Enhancement of bio-protective functions by low dose/dose-rate radiation

Abstract

Effects of low dose rate gamma-irradiation on the process of tumorigenesis were investigated in mice treated with a carcinogenic agent or irradiated with high dose X-rays. A prolonged gamma irradiation at approximately 1 mGy/hr suppressed the appearance of skin tumors induced by methylcholanthrene and delayed the appearance of radiation-induced thymic lymphomas in C57BL/6 mice. We also investigated the effects of low dose rate irradiation on disease model mice. In Type 11 diabetic C57BL/KsJ-db/db (db) mice, the urine glucose level was improved in some of the mice irradiated at 0.70 mGy/hr, but not in non-irradiated control mice. In severe autoimmune MRL-lpr/lpr (lpr) mice, immunological status was kept better in the mice irradiated at 0.35 or 1.2 mGy/hr. The incidence of a number of symptoms, including lymphadenopathy and proteinuria, was suppressed by the irradiation. Furthermore, for both of the strains, the low dose rate irradiation prolonged the life span of the irradiated mice.