Bronchial Smooth Muscle Responsiveness Research Articles

The effects of cannabidiol on the antigen-induced contraction of airways smooth muscle in the guinea-pig

(−)-Δ9-Tetrahydrocannabinol has been demonstrated to have beneficial effects in the airways, but its psychoactive effects preclude its therapeutic use for the treatment of airways diseases. In the present study we have investigated the effects of (−)-cannabidiol, a non-psychoactive component of cannabis for its actions on bronchial smooth muscle in vitro and in vivo.Guinea-pig bronchial smooth muscle contractions induced by exogenously applied spasmogens were measured isometrically. In addition, contractile responses of bronchial smooth muscle from ovalbumin-sensitized guinea-pigs were investigated in the absence or presence of (−)-cannabidiol. Furthermore, the effect of (−)-cannabidiol against ovalbumin-induced airway obstruction was investigated in vivo in ovalbumin-sensitized guinea-pigs.(−)-Cannabidiol did not influence the bronchial smooth muscle contraction induced by carbachol, histamine or neurokinin A. In contrast, (−)-cannabidiol inhibited anandamide- and virodhamine-induced responses of isolated bronchi. A fatty acid amide hydrolase inhibitor, phenylmethanesulfonyl fluoride reversed the inhibitory effect of (−)-cannabidiol on anandamide-induced contractions. In addition, (−)-cannabidiol inhibited the contractile response of bronchi obtained from allergic guinea-pigs induced by ovalbumin. In vivo, (−)-cannabidiol reduced ovalbumin-induced airway obstruction.In conclusion, our results suggest that cannabidiol can influence antigen-induced airway smooth muscle tone suggesting that this molecule may have beneficial effects in the treatment of obstructive airway disorders.

The influence of propofol, remifentanil and lidocaine on the tone of human bronchial smooth muscle

BackgroundBronchoscopy is generally a safe procedure, but the induction of anaesthesia can induce bronchospasm. Consequently we investigated the influence of propofol, remifentanil and lidocaine on the tone of the human bronchial smooth muscle. Materials and methodsThe influence of propofol, remifentanil and lidocaine on the contractile response of human bronchial smooth muscle to electrical field stimulation (EFS) has been evaluated. The role of capsaicin-sensitive sensory nerves and of inducible nitric oxide synthase has also been assessed. Furthermore, the interaction between these three dugs has been measured by Bliss Independence (BI) theory. Statistical significance (P < 0.05) was assessed by Student's t test or ANOVA. ResultsPropofol (1.3 μg ml−1) and lidocaine (1 mg ml−1) reduced the baseline tone of bronchial rings (−14.45 ± 4.53% and −33.40 ± 1.07%, respectively, P < 0.05), whereas remifentanil had not such effect. Aminoguanidine prevented the relaxant effect of propofol. Propofol did not alter the bronchial contractile response to EFS following 30 min of treatment, whereas remifentanil enhanced the bronchial tension (133.83 ± 9.38%, control 101.93 ± 6.82%, P < 0.05 P < 0.05) and lidocaine completely abolished the contractility at 1 mg ml−1 (P < 0.05). The desensitization of capsaicin-sensitive sensory nerves normalized the hyperresponsiveness induced by remifentanil (−26.77 ± 1.68%, P < 0.05). Significant BI antagonism (P < 0.001) was detected for propofol and lidocaine on the bronchial hyperresponsiveness induced by remifentanil. ConclusionPropofol and remifentanil may be used safely for bronchoscopy, although remifentanil should be associated with propofol or lidocaine to prevent the potential opioid-mediated bronchospasm.

