Dose- and time-dependence of radiation-induced nitric oxide formation in mice as quantified with electron paramagnetic resonance

lit vivo nitric oxide (NO) formation was quantified in mice after exposure to high-dose whole-body X-ray irradiation. NO produced and accumulated in t he livers of irradiated mice was determined using NO trapping method with i ron-dithiocarbamate complex combined with electron paramagnetic resonance ( EPR) spectroscopy. When mice were irradiated with 50 Gy X-ray, NO formation peaked in approximately 3 h after the irradiation was terminated. Dose-dep endence study indicated that NO formation measured 5 h after irradiation wa s leveled off at the dose higher than 50 Gy. Administration of NO synthase inhibitor, No-monomethyl L-arginine (L-NMMA) shortly after irradiation comp letely abolished the NO signal, indicating that radiation-induced NO is pro duced through L-arginine-dependent NO synthase pathways. These results sugg est that irradiation of X-ray initiates inflammation processes, resulting i n delayed NO synthase expression and NO formation. (C) 2001 Academic Press.