title: Radiation-induced inhibition of thymidine incorporation in vivo as a measure of the initial slope and RBEn/gamma.
abstract: Radiation damage can be measured by decreased incorporation of 3H-TdR. The early effect of total body irradiation of mice, with doses up to 300-400 rad, of gamma rays of neutrons, on thymidine-3H incorporation into the DNA of murine proliferating normal and tumor cells are described. Total body irradiation with single doses up to 300 rad resulted in a steep dose-dependent depression of 3H-TdR incorporation into the DNA of the jejunal crypt, testis, spleen, fibrosarcoma (FSa), and FSa metastasis cells. The dose required to depress 3H-TdR incorporation values to 37% of control level (D37/thymidine) after gamma-irradiation was calculated to be 405, 443, 72, 303, and 531 rad, for jejunal crypt, testis, spleen, FSa metastasis, and FSa tumor cells, respectively. The depression progressed during the first 3 hours after irradiation. After neutron irradiation, the D37/thymidine was calculated to be 81, 140, 35, and 155 rad for jejunal crypt, testis, spleen, and FSa metastasis cells, respectively. The RBEn/gamma derived from these results were 5.00, 3.16, 2.06, and 1.95 for jejunal crypt, testis, spleen, and FSa metastasis cells, respectively. These results of D37/thymidine after gamma-irradiation and the RBEn/gamma correlate well with the 1Do for the initial slope of the survival curve and RBEn/gamma published in the literature for C3H/Kam mice using the same gamma and neutron beams. These findings show that cell survival after small doses of irradiation correlate with the effect of irradiation on the actively proliferating cells at the time of irradiation.
mesh_terms: D000818:Animals; D003037:Cobalt Radioisotopes; D004247:DNA / Q000096:biosynthesis*; D004273:DNA, Neoplasm / Q000096:biosynthesis*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005354:Fibrosarcoma / Q000378:metabolism; D005720:Gamma Rays; D007583:Jejunum / Q000378:metabolism; D008297:Male; D051379:Mice; D009502:Neutrons; D011830:Radiation Effects; D012062:Relative Biological Effectiveness; D013154:Spleen / Q000378:metabolism; D013737:Testis / Q000378:metabolism
chemical_list: D003037:Cobalt Radioisotopes; D004273:DNA, Neoplasm; D004247:DNA