Selective Inhibition of Nitric Oxide in Hypoxic-Ischemic Brain Model in Newborn Rats: Is It an Explanation for the Protective Role of Erythropoietin?

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Abstract
Erythropoietin (Epo) exerts neuroprotection against neuronal death induced by ischemia and hypoxia in vitro and in vivo. Recent studies suggest that the neuroprotective effects of Epo may depend upon different mechanisms, including the inhibition of nitric oxide (NO). We recently demonstrated that Epo exerts neuroprotection in a model of neonatal hypoxic-ischemic brain damage. In the present study, we directly determined whether systemic administration of recombinant Epo modulates cerebral NO production in a neonatal rat model of hypoxic-ischemic brain injury. Seven-day-old Wistar rat pups were subjected to left carotid artery occlusion followed by 2.5 h of hypoxic exposure. Brain nitrite levels were evaluated in both hemispheres (carotid ligated or nonligated) by Griess reagent 72 h after the hypoxic-ischemic insult. Our results show that hypoxic-ischemic insult results a significant increase in NO production as compared with NO levels in hypoxic hemispheres and control animals. A single dose of Epo treatment (1,000 U/kg i.p.) significantly decreased NO overproduction in the hypoxic-ischemic hemisphere, whereas no significant change appeared in hypoxia alone or in controls. These data suggest that the selective inhibitory effect of Epo on NO overproduction could have a neuroprotective effect in neonatal hypoxic-ischemic brain injury.