The influence of storage time and storage temperature on the yield of chromosomal aberrations after in vitro exposure of blood lymphocytes has been investigated. Heparinized venous blood was stored at 5°, 20°, or 37°C for periods of 0, 24, 48, or 173 hr and was then given 0, 125, 250, or 500 R of x-irradiation. Immediately after exposure, the blood was cultured under standard conditions for 48 hr. Metaphases were examined for the presence of polycentrics, rings, minutes, chromatid exchanges, and breaks. Storage for 24 hr, particularly at higher temperatures, increases significantly the yield of aberrations. Storage at 5°C for 173 hr doubles the yield of radiation-induced aberrations but has no influence on aberrations present in nonirradiated blood.

The influence of AET (2-aminoethylisothiuronium bromide hydrobromide) on cytologically detectable translocations at the diakinesis-first metaphase stage of meiosis was studied and compared with earlier data on dominant lethality. AET per se does not cause any additional translocations and is ineffective in modifying nature and rate of chromosome rearrangements induced by 500R given to spermatogonia of mice. The failure of AET to modify the rate of translocations induced by x-irradiation might be explained on the basis of some germinal selection but more likely could be related to a specific action of AET on a certain male germcell stage.

The influence of fractionation intervals has been studied by scoring at the diakinesis-first metaphase stage of meiosis, the rate of translocations induced in spermatogonia by two x-irradiation exposures separated by varying time intervals. After an exposure of 500 R delivered to mouse spermatogonia in a single dose the incidence of spermatocytes carrying translocations was found to be 8.05%. The yield of translocations falls to a minimum of 5.73% at a fractionation interval of 2 hours. At a 4-hour fractionation interval the yield is significantly increased and is equal to the yield obtained with a single exposure of 500 R. The rate of translocated cells falls again to a minimum of 4.44% at the 7-hour fractionation interval and rises up to 8.40% at the 16-hour interval. Those results are interpreted in terms of differential radiosensitivity of the cell-cycle stages.

Male BALB/c mice received local irradiation to the testes with exposures of 250, 500, 750, 1000, or 1250 R of x-rays. Thirty weeks after treatment, the mice were killed, the testes were removed and used for cytological examination of spermatocytes. The chromosome rearrangements identified cytologically were all reciprocal translocations. The percentage of abnormal cells increases from 4.50% after 250 R to 7.29% after 500 R and confirms the linearity of the dose-response relationship up to 600 R. Reduction in the yield of translocations was recorded after higher x-ray doses presumably because of germinal selection. The x-ray kinetic data suggests that, at the dose levels used, the major proportion of chromosome rearrangements was produced by the passage of only one electron track and not by the interaction of two.

Male mice from the BALB/c strain were irradiated with increasing doses of X-irradiation. Ten weeks after the treatment, meiotic preparations from the testes were made by an air-drying technique. The reciprocal translocation was the most frequent chromosome rearrangement seen. No relation was found between the nature of the rearrangements and the X-ray dose. The relationship between the X-ray dose and the rate of abnormal cells appears to be linear with a regression coefficient b = 0.017121 ± 0.001048.