Nitric oxide generation from sodium nitroprusside and hydroxylamine in brain.

We aimed to demonstrate different modes of in situ nitric oxide (NO) generation from two NO donors in cerebral cortex of halothane anesthetized cats. NO donors were delivered by in vivo microdialysis into the cortical tissue where an NO electrode measured real-time changes in extracellular NO concentration. In vitro testing in Finger's solution revealed that sodium nitroprusside (SNP) liberates NO spontaneously in the presence of light, whereas hydroxylamine does not generate any NO under these conditions. Supplementation with 200 mM of the NO donors SNP and hydroxylamine evoked dose-related increases in NO concentration (52.0 +/- 6.7 nM, n = 5, and 14.0 +/- 3.8 nM, n = 5, respectively). The increase in NO concentration was significantly greater during SNP than during hydroxylamine delivery (p < 0.001). In contrast, CBF increased similarly under the influence of both NO donors. Electrocorticogram and cortical direct current potential remained unaffected. In conclusion, hydroxylamine is degraded into NO intracellularly and efficiently dilates cerebral blood vessels. SNP, in contrast, generates NO mainly in the extracellular space.