ENHANCEMENT OF NO PRODUCTION FROM RESIDENT PERITONEAL-MACROPHAGES BY IN-VITRO GAMMA-IRRADIATION AND ITS RELATIONSHIP TO REACTIVE OXYGEN INTERMEDIATES

The functional changes in macrophages (M phi) following exposure to a high dose (6 Gy) of gamma-rays in vitro were investigated. Resident pe ritoneal M phi obtained from C57BL/6 mice were irradiated with gamma-r ays (Cs-137, 0.3 Gy/min). High-dose irradiation enhanced nitric oxide (NO) production from M phi treated with interferon-gamma and their cyt otoxic activity. The enhancement of NO production by irradiation was a ttributed to high levels of expression of the inducible nitric oxide s ynthase. Furthermore, the participation of reactive oxygen intermediat es in NO production was examined. Nitric oxide production was not enha nced by treatment with the membrane-oxidizing agent tert-butyl hydrope roxide or the hypoxanthine/xanthine oxidase superoxide (O-2(.-))-gener ating system. On the other hand, NO production was enhanced by treatme nt with a low dose of hydrogen peroxide (H2O2), which can diffuse pass ively through the cell membrane and can be converted into hydroxyl rad icals (HO.) that cause DNA breaks. In addition, treatment with low-dos e actinomycin D, which induces DNA strand breaks, enhanced NO producti on, but hydroxyurea, which stops DNA replication without DNA strand br eaks, had no such effect. These findings suggest that DNA strand break s caused by hydroxyl radicals formed inside the cells by gamma-irradia tion, or strand breaks caused directly by radiation, plays an importan t role in the enhancement of NO production, but peroxidation of cell m embranes has little effect. Copyright (C) 1997 Elsevier Science Inc.