ABSTRACT
It has been reported that several bronchoconstrictors generate nitric oxide (NO), counteracting bronchoconstriction, and removal of bronchial epithelia reduces NO production. However, it has not been elucidated whether neurokinin A (NKA), a potent bronchoconstrictor liberated from nerve terminals, generates NO. Specific questions in this study were (1) does NKA also generate NO, (2) does NO counteract NKA-induced bronchoconstriction, and (3) does the NO generation require bronchial epithelial cells? In an in vivo study exogenous as well as endogenous (capsaicin-induced) NKA increased airway opening pressure (P(ao)) and the exhaled NO level, and both were inhibited by an antagonist selective for NK(2) receptor (a receptor for NKA), SR48968. The exhaled NO level became negligible with an inhibitor of NO synthase (NOS) type 1-3 (N(G)-nitro-L-arginine methyl ester, L-NAME) with increased P(ao), but not with a NOS type 2 inhibitor. In an in vitro study, NKA increased the nitrite/nitrate level in superfused fluid of tracheal segments. Removing smooth muscle reduced nitrite/nitrate in the fluid to negligible levels, while the level was unchanged with removal of the epithelia. Pretreatment with l-NAME enhanced the tension of epithelia-removed tracheal segments. These findings indicate that (1) NKA generates NO, (2) NO counteracts NKA-induced bronchoconstriction, and (3) NKA activates NOS in the muscle layer, independently of bronchial epithelia.
Subject(s)
Bronchoconstriction/drug effects , Muscle, Smooth/drug effects , Neurokinin A/pharmacology , Nitric Oxide/biosynthesis , Airway Resistance/drug effects , Animals , Benzamides/pharmacology , Capsaicin/pharmacology , Dose-Response Relationship, Drug , Enzyme Inhibitors/pharmacology , Epithelial Cells/physiology , Guanidines/pharmacology , Guinea Pigs , In Vitro Techniques , Male , Muscle, Smooth/metabolism , NG-Nitroarginine Methyl Ester/pharmacology , Nitrates/metabolism , Nitric Oxide Synthase/antagonists & inhibitors , Nitric Oxide Synthase/metabolism , Nitric Oxide Synthase Type I , Nitric Oxide Synthase Type II , Nitric Oxide Synthase Type III , Nitrites/metabolism , Piperidines/pharmacology , Receptors, Neurokinin-2/agonists , Receptors, Neurokinin-2/antagonists & inhibitors , Trachea/physiologyABSTRACT
The objective of this study was to determine whether endogenous nitric oxide (NO), specifically the inducible NO synthase isoform (iNOS: NOS II), reduces or amplifies lung injury in mice breathing at a high oxygen tension. Previous studies have shown that exogenous (inhaled) NO protects against hyperoxia-induced lung injury, and that endogenous NO derived from iNOS inhibits leukocyte recruitment and protects against lung injury induced by lipopolysaccharide. In the present study, hyperoxia (> 98% O(2) for 72 h) induced acute lung injury in both wild-type and iNOS-deficient mice as determined by elevated albumin and lactate dehydrogenase levels in bronchoalveolar lavage fluid (BALF) and by increased extravascular lung water. Lung injury was greater in iNOS-deficient mice than in wild-type mice and was associated with an increased number of polymorphonuclear leukocytes in BALF. iNOS messenger RNA expression levels increased in the lungs of wild-type hyperoxic mice. Nitrotyrosine, a marker of reactive NO species, was expressed in both wild-type and iNOS-deficient mice in hyperoxia, indicating an iNOS-independent pathway for protein nitration. We conclude that iNOS is capable of reducing pulmonary leukocyte accumulation and lung injury. The data indicate that iNOS induction serves as a protective mechanism to minimize the effects of acute exposure to hyperoxia.
Subject(s)
Hyperoxia/immunology , Lung Diseases/immunology , Nitric Oxide Synthase/genetics , Nitric Oxide Synthase/immunology , Acute Disease , Albumins/analysis , Animals , Bronchoalveolar Lavage Fluid/chemistry , Bronchoalveolar Lavage Fluid/cytology , Bronchoalveolar Lavage Fluid/immunology , Cell Count , Gene Expression Regulation, Enzymologic/immunology , L-Lactate Dehydrogenase/analysis , Lung Diseases/metabolism , Mice , Mice, Inbred C57BL , Mice, Knockout , Nitric Oxide Synthase Type II , Organ Size , Reverse Transcriptase Polymerase Chain Reaction , WaterABSTRACT
Exhaled nitric oxide (NO) level decreases after corticosteroid treatment in asthmatics, but the effect of a leukotriene receptor antagonist, pranlukast, on exhaled NO has not been elucidated. Pranlukast treatment in mild persistent asthmatics for 4 weeks decreased the exhaled NO level, which did not differ from the levels in healthy subjects.
Subject(s)
Anti-Asthmatic Agents/administration & dosage , Asthma/drug therapy , Asthma/metabolism , Chromones/administration & dosage , Leukotriene Antagonists/administration & dosage , Nitric Oxide/metabolism , Adult , Female , Humans , Male , Middle Aged , Receptors, Leukotriene/metabolismABSTRACT
Nitric oxide (NO) may either protect against or contribute to inflammatory lung injury. In this study we investigated whether inhalation of 20 ppm NO alters tyrosine nitration, and we assessed the degree of lung inflammation and edema in rats after lipopolysaccharide (LPS) instillation. The amount of nitrotyrosine relative to the total amount of tyrosine was measured in lung homogenates, and lung tissue sections were stained for nitrotyrosine and aminotyrosine (a reduced form of nitrotyrosine). Leukocytes in bronchoalveolar lavage fluid (BALF) were counted, and myeloperoxidase activity was measured in lung homogenate. Lung edema and inflammatory cell accumulation in lung tissue were estimated by extravascular lung water weight (EVLW) and extravascular dry lung weight (EVDW), respectively. LPS instillation caused increases in nitrotyrosine concentration and immunohistochemical staining of nitrotyrosine and aminotyrosine in the lungs. LPS instillation increased the BALF leukocyte count, myeloperoxidase activity in lung tissue, and both EVLW and EVDW. Inhalational exposure to 20 ppm NO induced nitrotyrosine and aminotyrosine formation only in bronchial epithelial cell surface of the lungs not instilled with LPS. NO inhalation reduced the increases in nitrotyrosine and aminotyrosine in LPS-instilled lung tissue as well as the leukocyte count in BALF and myeloperoxidase activity in lung tissue, but it did not significantly change EVLW or EVDW. Leukocyte depletion in LPS-instilled rats reduced interstitial inflammatory cells, which were stained with nitrotyrosine and aminotyrosine, and attenuated the nitrotyrosine staining of alveolar capillaries. These results suggest that inhalation of 20 ppm NO reduces leukocyte accumulation in the lungs and inhibits tyrosine nitration caused by LPS instillation.
