Catecholaminergic microcircuitry controlling the output of airway-related vagal preganglionic neurons.

In this study, we have investigated the ultrastructure and function of the catecholaminergic circuitry modulating the output of airway-related vagal preganglionic neurons (AVPNs) in ferrets. Immunoelectron microscopy was employed to characterize the nature of catecholaminergic innervation of AVPN at the ultrastructural level. In addition, immunofluorescence was used to examine the expression of the alpha(2A)-adrenergic receptor (alpha(2A)-AR) on AVPNs, and norepinephrine release within the rostral nucleus ambiguous (rNA) was measured by using microdialysis. Physiological experiments were performed to determine the effects of stimulation of the noradrenergic locus coeruleus (LC) cell group on airway smooth muscle tone. The results showed that 1) catecholaminergic nerve endings terminate in the vicinity of identified AVPNs but very rarely form axosomatic or axodendritic synapses with the AVPNs that innervate the extrathoracic trachea; 2) AVPNs express the alpha(2A)-AR; 3) LC stimulation-induced norepinephrine release within the rNA region was associated with airway smooth muscle relaxation; and 4) blockade of alpha(2A)-AR on AVPNs diminished the inhibitory effects of LC stimulation on airway smooth muscle tone. It is concluded that a noradrenergic circuit originating within the LC is involved in the regulation of AVPN activity within the rNA, and stimulation of the LC dilates the airways by the release of norepinephrine and activation of alpha(2A)-AR expressed by AVPNs, mainly via volume transmission.     

Brain stem excitatory and inhibitory signaling pathways regulating bronchoconstrictive responses.

This review summarizes recent work on two basic processes of central nervous system (CNS) control of cholinergic outflow to the airways: 1) transmission of bronchoconstrictive signals from the airways to the airway-related vagal preganglionic neurons (AVPNs) and 2) regulation of AVPN responses to excitatory inputs by central GABAergic inhibitory pathways. In addition, the autocrine-paracrine modulation of AVPNs is briefly discussed. CNS influences on the tracheobronchopulmonary system are transmitted via AVPNs, whose discharge depends on the balance between excitatory and inhibitory impulses that they receive. Alterations in this equilibrium may lead to dramatic functional changes. Recent findings indicate that excitatory signals arising from bronchopulmonary afferents and/or the peripheral chemosensory system activate second-order neurons within the nucleus of the solitary tract (NTS), via a glutamate-AMPA signaling pathway. These neurons, using the same neurotransmitter-receptor unit, transmit information to the AVPNs, which in turn convey the central command to airway effector organs: smooth muscle, submucosal secretory glands, and the vasculature, through intramural ganglionic neurons. The strength and duration of reflex-induced bronchoconstriction is modulated by GABAergic-inhibitory inputs and autocrine-paracrine controlling mechanisms. Downregulation of GABAergic inhibitory influences may result in a shift from inhibitory to excitatory drive that may lead to increased excitability of AVPNs, heightened airway responsiveness, and sustained narrowing of the airways. Hence a better understanding of these normal and altered central neural circuits and mechanisms could potentially improve the design of therapeutic interventions and the treatment of airway obstructive diseases.     

A GABAergic inhibitory microcircuit controlling cholinergic outflow to the airways.

GABA is the main inhibitory neurotransmitter that participates in the regulation of cholinergic outflow to the airways. We have tested the hypothesis that a monosynaptic GABAergic circuit modulates the output of airway-related vagal preganglionic neurons (AVPNs) in the rostral nucleus ambiguus by using a dual-labeling electron microscopic method combining immunocytochemistry for glutamic acid decarboxylase (GAD) with retrograde tracing from the trachea. We also determined the effects of blockade of GABAA receptors on airway smooth muscle tone. The results showed that retrogradely labeled AVPNs received a significant GAD-immunoreactive (GAD-IR) terminal input. Out of a pooled total of 3,161 synaptic contacts with retrogradely labeled somatic and dendritic profiles, 20.2% were GAD-IR. GAD-IR terminals formed significantly more axosomatic synapses than axodendritic synapses (P < 0.02). A dense population of GABAergic synaptic contacts on AVPNs provides a morphological basis for potent physiological effects of GABA on the excitability of AVPNs. GAD-IR terminals formed exclusively symmetric synaptic specializations. GAD-IR terminals were significantly larger (P < 0.05) in both length and width than unlabeled terminals synapsing on AVPNs. Therefore, the structural characteristics of certain nerve terminals may be closely correlated with their function. Pharmacological blockade of GABAA receptors within the rostral nucleus ambiguus increased activity of putative AVPNs and airway smooth muscle tone. We conclude that a tonically active monosynaptic GABAergic circuit utilizing symmetric synapses regulates the discharge of AVPNs.     

