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  • Title: [The effect of small radiation doses: desoxyribonucleic acid (DNA) synthesis and DNA repair by the thymus, spleen and bone marrow cells of rats following fractionated whole-body X-ray irradiation].
    Author: Tempel K, Ehling G.
    Journal: Strahlenther Onkol; 1989 Sep; 165(9):672-9. PubMed ID: 2678548.
    Abstract:
    After three to seven days following to fractionated total body X-ray irradiation (TBI) (four exposures with doses of 0.3 to 5.0 cGy per fraction at intervals of 24 hours), a maximum 50 percent stimulation of the semiconservative DNA synthesis (SDS) of spleen cells was measured in vitro. This was not dependent of the fact if an acute high-dose (400 and/or 800 cGy) unique irradiation was applied after the fractionated TBI at the moment of stimulation. A significant increase of 3H-thymidine incorporation into the DNA of bone marrow and thymus cells was only found when doses of 1.25 cGy per fraction had been used. After fractionated TBI with doses of greater than or equal to 5 cGy per fraction, an increase of DNA synthesis resistant to hydroxyurea ("unprogrammed" DNA synthesis, UDS) was demonstrated in spleen cells. The UV-stimulated UDS decreased proportionately. The sedimentation of thymus, spleen, and bone marrow nucleoids in a neutral saccharose gradient gave no evidence of an increased DNA repair capacity after fractionated TBI. Whereas the SDS stimulation by fractionated TBI with small doses can be explained by a modified proliferation behavior of exposed cells, the UDS behavior of spleen cells after considerably higher radiation doses suggests regenerative processes correlated with an increased number of cells resistant to hydroxyurea and cells presenting an UV repair deficiency. These findings can be considered to be a further proof of the assumed immune-stimulating effect of small radiation doses.
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