Regulation of NANC neural bronchoconstriction in vivo in the guinea-pig: involvement of nitric oxide, vasoactive intestinal peptide and soluble guanylyl cyclase

Spasmolytic Activity of Carvone and Limonene Enantiomers

Aromatic plants produce volatile substances with high therapeutic potential. In view of the need for new respiratory and cardiovascular system pharmacological agents, the present study reports on the spasmolytic activity of two enantiomers of carvone and limonene, constituents of essential oils. The enantiomers tested showed pharmacological activity in Guinea pig trachea and rat aorta smooth muscle. No differences were observed in the pharmacological profiles of the enantiomer pairs. The oxygenated monoterpenes (+)-carvone and (-)-carvone were pharmacologically more effective than the hydrocarbon monoterpenes (+)-limonene and (-)-limonene. The results of this study show the therapeutic potential of these compounds found in many aromatic plants for the treatment of respiratory and cardiovascular system diseases.

The selective PAC1 receptor agonist maxadilan inhibits neurogenic vasodilation and edema formation in the mouse skin

We have earlier shown that PACAP-38 decreases neurogenic inflammation. However, there were no data on its receptorial mechanism and the involvement of its PAC1 and VPAC1/2 receptors (PAC1R, VPAC1/2R) in this inhibitory effect. Neurogenic inflammation in the mouse ear was induced by topical application of the Transient Receptor Potential Ankyrin 1 (TRPA1) receptor activator mustard oil (MO). Consequent neurogenic edema, vasodilation and plasma leakage were assessed by measuring ear thickness with engineer's micrometer, detecting tissue perfusion by laser Doppler scanning and Evans blue or indocyanine green extravasation by intravital videomicroscopy or fluorescence imaging, respectively. Myeloperoxidase activity, an indicator of neutrophil infiltration, was measured from the ear homogenates with spectrophotometry. The selective PAC1R agonist maxadilan, the VPAC1/2R agonist vasoactive intestinal polypeptide (VIP) or the vehicle were administered i.p. 15 min before MO. Substance P (SP) concentration of the ear was assessed by radioimmunoassay. Maxadilan significantly diminished MO-induced neurogenic edema, increase of vascular permeability and vasodilation. These inhibitory effects of maxadilan may be partially due to the decreased substance P (SP) levels. In contrast, inhibitory effect of VIP on ear swelling was moderate, without any effect on MO-induced plasma leakage or SP release, however, activation of VPAC1/2R inhibited the increased microcirculation caused by the early arteriolar vasodilation. Neither the PAC1R, nor the VPAC1/2R agonist influenced the MO-evoked increase in tissue myeloperoxidase activity. These results clearly show that PAC1R activation inhibits acute neurogenic arterial vasodilation and plasma protein leakage from the venules, while VPAC1/2R stimulation is only involved in the attenuation of vasodilation.

Autonomic neural control of the airways

The airways and lungs are innervated by both sympathetic and parasympathetic nerves. Cholinergic parasympathetic innervation is well conserved in the airways while the distribution of noncholinergic parasympathetic and adrenergic sympathetic nerves varies considerably amongst species. Autonomic nerve function is regulated primarily through reflexes initiated upon bronchopulmonary vagal afferent nerves. Central regulation of autonomic tone is poorly described but some key elements have been defined.

Low voltage vagal nerve stimulation reduces bronchoconstriction in guinea pigs through catecholamine release

OBJECTIVE

  Electrical stimulation of the vagus nerve at relatively high voltages (e.g., >10 V) can induce bronchoconstriction. However, low voltage (≤2 V) vagus nerve stimulation (VNS) can attenuate histamine-invoked bronchoconstriction. Here, we identify the mechanism for this inhibition.

METHODS

  In urethanea-nesthetized guinea pigs, bipolar electrodes were attached to both vagus nerves and changes in pulmonary inflation pressure were recorded in response to i.v. histamine and during VNS. The attenuation of the histamine response by low-voltage VNS was then examined in the presence of pharmacologic inhibitors or nerve ligation.

RESULTS

  Low-voltage VNS attenuated histamine-induced bronchoconstriction (4.4 ± 0.3 vs. 3.2 ± 0.2 cm H(2) O, p < 0.01) and remained effective following administration of a nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester, and after sympathetic nerve depletion with guanethidine, but not after the β-adrenoceptor antagonist propranolol. Nerve ligation caudal to the electrodes did not block the inhibition but cephalic nerve ligation did. Low-voltage VNS increased circulating epinephrine and norepinephrine without but not with cephalic nerve ligation.

CONCLUSION

  These results indicate that low-voltage VNS attenuates histamine-induced bronchoconstriction via activation of afferent nerves, resulting in a systemic increase in catecholamines likely arising from the adrenal medulla.