Counterpoint: Alterations in airway smooth muscle phenotype do not cause airway hyperresponsiveness in asthma

We have been assigned the task of showing that “alterations in airway smooth muscle phenotype DO NOT cause the airways hyperresponsiveness of asthma.” In the following paragraphs we will briefly review the overwhelming lack of evidence that any fundamental change in the intrinsic properties of

Effect of sugammadex on bronchial smooth muscle function in rats

Sugammadex can encapsulate the steroid-based neuromuscular blocker molecule and results in rapid reversal of neuromuscular blockade induced by rocuronium and vecuronium. However, several cases of bronchospasm after the administration of sugammadex have been reported. The current study was carried out to determine whether sugammadex directly affects smooth muscle function of the airways. The ring strips of left main bronchi were isolated from male Wistar rats and isometric forces were measured. In the isolated bronchial smooth muscle tissues, sugammadex (10⁻⁸-10⁻³ M) had no effect on baseline tension or the acetylcholine (ACh; 30 µM)-induced sustained contraction. Moreover, sugammadex did not affect bronchial smooth muscle responsiveness to ACh. These findings indicate that sugammadex itself does not affect contractile function in bronchial smooth muscle of the rat.

Contribution of K-channel and Na-K-ATPase to the relaxant responses of canine bronchial smooth muscle to various bronchodilators

To determine whether activations of K-channel and Na-K-ATPase are involved in the action of bronchodilating agents, we studied the effects of various K-channel blockers and ouabain, a Na-K-ATPase inhibitor, on the relaxant responses of canine airway smooth muscle in vitro. Addition of charybdotoxin (ChTx), a Ca-activated potassium channel blocker, and ouabain had no effect on the responses to verapamil and BRL 38227, but inhibited those to salbutamol, forskolin, DBcAMP, and nitroprusside. Apamin, a low-conductance K-channel blocker, and glibenclamide, an ATP-sensitive K-channel blocker, had no effect on the smooth muscle relaxation induced by any agents. The inhibitory effect of ChTx was predominant when the concentration of bronchodilator was low, whereas the effect of ouabain was observed in the presence of a high concentration of bronchodilator. These results suggest that Ca-activated K-channel and Na-K-ATPase may participate in the relaxation induced by bronchodilators that can raise intracellular cyclic nucleotides, and that the contribution of each component differs under different concentrations of the drugs.

Organ bath in detecting the effect of one-hour warm ischemia on pulmonic arteries and bronchi from non-heart-beating donor lungs.

Non-heart-beating donor lung has been a promising source of lung transplantation. Many studies on non-heart-beating donor lungs are based on animal lung transplantation. In this study, we assessed by organ bath the effect of one-hour warm ischemia on the non-heart-beating donor lung in terms of the integrity of contractile and relaxant functions and tissue structures of pulmonic arteries and bronchi. Sixteen Swedish pigs were randomly classified into two groups: heart-beating donor group and 1-hour warm ischemia non-heart-beating donor group. Pulmonic and bronchial rings were taken from the isolated left lungs of the pigs. The pulmonic rings were stimulated by U-46619 (5.7 mol/L) and acetylcholine (10(-4) mmol/L) to assess the contractile abilities of smooth muscle and the endothelium-dependent relaxation response, respectively. As such, acetylcholine (10(-5) mmol/L) and natrium arachidonic acid (0.01%) were used to detect the contraction of bronchial smooth muscle and epithelium-dependent relaxation response. Meanwhile, the variances of precontraction tension of control groups were recorded to measure whether there was spontaneous relaxation during endothelium/epithelium-dependent relaxation course. Finally, papaverine solution (10(-4) mmol/L) was used to detect the non-endothelium/epithelium-dependent relaxant abilities of pulmonic and bronchial smooth muscles. There was no significant difference in the tension values of precontraction of pulmonic rings (P > 0.05), endothelium-dependent relaxation (P > 0.05), precontraction of bronchial rings (P > 0.05) and epithelium-dependent relaxation (P > 0.05) between the heart-beating donor group and the 1-hour warm ischemia non-heart-beating donor group. And the pulmonic and bronchial rings of each subgroup B had no spontaneous relaxation. Finally, papaverine solution relaxed the smooth muscle of all the rings completely. The results of this experiment suggest that the contractile and relaxant functions and tissue structures of pulmonic arteries and bronchi are not damaged after warm ischemia for 1 hour, and support the further study of non-heart-beating donor lung.

