NITRIC OXIDE SYNTHASE INHIBITION ON FREE RADICAL GENERATION DURING CEREBRAL HYPOXIA IN NEWBORN PIGLETS. ▴ 1389

Abstract

Previous studies in vitro have shown that nitric oxide (NO) reacts with superoxide anion to form a strong oxidant, peroxinitrite, that can cause lipid peroxidation. The present study tests the hypothesis that inhibition of nitric oxide synthase by N-omega-nitro-L-arginine (NNLA) will result in decreased free radical generation and brain cell membrane lipid peroxidation during hypoxia in vivo. Twenty anesthetized, ventilated piglets were divided into 4 groups: Vn: vehicle (pH adjusted saline), normoxia; Vh: vehicle, hypoxia: Nn: NNLA, normoxia and Nh: NNLA, hypoxia. Vehicle and NNLA treated groups received 40 mg/Kg NNLA or its vehicle, respectively. Hypoxia induced with FiO2 0.07 for 60 min resulted in PaO2 18-20 mmHg, and documented biochemically by decreased ATP and phosphocreatine. Cerebral cortex was homogenized inα-phenyl-N-tert-butylnitrone (PBN). The PBN adducts were extracted in toluene and electron spin resonance spectroscopy (ESR) performed. Signal height (intensity) of spectrum divided by tissue weight is expressed in mm/g tissue. The character of the spin adduct signal was similar to that from the chemically produced alkoxyl radical. Free radical intensity in groups Vn. Vh. Nn and Nh was 11.6 ± 4.4, 27.7 ± 18.8, 15.3 ± 6.5, and 11.6 ± 2.0, respectively. Lipid peroxidation products (conjugated dienes) in groups Vn, Vh, Nn and Nh were 15 ± 34, 149 ± 46, 53± 55, and 99 ± 29 nmole/g brain, respectively. The results show that free radical production and lipid peroxidation products were increased in Vh compared with Vn and Nn (p<0.05). However, administration of NNLA significantly reduced the formation of predominantly alkoxyl radicals in the hypoxic brain (p<0.05) and reduced lipid peroxidation products. These data suggest that NO is a limiting factor in the reaction of peroxinitrite-mediated lipid peroxidation, presumably by the fact that NOS blockade directly inhibit peroxinitrite formation by reducing the one reactant, NO. (Funded by NIH20337, MOD #94-0135, UCPR-506-93)