Regulation of macrophage nitric oxide synthesis by endothelial cells: a role for N-G,N-G-dimethylarginine

N-G,N-G-dimethylarginine is an endogenous inhibitor of nitric oxide synthes is produced by endothelial cells and found in the plasma and urine of norma l adults. We have examined the ability of N-G,N-G-dimethylarginine, produce d by endothelial cells (SGHEC-7), to regulate the production of nitric oxid e by lipopolysaccharide-stimulated mouse macrophage cells (J774.2). Stimula tion of SGHEC-7 or J774.2 cells with lipopolysaccharide had no effect on th eir release of N-G,N-G-dimethylarginine into the culture supernatant. Stimu lation of J774.2 cells with lipopolysaccharide for 24 h significantly stimu lated nitric oxide production by J774.2 bur: not SGHEC-7 cells. When lipopo lysaccharide-stimulated J774.2 cells were co-cultured with endothelial cell s for 24 h, there was a significant inhibition of nitrite accumulation. The inhibition observed was dependent on the endothelial cell number (12 +/- 5 % [mean +/- SEM] following incubation with 0.6 x 10(5) cells, up to 47 +/- 8% with 4.8 x 10(5) cells). The inhibitory effect of endothelial cells was prevented by incubation with increasing concentrations of L-arginine; the I C50 was 2.9 +/- 0.6 mM arginine. Western blot analysis indicated that the e xpression of inducible nitric oxide synthase was not inhibited by co-cultur e with SGHEC-7 cells. The results presented here demonstrate that N-G,N-G-d imethylarginine synthesized by endothelial cells may inhibit nitric oxide s ynthase in adjacent cells and play a role in the regulation of nitric oxide synthesis by macrophages.