Nitric oxide generation from extracellularly applied NG-hydroxy- l-arginine in LPS-activated RAW 264 macrophages

Abstract

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 NO 2 − and NO 3 −. This production was inhibited by N G-nitro- l-arginine methyl ester and N G-monomethyl- l-arginine, NO-synthase inhibitors, as well as by l-lysine, a competitor for the y + amino acid carrier system. No significant differences were found between l-NOHA and l-arginine with respect to the rate of NO production 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 NO-synthase. The data also suggest that no alternative pathway exists for NO production from l-NOHA in non-activated RAW 264 macrophages.