Nitric oxide modulates high-energy phosphates in brain regions of rats intoxicated with diisopropylphosphorofluoridate or carbofuran: prevention by N-tert-butyl-alpha-phenylnitrone or vitamin E

Acute effects of seizure-inducing doses of the organophosphate compound dii sopropylphosphorofluoridate (DFP, 1.25 mg/kg s.c.) or the carbamate insecti cide carbofuran (CF, 1.25 mg/kg s.c.) on nitric oxide (NO) were studied in the brain of rats. Brain regions (pyriform cortex, amygdala, and hippocampu s) were assayed for citrulline as the determinant of NO and for high-energy phosphates (ATP and phosphocreatine) as well as their major metabolites (A DP, AMP, and creatine). Rats, anesthetized with sodium pentobarbital (50 mg /kg i.p.), were killed using a head-focused microwave (power, 10 kW; durati on, 1.7 s). Analyses of brain regions of controls revealed significantly hi gher levels of citrulline in the amygdala (289.8 +/- 7.0 nmol/g), followed by the hippocampus (253.8 +/- 5.5 nmol/g), and cortex (121.7 +/- 4.3 nmol/g ). Levels of energy metabolites were significantly higher in cortex than in amygdala or hippocampus. Within 5 min of CF injection, the citrulline leve ls were markedly elevated in all three brain regions examined, while with D FP treatment, only the cortex levels were elevated at this time. With eithe r acetylcholinesterase (AChE) inhibitor, the maximum increase in citrulline levels was noted 30 min post-injection (> 6- to 7-fold in the cortex, and > 3- to 4-fold in the amygdala or hippocampus). Within I h following DFP or CF injection, marked declines in ATP (36-60%) and phosphocreatine (28-53%) were seen. Total adenine nucleotides and total creatine compounds were red uced (36-58% and 28-48%, respectively). The inverse relationship between th e increase in NO and the decease in high-energy phosphates, could partly be due to NO-induced impaired mitochondrial respiration leading to depletion of energy metabolites. Pretreatment of rats with an antioxidant, the spin t rapping agent N-tert-butyl-alpha -phenylnitrone (PBN, 200 mg/kg i.p.), prev ented DFP- or CF-induced seizures, while the antioxidant vitamin E (100 mg/ kg i.p. per day for 3 days) had no anticonvulsant effect. Both antioxidants , however, significantly prevented the increase of citrulline and the deple tion of high-energy phosphates. It is concluded that seizures induced by DF P and CF produce oxidative stress due to a marked increase in NO, causing m itochondrial dysfunction, and thereby depleting neuronal energy metabolites . PBN pretreatment provides protection against AChE inhibitor-induced oxida tive stress mainly by preventing seizures. Additional antioxidant actions o f PBN may contribute to its protective effects. Vitamin E has direct antiox idant effects by preventing excessive NO production.