Inhibition of antigen-induced bronchial smooth muscle hyperresponsiveness by lovastatin in mice

Statins have been proposed as a novel treatment of respiratory diseases. To determine the beneficial effects of statins on the airway hyperresponsiveness, a characteristic feature of allergic bronchial asthma, the effect of systemic treatment with lovastatin on antigen-induced bronchial smooth muscle hyperresponsiveness was investigated in mice. Male BALB/c mice were sensitized and repeatedly challenged with ovalbumin antigen. Animals were also treated with lovastatin (4 mg/kg/day, i.p.) once a day prior to and during the antigen inhalation period. The bronchial smooth muscle responsiveness to acetylcholine, but not to high K(+)-depolarization, was markedly and significantly augmented in the repeatedly antigen challenged mice. The bronchial smooth muscle hyperresponsiveness to acetylcholine induced by antigen exposure was significantly attenuated by the systemic treatment with lovastatin. Thus, lovastatin might have therapeutic potential to ameliorate airway hyperresponsiveness in allergic bronchial asthma.

Soluble guanylate cyclase-dependent relaxation is reduced in the adult rat bronchial smooth muscle

Cyclic nucleotides are relaxants of the airway smooth muscle, yet most of the available data were obtained in adult animals. The expression and activity of cyclases have been reported to be developmentally regulated in the lung, and little is known about the age-related changes in their bronchial muscle relaxation potential. We evaluated and compared the newborn and adult rat bronchial smooth muscle response to cyclic AMP- and GMP-dependent agonists in isometric mounted bronchial rings. In acetylcholine-precontracted bronchial muscle, the relaxant response to the cAMP agonist forskolin was not age dependent, but the relaxant response to the nitric oxide (NO) donor sodium nitroprusside (SNP) was significantly greater (P<0.01) in the newborn. To further evaluate the cGMP pathway, we stimulated the soluble guanylate cyclase (sGC) with the specific agonists BAY 41-2272 and YC-1. In keeping with the SNP dose-response curves, the sGC agonists significantly relaxed the newborn, but not the adult bronchial muscle. Protein expression of the sGC alpha1- and beta1-subunits were significantly lower (P<0.01) in the adult compared with the newborn bronchial tissue. Consistent with these results, the NO-stimulated sGC activity was significantly greater in the newborn compared with the adult (P<0.01). In conclusion, the bronchial smooth muscle cGMP-, but not cAMP-dependent, relaxant response is developmentally regulated and significantly reduced in the adult rat.

Hyperresponsiveness of bronchial but not tracheal smooth muscle in a murine model of allergic bronchial asthma

To determine a change in airway smooth muscle contractility in a murine model of allergic asthma, the responsiveness of airway smooth muscles isolated from ovalbumin (OA)-sensitized and -challenged mice was compared with that from control animals. Actively sensitized mice were repeatedly challenged by ovalbumin (OA) antigen inhalation. Twenty-four h after the last antigen challenge, tracheal and bronchial smooth muscle responsiveness to acetylcholine (ACh) and endothelin-1 (ET-1) were measured. Airway microvascular leakage and histochemistry were also determined as indices of airway inflammation. Both the ACh and ET-1 responsiveness of bronchial, but not tracheal, smooth muscles were significantly augmented in OA-challenged mice, whereas no significant change in the expression levels of M2, M3 and ETB receptors was observed. The Evans blue dye extravasation in the main bronchial, but not tracheal, tissue of OA-challenged mice was significantly increased as compared with that of sensitized control animals. A marked inflammatory cells infiltration was also observed in bronchial but not tracheal tissues of OA-challenged mice. Repeated antigen challenge to sensitized mice caused a hyperresponsiveness of bronchial, but not tracheal, smooth muscle accompanied with bronchial tissue inflammation.

