Deficiency of nitric oxide in allergen‐induced airway hyperreactivity to contractile agonists after the early asthmatic reaction: an ex vivo study

Abstract

Using a guinea‐pig model of allergic asthma, we investigated the role of nitric oxide (NO) in allergen‐induced airway hyperreactivity after the early asthmatic reaction, by examining the effects of the NO‐synthase inhibitor Nω‐nitro‐L‐arginine methyl ester (L‐NAME) on the responsiveness to methacholine and histamine of isolated perfused tracheae from unchallenged (control) animals and from animals 6 h after ovalbumin challenge. All animals developed airway hyperreactivity to inhaled histamine at 6 h after ovalbumin challenge, with a mean 3.11 ± 0.45 fold increase in sensitivity to the agonist (P < 0.001). In perfused tracheal preparations from the ovalbumin‐challenged guinea‐pigs, the maximal responses (Emax) to methacholine and histamine were significantly enhanced compared to controls, both after intraluminal (IL) and extraluminal (EL) administration of the contractile agonists. In addition, a small but significant increase in the pD2 (‐log10 EC50) for IL and EL methacholine and for IL histamine was observed. As a consequence, the ΔpD2 (EL‐IL) for histamine was slightly decreased from 1.67 ± 0.13 to 1.23 ± 0.14 (P < 0.05). However, the ΔpD2 for methacholine was unchanged (1.85 ± 0.11 and 1.77 ± 0.12, respectively; NS). Incubation of control tracheae with 100 μm L‐NAME (IL) significantly enhanced the Emax for both IL and EL methacholine and histamine to approximately the same degree as observed after ovalbumin challenge, with no effect on the pD2 and ΔpD2 for both agonists. On the contrary, L‐NAME had no effect on Emax and pD2 values of tracheal preparations from ovalbumin‐challenged guinea‐pigs. L‐NAME (10 μm‐l mM) had no effect on methacholine‐induced contraction of isolated tracheal strip preparations obtained from control animals, indicating that L‐NAME has no antimuscarinic effect on tracheal smooth muscle. Histological examination of the intact tracheal preparations indicated epithelial and subepithelial infiltration of eosinophils after ovalbumin challenge. However, no apparent damage of the airway epithelium was observed in these preparations. The results indicate that a deficiency of NO contributes to allergen‐induced airway hyperreactivity after the early asthmatic reaction and that this deficiency appears not to be due to epithelial shedding.

Airway hyperresponsiveness in asthma: lessons fromin vitromodel systems and animal models: Fig. 1—

“…Indeed, both in vivo and ex vivo studies using the same species indicate that a deficiency of both epithelial and neuronal cNOS-derived NO underlies the development of AHR following the allergen-induced early asthmatic reaction ( fig. 1) [77,96,97]. A deficiency of cNOS activity and endogenous bronchodilating NO contributing to AHR was also demonstrated after repeated allergen challenge of sensitised guinea pigs [98,99].…”

“…In the respiratory tract, isoforms of constitutive NO synthase (NOS; cNOS) are mainly expressed in iNANC neurons (neuronal NOS (nNOS)), the endothelium (endothelial NOS (eNOS)) and the epithelium (nNOS and eNOS), which are primarily involved in the regulation of airway and vascular smooth muscle tone [76][77][78]. Moreover, eNOS-derived NO has been shown to inhibit airway inflammation by suppressing the activation of nuclear factor-kB, thereby inhibiting the expression of inducible NOS (iNOS), as well as the production of inflammatory cytokines [79][80][81][82].…”

Effect of nitric oxide synthase inhibitor on allergen- and hyperventilation-induced bronchoconstriction in guinea-pigs

“…Pulmonary iNOS has been described in endothelial and epithelial cells and in macrophages of inflamed airways, and its induction results in the production of high (micromolar) levels of NO. However, BOER et al [14] suggested that contractile agonists, such as histamine, enhanced the production of constitutive NOS (cNOS), and not iNOS. cNOS, in the airways, is basally expressed in neuronal, endothelial and epithelial cells and its activation is dependent on an agonist-or depolarization-induced increase in intracellular Ca 2+ concentration, causing the production of small (picomolar) amounts of NO.…”

Increased arginase activity contributes to airway remodelling in chronic allergic asthma

“…The preparations were attached to a perfusion holder and placed in an organ bath (37u) containing 20 mL gassed KH solution (extraluminal compartment) as described previously [17]. The tracheal lumen was perfused with recirculating KH solution from a separate 20-mL bath (intraluminal compartment) at constant flow rate, and hydrostatic pressure was measured at the proximal and distal ends of the trachea using axially centred side-hole catheters.…”

“…Increased consumption of L-arginine by arginase contributes to the development of allergen-induced AHR in acute allergic asthma by limiting the bioavailability of L-arginine to nitric oxide synthase (NOS) isozymes [13][14][15], which hydrolyse the amino acid into nitric oxide and Lcitrulline. This leads to a deficiency of bronchodilating nitric oxide, and increased formation of the highly reactive proinflammatory and procontractile nitric oxide metabolite peroxynitrite, both of which underlie AHR in animal models of allergic asthma [13][14][15][16][17][18]. In a guinea pig model of allergic asthma, inhalation of the specific arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH) acutely reversed allergeninduced AHR in vivo both after the early and late asthmatic reaction, to a similar extent as treatment with inhaled L-arginine [19].…”