Competition between nitric oxide synthases (NOS) and arginases for their common substrate L-arginine could be involved in the regulation of cholinergic airway reactivity and subsequent airway remodeling. The aims of this study were to evaluate the relationships between the expression of this enzymatic balance and the effects of NOS and arginase inhibition on bronchoconstrictive response to acetylcholine of patients without and with early COPD. Twenty-two human bronchi (15 COPD [9 GOLD 0, 6 GOLD I, II-A], 7 non smokers) were investigated for immunohistochemistry and modulation of acetylcholine-induced airway constriction. A significantly increased expression of NOS2 in immunoblots of bronchial tissue and of its staining in smooth muscle cells was evidenced in patients with COPD as compared with control subjects whereas no modification of arginase expression was evidenced. Forced expiratory volume in one second (FEV₁) and NOS2 expression were negatively correlated (Rho=-0.54, p=0.027). Pharmacological experiments demonstrated that in COPD as compared to controls resting tension was elevated (2243±154 versus 1574±218 mg, p=0.03) and was positively correlated with the expression of NOS2 (Rho=0.61, p=0.044), whereas constrictor response to acetylcholine was similar (active tension, sensitivity [-logEC₁₀] and reactivity [slope]). The sole effect of the specific arginase inhibitor N(Omega)-hydroxy-nor-L-arginine 1 µM was to decrease sensitivity in COPD patients, whereas 1 mM L-NAME unexpectedly decreased resting tension, due to a non cGMP-dependent effect. In conclusion, an upregulation of NOS2 expression in COPD patients is involved in airway tone regulation and functional airflow limitation, whereas increased arginase activity is involved in airway sensitivity.