Determination of kainic acid-induced release of nitric oxide using a novel hemoglobin trapping technique with...

We have demonstrated the usefulness of a novel hemoglobin-trapping technique to quantify nitric oxide (NO) concentrations in vivo. Concentric microdialysis probes were implanted into the hippocampus of rats under urethane anesthesia and perfused with 1 microM oxyhemoglobin in artificial CSF to sequester NO in extracellular fluid. The concentration of methemoglobin was then determined spectrophotometrically. The basal level of NO in hippocampus was 2.2 +/- 0.5 nM (in vitro sensitivity of the probe was 0.2 nM). Administration of 13 mg/kg, i.p., of kainic acid (KA) produced a maximal 5.3-fold increase at 100 min in NO levels (11.8 +/- 0.2 nM). This response was significantly attenuated by pretreatment with the NO synthase inhibitor N-monomethyl-L-arginine (50 mg/kg, 30 min before KA). These results demonstrate that a microdialysis probe using a novel hemoglobin-trapping technique possesses adequate sensitivity to determine the basal levels of NO and document the ability of KA to increase these levels via a NO synthase-mediated mechanism.