BACKGROUND: Previous researches have proved that aminoguanidin can cure cerebral ischemic injury remarkably as a selective induced nitricoxide synthase (iNOS) inhibitor. However, whether nonselective NOS inhibitor could protect cerebral ischemic injury or not is unclear.OBJECTIVE: To investigate the effects of NG-nitro-L-arginine (L-NA), a nonselective nitricoxide synthase (NOS) inhibitor, on cerebral ischemic injury of rats and the possible mechanism.DESIGN: Randomized controlled study.SETTING: Pharmacological Department of Medical Academy of Science of Hebei Province.MATERIALS: A total of 56 male healthy SD rats, of grade II, weighting 250-290 g, were provided by the Experimental Animal Center of Hebei Province (certification: 04036).METHODS: The experiment was completed in the Pharmacological Department of Medical Academy of Science of Hebei Province from March 2005 to January 2006. ① Grouping: Rats were randomly divided into 3 groups: sham operation group (n=8), model group (n=24) and L-NA group (n=24). ② Modeling:Middle cerebral artery (MCA) was established on rats in model group and L-NA group with intraluminal line occlusion methods, and rats in sham operation group were separated their extal carotid arteries without occlusion of intal carotid artery. ③ Intervention study: Rats in model group and L-NA group were injected intraperitoneally with 10 mL/kg and 20 mg/kg L-NA at 2, 6 and 12 hours respectively after ischemia twice a day for 3 consecutive days. ④ Rats were sacrificed on the third day for measuring volume of cerebral infarction with image analysis and swelling degrees and activities of mitochondria with electron microscope. Effect of L-NA on ultrastructural changes of neurons in cortex was observed after ischemia.MAIN OUTCOME MEASURES: ① Volume of cerebral infarction; ② Swelling degrees, contents of nitric oxide (NO) and malondialdehyde (MDA) and activities of adenosine triphosphatase (ATPase), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in mitochondria; ③ Ultrastructural changes of mitochondria in brain tissue after cerebral ischemia.RESULTS: ① At 12 hour after ischemia, volume of cerebral infarction in L-NA group was lower than that in model group (P ＜ 0.01). ② Content of NO in mitochondria in L-NA group was decreased as compared with that in model group at 2, 6 and 12 hours after ischemia (P ＜ 0.05); swelling degree of mitochondria in brain tissue was relieved in L-NA group at 12 hour after ischemia, and content of MDA was decreased (P＜ 0.05); mitochondrial activity in L-NA group was increased at 12 hour after ischemia, and activities of ATPase, SOD and GSH-Px in mitochondria were increased (P ＜ 0.05). ③ Degrees of mitochondrial injury in brain tissue were relieved in L-NA group at 12 hour after ischemia as compared with those in model group and L-NA group at 2 and 6 hours after ischemia. CONCLUSION: ① L-NA can beneficially inhibit NO production, but not protect brain against damage in ischemia acute stage. ② L-NA might have protective effects on cerebral injury through inhibiting the production of oxygen free radical, increasing antioxidation, ameliorating energy metabolism, beneficially improving the integrity of form and function of mitochondria in brain tissue during postischemia in rats.