Immature Brain Injury via Peroxynitrite Production Induced by Inducible Nitric Oxide Synthase after Hypoxia-Ischemia in Rats

Objective: To determine whether, and if so how, iNOS expresses and affects brain injury induced by hypoxia‐ischemia in an immature brain. Material and Methods: Seven‐day‐old Wistar rat pups were exposed to right common carotid artery ligation followed by 1.5 hours of hypoxia. The time course of iNOS mRNA expression, enzymatic activity, and protein production in the cerebral cortex were determined. The extent of the infarct area in the cerebral cortex and the production of 3‐nitrotyrosine (a biomarker of peroxynitrite) were compared between the control pups and pups treated with S‐methyl‐isothiourea (a selective iNOS inhibitor). Results: In the cortex ipsilateral to carotid ligation, iNOS mRNA appeared from 6 hours to 24 hours after hypoxia‐ischemia and disappeared at 48 hours. The iNOS protein and its activity also increased at 12 hours and reached a maximum level at 48 hours after the insult. The percentage of damage in the cerebral cortex was significantly higher in the control pups than in treated pups (31.9 vs 10.6%). Tri‐nitrotyrosine following iNOS expression‐positive cells were located predominantly at the infarct and peri‐infarct regions. Conclusions: iNOS expression might be an important determinant of ischemic immature brain injury.