Abstract
It is well known that a reduced oxygen tension during irradiation causes a corresponding reduction in sensitivity to ionizing radiations. The literature on this phenomenon at the cellular level has been reviewed by Giles(1) (chromosome breakage), Muller(2) (mutations), and Gray(3). Recovery from X-ray-induced mitotic inhibition in grasshopper neuroblasts as affected by oxygen tension during irradiation of the intact egg was observed by Gaulden, Nix, and Moshman(4). They found that at 64 r the delay of mitosis was detectably decreased when embryos in vivo were irradiated in vacuo. At lower doses (3.5 and 8 r) the recovery of mitotic activity appeared to be independent of the oxygen tension around the eggs during irradiation. The small “oxygen effect'at the high dose and the lack of a detectable one at low doses may be due to the inefficiency of a vacuum in removing dissolved oxygen from the fluids of the egg. To eliminate oxygen by a vacuum or by changing the gaseous atmosphere around embryos from which the protecting egg membranes have been removed is not feasible with present technics, because osmotic changes resulting from the evaporation of water interfere with the determination of the X-ray-induced effect. Sodium hydrosulfite is very efficient in protecting bacteria against the lethal effects of X rays(5,6) and in reducing the frequency of radiation-induced chromosome aberrations(7,8). Therefore, sodium hydrosulfite, which readily combines with molecular oxygen in solution(9), was used in the following experiments to remove the oxygen dissolved in the medium.
Materials and methods. Embryos of the grasshopper Chortophaga viridifasciata (De Geer) at a stage comparable to 14 days of development at 26°C were dissected in a medium described by Shaw(10). The embryos were pretreated by transfer from the dissecting medium into paraffin chambers filled with medium that contained freshly prepared sodium hydrosulfite.
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