NITRIC-OXIDE SYNTHASE MESSENGER-RNA IN ENDOTHELIAL-CELLS - SYNERGISTIC INDUCTION BY INTERFERON-GAMMA, TUMOR-NECROSIS-FACTOR-ALPHA AND LIPOPOLYSACCHARIDE AND INHIBITION BY DEXAMETHASONE

Regulation of nitric oxide synthase mRNA by interferon-gamma, tumor ne crosis factor-alpha, bacterial lipopolysaccharide (LPS) and dexamethas one in rat aortic endothelial cells was examined. The combination of i nterferon-gamma (100 U/ml) and tumor necrosis factor-alpha (5000 U/ml) evoked a time-dependent increase in nitric oxide synthase mRNA and ni trite/nitrate production, both of which were inhibited by dexamethason e. Neither interferon-gamma (100 U/ml), tumor necrosis factor-alpha (5 000 U/ml) nor LPS (100 ng/ml) alone was capable of increasing nitric o xide synthase mRNA and nitrite/nitrate production in these cells. Howe ver, combinations of two of the three agents synergistically increased both nitric oxide synthase mRNA and nitrite/nitrate production. When the three agents were applied simultaneously, nitric oxide synthase mR NA and nitrite/nitrate production were both markedly increased. LPS co ntamination, which may affect the induction of nitric oxide synthase, was below 20 pg/ml in all experiments unless LPS was added exogenously , namely, the effects observed were those of the cytokines themselves. Our results suggest that in endothelial cells, these cytokines regula te the production of nitric oxide at the level of nitric oxide synthas e mRNA induction.