Mechanical and Electrophysiological Effects of Isoprostanes on Bronchial Arterial Smooth Muscle

We investigated the mechanical and electrophysiological responses of human and porcine bronchial arterial smooth muscle to isoprostanes (metabolites of membrane lipid peroxidation). These evoked a constrictor response which was sensitive to blockade of thromboxane receptors, as well as to a non-specific tyrosine kinase inhibitor and an inhibitor of Rho-kinase. The patch clamp technique was used to characterize the K+ and Ca2+ currents in these tissues, and to show that isoprostanes caused a brief enhancement of K+ currents followed by prolonged and marked suppression of the same.

Airways reactivity in patients with CF.

Airways reactivity, hyper-reactivity, and hyper-responsiveness are terms used to describe airways for which there appears to be increased bronchial smooth muscle tone or responsiveness. Some patients with cystic fibrosis (CF) have concomitant asthma causing airway hyperresponsiveness as manifested by recurrent acute symptoms of dyspnea that is impressively responsive to an inhaled beta 2 agonist and/or systemic corticosteroids. However, many others have a degree of bronchodilator responsiveness in the absence of an impressive clinical response to such anti-asthmatic treatment. In contrast to those with asthma, exercise does not induce bronchospasm and can even cause bronchodilatation in patients with CF who have bronchodilator responsiveness in the absence of asthma. The airway hyperresponsiveness of CF also differs in its response to histamine induced bronchospasm which is effectively reversed with ipratropium in patients with CF who symptomatically do not have asthma, whereas ipratropium does not adequately reverse histamine-induced bronchospasm in those with concomitant symptoms of asthma. These and other data suggest that the increased airway reactivity in patients with CF is vagally mediated and results from the airway damage caused by the lung disease. The use of bronchodilators as a routine part of CF lung disease care is controversial, but there is little evidence that treating airway reactivity in patients with CF is of clinical importance as a routine measure in the absence of clinical asthma. Definite subjective improvement in symptoms or improved sputum production when a bronchodilator precedes chest physical therapy should be sought to justify continued use in individual patients.

Effects of 8-epi-PGF2alpha on isolated bronchial smooth muscle of healthy and heaves-affected horses.

8-Epi-PGF2alpha, a prostaglandin-like compound generated by oxidative stress, has been shown to be an in vitro bronchoconstrictor in airways from healthy laboratory animals and healthy humans, but it has never been studied in diseased airways. Here, the bronchoconstrictive capacity of 8-epi-PGF2alpha on isolated bronchial rings (BR) of healthy and heaves-affected horses was evaluated by comparing the maximal effect and the potency of 8-epi-PGF2alpha to those of (1) acetylcholine (ACh), (2) its stereoisomer PGF2alpha and (3) its synthetic receptor agonist, U46619. Furthermore, the potential capacity of 8-epi-PGF2alpha to enhance the cholinergic (ACh) responsiveness of bronchial smooth muscle was investigated. 8-Epi-PGF2alpha contracted BR with a rank order of efficacy of Ach > U44619 > PGF2alpha > 8-epi-PGF2alpha in both healthy and heaves-affected horses. The contractile maximal response elicited by 8-epi-PGF2alpha was significantly smaller than that elicited by the other drugs, but was significantly higher in BR from heaves-affected horses than in those sampled in healthy horses, whilst pD2 values were similar. A subthreshold concentration of 8-epi-PGF2alpha (10-7 M) did not induce in vitro cholinergic hyper-responsiveness in BR of either healthy or heaves-affected horses. In conclusion, it has been demonstrated that 8-epi-PGF2alpha is an in vitro bronchoconstrictor of minor importance in healthy horses, but whose efficacy is significantly increased in heaves-affected horses.

