INTERLEUKIN-1 ACTIVATES SOLUBLE GUANYLATE-CYCLASE IN HUMAN VASCULAR SMOOTH-MUSCLE CELLS THROUGH A NOVEL NITRIC OXIDE-INDEPENDENT PATHWAY

Recent demonstration of cytokine-inducible production of nitric oxide (NO) in vascular smooth muscle cells (VSMC) from rat aorta has implica ted VSMC-derived NO as a key mediator of hypotension in septic shock. Our studies to determine whether an inducible NO pathway exists in hum an VSMC have revealed a novel cytokine-inducible, NO-independent pathw ay of guanylate cyclase activation in VSMC from human saphenous vein ( HSVSMC). Interleukin 1 (IL-1), tumor necrosis factor (TNF), interferon gamma (IFN-gamma) and Escherichia coli lipopolysaccharide (LPS) incre ased cGMP at 24 h, whereas IL-2 and IL-6 were ineffective. The effect of IL-1 on cyclic guanosine 3',5'-monophosphate (cGMP) was delayed, oc curring after 6 h of exposure, and was maximal after 10 h. Methylene b lue and LY83583 reversed the IL-1-induced increase in cGMP, suggesting that it was mediated by activation of soluble guanylate cyclase. Howe ver, IL-1-induced cGMP in HSVSMC was not inhibited by extracellular he moglobin. Also, the effect of IL-1 on cGMP was not reversed by nitro- or methyl-substituted L-arginine analogs, aminoguanidine, or diphenyle neiodonium, all of which inhibit IL-1-induced NO synthase in rat aorti c VSMC (RAVSMC). IL-1-induced cGMP in HSVSMC was also independent of t etrahydrobiopterin and extracellular L-arginine, as it was not affecte d by 2,4-diamino-6-hydroxyprytimidine, an inhibitor of tetrahydrobiopt erin biosynthesis, and was similar in L-arginine-free and L-arginine-c ontaining media. Analysis of NO synthase mRNA with the use of polymera se chain reaction indicates that levels of mRNA for inducible NO synth ase are several orders of magnitude lower in IL-1-treated human HSVSMC than in IL-1-treated RAVSMC. IL-1-induced cGMP was also NO independen t in human umbilical artery VSMC, and NO dependent in rat vena cava VS MC. Together these results indicate that IL-1 activates a novel NO-ind ependent pathway of soluble guanylate cyclase activation in human VSMC .