R X-rays or in fractions to 125+125 R X-rays at varying cell cycle times, namely, 0, 2, 4, 6, 8, 12, 16, 24, 30, 40 or 45 hours after culture initiation. Well spread metaphase chromosomes were examined for the following types of structural chromosome aberrations: dicentrics, rings, interstitial deletions, symetrical translocations, chromatid and chromosome fragments. Most noteworthy were found to be the polycentric + ring data. With acute radiation given at any of the times over the presynthetic period, the yields of these aberrations were consistently within the range of 17-20% for the 125 R dose and 66-73% for 250 R. For either acute dose given at later times, the aberration yields decreased to fall to 1% by the end of the synthetic period. With fractionated 125+125 R exposures the following rates were obtained: irradiation at 2 hr time in culture, 44.15%; 4 hr, 50.82%; 6 hr, 55.16%; 8 hr, 58,32% (peak rate): 12 hr, 55.48%. The downward trend persisted to the end of the presynthetic period and during the synthetic period. Statistical data treatment indicated acute and fractionated exposures to differ significantly in production of polycentric+ring yields, as well as in those of other aberration types and total breakage per cell. It may be concluded from our findings that the time course of repair processes is of an undulated pattern, with peak intensity within the first hours of the presynthetic period, a fall by 8 hr and a following renewed rise; repair was found to occur nearly to the end of the synthetic period.