LIPID-FREE RADICAL GENERATION AND BRAIN-CELL MEMBRANE-ALTERATION FOLLOWING NITRIC-OXIDE SYNTHASE INHIBITION DURING CEREBRAL HYPOXIA IN THE NEWBORN PIGLET

Nitric oxide (NO) is reported to cause neuronal damage through various mechanisms. The present study tests the hypothesis that NO synthase i nhibition by N-omega-nitro-L-arginine (NNLA) will result in decreased oxygen-derived free radical production leading to the preservation of cell membrane structure and function during cerebral hypoxia. Ten newb orn piglets were pretreated with NNLA (40 mg/kg); five were subjected to hypoxia, whereas the other five were maintained with normoxia. An a dditional 10 piglets without NNLA treatment underwent the same conditi ons. Hypoxia was induced with a lowered FiO(2) and documented biochemi cally by decreased cerebral ATP and phosphocreatine levels. Free radic als were detected by using electron spin resonance spectroscopy with a spin trapping technique. Results demonstrated that free radicals, cor responding to alkoxyl radicals, were induced by hypoxia but were inhib ited by pretreatment with NNLA before inducing hypoxia. NNLA also inhi bited hypoxia-induced generation of conjugated dienes, products of lip id peroxidation. Na+,K+-ATPase activity, an index of cellular membrane function, decreased following hypoxia but was preserved by pretreatme nt with NNLA. These data demonstrate that during hypoxia NO generates free radicals via peroxynitrite production, presumably causing lipid p eroxidation and membrane dysfunction. These results suggest that NO is a potentially limiting factor in the peroxynitrite-mediated lipid per oxidation resulting in membrane injury.