NITRIC-OXIDE GENERATION FROM EXTRACELLULARLY APPLIED N-G-HYDROXY-L-ARGININE IN LPS-ACTIVATED RAW-264 MACROPHAGES

Lipopolysaccharide (LPS)-activated but not control RAW 264 macrophages produced nitric oxide (NO) from extracellularly-applied N-G-hydroxy-L -arginine (L-NOHA) in a concentration-dependent manner, as measured by EPR spin trapping and assays for NO2- and NO3-. This production was i nhibited by N-G-nitro-L-arginine methyl ester and N-G-monomethyl-L-arg inine, NO-synthase inhibitors, as well as by L-lysine, a competitor fo r the y(+) amino acid carrier system. No significant differences were found between L-NOHA and L-arginine with respect to the rate of NO pro duction and the effects of inhibitors. These results provide evidence that extracellular L-NOHA can enter LPS-activated RAW 264 macrophages via a cationic amino acid carrier system and be metabolized to NO by N O-synthase. The data also suggest that no alternative pathway exists f or NO production from L-NOHA in non-activated RAW 264 macrophages.