Possible involvement of G i3 protein in augmented contraction of bronchial smooth muscle from antigen-induced airway hyperresponsive rats

To investigate a possible involvement of pertussis toxin (PTX)-sensitive heterotrimeric G proteins in the pathogenesis of airway hyperresponsiveness, the effect of PTX treatment on the augmented contractile response to acetylcholine (ACh) in bronchial smooth muscle of antigen-induced airway hyperresponsive rats was determined. In bronchial smooth muscle of airway hyperresponsive rats that were actively sensitized and repeatedly challenged with 2,4-dinitrophenylated Ascaris suum antigen, ACh-induced contractions were markedly augmented. The augmented contractile responses in the airway hyperresponsive group were significantly inhibited after treatment with PTX (1 μg/mL for 6 hr, 37°), whereas only a slight attenuation was observed in the normal control group. The level of Gα i3 (measured by immunoblotting), but not other α-subunits of G i/o family proteins, in bronchial smooth muscle of the airway hyperresponsive rats was significantly increased as compared with that of control animals. It is concluded that PTX-sensitive muscarinic contractile responses of bronchial smooth muscle might be augmented upon antigen-induced airway hyperresponsiveness in rats, probably due to an up-regulation of Gα i3 protein of bronchial smooth muscle.

Bronchopulmonary inflammation and airway smooth muscle hyperresponsiveness induced by nitrogen dioxide in guinea pigs

We investigated whether acute exposure to nitrogen dioxide (NO 2) causes major inflammatory responses (inflammatory cell recruitment, oedema and smooth muscle hyperresponsiveness) in guinea pig airways. Anaesthetised guinea pigs were exposed to 18 ppm NO 2 or air for 4 h through a tracheal cannula. Bronchoalveolar lavage was performed and airway microvascular permeability and in vitro bronchial smooth muscle responsiveness were measured. Exposure to NO 2 induced a significant increase in eosinophils and neutrophils in bronchoalveolar lavage fluid, microvascular leakage in the trachea and main bronchi (but not in peripheral airways), and a significant in vitro hyperresponsiveness to acetylcholine, electrical field stimulation, and neurokinin A, but not to histamine. Thus, this study shows that in vivo exposure to high concentrations of NO 2 induces major inflammatory responses in guinea pig airways that mimic acute bronchitis induced by exposure to irritant gases in man.

The relevance of resting tension to responsiveness and inherent tone of human bronchial smooth muscle.

1. In the present study the effects of resting tension on isometric responses of human airway smooth muscle to contractile and relaxant stimuli were investigated. Also, its effects on inherent smooth muscle tone were examined, in an effort to determine a pre-defined resting tension which can be considered optimal for in vitro studies. 2. Bronchial ring preparations (2-4 mm internal diameter) were suspended in tissue baths at a range of levels of resting tension (200-1600 mg). The responses to electrical field stimulation (EFS, 30 V, 0.2 ms, 8-30 Hz), carbachol (3 microM), isoprenaline (1 microM) and the 5-lipoxygenase inhibitor, zileuton (10 microM) were investigated along with the ability of the preparations to recover stable resting tension after 60 min of washing post challenge. 3. EFS induced monophasic contractions at low stimulation frequency (8 Hz). However, with increasing frequency and tension (15 and 30 Hz; > 400 mg) contractile responses were accompanied by a relaxant component. The magnitude of contractile responses increased with increasing resting tension to a plateau at between 500 and 700 mg. Relaxant responses when present, increased in magnitude with increasing resting tension. 4. The level of resting tension did not significantly alter responses to carbachol, but tissues at tensions > or = 1000 mg showed poor tension recovery after washing. Isoprenaline-induced relaxations increased with increasing resting tension (P<0.05) and tension recovery after washing was complete. The 5-lipoxygenase sensitive portion of the tension (33+/-4%) was not altered by the level of resting tension. 5 These results suggest that in human bronchial ring preparations of 2-4 mm internal diameter, resting tensions within the range 400-1000 mg could be considered optimal for isometric tension recordings of protocols involving both contraction and relaxation procedures.

