title: Role of the L-citrulline/L-arginine cycle in iNANC nerve-mediated nitric oxide production and airway smooth muscle relaxation in allergic asthma.
abstract: Nitric oxide synthase (NOS) converts L-arginine into nitric oxide (NO) and L-citrulline. In NO-producing cells, L-citrulline can be recycled to L-arginine in a two-step reaction involving argininosuccinate synthase (ASS) and -lyase (ASL). In guinea pig trachea, L-arginine is a limiting factor in neuronal nNOS-mediated airway smooth muscle relaxation upon inhibitory nonadrenergic noncholinergic (iNANC) nerve stimulation. Moreover, in a guinea pig model of asthma iNANC nerve-induced NO production and airway smooth muscle relaxation are impaired after the allergen-induced early asthmatic reaction, due to limitation of L-arginine. Using guinea pig tracheal preparations, we now investigated whether (i) the L-citrulline/L-arginine cycle is active in airway iNANC nerves and (ii) the NO deficiency after the early asthmatic reaction involves impaired L-citrulline recycling. Electrical field stimulation-induced relaxation was measured in tracheal open-rings precontracted with histamine. L-citrulline as well as the ASL inhibitor succinate did not affect electrical field stimulation-induced relaxation under basal conditions. However, reduced relaxation induced by a submaximal concentration of the NOS inhibitor N(omega)-nitro-L-arginine was restored by L-citrulline, which was prevented by the additional presence of succinate or the ASS inhibitor alpha-methyl-D,L-aspartate. Remarkably, the impaired iNANC relaxation after the early asthmatic reaction was restored by L-citrulline. In conclusion, the L-citrulline/L-arginine cycle is operative in guinea pig iNANC nerves in the airways and may be effective under conditions of low L-arginine utilization by nNOS (caused by NOS inhibitors), and during reduced L-arginine availability after allergen challenge. Enzymatic dysfunction in the L-citrulline/L-arginine cycle appears not to be involved in the L-arginine limitation and reduced iNANC activity after the early asthmatic reaction.
authors.affiliation: Department of Molecular Pharmacology, University Centre for Pharmacy, A. Deusinglaan 1, 9713 AV Groningen, The Netherlands. h.maarsingh@rug.nl
authors.forename: Harm
authors.initials: H
authors.lastname: Maarsingh
authors.forename: John
authors.initials: J
authors.lastname: Leusink
authors.forename: Johan
authors.initials: J
authors.lastname: Zaagsma
authors.forename: Herman
authors.initials: H
authors.lastname: Meurs
mesh_terms: D000485:Allergens / Q000276:immunology; D000818:Animals; D001120:Arginine / Q000378:metabolism*; D001123:Argininosuccinate Lyase / Q000037:antagonists & inhibitors / Q000378:metabolism; D001124:Argininosuccinate Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D001249:Asthma / Q000276:immunology / Q000378:metabolism* / Q000503:physiopathology; D002956:Citrulline / Q000378:metabolism* / Q000494:pharmacology; D004195:Disease Models, Animal; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D008297:Male; D009126:Muscle Relaxation; D009130:Muscle, Smooth / Q000294:innervation / Q000378:metabolism*; D016202:N-Methylaspartate / Q000031:analogs & derivatives / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009433:Neural Inhibition / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I / Q000037:antagonists & inhibitors / Q000378:metabolism; D010047:Ovalbumin / Q000276:immunology; D013047:Specific Pathogen-Free Organisms; D019802:Succinic Acid / Q000494:pharmacology; D014132:Trachea / Q000294:innervation / Q000378:metabolism*
chemical_list: D000485:Allergens; D004791:Enzyme Inhibitors; D002956:Citrulline; D009569:Nitric Oxide; D016202:N-Methylaspartate; C037699:2-methylaspartic acid; D010047:Ovalbumin; D001120:Arginine; D019802:Succinic Acid; D052248:Nitric Oxide Synthase Type I; D001123:Argininosuccinate Lyase; D001124:Argininosuccinate Synthase; D019331:NG-Nitroarginine Methyl Ester