Oxidative stress alters arginine metabolism in rat brain: effect of sub-convulsive hyperbaric oxygen exposure

The effect of hyperbaric oxygenation on arginine metabolism was investigated. Rats were exposed to oxygen at 3 atmospheres absolute for 2 h. Under these conditions, lipid peroxidation and activation of the anti-oxidant system were observed. Levels of thiobarbiturate reactive substances and carbon-centered radicals were increased in the cerebral cortex, while superoxide dismutase activity was also increased in the mitochondrial and cytosolic fraction of cerebrocortical homogenates. This suggested that the increase of both Mn and Cu,Zn-superoxide dismutase activities was probably an early compensatory reaction to oxidative stress. Levels of arginine as well as its metabolite, guanidinoacetic acid, were increased in the cerebral cortex. This increase seemed to be, at least in part, explained by a decrease in the arginase activity in the same region. Moreover, arginase activity in the brain showed heterogeneous distribution. Arginine: glycine amidinotransferase activity was decreased in the pons-medulla oblongata. The observed effects of hyperbaric oxygenation seem to favor nitric oxide generation.