Acute cigarette smoke inhalation blunts lung responsiveness to methacholine and allergen in rabbit: differentiation of central and peripheral effects

Despite the prevalence of active smoking in asthmatics, data on the short-term effect of acute mainstream tobacco smoke exposure on airway responsiveness are very scarce. The aim of this study was to assess the immediate effect of acute exposure to mainstream cigarette smoke on airway reactivity to subsequent nonspecific and allergenic challenges in healthy control ( n = 5) and ovalbumin-sensitized rabbits ( n = 6). We combined low-frequency forced oscillations and synchrotron radiation CT imaging to differentiate central airway and peripheral airway and lung parenchymal components of the response to airway provocation. Acute exposure to smoke generated by four successive cigarettes (CS) strongly inhibited the central airway response to subsequent IV methacholine (MCh) challenge. In the sensitized animals, although the response to ovalbumin was also inhibited in the central airways, mainstream CS did not blunt the peripheral airway response in this group. In additional groups of experiments, exposure to HEPA-filtered CS ( n = 6) similarly inhibited the MCh response, whereas CO (10,000 ppm for 4 min, n = 6) or nitric oxide inhalation instead of CS (240 ppm, 4 × 7 min, n = 5) failed to blunt nonspecific airway responsiveness. Pretreatment with α-chymotrypsin to inhibit endogenous VIP before CS exposure had no effect ( n = 4). Based on these observations, the gas phase of mainstream cigarette smoke may contain one or more short-term inhibitory components acting primarily on central airways and inhibiting the response to both specific and nonspecific airway provocation, but not on the lung periphery where both lung mechanical parameters, and synchrotron-imaging derived parameters, showed large changes in response to allergen challenge in sensitized animals.

Inhibition of nitric-oxide synthase enhances antigen-induced contractions and increases release of cysteinyl-leukotrienes in guinea pig lung parenchyma: nitric oxide as a protective factor

Nitric oxide (NO) in exhaled air is a biomarker of airway inflammation. However, the role of NO in the peripheral lung is not known. The aim of this study was to determine the role of endogenous NO in antigen-induced contractions of ovalbumin (OVA)-sensitized guinea pig lung parenchyma (GPLP). The contraction in this in vitro model of the peripheral lung closely resembles the corresponding response in human airways. Cumulatively increasing concentrations (10-10,000 microg/l) of OVA induced concentration-dependent contractions of the GPLP that were enhanced by the NO synthase (NOS) inhibitors N(omega)-nitro-L-arginine (L-NOARG; 100 microM), N(omega)-monomethyl-L-arginine (100 microM), N(omega)-nitro-L-arginine methyl ester (100 microM), and N-(3-(aminomethyl)benzyl)acetamidine (1400W; 1 microM). The enhancement induced by L-NOARG was reversed by coadministration with the 5-lipoxygenase inhibitor (R)-2-[4-(quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid (BAY x1005; 3 microM), whereas coadministration of L-NOARG with the cyclooxygenase inhibitor indomethacin (10 microM) did not change the effect of L-NOARG alone. L-NOARG (100 microM) did not affect the cumulative concentration-response relations for either leukotriene (LT) D4 (0.1-100 nM) or histamine (1-30 microM). The NO donor NONOate (0.001-100 microM) was ineffective in GPLP but potently relaxed precontracted guinea pig pulmonary artery. Furthermore, L-NOARG enhanced the release of LTE4 and decreased the release of prostaglandin E2 induced by OVA. In conclusion, endogenous NO exerts an inhibitory effect on antigen-induced contractions in the peripheral lung. The action of NO apparently involves inhibition of the release of mediators rather than direct relaxation of airway smooth muscle. The findings support the belief that endogenous NO has a protective anti-inflammatory effect in the airways.

Nitric oxide in health and disease of the respiratory system

During the past decade a plethora of studies have unravelled the multiple roles of nitric oxide (NO) in airway physiology and pathophysiology. In the respiratory tract, NO is produced by a wide variety of cell types and is generated via oxidation of l-arginine that is catalyzed by the enzyme NO synthase (NOS). NOS exists in three distinct isoforms: neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS). NO derived from the constitutive isoforms of NOS (nNOS and eNOS) and other NO-adduct molecules (nitrosothiols) have been shown to be modulators of bronchomotor tone. On the other hand, NO derived from iNOS seems to be a proinflammatory mediator with immunomodulatory effects. The concentration of this molecule in exhaled air is abnormal in activated states of different inflammatory airway diseases, and its monitoring is potentially a major advance in the management of, e.g., asthma. Finally, the production of NO under oxidative stress conditions secondarily generates strong oxidizing agents (reactive nitrogen species) that may modulate the development of chronic inflammatory airway diseases and/or amplify the inflammatory response. The fundamental mechanisms driving the altered NO bioactivity under pathological conditions still need to be fully clarified, because their regulation provides a novel target in the prevention and treatment of chronic inflammatory diseases of the airways.

Nitric oxide and vasoactive intestinal peptide as co-transmitters of airway smooth-muscle relaxation: analysis in neuronal nitric oxide synthase knockout mice

BACKGROUND

Both vasoactive intestinal peptide (VIP) and nitric oxide (NO) relax airway smooth muscle and are potential co-transmitters of neurogenic airway relaxation. The availability of neuronal NO synthase (nNOS) knockout mice (nNOS-/-) provides a unique opportunity for evaluating NO.

OBJECTIVE

To evaluate the relative importance of NO, especially that generated by nNOS, and VIP as transmitters of the inhibitory nonadrenergic, noncholinergic (NANC) system.

STUDY DESIGN

In this study, we compared the neurogenic (tetrodotoxin-sensitive) NANC relaxation of tracheal segments from nNOS-/- mice and control wild-type mice (nNOS(+/+)), induced by electrical field stimulation (EFS). We also examined the tracheal contractile response to methacholine and its relaxant response to VIP.

