FLUOROMETRIC ASSAY OF NITRITE AND NITRATE IN BRAIN-TISSUE AFTER TRAUMATIC BRAIN INJURY AND CEREBRAL-ISCHEMIA

Nitric oxide synthase (NOS) is distributed within the brain, and nitri c oxide (NO) is felt to be involved in the pathophysiology of deterior ation after head injury and cerebral ischemia. This study determined t he levels of the stable end products of NOS (NOx = nitrite + nitrate) after traumatic brain injury (TBI) and transient cerebral ischemia. A fluorometric assay using nitrate reductase and the NADPH regenerating system was used to quantitate NOx in ultrafiltered (10-kDa cutoff) cor tical and hippocampal extracts after reduction of nitrate. In TBI rats , both the plasma and tissue showed a sharp increase in NOx levels 5 m in after injury. Plasma NOx returned to control levels by 2 h after in jury. Ipsilateral-cortex NOx levels returned to control levels similar to 6 h after injury and remained constant from 6-24 h. Contralateral- cortex returned near to control levels after 1 h. Hippocampus also fol lowed a similar trend. In gerbils, there was a significant elevation i n tissue NOx levels immediately after 10 min transient cerebral ischem ia, which gradually returned to control levels over 24 h reperfusion. This striking burst of NO synthesis immediately after injury is clearl y evident whether the injury is head trauma or ischemia, or whether th e measurements were performed on tissue or plasma. It is unknown wheth er endothelial NOS, neuronal NOS, or both caused the elevation of the NO end products seen after the CNS insults. (C) 1998 Elsevier Science B.V. All rights reserved.