A CYTOKINESIS-BLOCKED MICRONUCLEUS STUDY OF THE RADIOADAPTIVE RESPONSE OF LYMPHOCYTES OF INDIVIDUALS OCCUPATIONALLY EXPOSED TO CHRONIC DOSES OF RADIATION

Human lymphocytes pre-exposed to very low doses of ionizing radiation show an adaptive response, which make these cells less sensitive to su bsequent higher exposures. To verify the hypothesis that a similar phe nomenon can be induced by occupationally (in vivo) received doses of i onizing radiation, the cytogenetic responses of 24 medical radiation w orkers to 1 and 2 Gy gamma-irradiation in comparison with 13 non-expos ed individuals have been studied. Cytokinesis-blocked micronucleus ass ay of lymphocytes revealed that although the frequencies of spontaneou s micronuclei in radiation workers are more than non-exposed individua ls, after 1 and 2 Gy irt vitro irradiation of lymphocytes this frequen cy was found to be lower for radiation workers. The results suggest th e existence of an in vivo adaptive response in individuals chronically exposed to low dose radiation. The observation of radioresistance to higher doses of radiation in pre-exposed lymphocytes might be due to i nitial DNA damage and an induced DNA repair mechanism.