Radiation-induced chromatid aberrations in the bone marrow and lymph nodes of the rat during the first 24 h after irradiation

Abstract

Wistar rats of both sexes were exposed to 100 R of X-rays. Chromatid-type aberrations in metaphase figures of bone marrow and lymph node cells were scored after 2, 4, 6, 8 and 24 h and 3, 5, 7, 9 and 24 h, respectively. The shape of the curve for chromatid plus isochromatid breaks in bone marrow cells versus time is exponential. It is suggested that this shape is mainly a consequence of the continuous entrance into mitosis of cells irradiated while in S phase, in addition to those that were irradiated in G 2. For lymph nodes the frequency of chromatid plus isochromatid deletions increased up to the 5th h, then began to fall off in a manner similar to that for the bone marrow. The difference in the shape of the two curves is the consequence of the different dependence on time for chromatid and isochromatid breaks in each tissue. While the frequency of chromatid breaks fell steeply with time both for the bone marrow and for lymph nodes, the frequency of isochromatid breaks remained nearly constant for bone marrow, whereas it rose to a peak at the 5th h for the lymph nodes. These differences are tentatively explained by a shift in the phases of the cell cycle sampled owing to the greater mitotic delay of G 2 cells in lymph nodes, with the suggestion that in the late S phase the frequency of isochromatid breaks is lower than in all other phases of the cell cycle.