Meurs H, Hamer M A, Pethe S, Vadon-Le Goff S, Boucher J L, Zaagsma J
Department of Molecular Pharmacology, University Centre for Pharmacy, A. Deusinglaan 1, 9713 AV Groningen, The Netherlands.
Br J Pharmacol. 2000 Aug;130(8):1793-8. doi: 10.1038/sj.bjp.0703488.
Cholinergic airway constriction is functionally antagonized by agonist-induced constitutive nitric oxide synthase (cNOS)-derived nitric oxide (NO). Since cNOS and arginase, which hydrolyzes L-arginine to L-ornithine and urea, use L-arginine as a common substrate, competition between both enzymes for the substrate could be involved in the regulation of cholinergic airway reactivity. Using a perfused guinea-pig tracheal tube preparation, we investigated the modulation of methacholine-induced airway constriction by the recently developed, potent and specific arginase inhibitor N(Omega)-hydroxy-nor-L-arginine (nor-NOHA). Intraluminal (IL) administration of nor-NOHA caused a concentration-dependent inhibition of the maximal effect (E(max)) in response to IL methacholine, which was maximal in the presence of 5 microM nor-NOHA (E(max)=31.2+/-1.6% of extraluminal (EL) 40 mM KCl-induced constriction versus 51.6+/-2.1% in controls, P<0.001). In addition, the pEC(50) (-log(10) EC(50)) was slightly but significantly reduced in the presence of 5 microM nor-NOHA. The inhibition of E(max) by 5 microM nor-NOHA was concentration-dependently reversed by the NOS inhibitor N(Omega)-nitro-L-arginine methyl ester (L-NAME), reaching an E(max) of 89.4+/-7.7% in the presence of 0.5 mM L-NAME (P<0.01). A similar E(max) in the presence of 0.5 mM L-NAME was obtained in control preparations (85.2+/-9.7%, n.s.). In the presence of excess of exogenously applied L-arginine (5 mM), 5 microM nor-NOHA was ineffective (E(max)=33.1+/-5.8 versus 31.1+/-7.5% in controls, n.s.). The results indicate that endogenous arginase activity potentiates methacholine-induced airway constriction by inhibition of NO production, presumably by competition with cNOS for the common substrate, L-arginine. This finding may represent an important novel regulation mechanism of airway reactivity.
胆碱能性气道收缩在功能上可被激动剂诱导的组成型一氧化氮合酶（cNOS）衍生的一氧化氮（NO）拮抗。由于cNOS和精氨酸酶（将L-精氨酸水解为L-鸟氨酸和尿素）都以L-精氨酸作为共同底物，这两种酶之间对底物的竞争可能参与胆碱能性气道反应性的调节。我们使用灌注豚鼠气管插管标本，研究了最近开发的强效特异性精氨酸酶抑制剂N（Ω）-羟基-L-精氨酸（nor-NOHA）对乙酰甲胆碱诱导的气道收缩的调节作用。腔内（IL）给予nor-NOHA对腔内给予乙酰甲胆碱后的最大效应（E(max)）产生浓度依赖性抑制，在5μM nor-NOHA存在时抑制作用最大（E(max)=管腔外（EL）40 mM KCl诱导收缩的31.2±1.6%，而对照组为51.6±2.1%，P<0.001）。此外，在5μM nor-NOHA存在时，pEC(50)（-log(10) EC(50)）略有但显著降低。5μM nor-NOHA对E(max)的抑制作用可被一氧化氮合酶抑制剂N（Ω）-硝基-L-精氨酸甲酯（L-NAME）浓度依赖性逆转，在0.5 mM L-NAME存在时E(max)达到89.4±7.7%（P<0.01）。在对照标本中，0.5 mM L-NAME存在时也获得了类似的E(max)（85.2±9.7%，无显著性差异）。在存在过量外源性L-精氨酸（5 mM）时，5μM nor-NOHA无效（E(max)=33.1±5.8%，对照组为31.1±7.5%，无显著性差异）。结果表明，内源性精氨酸酶活性通过抑制NO生成增强乙酰甲胆碱诱导的气道收缩，推测是通过与cNOS竞争共同底物L-精氨酸实现的。这一发现可能代表了气道反应性的一种重要的新调节机制。