RESULTS

EFS (at 60 V for 2 ms, at 10, 15, or 20 Hz) dose-dependently reduced tracheal tension, and the relaxations were consistently smaller (approximately 40%) in trachea from nNOS-/- mice than from control wild-type mice (p < 0.001). VIP (10(- 8) to 10(-6) mol/L) induced concentration-dependent relaxations that were approximately 50% smaller in nNOS-/- tracheas than in control tracheas. Methacholine induced concentration-dependent contractions that were consistently higher in the nNOS-/- tracheas relative to wild-type mice tracheas (p > 0.05).

CONCLUSION

Our data suggest that, in mouse trachea, NO is probably responsible for mediating a large (approximately 60%) component of neurogenic NANC relaxation, and a similar (approximately 50%) component of the relaxant effect of VIP. The results imply that NO contributes significantly to neurogenic relaxation of mouse airway smooth muscle, whether due to neurogenic stimulation or to the neuropeptide VIP.

Multiple roles of nitric oxide in the airways

Nitric oxide is endogenously released in the airways by nitric oxide synthase. Functionally, two isoforms of this enzyme exist: constitutive and inducible. The former seems to protect airways from excessive bronchoconstriction while the latter has a modulatory role in inflammatory disorders of the airways such as asthma. This review explores the physiological and pathophysiological role of endogenous nitric oxide in the airways, and the clinical aspects of monitoring nitric oxide in exhaled air of patients with respiratory disease.

Reactive nitrogen and oxygen species in airway inflammation

The free radical nitric oxide (NO) is an important mediator of many biological processes. Interestingly, the molecule appears to be a two-edged sword. Apart from NO having a function as a paracrine messenger, NO-derived oxidants are important weapons against invading pathogens. The role of NO in the airways is similarly ambiguous. Besides the task as a bronchodilator, NO and its derivatives play a role in the pathophysiology of asthma via their putative damaging effects on the airways. This deleterious effect can be increased by a nitrosative response to respiratory tract infections, since both the infectious agent and the host may suffer from the consequent nitrosative stress. Interestingly, respiratory infections can also compromise the beneficial (bronchodilator) effects of NO. This paper gives an overview on NO and its derivatives in the pathophysiology of airway inflammation.

Apocynin and 1400 W prevents airway hyperresponsiveness during allergic reactions in mice

1. The contribution of reactive nitrogen species to the development of airway hyperresponsiveness in a mouse model of allergic inflammation was investigated by the use of selective inhibitors of nitric oxide and superoxide formation. 2. Sensitized mice, repeatedly challenged with ovalbumin showed a significant (P<0.001, n=9) increase in airway responsiveness measured using whole body plethysmography. This hyperresponsiveness was accompanied by an influx of eosinophils into the airway lumen and increased levels of ovalbumin-specific serum IgE. 3. Treatment of mice with the iNOS inhibitor 1400 W or the NADPH-oxidase inhibitor apocynin did not significantly alter cellular influx into the airway lumen nor serum ovalbumin specific IgE. In contrast, apocynin as well as 1400 W inhibited ovalbumin-induced airway hyperresponsiveness (P<0.001 and P<0.05 respectively, n=9). Furthermore, the airways of allergen challenged animals showed clear 3-nitrotyrosine staining, which was mainly located in eosinophils. Remarkably, treatment with apocynin or 1400 W did not alter 3-nitrotyrosine staining. 4. These data suggest that the development of airway hyperresponsiveness during the airway inflammation upon ovalbumin challenge is dependent on the release of both superoxide and nitric oxide and is therefore likely to be dependent on reactive nitrogen species. This mechanism, however, is not reflected by 3-nitrotyrosine formation in the airways.

Effects of the nitric oxide/cGMP system compared with the cAMP system on airway mucus secretion in the rat

Mucus secretion of the airways is under the control of a variety of intracellular second messenger systems. Cyclic nucleotides such as cGMP, coupled to the recently discovered nitric oxide system, and cAMP are of outstanding interest in this respect. The present study used the modified Ussing chamber technique and mucins labelled with (35)SO(4) to investigate mucus secretion in the rat trachea to clarify the contribution of these different second messenger systems to the control of mucin secretion.A variety of drugs affecting either the generation or the breakdown of the respective cyclic nucleotides were used. Neither drugs interfering with nitric oxide synthase nor the phosphodiesterase isoenzyme responsible for cGMP breakdown nor cGMP analogues were able to affect mucus secretion. In contrast, stimulation of adenylate cyclase or inhibition of the respective phosphodiesterase resulted in a potent increase of mucus secretion. In conclusion, we failed to show the involvement of the nitric oxide/cGMP system, whereas the cAMP system seems to be a very efficient regulator of mucus secretion in the rat trachea.

