Arginase strongly impairs neuronal nitric oxide-mediated airway smooth muscle relaxation in allergic asthma.
BACKGROUND
Using guinea pig tracheal preparations, we have recently shown that endogenous arginase activity attenuates inhibitory nonadrenergic noncholinergic (iNANC) nerve-mediated airway smooth muscle relaxation by reducing nitric oxide (NO) production--due to competition with neuronal NO-synthase (nNOS) for the common substrate, L-arginine. Furthermore, in a guinea pig model of allergic asthma, airway arginase activity is markedly increased after the early asthmatic reaction (EAR), leading to deficiency of agonist-induced, epithelium-derived NO and subsequent airway hyperreactivity. In this study, we investigated whether increased arginase activity after the EAR affects iNANC nerve-derived NO production and airway smooth muscle relaxation.


METHODS
Electrical field stimulation (EFS; 150 mA, 4 ms, 4 s, 0.5-16 Hz)-induced relaxation was measured in tracheal open-ring preparations precontracted to 30% with histamine in the presence of 1 microM atropine and 3 microM indomethacin. The contribution of NO to EFS-induced relaxation was assessed by the nonselective NOS inhibitor Nomega-nitro-L-arginine (L-NNA, 100 microM), while the involvement of arginase activity in the regulation of EFS-induced NO production and relaxation was investigated by the effect of the specific arginase inhibitor Nomega-hydroxy-nor-L-arginine (nor-NOHA, 10 microM). Furthermore, the role of substrate availability to nNOS was measured in the presence of exogenous L-arginine (5.0 mM).


RESULTS
At 6 h after ovalbumin-challenge (after the EAR), EFS-induced relaxation (ranging from 3.2 +/- 1.1% at 0.5 Hz to 58.5 +/- 2.2% at 16 Hz) was significantly decreased compared to unchallenged controls (7.1 +/- 0.8% to 75.8 +/- 0.7%; P < 0.05 all). In contrast to unchallenged controls, the NOS inhibitor L-NNA did not affect EFS-induced relaxation after allergen challenge, indicating that NO deficiency underlies the impaired relaxation. Remarkably, the specific arginase inhibitor nor-NOHA normalized the impaired relaxation to unchallenged control (P < 0.05 all), which effect was inhibited by L-NNA (P < 0.01 all). Moreover, the effect of nor-NOHA was mimicked by exogenous L-arginine.


CONCLUSIONS
The results clearly demonstrate that increased arginase activity after the allergen-induced EAR contributes to a deficiency of iNANC nerve-derived NO and decreased airway smooth muscle relaxation, presumably via increased substrate competition with nNOS.
Maarsingh
Harm
H
Department of Molecular Pharmacology, Centre for Pharmacy, University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands. h.maarsingh@rug.nl
Leusink
John
J
Bos
I Sophie T
IS
Zaagsma
Johan
J
Meurs
Herman
H
D000818:Animals; D001119:Arginase / Q000378:metabolism*; D001120:Arginine / Q000494:pharmacology; D001249:Asthma / Q000378:metabolism* / Q000503:physiopathology*; D016084:Bronchoconstriction / Q000502:physiology; D004558:Electric Stimulation; D006168:Guinea Pigs; D006967:Hypersensitivity / Q000378:metabolism / Q000503:physiopathology; D066298:In Vitro Techniques; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000201:enzymology* / Q000294:innervation; D009569:Nitric Oxide / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism; D010047:Ovalbumin / Q000494:pharmacology; D013047:Specific Pathogen-Free Organisms; D014132:Trachea / Q000201:enzymology / Q000294:innervation
D009569:Nitric Oxide; D010047:Ovalbumin; D001120:Arginine; D052248:Nitric Oxide Synthase Type I; D001119:Arginase