Chemical profile of vagal preganglionic motor cells innervating the airways in ferrets: the absence of noncholinergic neurons.

In ferrets, we investigated the presence of choline acetyltransferase (ChAT), vasoactive intestinal peptide (VIP), and markers for nitric oxide synthase (NOS) in preganglionic parasympathetic neurons innervating extrathoracic trachea and intrapulmonary airways. Cholera toxin beta-subunit, a retrograde axonal transganglionic tracer, was used to identify airway-related vagal preganglionic neurons. Double-labeling immunohistochemistry and confocal microscopy were employed to characterize the chemical nature of identified airway-related vagal preganglionic neurons at a single cell level. Physiological experiments were performed to determine whether activation of the VIP and ChAT coexpressing vagal preganglionic neurons plays a role in relaxation of precontracted airway smooth muscle tone after muscarinic receptor blockade. The results showed that 1) all identified vagal preganglionic neurons innervating extrathoracic and intrapulmonary airways are acetylcholine-producing cells, 2) cholinergic neurons innervating the airways coexpress ChAT and VIP but do not contain NOS, and 3) chemical stimulation of the rostral nucleus ambiguus had no significant effect on precontracted airway smooth muscle tone after muscarinic receptor blockade. These studies indicate that vagal preganglionic neurons are cholinergic in nature and coexpress VIP but do not contain NOS; their stimulation increases cholinergic outflow, without activation of inhibitory nonadrenergic, noncholinergic ganglionic neurons, stimulation of which induces airway smooth muscle relaxation. Furthermore, these studies do not support the possibility of direct inhibitory innervation of airway smooth muscle by vagal preganglionic fibers that contain VIP.     

Activation of the midbrain periaqueductal gray induces airway smooth muscle relaxation.

In this study, we examined effects of chemical stimulation of the ventrolateral region of the midbrain periaqueductal gray (vl PAG) on airway smooth muscle tone. We observed that in anesthetized, paralyzed, and artificially ventilated ferrets, vl PAG stimulation elicited airway smooth muscle relaxation. To clarify the mechanisms underlying this observation, we examined the GABA-GABA(A) receptor signaling pathway by 1) examining the expression of GABA(A) receptors on airway-related vagal preganglionic neurons (AVPNs) located in the rostral nucleus ambiguus region (rNA), by use of receptor immunochemistry and confocal microscopy; 2) measuring GABA release within the rNA by using microdialysis; and 3) performing physiological experiments to determine the effects of selective blockade of GABA(A) receptors expressed by AVPNs in the rNA region on vl PAG-induced airway relaxation, thereby defining the role of the GABA(A) receptor subtype in this process. We observed that AVPNs located in the rNA region do express the GABA(A) receptor beta-subtype. In addition, we demonstrated that activation of vl PAG induced GABA release within the rNA region, and this release was associated with airway smooth muscle relaxation. Blockade of the GABA(A) receptor subtype expressed by AVPNs in the rNA by bicuculline diminished the inhibitory effects of vl PAG stimulation on airway smooth muscle tone. These data indicate, for the first time, that activation of vl PAG dilates the airways by a release of GABA and activation of GABA(A) receptors expressed by AVPNs.     

