INTERLEUKIN-1-BETA AND TUMOR-NECROSIS-FACTOR-ALPHA SYNERGISTICALLY INDUCE NO SYNTHASE IN RAT VASCULAR SMOOTH-MUSCLE CELLS

Cytokine-inducible nitric oxide (NO) production has been implicated in the pathogenesis of septic shock. The present study was designed to d etermine which cytokines induce expression of the NO synthase gene in rat aortic vascular smooth muscle cells (VSMC) in vitro and whether NO synthase gene expression is inducible in vivo. NO synthase mRNA appea red after 4-h exposure to interleukin-1 beta (IL-1 beta), and levels c ontinued to increase up to 24 h. Levels of NO synthase transcripts wer e greatest in VSMC treated with IL-1 beta (1 nM), lower in VSMC treate d with Escherichia coli lipopolysaccharide (LPS; 100 mu g/ml), and jus t detectable in VSMC treated with tumor necrosis factor-alpha (TNF-alp ha; 1 nM). IL-1 beta, TNF-alpha, and LPS each induced NO synthase acti vity, assessed by release of nitrite, conversion of L-arginine to L-ci trulline, and increased levels of guanosine 3',5'-cyclic monophosphate , whereas IL-2, IL-6, and interferon-gamma were ineffective. IL-1 beta was more potent and effective than TNF-alpha; however, submaximal con centrations of TNF-alpha acted synergistically with IL-1 beta to induc e NO synthase gene expression and activity. Inducible NO synthase mRNA was present in aorta from rats 6 h after treatment with LPS (5 mgikg) , but not at 24 h. Synergistic activation of NO synthase gene expressi on in VSMC by IL-1 beta and TNF-alpha may contribute to hypotension in sepsis.