Alkoxyl Radical Generation Following Nitric Oxide Synthase Inhibition 179

Abstract

Background: Previous studies suggest that peroxynitrite is a mediator of lipid peroxidation. Hypothesis: Nitric oxide (NO) synthase inhibition by Nω-nitro-L-arginine (NNLA) will result in decreased peroxynitrite, leading to decreased alkoxyl radical, an index of lipid peroxidation during cerebral hypoxia. Subjects: 20 piglets Vn: vehicle, normoxia; Vh: vehicle, hypoxia; Nn: NNLA (40 mg/Kg), normoxia and Nh: NNLA, hypoxia. (n=5, each). Method: Tissue hypoxia was documented by measuring levels of ATP and phosphocreatine. Free radicals, trapped with PBN were measured by electron spin resonance spectroscopy (ESR). Signal characteristics were compared with chemically produced alkoxyl and hydroxyl radical. Results: Hyperfine splitting constant (Hfsc) of brain sample (αN=13.5-13.8 G, αH=2.1-2.3 G) were closely identical to reported Hfsc of alkoxyl and hydroxyl radical. The alkoxyl radical(αN=13.7 G, αH=2.2 G) was identical to those observed in hypoxic brain. Hypoxic brain tissue addition to the hydroxyl radical generating system decreased the signal by 63%, and increased signal 2500% for alkoxyl radical. Free radical intensity in Vn, Vh, Nn and Nh was 11.6 ± 4.4, 27.7± 18.8, 15.3 ± 6.5, and 11.6 ± 2.0, respectively. Free radical production was increased in Vh vs Vn and Nn (p<0.05). NNLA reduced predominantly alkoxyl radical in Nh vs Vh (p<0.05).Conclusion: Decreased generation of alkoxyl radical by NNLA suggests that peroxynitrite is a mediator of lipid peroxidation during hypoxia and NO is a limiting factor. (By NIH-HD-20337)