Increased bronchovascular permeability after allergen exposure in sensitive asthmatics

To investigate the possibility that an increase in bronchovascular permeability is associated with allergen exposure in sensitive asthmatics we evaluated the amounts of serum proteins in bronchoalveolar lavage (BAL) effluents before and after local challenge with allergen. After exposure of sensitive asthmatic airways (n = 15) to allergen significant increases in total protein compared with controls were observed: 0.08 +/- 0.01 mg/ml in control airways and 0.13 +/- 0.02 mg/ml in challenged airways; P less than 0.05. The greatest changes induced by allergen exposure involved small-molecular-weight proteins (less than 345,000) and an inverse correlation was observed between log molecular weight and percent increase in the concentrations of the specific proteins; r = -0.61. BAL-serum distribution coefficients of serum proteins in airway fluids reflected a greater diffusability of low-molecular-weight proteins immediately after allergen exposure. We also evaluated the movement of serum proteins into lung after local allergen exposure using intravenously administered 99mTc-albumin (n = 10) and found an immediate 3.8-fold increase in amounts of radioactive albumin in allergen exposed airways compared with airways exposed to diluent. Most of the radioactivity was recovered in the first 5 ml of aliquot withdrawn, suggesting a marked increase in the permeability of the bronchial (large airway) vascular-epithelial membrane. An increase in serum proteins was also observed in BAL fluid of asthmatics 2-4 h after aerosol challenge (n = 4), including all proteins in the molecular weight range 45,000-900,000. These studies suggest that allergen exposure in sensitive asthmatics causes an acute increase in bronchovascular permeability to serum proteins.     

Altered allergen-induced eosinophil trafficking and physiological dysfunction in airways with preexisting virus-induced injury

Although both asthmatics and allergic rhinitics develop an acute inflammatory response to lower airway allergen challenge, only asthmatics experience airway obstruction resulting from chronic environmental allergen exposure. Hypothesizing that asthmatic airways have an altered response to chronic allergic inflammation, we compared the effects of repeated low-level exposures to inhaled Alternaria extract in sensitized rats with preexisting chronic postbronchiolitis airway dysfunction versus sensitized controls with normal airways. Measurements of air space (bronchoalveolar lavage) inflammatory cells, airway goblet cells, airway wall collagen, airway wall eosinophils, airway alveolar attachments, and pulmonary physiology were conducted after six weekly exposures to aerosolized saline or Alternaria extract. Postbronchiolitis rats, but not those starting with normal airways, had persistent increases in airway wall eosinophils, goblet cell hyperplasia in small airways, and loss of lung elastic recoil after repeated exposure to aerosolized Alternaria extract. Despite having elevated airway wall eosinophils, the postbronchiolitis rats had no eosinophils in bronchoalveolar lavage at 5 days after the last allergen exposure, suggesting altered egression of tissue eosinophils into the air space. In conclusion, rats with preexisting airway pathology had altered eosinophil trafficking and allergen-induced changes in airway epithelium and lung mechanics that were absent in sensitized control rats that had normal airways before the allergen exposures.     

Alpha-adrenergic receptor (α2A ) is colocalized in basal forebrain cholinergic neurons: A light and electron microscopic double immunolabeling study

A variety of data suggest that noradrenaline and acetylcholine may interact in the basal forebrain, however no morphological studies have addressed whether indeed cholinergic neurons express adrenergic receptors. We have investigated the presence of alpha-adrenergic receptor subtype α_2A -AR in cholinergic neurons of the basal forebrain. Cholinergic neurons were identified with an antibody against choline acetyltransferase and the receptor with a polyclonal antibody raised against a 47 amino acid fragment of the third intracellular loop of the α_2A -AR. For double labeling at the light microscopic level the Ni-DAB/DAB technique was used, and for electron microscopy an immunoperoxidase/immunogold method was applied. We detected the α_2A -AR protein in cholinergic as well as in non-cholinergic neurons. Almost half of all cholinergic neurons contained this adrenergic receptor. Double-labeled neurons were distributed throughout the rostro-caudal extent of the basal forebrain cholinergic continuum, including the medial septum, vertical and horizontal diagonal band nuclei, pallidal regions, substantia innominata and the internal capsule. Non-cholinergic neurons that expressed the α_2A -AR outnumbered cholinergic/α_2A -AR neurons by several factors. Electron microscopy confirmed the presence of α_2A -AR in cholinergic neurons in the medial septum, vertical and horizontal diagonal band nuclei. Gold particles (10 nm) indicative of α_2A -AR were diffusely distributed in the cytoplasm and accumulated in cytoplasmic areas near the Golgi complex and cysterns of the endoplasmic reticulum and were associated with the cellular membranes at synaptic and non-synaptic locations. Since many of the α_2A -AR+/non-cholinergic neurons we detected are likely to be GABAergic cells, our data support the hypothesis that noradrenaline may act via basal forebrain cholinergic and non-cholinergic neurons to influence cortical activity.     

