Involvement of peroxynitrite and hydroxyradical generated from nitric oxide in hypoxia/reoxygenation injury in rat cerebrocortical slices

The changes in nitric oxide (NO) formation during hypoxia and reoxygenation were measured in slices of rat cerebral cortex, and the possible involveme nt of NO and its decomposition products, including peroxynitrite and hydrox yradical, in the hypoxia/reoxygenation injury was subsequently investigated . NO formation estimated from cGMP accumulation in the extracellular fluids . was enhanced during hypoxia and to a lesser extent in the reoxygenation p eriod. The mRNA for inducible NO synthase (NOS) was detected 3-5 h after re oxygenation, although neuronal NOS mRNA decreased after reoxygenation. Seve ral NOS inhibitors such as N-G-monomethyl-L-arginine and N-G-nitro-L-argini ne blocked not only the NO formation but also the hypoxia/reoxygenation inj ury as determined by lactate dehydrogenase (LDH) leakage. The hypoxia/reoxy genation injury was prevented by peroxynitrite scavengers including deferox amine and uric acid, or several hydroxyradical scavengers such as dimethylt hiourea, 2-mercaptopropionylglycine and D(-) mannitol. In addition, the hyp oxia/reoxygenation injury was attenuated by poly(ADP-ribose)synthetase inhi bitors such as banzamide, 3-aminobenzamide and 1,5-isoquinolinediol. On the other hand, both N-morpholinosidnonimine, a peroxynitrite generator, and h ydroxyradical-liberating solution containing FeCl3-ADP and dihydroxyfumarat e caused a marked LDH leakage in normoxic slices. These findings suggest th at the enhanced formation of NO causes hypoxia/reoxygenation injury after d egradation to peroxynitrite and hydroxyradical and the resultant activation of poly(ADP-ribose)synthetase. (C) 2000 Elsevier Science Ltd. All rights r eserved.