Critical dependence of the NO‐mediated component of cyclic AMP‐induced vasorelaxation on extracellular L‐arginine in pulmonary arteries of the rat

Abstract

1 A component of isoprenaline-mediated vasorelaxation in pulmonary arteries is mediated by nitric oxide (NO). We examined the eects of physiological concentrations (4400 mM) of L-arginine on isoprenaline-induced relaxation in rat pulmonary arteries, and following inhibition of L-arginine uptake with L-lysine. In addition, we examined the role of the endothelium, and whether L-arginine aected acetylcholine (ACh)-induced relaxation. 2 Isoprenaline-induced relaxation was potentiated by 400 mM L-arginine in pulmonary arteries; maximum relaxation was increased from 83+4% of initial tone to 94+4% (P50.05). L-lysine (10 mM) not only abolished the potentiation by L-arginine, but suppressed relaxation compared to control (70+4%, P50.05), even in the absence of L-arginine added to the bath. Blockade of NO synthase with 100 mM L-NMMA or removal of the endothelium inhibited isoprenaline-induced relaxation to the same extent as L-lysine, and under these conditions the presence or absence of 400 mM L-arginine made no dierence. L-lysine had no additional eect when applied in combination with L-NMMA. 3 The eect of extracellular L-arginine was concentration dependent, with an apparent EC 50 of *1±7 mM. 4 Relaxation to the membrane permeant cyclic AMP analogue CPT cyclic AMP was also potentiated by L-arginine and inhibited by L-lysine. There was however no dierence in relaxation induced by acetylcholine (ACh) in the presence of L-arginine or L-lysine, and isoprenaline-induced relaxation of mesenteric arteries was unaected by L-arginine or L-lysine. 5 These results strongly suggest that extracellular L-arginine is critically important for development of the NO-and endothelium-dependent component of cyclic AMP-induced vasorelaxation in rat pulmonary arteries, but is not required for ACh-induced relaxation. As the apparent EC 50 for this eect is in the low micromolar range it is likely to be fully activated in vivo, as plasma L-arginine is 4150 mM.

Essential role of L‐arginine uptake and protein tyrosine kinase activity for NO‐dependent vasorelaxation induced by stretch, isometric tension and cyclic AMP in rat pulmonary arteries

“…In the absence of added L-arginine the length-tension curve lay approximately midway between that in the presence of Larginine alone and those following addition of the inhibitors. This is consistent with our recent report on cyclic AMPmediated vasorelaxation, and the suggestion that even in the absence of L-arginine in the PSS there is sucient extracellular L-arginine adjacent to the endothelium, derived from endogenous sources, to partially activate the mechanism (Hucks & Ward, 2000).…”

“…Blockade of L-arginine uptake with L-lysine had an identical eect to L-NAME (EC 50 : 5.3 [71.7,+2.5] mM; maximum tension: 91+4%, n=8; P50.001); no further eect was observed when both were combined (n=4; not shown). This was similar to the eects observed for the length-tension relationship (Figure 1), and as previously described for cyclic AMP (Hucks & Ward, 2000).…”

“…Figure 4 shows the eect of erbstatin A on CPT cyclic AMPinduced vasorelaxation of PGF 2a constricted arteries. As we have previously described for phenylephrine constricted arteries (Hucks & Ward, 2000), 10 mM L-lysine caused a signi®cant rightward shift of the concentration-response curve (EC 50 : 400 mM L-arginine: 33 [76, +7] mM, n=8; L-lysine+L-arginine: 101 [725, +33] mM, n=9; P50.001), without aecting maximum relaxation (L-arginine: 115+2% initial tension; L-lysine: 121+12%). Again, erbstatin A in the presence of L-arginine had an identical eect to L-lysine (EC 50 : 102 [743, +73] mM, n=7, P50.001 compared to Larginine; maximum relaxation: 123+5%).…”

“…Indeed, classical endothelium-dependent vasodilators such as acetylcholine (ACh) do not require the presence of extracellular L-arginine (e.g. Peng et al, 1996;Hucks & Ward, 2000). It is well known however that in various systemic and pulmonary vascular diseases application of extracellular L-arginine can restore NO-dependent vasorelaxation, even though intracellular L-arginine is not decreased (e.g.…”

“…It is therefore of interest that we recently found that the NO-dependent component of isoprenaline and cyclic AMPinduced vasorelaxation in pulmonary arteries of the rat is critically dependent on uptake of extracellular L-arginine, with an EC 50 of *1 ± 7 mM (Hucks & Ward, 2000). Full activation required an extracellular concentration of *100 mM, not substantially less than that found in the plasma (*160 mM; Peng et al, 1996).…”