Eosinophilopoiesis in a murine model of allergic airway eosinophilia: involvement of bone marrow IL-5 and IL-5 receptor alpha

The airway inflammation in asthma is dominated by eosinophils. The aim of this study was to elucidate the contribution of newly produced eosinophils in airway allergic inflammation and to determine mechanisms of any enhanced eosinophilopoiesis. OVA-sensitized BALB/c mice were repeatedly exposed to allergen via airway route. Newly produced cells were identified using a thymidine analog, 5-bromo-2'-deoxyuridine, which is incorporated into DNA during mitosis. Identification of IL-5-producing cells in the bone marrow was performed using FACS. Bone marrow CD3+ cells were enriched to evaluate IL-5-protein release in vitro. Anti-IL-5-treatment (TRFK-5) was given either systemically or directly to the airways. IL-5R-bearing cells were localized by immunocytochemistry. Repeated airway allergen exposure caused prominent airway eosinophilia after three to five exposures, and increased the number of immature eosinophils in the bone marrow. Up to 78% of bronchoalveolar lavage (BAL) granulocytes were 5-bromo-2'-deoxyuridine positive. After three allergen exposures, both CD3+ and non-CD3 cells acquired from the bone marrow expressed and released IL-5-protein. Anti-IL-5 given i.p. inhibited both bone marrow and airway eosinophilia. Intranasal administration of anti-IL-5 also reduced BAL eosinophilia, partly via local effects in the airways. Bone marrow cells, but not BAL eosinophils, displayed stainable amounts of the IL-5R alpha-chain. We conclude that the bone marrow is activated by airway allergen exposure, and that newly produced eosinophils contribute to a substantial degree to the airway eosinophilia induced by allergen. Airway allergen exposure increases the number of cells expressing IL-5-protein in the bone marrow. The bone marrow, as well as the lung, are possible targets for anti-IL-5-treatment.     

Differential effects of clonidine on upper airway abductor and adductor muscle activity in awake goats.

The purpose of this study was to determine the extent to which alpha(2)-adrenoceptor (alpha(2)-AR) pathways affect the central motor output to upper airway muscles that regulate airflow. Electromyogram (EMG) measurements were made from posterior cricoarytenoid (PCA), cricothyroid (CT), thyroarytenoid (TA), and middle (MPC) and inferior (IPC) pharyngeal constrictor muscles in awake standing goats. Systemic administration of the alpha(2)-AR agonist clonidine induced a highly dysrhythmic pattern of ventilation in all animals that was characterized by alternating episodes of tachypnea and slow irregular breathing patterns, including prolonged and variable expiratory time intervals. Periods of apnea were commonly observed. Dysrhythmic ventilatory patterns induced by clonidine were associated with differential recruitment of upper airway muscles. alpha(2)-AR stimulation preferentially decreased the activity of the PCA, CT, and IPC muscles while increasing TA and MPC EMG activities. Clonidine-induced apneas were associated with continuous tonic activation of laryngeal (TA) and pharyngeal (MPC) adductors, leading to airway closure and arterial oxygen desaturation. Tonic activation of the TA and MPC muscles was interrupted only during the first inspiratory efforts after central apnea. Laryngeal abductor, diaphragm, and transversus abdominis EMG activities were completely silenced during apneic events. Ventilatory and EMG effects were reversed by selective alpha(2)-AR blockade with SKF-86466. The results demonstrate that alpha(2)-AR pathways are important modulators of central respiratory motor outputs to the upper airway muscles.     