Detection of nitric oxide release induced by bradykinin in guinea pig trachea and main bronchi using a porphyrinic microsensor

Indirect evidence using nitric oxide (NO) synthase (NOS) inhibitors suggests that in guinea-pig airways bradykinin releases bronchoprotective NO. In this study, using a recently developed electrochemical method of NO measurement based on a porphyrinic microsensor, we investigated whether bradykinin releases NO from guinea-pig airways and whether the epithelium is the main source of NO. Further, the Ca(2+)-dependence of bradykinin-induced NO release was assessed stimulating airway preparations with bradykinin in Ca(2+)-free conditions. We also studied the immunohistochemical distribution of the Ca(2+)- dependent constitutive isoforms of NOS (constitutive NOS [cNOS]: neuronal and endothelial [ecNOS]) in our preparations. The porphyrinic microsensor was placed in the bathing fluid onto the mucosal surface of tracheal or main bronchial segments. Addition of bradykinin vehicle (0.9% saline) did not cause any detectable change of the baseline signal. Addition of bradykinin caused an upward shift of the baseline that reached a maximum within 1 to 2 s. The amplitude of the response to bradykinin was concentration-dependent between the range 1 nM to 10 microM, with a maximum effect at 10 microM. Bradykinin-induced NO release was higher in tracheal than in main bronchial segments. The selective bradykinin B(2) receptor antagonist D-Arg(0)-[Hyp(3), Thi(5), D-Tic(7), Oic(8)]bradykinin (1 microM) inhibited NO release induced by a submaximum concentration of bradykinin (1 microM). The ability of bradykinin to release NO was markedly reduced in epithelium-denuded segments, and abolished in Ca(2+)-free conditions and after pretreatment with N(G)-monomethyl-L-arginine (100 microM), but not with N(G)-monomethyl-D-arginine. Both cNOS isoforms were present in trachea and main bronchi, ecNOS being the predominant isoform in the epithelium. The study shows that bradykinin via B(2) receptor activation caused a rapid and Ca(2+)-dependent release of NO, mainly, but not exclusively, derived from the epithelium. It also shows that both cNOS isoforms may be involved in bradykinin-evoked NO release.

Bronchoconstriction induced by citric acid inhalation in guinea pigs: role of tachykinins, bradykinin, and nitric oxide

Gastroesophageal acid reflux into the airways can trigger asthma attacks. Indeed, citric acid inhalation causes bronchoconstriction in guinea pigs, but the mechanism of this effect has not been fully clarified. We investigated the role of tachykinins, bradykinin, and nitric oxide (NO) on the citric acid- induced bronchoconstriction in anesthetized and artificially ventilated guinea pigs. Citric acid inhalation (2-20 breaths) caused a dose-dependent increase in total pulmonary resistance (RL). RL value obtained after 10 breaths of citric acid inhalation was not significantly different from the value obtained after 20 breaths (p = 0.22). The effect produced by a half-submaximum dose of citric acid (5 breaths) was halved by the bradykinin B2 receptor antagonist HOE 140 (0.1 micromol x kg-1, intravenous) and abolished by the tachykinin NK2 receptor antagonist SR 48968 (0.3 micromol x kg-1, intravenous). Bronchoconstriction induced by a submaximum dose of citric acid (10 breaths) was partially reduced by the administration of HOE 140, SR 48968, or the NK1 receptor antagonist CP-99,994 (8 micromol x kg-1, intravenous) alone and completely abolished by the combination of SR 48968 and CP-99,994. Pretreatment with the NO synthase inhibitor, L-NMMA (1 mM, 10 breaths every 5 min for 30 min) increased in an L-arginine-dependent manner the effect of citric acid inhalation on RL. HOE 140 and CP-99,994 markedly reduced the L-NMMA-potentiated bronchoconstriction to inhaled citric acid. We conclude that citric acid-induced bronchoconstriction is caused by tachykinin release from sensory nerves, which, in part, is mediated by endogenously released bradykinin. Simultaneous release of NO by citric acid inhalation counteracts tachykinin-mediated bronchoconstriction. Our study suggests a possible implication of these mechanisms in asthma associated with gastroesophageal acid reflux and a potential therapeutic role of tachykinin and bradykinin antagonists.

Transition of functional innervation in the developing porcine airway from nitrergic to catecholaminergic

1. We determined the distribution and chemical nature of the inhibitory neurotransmitter(s) to the airway smooth muscle (ASM) before and after birth. 2. Relaxation responses to electrical field stimulation (EFS) were studied in isovolumic bronchial segments from foetal (approximately 100/115 days gestation) and adult (25 kg) pigs, and in isovolumic tracheal segments from the foetus, and tracheal smooth muscle strips from the adult pig. Preparations were conditioned in low doses of atropine (10(-7) M) to reduce the effects of excitatory neurotransmission and then exposed to carbachol to produce submaximal muscle tone. Some studies were also carried out on bronchial segments from 4 week old pigs. 3. EFS (65 V, 2 ms, 5-20 Hz for 5 s) produced a TTX-sensitive relaxation in epithelium-intact and epithelium-denuded preparations. In foetal bronchial and tracheal preparations, EFS-induced relaxation was strongly inhibited by N(G)-nitro-L-arginine (L-NOARG, 10(-6) to 10(-4) M; P<0.01-0.001). However, in the adult, only relaxations of the trachea were inhibited by L-NOARG; bronchi were resistant to L-NOARG and also to N-nitro-L-arginine methyl ester (L-NAME, 10(-4) M). The inhibitory actions of L-NOARG (10(-6) to 10(-4) M) were substantially reversed by 10(-2) M L-arginine. Experiments with bronchial segments from 4 week old pigs showed partial inhibition of relaxations by L-NOARG. 4. The L-NOARG-insensitive relaxations recorded in the adult bronchus were blocked by propranolol (10(-6) M). 5. The onset of relaxation to EFS was more prompt and the rate of relaxation more rapid in foetal bronchi than in adult bronchi (P<0.0005). Maximum relaxation and recovery times were the same. 6. Foetal and adult bronchi were relaxed by sodium nitroprusside (SNP) with similar sensitivity and maximum effect. The rate of relaxation to SNP was not different in the two ages. 7. In the absence of atropine and carbachol, excitatory cholinergic responses to EFS (65 V, 2 ms, 5 Hz for 20 s) were not altered by L-NOARG (10(-4) M) or L-NAME (10(-4) M) in the adult bronchus but were modestly increased by L-NOARG in the foetal bronchus (P<0.01). 8. The tracheobronchial tree appears functionally innervated by nitrergic input to the smooth muscle before birth. However, at or after 4 weeks of age the inhibitory neural input to the bronchi is catecholaminergic, but it remains nitrergic in the trachea. There is also a weak nitrergic pre- or postsynaptic inhibition of the effects of cholinergic neurotransmission in the foetal bronchus but not in the adult.

