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The Journal of Neurophysiology Vol. 83 No. 4 April 2000, pp. 2022-2029
Copyright ©2000 by the American Physiological Society
Naval Medical Research Center, National Naval Medical Center, Bethesda, Maryland 20889-5607
Elayan, Ikram M.,
Milton J. Axley,
Paruchuri V. Prasad,
Stephen T. Ahlers, and
Charles R. Auker.
Effect of Hyperbaric Oxygen Treatment on Nitric Oxide and Oxygen
Free Radicals in Rat Brain. J. Neurophysiol. 83: 2022-2029, 2000. Oxygen (O2) at high
pressures acts as a neurotoxic agent leading to convulsions. The
mechanism of this neurotoxicity is not known; however, oxygen free
radicals and nitric oxide (NO) have been suggested as contributors.
This study was designed to follow the formation of oxygen free radicals
and NO in the rat brain under hyperbaric oxygen (HBO) conditions using
in vivo microdialysis. Male Sprague-Dawley rats were exposed to 100%
O2 at a pressure of 3 atm absolute for 2 h. The
formation of 2,3-dihydroxybenzoic acid (2,3-DHBA) as a result of
perfusing sodium salicylate was followed as an indicator for the
formation of hydroxyl radicals. 2,3-DHBA levels in hippocampal and
striatal dialysates of animals exposed to HBO conditions were not
significantly different from controls. However, rats treated under the
same conditions showed a six- and fourfold increase in nitrite/nitrate,
break down products of NO decomposition, in hippocampal and striatal
dialysates, respectively. This increase was completely blocked by the
nitric oxide synthase (NOS) inhibitor L-nitroarginine
methyl ester (L-NAME). Using neuronal NOS, we determined
the NOS O2 Km to be 158 ± 28 (SD) mmHg, a value which suggests that production of NO by NOS would
increase approximately four- to fivefold under hyperbaric
O2 conditions, closely matching the measured increase in
vivo. The increase in NO levels may be partially responsible for some
of the detrimental effects of HBO conditions.
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