Differences in control by UV radiation of inflammatory airways disease in na?ve and allergen pre-sensitised mice

Exposure of skin to UV radiation (UVR) prior to allergen exposure can inhibit inflammatory airways disease in mice by reducing effector CD4+ T cells in both the trachea and the airway draining lymph nodes. This study analysed the immunomodulatory properties of UVR delivered to na?ve versus allergen pre-sensitised mice. In a model of inflammatory airways disease, BALB/c mice were sensitised by peritoneal injection of the allergen, ovalbumin (OVA) (20 μg/mouse), in the adjuvant, alum (4 mg/mouse), on days 0 and 14. On day 21, the mice were exposed to aerosolised OVA and 24 h later, proliferative responses by the cells in the airway draining lymph nodes were examined. UVR (8 kJ m(-2)) was administered 3 days prior to first OVA sensitisation (day -3), or OVA aerosol challenge (day 18). UVR before sensitisation reduced immune responses associated with expression of allergic airways disease; seven days after first OVA sensitisation, regulation of OVA-induced proliferation in vitro but not in vivo by CD4+CD25+ cells from UV-irradiated mice was detected. UVR administered to pre-sensitised mice regulated allergen responsiveness by cells from the airway draining lymph nodes only with a sensitisation protocol involving allergen and adjuvant at 5% strength of the original dose (1 μg OVA in 0.2 mg alum/mouse). These results suggest that UVR may modulate allergic airways disease by two mechanisms. The first, and more potent, is by reducing effector cells in respiratory tissues and requires UV delivery prior to sensitisation. The second, associated with administration to pre-sensitised mice, is weaker and is detected when the mice are sensitised with lower levels of allergen and adjuvant.     

Substance P released from intrinsic airway neurons contributes to ozone-enhanced airway hyperresponsiveness in ferret trachea.

Exposure to ozone (O3) induces airway hyperresponsiveness mediated partly through the release of substance P (SP) from nerve terminals in the airway wall. Although substantial evidence suggests that SP is released by sensory nerves, SP is also present in neurons of airway ganglia. The purpose of this study was to investigate the role of intrinsic airway neurons in O3-enhanced airway responsiveness in ferret trachea. To remove the effects of sensory innervation, segments of ferret trachea were maintained in culture conditions for 24 h before in vitro exposure to 2 parts/million of O3 or air for 1 h. Sensory nerve depletion was confirmed by showing that capsaicin did not affect tracheal smooth muscle responsiveness to cholinergic agonist or contractility responses to electrical field stimulation (EFS). Contractions of isolated tracheal smooth muscle to EFS were significantly increased after in vitro O3 exposure, but the constrictor response to cholinergic agonist was not altered. Pretreatment with CP-99994, an antagonist of the neurokinin 1 receptor, attenuated the increased contraction to EFS after O3 exposure but had no effect in the air exposure group. The number of SP-positive neurons in longitudinal trunk ganglia, the extent of SP innervation to superficial muscular plexus nerve cell bodies, and SP nerve fiber density in tracheal smooth muscle all increased significantly after O3 exposure. The results show that release of SP from intrinsic airway neurons contributes to O3-enhanced tracheal smooth muscle responsiveness by facilitating acetylcholine release from cholinergic nerve terminals.     

Repeated Delivery of Adeno-Associated Virus Vectors to the Rabbit Airway

Efficient local expression from recombinant adeno-associated virus (rAAV)-cystic fibrosis (CF) transmembrane conductance regulator (CFTR) vectors has been observed in the airways of rabbits and monkeys for up to 6 months following a single bronchoscopic delivery. However, it is likely that repeated administrations of rAAV vectors will be necessary for sustained correction of the CF defect in the airways. The current study was designed to test the feasibility of repeated airway delivery of rAAV vectors in the rabbit lung. After two doses of rAAV-CFTR to the airways, rabbits generated high titers of serum anti-AAV neutralizing antibodies. Rabbits then received a third dose of a rAAV vector containing the green fluorescent protein (GFP) reporter gene packaged in either AAV serotype 2 (AAV2) or serotype 3 (AAV3) capsids. Each dose consisted of 1 ml containing 5 x 10(9) DNase-resistant particles of rAAV vector, having no detectable replication-competent AAV or adenovirus. Three weeks later, GFP expression was observed in airway epithelial cells despite high anti-AAV neutralizing titers at the time of delivery. There was no significant difference in the efficiency of DNA transfer or expression between the rAAV3 and rAAV2 groups. No significant inflammatory responses to either repeated airway exposure to rAAV2-CFTR vectors or to GFP expression were observed. These experiments demonstrate that serum anti-AAV neutralizing antibody titers do not predict airway neutralization in vivo and that repeated airway delivery rAAV allows for safe and effective gene transfer.     