Eosinophilic leukocyte accumulation during vagally induced bronchoconstriction

Eosinophilic leukocytes (eosinophils) are important effector cells in allergic inflammatory diseases such as asthma, in which significant accumulation of these cells is observed in the bronchial mucosa. However, there is little information about the relationships between bronchoconstriction and accumulation of eosinophils. We hypothesized that eosinophils are retained in the bronchial vasculature in the inner airway wall during bronchoconstriction because of deformation of the mucosal membrane. To test this hypothesis we induced unilateral bronchoconstriction in open chest guinea pigs by stimulating the right vagus nerve and compared the accumulation of eosinophils in the airway wall of the constricted and contralateral unconstricted lungs using histologic specimens. Results show that the density of eosinophils (number of cells/wall area) significantly increased in the inner wall and decreased in the adventitia of the constricted airways compared with the contralateral unconstricted airways. There was a positive relationship between the amount of smooth muscle shortening and the eosinophil density in the inner wall. On the other hand, this relationship was significantly negative in the adventitia. Atropine completely inhibited the eosinophil accumulation in the inner wall. These data suggest that eosinophils can accumulate in the airway inner wall during bronchoconstriction because of geometrical factors.

Cigarette smoke-inhibition of neurogenic bronchoconstriction in guinea-pigs in vivo: involvement of exogenous and endogenous nitric oxide

1. We investigated the effect of acute inhalation of cigarette smoke on subsequent non-adrenergic, non-cholinergic (NANC) neural bronchoconstriction in anaesthetized guinea-pigs in vivo by use of pulmonary insufflation pressure (PIP) as an index of airway tone. The contribution of endogenous nitric oxide (NO) was investigated with the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). The contribution of plasma exudation to the response was investigated with Evans blue dye as a plasma marker. 2. Inhalation of 50 tidal volumes of cigarette smoke or air had no significant effect on baseline PIP. In the presence of propranolol and atropine (1 mg kg(-1) each), electrical stimulation of the vagus nerves in animals given air 30 min previously induced a frequency-dependent increase in PIP above sham stimulated controls (16 fold increase at 2.5 Hz, 24 fold increase at 10 Hz). In contrast, in smoke-exposed animals, the increase in subsequent vagally-induced PIP was markedly less than in the air controls (90% less at 2.5 Hz, 76% less at 10 Hz). 3. L-NAME (10 mg kg[-1]), given 10 min before air or smoke, potentiated subsequent vagally-induced (2.5 Hz) NANC bronchoconstriction by 338% in smoke-exposed animals, but had no significant effect in air-exposed animals. The inactive enantiomer D-NAME (10 mg kg[-1]) had no effect, and the potentiation by L-NAME was partially reversed by the NO-precursor L-arginine (100 mg kg[-1]). Vagal stimulation did not affect the magnitude of vagally-induced bronchoconstriction 30 min later. 4. Cigarette smoke exposure reduced the magnitude of subsequent bronchoconstriction induced by neurokinin A (NKA) by 37% compared with the effect of NKA in air-exposed animals. L-NAME had no significant effect on the smoke-induced inhibition of NKA-induced bronchoconstriction. 5. Vagally-induced plasma exudation in the main bronchi was greater in smoke-exposed animals compared with air-exposed animals (120% greater at 2.5 Hz, 82% greater at 10 Hz). 6. We conclude that cigarette smoke-induced inhibition of subsequent NANC neurogenic bronchoconstriction is not associated with inhibition of airway plasma exudation and is mediated in part via exogenous smoke-derived NO, or another bronchoprotective molecule, and by endogenous NO.

Histaminic bronchospasm potentiated by adenosine: investigation of the mechanisms

In anaesthetized guinea pigs, adenosine enhances the histamine-induced bronchospasm by means of a mechanism partly involving non-adrenergic-non-cholinergic (NANC) nerves, not related to capsaicin-sensitive neurons (Breschi et al., 1994). In the present paper, we excluded any interference by adenosine with the mediators known to be present in the airway inhibitory NANC system, VIP (vasoactive intestinal polypeptide) and NO (nitric oxide). The use of alpha-chymotrypsin or L-N(G)-nitro-arginine methyl ester (L-NAME) failed to modify the potentiation under study. The effects of adenosine were further investigated by studying whether an increased release of excitatory mediators from non-neural cells, in particular 5-HT (5-hydroxytryptamine, serotonin) and arachidonic products, was involved. In this connection, methysergide did not significantly affect the modulatory action of adenosine, revealing that the release of 5-HT was also not involved. Inhibition was obtained with hydrocortisone and with nordihydroguaiaretic acid, but not with indomethacin or with the mastocyte membrane stabilizer, sodium cromoglycate. This evidence suggests that lipooxygenase products, not derived from mastocytes, probably participate in the potentiating effect of adenosine.

