Function of cell membranes in cerebral cortical tissue of newborn piglets after hypoxia and inhibition of nitric oxide synthase

Hypoxia-induced brain cell membrane lipid peroxidation can be caused by free radicals that are produced during hypoxia. Recently, the production of nitric oxide (NO), a free radical, has been shown to be increased during cerebral hypoxia-ischemia. The present study tested the hypothesis that inhibition of NO synthase (NOS) reduced hypoxia-induced modifications of Na⁺,K⁺-ATPase activity, lipid peroxidation, and [³H]MK-801 binding to the N-methyl-D-aspartate (NMDA) receptor in cerebral cortical tissue of newborn piglets. Studies were performed in 26 newborn piglets. Cerebral NOS was inhibited by the i.v. administration of 25 or 50 mg/kg N(ω)-nitro-L-arginine (NNLA) over 30 min. Control animals received normal saline. Six groups of piglets were thus created (normoxia, no NNLA; normoxia + NNLA 25 mg/kg; normoxia + NNLA 50 mg/kg; hypoxia, no NNLA; hypoxia + NNLA 25 mg/kg; hypoxia + NNLA 50 mg/kg). One hour after the start of NNLA or saline infusion, hypoxia was induced by lowering the FiO₂ to 0.07 in the three hypoxia groups, whereas in the three other groups normoxia was maintained. After 60 min of hypoxia, the brain was taken out and frozen. NOS activity, Na⁺,K⁺- ATPase activity, conjugated dienes, and [³H]MK-801 binding to the NMDA receptor of cerebral cortical tissue were determined. NOS activity was reduced to 34% of its baseline value with NNLA 25 mg/kg, and to 19-27% of its baseline value with NNLA 50 mg/kg, respectively. Administration of NNLA did neither significantly alter the hypoxia-induced production of conjugated dienes, indicating lipid peroxidation nor the decrease of Na⁺,K⁺-ATPase activity after hypoxia. [³H]MK-801 binding studies of the NMDA receptor, however, showed that NNLA preserved B(max), and K(d) after hypoxia. We conclude that inhibition of NOS does not change the hypoxia-induced decrease of Na⁺,K⁺-ATPase activity and production of conjugated dienes in brain cell membranes. Inhibition of NOS preserved the binding of [³H]MK-801 to the NMDA receptor after hypoxia.