Production of an arginine-derived relaxing factor induced by IFN-gamma plus endotoxin in murine adenocarcinoma EMT 6 cells.

Treatment of EMT 6 mammary adenocarcinoma cells with Interferon-gamma (IFN-gamma, 10 U.ml-1) plus endotoxin lipopolysaccharide (LPS, 100 ng.ml-1) induces concomitantly a growth arrest and production of citrulline and nitrite from L-arginine. A similar L-arginine-dependent metabolism is responsible for the vascular smooth muscle relaxing effect of stimulated endothelial cells. We therefore investigated the ability of EMT 6 cells to induce the relaxation of endothelium-denuded rat aortic rings precontracted with noradrenaline (1 microM). Pretreatment of EMT 6 cells with IFN-gamma + LPS increased their relaxing potency by 5-10 times. The relaxin effects of control and treated EMT 6 cells were entirely counteracted by NG-monomethyl-L-arginine (300 microM), a specific inhibitor of nitrite and citrulline production from L-arginine, and by methylene blue (10 microM) and LY 83583 (10 microM), two inhibitors of NOo-induced activation of guanylate cyclase. The effect of NG-monomethyl-L-arginine was reversed by L- but not D-arginine (1 mM). It is concluded that IFN-gamma + LPS increase the production of a relaxing factor in EMT 6 cells through the L-arginine-NOo-synthase pathway.