Neural reflex-mediated tracheal response during bronchoconstriction induced by ovalbumin antigen in guinea pigs

1. The biphasic reflex tracheal response (constriction followed by dilatation) occurred during bronchoconstriction induced by inhalation of ovalbumin antigen (OA) in sensitized guinea pigs. 2. The reflex tracheal constriction was largely reduced by atropine, and the dilatation was inhibited by propranolol and N omega-nitro-L-arginine methyl ester (L-NAME). The noradrenaline, adrenaline, cyclic AMP, and cyclic GMP contents in the tracheal segment were significantly higher during reflex tracheal dilatation. 3. These findings suggest that cholinergic nerves may mediate reflex tracheal constriction and that adrenergic and NOergic nerves may mediate the ensuing reflex tracheal dilatation.

Inhibitory effect of KW-4679, an anti-allergic drug, on tachykinin-mediated airway response induced by electrical vagal stimulation in guinea pigs

We examined the effect of KW-4679 ((Z)-11-[(3-dimethylamino) propylidene]-6,11-dihydro-dibenz[b,e]oxepin-2-acetic acid monohydrochloride), an anti-allergic drug, on the tachykinin-mediated airway response in guinea pigs. Electrical stimulation of the vagus nerve in atropine-treated and propranolol-treated guinea pigs caused a 38.1% decrease in dynamic compliance (Cdyn), which was suppressed by the combination of the tachykinin NK1-receptor antagonist (+/-)-CP-96345 and NK2-receptor antagonist SR 48968. KW-4679 at a dose of 3 mg/kg significantly reduced the decrease in Cdyn (P < 0.05). On the other hand, KW-4679 did not inhibit substance P or neurokinin A-induced decrease in Cdyn. These results suggest that KW-4679 may inhibit the tachykininergic airway response by prejunctional inhibition of peripheral sensory nerves.

Nitric oxide inhibition of basal and neurogenic mucus secretion in ferret trachea in vitro

1. In order to examine the role of nitric oxide (NO) on airway mucus secretion we studied the effects of the nitric oxide synthase (NOS) inhibitor L-N(G)-monomethyl-L-arginine (L-NMMA), a novel nitric oxide donor, (+/-)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide (FK409), and the NO precursor L-arginine on basal mucus secretion in the ferret trachea in vitro in Ussing chambers. We also determined the effects of these agents upon secretion induced by electrical stimulation of nerves or by acetylcholine (ACh). We used 35SO4 as a mucus marker. 2. L-NMMA (0.01-1 mM) increased basal output of 35SO4-labelled macromolecules with a maximal increase above baseline of 248% at 0.1 mM L-NMMA. L-Arginine (1 mM) alone had no significant effect on basal secretion but reversed the potentiating effect of L-NMMA on basal secretion. L-NMMA-induced increases in basal mucus secretion were sustained for at least 30 min in the continuing presence of the NOS inhibitor. In contrast to the potentiating effects of L-NMMA, FK409 (100 nM) reduced basal secretion by 60% (at 1 nM and at 10 nM it was without effect). 3. Electrical stimulation (50 V, 10 Hz, 0.5 ms for 5 min) increased 35SO4 output by 174%. L-NMMA (1 and 10 mM) present during stimulation of tracheal segments resulted in significant potentiations of 214% and 116%, respectively, of the neurogenic response. The potentiated response to 10 mM L-NMMA was reversed by L-arginine (1 mM). At this dose L-arginine had no effect itself on basal secretion. In contrast to the potentiating effects of L-NMMA on neurogenic secretion, FK409 at 10 nM and 100 nM inhibited the neurogenic response by 98% and 99%. 4. At all concentrations tested, neither L-NMMA (0.01 mM-1 mM) nor FK409 (1-100 mM) had any significant effect on ACh-induced mucus secretion. 5. These observations lead us to conclude that nitric oxide, derived from constitutive NO synthase, acts as an endogenous inhibitor of both basal and neurogenic mucus secretion in ferret trachea in vitro.

Characteristics of vagal reflex-mediated tracheal response induced by bronchoconstriction in guinea pigs

The reflex tracheal response induced by bronchoconstriction was investigated using a newly devised tracheo-bronchi preparation in anesthetized guinea pigs. Tracheal constriction and subsequent dilatation were observed in response to bronchoconstriction induced by the inhalation of 0.001-0.01% histamine and 0.003-0.03% acetylcholine. These tracheal responses were abolished by cervical vagotomy or treatment of the tracheal site with 1% tetrodotoxin. Tracheal constriction and dilatation were significantly inhibited by 0.1% atropine and 1% propranolol, respectively. When high tracheal tone was induced by 0.01% serotonin, the residual tracheal dilatation observed in the presence of propranolol was enhanced, while dilatation was completely inhibited by 1% hexamethonium. Dilatation was also suppressed by 1% N omega-nitro-L-arginine methyl ester (L-NAME) and 1% methylene blue. The tracheal constriction produced by bronchoconstriction was significantly enhanced by propranolol 2 mg/kg, i.v. and L-NAME 10 mg/kg, i.v. These results demonstrate that a vagally mediated reflex tracheal response (constriction followed by dilatation) is induced by bronchoconstriction in anesthetized guinea pigs. Cholinergic nerves may mediate the constriction, and adrenergic and nonadrenergic noncholinergic (NANC) inhibitory nerves may mediate the dilatation. Furthermore, NO may be involved in the NANC reflex tracheal dilatation.

