title: Exposure of human lymphocytes to ionizing radiation reduces mutagenesis by subsequent ionizing radiation.
abstract: The effect of prior incubation with [3H]thymidine on survival and mutagenesis after X-irradiation of human lymphocytes was studied by incubating lymphocytes with 0.001-1.0 mu Ci/ml [3H]thymidine for 6 h at 37 degrees C and then irradiating with 150 or 300 rad. Survival was measured using lymphocyte cloning and mutagenesis was measured using 6-thioguanine selection to detect clones mutated at the hypoxanthine phosphoribosyltransferase locus. [3H]Thymidine alone had no effect on survival or mutagenesis and X-radiation alone produced the expected decrease in survival and increase in mutations. [3H]Thymidine prior to X-radiation had no effect on lethality of X-radiation but at concentrations of 0.1 and 1.0 mu Ci/ml produced a significant decrease in the number of mutations induced after both 150 and 300 rad. The results suggest that ionizing radiation, produced by disintegration of 3H, reduces the mutagenic effect of a subsequent exposure to ionizing radiation by induction of a system which prevents or repairs a restricted class of radiation damage.
mesh_terms: D002470:Cell Survival / Q000528:radiation effects; D002478:Cells, Cultured; D004261:DNA Replication / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics / Q000528:radiation effects; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects*; D009153:Mutagens; D009154:Mutation; D013866:Thioguanine / Q000633:toxicity*; D013936:Thymidine / Q000378:metabolism
chemical_list: D009153:Mutagens; D007041:Hypoxanthine Phosphoribosyltransferase; D013866:Thioguanine; D013936:Thymidine