LATE EFFECTS OF X-IRRADIATION IN RATS: I. LASTING CHROMOSOME ABNORMALITIES IN BONE MARROW CELLS

Abstract

The present cytogenetic study was made on the bone marrow cells of 48 male rats killed after 9 to 17 months following acute whole-body X-irradiation.
We found that exposure to a dose of 700rads of X-rays, delivered to animals at a high dose-rate (100rads/min) resulted in a widespread karyotype variability. The number of cell types were existing independently in the haemopoietic tissue within the first week after irradiation, decreased with time. The selection process of persisting abnormalities as well a further evolution of the cells with new karyotypes to clones, were evident after a month following irradiation. Consequently, the analysis of haemopoietic tissue revealed, in 92% of the late survivors, a genetically heterogeneous cell population in which the number of normal diploid cells decreased to a considerable extent. Clones increased in size with elapsing time from exposure to radiation. Thus, the mean clone cell frequency for animals killed after 9 to 17 months following irradiation ranged from 20.6±3.42% to 61.6±4.26%. Analysis of the data showed a significant positive correlation between development of clones in vivo and the survival time after irradiation (r=0.820; P<0.01). For such a finding, the occurence of large clones especially in the bone marrow of rats with growing tumors was of the great influence. Relationship between the degree of mutagenesis on the chromosome level and the process of tumor advancement is discussed.