K+ channel openers produce epithelium-dependent relaxation of the guinea-pig trachea

The relaxant effects of the K+ channel openers, NIP-121, (+)-7,8-dihydro-6,6-dimethyl-7-hydroxy-8-(2-oxo-piperidin-1-yl)-6H - pyrano[2,3-f]benz-2,1,3-oxadiazole, and cromakalim, were investigated in epithelium-intact and -denuded tracheal spirals isolated from guinea-pigs. In the presence of 5 microM indomethacin, NIP-121 (0.01-1 microM) and cromakalim (0.1-10 microM) relaxed, in a concentration-dependent manner, epithelium-intact and -denuded trachea precontracted with a thromboxane A2 mimetic, U46619, 9,11-dideoxy-9 alpha, 11 alpha-methanoepoxy-prostaglandin F2 alpha (30 nM). The relaxations of epithelium-denuded trachea were significantly decreased as compared with those of epithelium-intact trachea. The relaxations induced by salbutamol or aminophylline were not affected by epithelium removal. In epithelium-intact trachea, the NIP-121- and cromakalim-induced relaxations were not modulated by the neutral endopeptidase inhibitor, phosphoramidon (10 microM), or the nitric oxide synthesis inhibitor, N omega-nitro-L-arginine (100 microM). However, the guanylate cyclase inhibitor, methylene blue (100 microM), significantly reduced NIP-121- and cromakalim-induced relaxation of epithelium-intact trachea. Methylene blue also reduced sodium nitroprusside-induced relaxation but did not affect isoprenaline-induced relaxation. These findings suggest that the K+ channel openers, NIP-121 and cromakalim, may induce, at least in part, epithelium-dependent and methylene blue-sensitive relaxation of the guinea-pig isolated trachea.

Endogenous nitric oxide modulation of potassium-induced changes in guinea-pig airway tone

1. An experimental set up is used whereby the serosal (out)side or mucosal (in)side of the guinea-pig isolated tracheal tube can be stimulated selectively with drugs and reactivity measured. 2. Potassium induces a concentration-dependent (5-70 mM) monophasic contraction of tracheal tubes when added on the outside. In contrast, on the inside, potassium induces a concentration-dependent relaxation at low concentrations (5-40 mM) which was reversed into a contraction up to approximately basal tone at higher concentrations (50-70 mM). 3. Epithelium denudation reversed the potassium-induced relaxation into a contraction. Interestingly, in the 'half' epithelium-denuded trachea the contractions were significantly (P < 0.01) reduced by 46% compared to complete epithelium-denuded tissues. 4. Incubation with the nitric oxide (NO) synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 120 microM) for 30 min on the inside of the tracheal tube completely prevented the relaxation. However, L-NAME did not reverse the potassium-induced relaxation into a contraction. This indicates that potassium does not penetrate through the epithelial layer. 5. It is concluded that depolarization of smooth muscle cells leads to a monophasic contraction and that depolarization of the epithelium leads to a relaxation of tracheal smooth muscle. The epithelial layer has an important barrier function and can release relaxing factors like NO.

Controlling the vasculature: angiogenesis, anti-angiogenesis and vascular targeting of gene therapy

Angiogenesis is the development of new blood vessels from an existing vascular bed. Normal vascular proliferation occurs only during embryonic development, the female reproductive cycle and wound repair. By contrast, many pathological conditions (for example, cancer, atherosclerosis and diabetic retinopathy), are characterized by persistent, unregulated angiogenesis. Conversely, inadequate angiogenesis can lead to failure of ulcers to heal and myocardial infarction. Control of vascular development could permit new therapeutic approaches to these disorders. For example, several anti-angiogenic drugs are currently undergoing clinical trials for the treatment of cancer, whereas enhancement of angiogenesis by exogenous growth factors can prevent or limit the damage in chronic wounds and duodenal ulcers. Here Tai-Ping Fan, Rhys Jaggar and Roy Bicknell highlight recent achievements and discuss the prospects of receptor antagonists, enzyme inhibitors, tumour suppressor genes and vascular targeted approaches, especially that of gene therapy, in the future development of angiotherapy.

Suppression of VEGF-induced angiogenesis by the protein tyrosine kinase inhibitor, lavendustin A

