Effect of cyclic GMP‐dependent vasodilators on the expression of inducible nitric oxide synthase in vascular smooth muscle cells: role of cyclic AMP

1 In the present study we examined whether interleukin‐1β (IL‐1β) increases the activity of adenylyl cyclase in vascular smooth muscle cells and determined its role in the cytokine‐induced expression of the inducible nitric oxide synthase (iNOS) and activation of nuclear transcription factor‐ k B (NF‐ k B). In addition the interaction between cyclic AMP‐ and cyclic GMP‐elevating agonists on the IL‐1β‐stimulated expression of iNOS was examined. 2 Exposure of vascular smooth muscle cells to IL‐1β stimulated the formation of cyclic AMP but not of cyclic GMP. The intracellular level of cyclic AMP reached a maximum within 1 h and then gradually declined over the next 5 h. This IL‐1β (60 u ml −1 )‐stimulated formation of cyclic AMP was modest (about 3 fold at 60 u ml −1 for 1 h) compared to that evoked by isoprenaline (about 9 fold at 3 × 10 −6 m for 2 min). 3 The IL‐1β (60 u ml −1 for 24 h)‐stimulated accumulation of nitrite, which was taken as an index of NO production, was concentration‐dependently increased by preferential inhibitors of cyclic AMP‐dependent phosphodiesterases (rolipram and trequinsin). This effect was reproduced by a specific activator of the cyclic AMP‐dependent protein kinase(s) A, Sp‐8‐CPT‐cAMPS (10 −4 m ) but was prevented by a specific inhibitor of cyclic AMP‐dependent protein kinase(s) A, Rp‐8‐CPT‐cAMPS (10 −4 m ). These compounds alone [rolipram (10 −6 m ), trequinsin (3 × 10 −6 m ) and Sp‐8‐CPT‐cAMPS (10 −4 m )] slightly but significantly increased the release of nitric oxide while Rp‐8‐CPT‐cAMPS elicited no such effect. 4 Inducible NOS protein was expressed in IL‐1β (30 u ml −1 , 24 h)‐stimulated smooth muscle cells as assessed by Western blot analysis. The level of iNOS protein was markedly increased in smooth muscle cells which had been exposed to IL‐1β in combination with either rolipram (3 × 10 −6 m ) or Sp‐8‐CPT‐cAMPS (10 −4 m ) but was reduced in those exposed to IL‐1β and Rp‐8‐CPT‐cAMPS (10 −4 m ). A weak expression of iNOS protein was found in smooth muscle cells which had been exposed to either Sp‐8‐CPT‐cAMPS or rolipram alone for 24 h while Rp‐8‐CPT‐cAMPS elicited no such effect. 5 Exposure of smooth muscle cells to IL‐1β (30 u ml −1 ) for 30 min increased the level of NF‐ k B‐DNA complexes in nuclear extracts as detected by electrophoretic mobility shift assay. Similar levels of NF‐ k B‐DNA complexes were found in cells which had been exposed to IL‐1β in combination with either Sp‐8‐CPT‐cAMPS (10 −4 m ), trequinsin (10 −5 m ) or rolipram (10 −5 m ). None of the modulators alone affected the basal level of NF‐ k B binding activity. 6 NO‐donors [sodium nitroprusside (SNP) 10 −4 m ; dinitrosyl‐iron‐di‐L‐cysteine‐complex (DNIC), 10 −4 m ; 3‐morpholino‐sydnonimine (SIN‐1), 10 −4 m ] and atrial natriuretic factor (10 −6 m ) significantly increased the IL‐1β (30 or 60 u ml −1 , 24 h)‐stimulated expression of iNOS protein and activity as assessed indirectly by the conversion of oxyhaemoglobin to methaemoglobin. In the absence of IL‐1β, SNP (10 −4 m , 24 h) but not the other cyclic GMP‐dependent vasodilators caused a modest expression of iNOS protein. No such effect was found in smooth muscle cells exposed to SNP in combination with Rp‐8‐CPT‐cAMPS (10 −4 m ) while an increased level of iNOS protein was found in those exposed to SNP in combination with either Sp‐8‐CPT‐cAMPS (10 −4 m ) or rolipram (3 × 10 −6 m ). 7 Exposure of vascular smooth muscle cells to either S‐nitroso‐L‐cysteine (Cys‐SNO, 10 −4 m ), SNP (10 −4 m ) or SIN‐1 (10 −4 m ) for 35 min affected minimally the basal activation of NF‐ k B but abolished that evoked by IL‐1β (30 u ml −1 added during the last 30 min). However, addition of Cys‐SNO following the stimulation with IL‐1β (during the last 5 min of the 30 min exposure period) reduced the level of NF‐ k B‐DNA complexes only slightly. 8 These data indicate that the cyclic AMP‐dependent pathway plays a decisive role in the signal transduction cascade initiated by the activation of the IL‐1β‐receptor and leading to iNOS expression in vascular smooth muscle cells. The stimulatory effect of the cyclic AMP pathway on iNOS expression appears not to be related to the activation of NF‐ k B. In addition, cyclic GMP‐dependent vasodilators potentiate the cytokine‐stimulated expression of iNOS probably by interaction with the cyclic AMP effector pathway.