Passive sensitization of human airways induces myogenic contractile responses in vitro.

We assessed effects of passive sensitization on human bronchial smooth muscle (BSM) response to mechanical stretching in vitro. Bronchial rings were sham (control) or passively sensitized overnight by using sera from donors demonstrating sensitivity to Dermatophagoides farinae and having immunoglobulin E (IgE) concentrations of 2,600 +/- 200 U/ml. Tissues were fixed isometrically to force transducers to measure responses to electrical field stimulation (EFS) and quick stretch (QS). The myogenic response to QS was normalized to the maximal response to EFS (%EFS). The myogenic response of sensitized BSM was 47.9 +/- 10.9 %EFS to a QS of approximately 6.5% optimal length (Lo); sham-sensitized tissues had a myogenic response of 13.5 +/- 6.4 %EFS (P = 0.012 vs. passively sensitized). A QS of approximately 13% Lo in sensitized BSM caused a response of 82.8 +/- 20.9 %EFS; sham-sensitized tissues developed a response of 38.2 +/- 17.3 %EFS (P = 0.004). BSM incubated with serum from nonallergic donors did not demonstrate increased QS response (4.6 +/- 1.4 %EFS, P = not significant vs. tissue exposed to atopic sera). However, tissues incubated in sera from nonatopic donors supplemented with hapten-specific chimeric IgE (JW8) demonstrated augmented myogenic response to QS of approximately 6.5% Lo (21.9 +/- 6.2 %EFS, P = 0. 027 vs. nonatopic sera alone). We demonstrate that passive sensitization of human BSM preparations causes induction and augmentation of myogenic contractions to QS; this hyperresponsiveness corresponds to the IgE concentration in sensitizing sera.

Muscarinic hyperresponsiveness of antigen-sensitized feline airway smooth muscle in vitro

Abstract Objective To determine the effect of in vivo antigen sensitization (Ascaris suum) of cats on tracheal smooth muscle (TSM) and bronchial smooth muscle (BSM) muscarinic reactivity in vitro. Animals Healthy domestic shorthair cats of either sex. Procedure Cats were sensitized and were longterm antigen (or sham) challenge exposed for 6 weeks by aerosolization with soluble Ascaris suum. Tracheal and BSM preparations were obtained and stimulated in vitro by electrical field stimulation (EFS), acetylcholine (ACh, a muscarinic agonist), and physostigmine (an AChase inhibitor). Responses were compared with responses of comparable tissues from sham antigen challenge-exposed cats. Results Tracheal and BSM from sensitized, compared with sham-sensitized (control), cats had greater isometric contraction (expressed as percentage of the response observed for isotonic, 63 mM KCl-elicited contraction [% KCI]) in response to endogenous (EFS) and exogenous muscarinic receptor activation (ACh). Contractions in response to EFS by TSM from control cats were 74 % KCI vs 97 %KCI for antigen-sensitized TSM (P &lt; 0.04). Muscarinic responses were augmented comparably by in vivo sensitization; TSM from control cats contracted to 190 % KCI vs 230 % KCl (P &lt; 0.03) for TSM from immune-sensitized cats. Physostigmine augmented responses of all tissues to ACh so that TSM from control (290 %KCI) and antigen-sensitized (257 %KCI) cats were similar. Responses of BSM from antigen-sensitized cats had similar augmentation of contractile response to EFS and ACh. Conclusions Long-term in vivo antigen sensitization increases numbers of muscarinic receptors on airway smooth muscle or decreases the availability or activity of AChase in cats. Clinical Relevance Modulation of muscarinic receptors may be useful for treatment of asthmatic cats with in vivo airway hyperreactivity. (Am J Vet Res 1997;58:672–676)

Human bronchial smooth muscle responsiveness after in vitro exposure to oxidizing pollutants.