1. Vascular endothelial growth factor (VEGF) is a heparin-binding angiogenic factor which specifically acts on endothelial cells via distinct membrane-spanning tyrosine kinase receptors. Here we used the rat sponge implant model to test the hypothesis that the angiogenic activity of VEGF can be suppressed by protein tyrosine kinase (PTK) inhibitors. 2. Neovascular responses in subcutaneous sponge implants were determined by measurements of relative sponge blood flow by use of a 133Xe clearance technique, and confirmed by histological studies and morphometric analysis. 3. Daily local administration of 250 ng VEGF165 accelerated the rate of 133Xe clearance from the sponges and induced an intense neovascularisation. This VEGF165-induced angiogenesis was inhibited by daily co-administration of the selective PTK inhibitor, lavendustin A (10 micrograms), but not its negative control, lavendustin B (10 micrograms). Blood flow measurements and morphometric analysis of 8-day-old sponges showed that lavendustin A reduced the 133Xe clearance of VEGF165-treated sponges from 32.9 +/- 1.5% to 20.9 +/- 1.6% and the total fibrovascular growth area from 62.4 +/- 6.1% to 21.6 +/- 6.8% (n = 12, P < 0.05). 4. Co-injection of suramin (3 mg), an inhibitor of heparin-binding growth factors, also suppressed the VEGF165-elicited neovascular response. In contrast, neither lavendustin A nor suramin produced any effect on the basal sponge-induced angiogenesis. 5. When given alone, low doses of VEGF165 (25 ng) or basic fibroblast growth factor (bFGF; 10 ng) did not modify the basal sponge-induced neovascularisation. However, co-administration of these two peptides to a single sponge together caused a significant increase in the rate of 133Xe clearance and angiogenesis similar to that seen with the high dose of VEGF165 (250 ng) acting alone. This VEGF/bFGF neovascular response was also blocked by daily co-administration of lavendustin A (10 jig),suramin (3 mg) or a monoclonal anti-bFGF antibody (DG2, I jig), but not lavendustin B (10 g).6 These results suggest that selective inhibition of PTK could have therapeutic potential in angiogenic diseases where VEGF plays a dominant role. Furthermore, blockade of the angiogenic activity of VEGF and VEGF,/bFGF by suramin reveals an alternative strategy in angio suppression.

Evidence for reduction of bradykinin-induced bronchoconstriction in guinea-pigs by release of nitric oxide

1. In this study the influence of nitric oxide (NO) on the bronchoconstriction induced by bradykinin in anaesthetized and artifically ventilated guinea-pigs pretreated with atropine was investigated. 2. Aerosol administration of bradykinin (0.1-1 mM, 40 breaths) caused a dose-dependent increase in lung resistance (RL): maximum increase in RL was 2.5 fold the baseline value. Pretreatment with aerosolized NG-nitro-L-arginine methyl ester (L-NAME) or NG-monomethyl-L-arginine (L-NMMA) (1 mM, 10 breaths every 5 min for 30 min), NO synthase inhibitors, markedly increased the bronchoconstrictor response to bradykinin. L-Arginine, but not D-arginine, (3 mM, 10 breaths every 5 min for 30 min) reversed the hyperresponsiveness to aerosolized bradykinin caused by L-NAME and L-NMMA. 3. L-NAME (1 mM, 10 breaths every 5 min for 30 min) increased the bronchoconstriction induced by intravenous bradykinin (1-10 nmol kg-1). L-Arginine, but not D-arginine, (10 breaths every 5 min for 30 min) reversed the hyperresponsiveness to intravenous bradykinin caused by L-NAME. 4. The increase in RL induced by capsaicin, either aerosol (10 microM, 10 breaths) or i.v. (20 nmol kg-1) was not affected by L-NAME (1 mM, 10 breaths every 5 min for 30 min). Acute resection of the vagi did not affect the bronchoconstriction evoked by bradykinin in guinea-pigs, either in the absence or presence of L-NAME (1 mM, 10 breaths every 5 min for 30 min). 4. These results suggest that, irrespective of the route of administration, bradykinin releases NO or a related molecule which exerts a bronchodilator action that opposes the bronchoconstrictor mechanisms activated by bradykinin itself.

Studies of human airways in vitro: a review of the methodology

The pathophysiology of human airway narrowing is only partly understood. In order to gain more insight in the mechanisms of human lung diseases and potential beneficial therapeutic agents, adequate models are needed. Animal airway models are of limited value since lung diseases such as asthma and chronic obstructive pulmonary disease (COPD) are unique to humans and because the mechanisms of airway narrowing differ between species. Therefore, it is important to perform studies on human isolated airways. We describe the models that have been developed to study airway function in vitro, emphasizing human airway preparations. The easily prepared airway strip and ring preparations are described first. The potential damage during preparation and the interference with airway structure are important drawbacks in these preparations. Lung parenchymal strips, described next, were designed in order to study responsiveness of small airways. However, parenchymal strips are anatomically complex, and responsiveness is determined by the relative amounts of airway and vascular smooth muscle. The lack of reproducibility between species and even within one animal limits their usefulness. Airway tube preparations, in which luminal and serosal stimulation can be separated, enable us to study the modulatory role of the airways epithelium in vitro. Furthermore, airway compliance can be measured. In the isolated perfused lung preparation, relationships between the airways and the vascular system are preserved and the interaction between these two systems can be studied. Weight gain due to fluid extravasation is a problem in this model which has not been used yet to study human lungs in vitro. Next, methodological aspects such as tissue handling and storage, recording of responses, removal of the epithelium, and electrical field stimulation are discussed in some detail. Although animal airways tissue can be studied immediately after removal, human tissue is often obtained with some delay. However, this seems tenable since electron microscopy of lung tissue obtained at autopsy showed that recovery of the preparation occurs during incubation of carbogenated Krebs-Henseleit (K-H) buffer. Dissected airways can be stored overnight in cooled K-H buffer until up to 55 hr after resection without losing viability. Commonly used physiological salt solutions which bath the tissue contain osmotic molecules, ions important for contractility, glucose as a substrate, and a bicarbonate-carbon dioxide buffer.(ABSTRACT TRUNCATED AT 400 WORDS)