Neonatal treatment with nerve growth factor antiserum eliminates cholinergic sympathetic innervation of rat sweat glands

Most mammalian sympathetic neurons are noradrenergic, and their dependence upon nerve growth factor (NGF) for survival during development is well established. A minor population of sympathetic neurons, including those that innervate sweat glands, is cholinergic. To determine whether cholinergic sympathetic neurons, like their noradrenergic counterparts, require NGF during development, neonatal rats were treated with NGF-antiserum and 3 weeks later their sweat glands were examined for the presence of innervation. Acetylcholinesterase (AChE) staining and vasoactive intestinal polypeptide-like immunoreactivity (VIP-IR) which mark the mature sweat gland innervation were absent from the sweat glands of the anti-NGF treated animals. Further, when the glands were examined with the electron microscope, no axons or nerve terminals were evident. These observations indicate that the elaboration of the sweat gland plexus is NGF-dependent and suggest that at least one population of cholinergic sympathetic neurons in the rat requires NGF for survival. Our findings are consistent with the idea that during development NGF is a required trophic factor not only for noradrenergic sympathetic but also for cholinergic sympathetic neurons.     

Silent alpha(2C)-adrenergic receptors enable cold-induced vasoconstriction in cutaneous arteries

Cold constricts cutaneous blood vessels by increasing the reactivity of smooth muscle alpha(2)-adrenergic receptors (alpha(2)-ARs). Experiments were performed to determine the role of alpha(2)-AR subtypes (alpha(2A)-, alpha(2B)-, alpha(2C)-ARs) in this response. Stimulation of alpha(1)-ARs by phenylephrine or alpha(2)-ARs by UK-14,304 caused constriction of isolated mouse tail arteries mounted in a pressurized myograph system. Compared with proximal arteries, distal arteries were more responsive to alpha(2)-AR activation but less responsive to activation of alpha(1)-ARs. Cold augmented constriction to alpha(2)-AR activation in distal arteries but did not affect the response to alpha(1)-AR stimulation or the level of myogenic tone. Western blot analysis demonstrated expression of alpha(2A)- and alpha(2C)-ARs in tail arteries: expression of alpha(2C)-ARs decreased in distal compared with proximal arteries, whereas expression of the glycosylated form of the alpha(2A)-AR increased in distal arteries. At 37 degrees C, alpha(2)-AR-induced vasoconstriction in distal arteries was inhibited by selective blockade of alpha(2A)-ARs (BRL-44408) but not by selective inhibition of alpha(2B)-ARs (ARC-239) or alpha(2C)-ARs (MK-912). In contrast, during cold exposure (28 degrees C), the augmented response to UK-14,304 was inhibited by the alpha(2C)-AR antagonist MK-912, which selectively abolished cold-induced amplification of the response. These experiments indicate that cold-induced amplification of alpha(2)-ARs is mediated by alpha(2C)-ARs that are normally silent in these cutaneous arteries. Blockade of alpha(2C)-ARs may prove an effective treatment for Raynaud's Phenomenon.     