The aims of this work were (1) to determine the dose-response relationship between ex vivo exposure to oxidizing pollutants such as nitrogen dioxide (NO2), the aldehyde acrolein, and ozone (O3), and the reactivity to agonists in isolated human bronchial smooth muscle; and (2) to investigate the alterations in the cellular mechanisms of human airway smooth muscle contraction induced by such exposures. Experiments were performed in isolated human bronchi obtained at thoracotomy. Isometric contraction in response to a variety of agonists was compared between pollutant-exposed preparations and paired controls. Short exposures to NO2, acrolein, or O3 altered the subsequent airway smooth muscle responsiveness in a dose-dependent manner. The cellular mechanisms producing the airway hyperresponsiveness observed in vitro are shared by the three pollutants and include alterations in airway smooth muscle excitation-contraction coupling as well as indirect effects on neutral endopeptidase activity.

Mechanisms of impaired beta-adrenoceptor-induced airway relaxation by interleukin-1beta in vivo in the rat.

We studied the in vivo mechanism of beta-adrenergic receptor (beta-AR) hyporesponsiveness induced by intratracheal instillation of interleukin-1beta (IL-1beta, 500 U) in Brown-Norway rats. Tracheal and bronchial smooth muscle responses were measured under isometric conditions ex vivo. Contractile responses to electrical field stimulation and to carbachol were not altered, but maximal relaxation induced by isoproterenol (10(-6)-10(-5) M) was significantly reduced 24 h after IL-1beta treatment in tracheal tissues and to a lesser extent, in the main bronchi. Radioligand binding using [125I]iodocyanopindolol revealed a 32+/-7% reduction in beta-ARs in lung tissues from IL-1beta-treated rats, without any significant changes in beta2-AR mRNA level measured by Northern blot analysis. Autoradiographic studies also showed significant reduction in beta2-AR in the airways. Isoproterenol-stimulated cyclic AMP accumulation was reduced by IL-1beta at 24 h in trachea and lung tissues. Pertussis toxin reversed this hyporesponsiveness to isoproterenol but not to forskolin in lung tissues. Western blot analysis revealed an IL-1beta-induced increase in Gi(alpha) protein expression. Thus, IL-1beta induces an attenuation of beta-AR-induced airway relaxation through mechanisms involving a reduction in beta-ARs, an increase in Gi(alpha) subunit, and a defect in adenylyl cyclase activity.

Effect of subchronic in vivo exposure to nitrogen dioxide on lung tissue inflammation, airway microvascular leakage, and in vitro bronchial muscle responsiveness in rats.

In a previous study on bronchoalveolar lavage fluid from rats exposed in vivo for seven days to 10 ppm nitrogen dioxide (NO2), it has been shown that there is an influx of macrophages into the airways. The present study investigated the effect of seven day exposure to 10 ppm NO2, on: (a) lung tissue inflammation and morphology; (b) airway microvascular leakage; (c) in vitro contractile response of main bronchi. Lung tissue was studied by light microscopy, after fixing the lungs by inflation with 4% formalin at a pressure of 20 cm H2O. Microvascular leakage was measured by extravasation of Evans blue dye in the larynx, trachea, main bronchi, and intrapulmonary airways. Smooth muscle responsiveness was evaluated by concentration-responses curves to acetylcholine (10(-9)-10(-3) M), serotonin (10(-9)-10(-4) M), and voltage-response curves (12-28 V) to electrical field stimulation. Histology showed an increased total inflammation at the level of respiratory bronchioles and alveoli. No influx of inflammatory cells was found in the main bronchi. A loss of cilia in the epithelium of small airways and ectasia of alveolar capillaries was also found. By contrast, no alterations to microvascular permeability or modification of bronchial smooth muscle responsiveness was found. Subchronic exposure to 10 ppm NO2 causes airway inflammation and structural damage, but does not cause any persistent alteration to microvascular permeability or bronchial smooth muscle responsiveness in rats.