IN-VIVO NITRIC-OXIDE DETECTION IN THE SEPTIC RAT-BRAIN BY ELECTRON-PARAMAGNETIC-RESONANCE

To detect nitric oxide (NO) in the rat brain during lipopolysaccharide (LPS)-induced sepsis, electron paramagnetic resonance (EPR) was emplo yed with the NO trapping technique, using an iron and N,N-diethyldithi ocarbamate (DETC) complex. An X-band (about 9.5 GHz) EPR system detect ed a triplet signal (g=2.038) derived from an NO-Fe-DETC complex being superimposed on the g(perpendicular to) signal of Cu-DETC complex at liquid nitrogen temperature. The height of the triplet signal peaked s even hours after injection of 40 mg/kg of LPS, and over 25 x 10(4) U/k g of IFN-gamma enhanced the LPS-induced NO formation. Pretreatment wit h N-G-monomethyl-L-arginine (NMMA), an NO synthase inhibitor, deleted only the triplet signal. A triplet signal (g(iso)=2.040, a(N)=1.28 mT) derived from the NO-Fe-DETC complex was also observed at ambient temp erature. Then, a home-built 700 MHz EPR system was used to detect an N O signal in the septic rat brain in vivo. We successfully monitored th e NO-Fe-DETC signal in the head region of a living rat under the condi tion that provided maximum height of the NO-Fe-DETC signal in the X-ba nd EPR study. Pretreatment with NMMA again deleted the NO-Fe-DETC sign al. This is the first EPR observation of endogenous NO in the brain of living rats.