Effet of Combined Nitrogen Dioxide and Carbon Nanoparticle Exposure on Lung Function During Ovalbumin Sensitization in Brown Norway Rat

The interaction of particulate and gaseous pollutants in their effects on the severity of allergic inflammation and airway responsiveness are not well understood. We assessed the effect of exposure to NO₂ in the presence or absence of repetitive treatment with carbon nanoparticle (CNP) during allergen sensitization and challenges in Borwn-Norway (BN) rat, in order to assess their interactions on lung function and airway responses (AR) to allergen and methacholine (MCH), end-expiratory lung volume (EELV), bronchoalveolar lavage fluid (BALF) cellular content, serum and BALF cytokine levels and histological changes. Animals were divided into the following groups (n = 6): Control; CNP (Degussa-FW2): 13 nm, 0.5 mg/kg instilled intratracheally ×3 at 7-day intervals; OVA: ovalbumin-sensitised; OVA+CNP: both sensitized and exposed to CNP. Rats were divided into equal groups exposed either to air or to NO₂, 10 ppm, 6 h/d, 5d/wk for 4 weeks. Exposure to NO₂, significantly enhanced lung inflammation and airway reactivity, with a significantly larger effect in animals sensitized to allergen, which was related to a higher expression of TH1 and TH2-type cytokines. Conversely, exposure to NO₂ in animals undergoing repeated tracheal instillation of CNP alone, increased BALF neutrophilia and enhanced the expression of TH1 cytokines: TNF-α and IFN-γ, but did not show an additive effect on airway reactivity in comparison to NO₂ alone. The exposure to NO₂ combined with CNP treatment and allergen sensitization however, unexpectedly resulted in a significant decrease in both airway reactivity to allergen and to methacholine, and a reduction in TH2-type cytokines compared to allergen sensitization alone. EELV was significantly reduced with sensitization, CNP treatment or both. These data suggest an immunomodulatory effect of repeated tracheal instillation of CNP on the proinflammatory effects of NO₂ exposure in sensitized BN rat. Furthermore, our findings suggest that NO₂, CNP and OVA sensitization may significantly slow overall lung growth in parenchymally mature animals.     

Mice that overexpress Cu/Zn superoxide dismutase are resistant to allergen-induced changes in airway control

Within the respiratory epithelium of asthmatic patients, copper/zinc-containing superoxide dismutase (Cu/Zn SOD) is decreased. To address the hypothesis that lung Cu/Zn SOD protects against allergen-induced injury, wild-type and transgenic mice that overexpress human Cu/Zn SOD were either passively sensitized to ovalbumin (OVA) or actively sensitized by repeated airway exposure to OVA. Controls included nonsensitized wild-type and transgenic mice given intravenous saline or airway exposure to saline. After aerosol challenge to saline or OVA, segments of tracheal smooth muscle were obtained for in vitro analysis of neural control. In response to electrical field stimulation, wild-type sensitized mice challenged with OVA had significant increases in cholinergic reactivity. Conversely, sensitized transgenic mice challenged with OVA were resistant to changes in neural control. Stimulation of tracheal smooth muscle to elicit acetylcholine release showed that passively sensitized wild-type but not transgenic mice released more acetylcholine after OVA challenge. Function of the M(2) muscarinic autoreceptor was preserved in transgenic mice. These results demonstrate that murine airways with elevated Cu/Zn SOD were resistant to allergen-induced changes in neural control.     

Effect of a thromboxane receptor antagonist on PGD2- and allergen-induced bronchoconstriction

In this study we investigated the effect of the selective and potent thromboxane A2 (TxA2) receptor antagonist GR32191 on smooth muscle contraction induced by the TxA2 analogue U46619, prostaglandin (PG) D2, PGF2 alpha, and methacholine (MCh) in guinea pig airways in vitro and the airways response provoked by inhaled PGD2 and MCh in asthmatic subjects in vivo. GR32191 antagonized competitively the contractile responses of all three prostanoids to a similar degree but had no effect on MCh-induced contractions. In asthmatic subjects GR32191, in a single oral dose of 80 mg, did not affect base-line airway caliber or MCh-induced broncho-constriction but caused significant inhibition of PGD2-induced bronchoconstriction, displacing the concentration-response curves to the right by greater than 10-fold. The effect of the same oral dose of GR32191 on allergen-induced immediate bronchoconstriction was subsequently investigated in allergic asthmatic subjects. In individual subjects, GR32191 inhibited to varying degrees the overall bronchoconstrictor response, with the maximum effect occurring between 10 and 30 min after allergen challenge. These studies suggest that prostanoids contribute to the immediate bronchoconstriction induced by inhaled allergen in allergic asthmatics, and that this effect is mediated by stimulation of a thromboxane receptor.