Oxidative stress during post-hypoxic-ischemic reperfusion in the newborn lamb: The effect of nitric oxide synthesis inhibition

Post-hypoxic-ischemic (HI) reperfusion induces endothelium and neurons to produce excessive amounts of nitric oxide and superoxide, leading to peroxynitrite formation, release of protein-bound metal ions (i.e. iron), and cytotoxic oxidants. We produced severe HI in 18 newborn lambs and serially determined plasma prooxidants (non protein-bound iron), lipid peroxidation (malondialdehyde), and antioxidative capacity [ratio of ascorbic acid/dehydroascorbic acid (AA/DHA), alpha-tocopherol, sulfhydryl groups, allantoin/uric acid ratio, and vitamin A] in blood effluent from the brain before and at 15, 60, 120, and 180 min after HI. The lambs were divided in three groups: six received a placebo (CONT), six received low dose (10 mg/kg/i.v.) N-omega-nitro-L-arginine (NLA-10) to block nitric oxide production, and six received high dose NLA (40 mg/kg/iv; NLA-40), immediately after completion of HI. Non-protein-bound iron increased in all groups after HI but was significantly lower in both NLA groups at 180 min post-HI (p < 0.05), the AA/DHA ratio showed a consistent decrease in CONT (at 60 min post-HI, p < 0.05), but remained stable in NLA lambs. alpha-Tocopherol decreased steadily in the CONT, but not in the NLA lambs [180 post-H: 1.9 +/- 0.9 versus 4.2 +/- 0.7 mu M (NLA-40), P < 0.05). Malondialdehyde was significantly higher in CONT lambs 120 min post-H compared with NLA groups [0.61 +/- 017 versus 0.44 +/- 0.05 mu M (NLA-40), p < 0.05]. Vitamin A and sulfhydryl groups did not differ among groups. We conclude that post-H inhibition of nitric oxide synthesis diminishes non-protein-bound iron increment and preserves antioxidant capacity.