Chronic tobacco smoke exposure increases airway sensitivity to capsaicin in awake guinea pigs

Minute ventilation during hypoxia is augmented with capsaicin supplementation in aged mice

Capsaicin is an agonist for transient receptor potential vanilloid 1 (TRPV1), and acute injection results in an increased frequency and tidal volume in young rats. It is unknown how capsaicin influences breathing in aged mice. We tested the hypothesis that capsaicin supplementation would elicit an augmented pattern of breathing in old mice compared to controls. Male 22-month old C57BL/6 J mice consumed a diet containing capsaicin (50 ppm) or lecithin control for one month. Breathing patterns were obtained prior to/following the dietary supplementation period using unrestrained barometric plethysmography. Frequency, tidal volume (VT), minute ventilation (VE), VE to expelled carbon dioxide ratio (VE/VCO₂) and VT divided by inspiratory time (VT/T_i) were analyzed at baseline and during a 15-minute hypoxic exposure (10% O₂). Capsaicin supplemented mice showed greater VE, VE/VCO₂ and TV/T_i during hypoxic exposure compared to controls, with no change at baseline. Overall, these findings suggest an acute augmented response to hypoxia following capsaicin administration in older mice.

Therapeutic effects of naringin in a guinea pig model of ovalbumin-induced cough-variant asthma

Naringin, a well known component isolated from Exocarpium Citri Grandis, has significant antitussive effects. Recently, Naringin exhibited novel anti-inflammatory effect in chronic inflammatory diseases. In this work, we firstly evaluated the effects of naringin on enhanced cough, airway hyper-responsiveness (AHR), and airway inflammation in an ovalbumin-induced experimental cough-variant asthma (CVA) model in guinea pigs. We investigated the effect of naringin (18.4 mg/kg, per os, single dose or consecutively) on cough to inhaled capsaicin after challenge with an aerosolized antigen in actively sensitized guinea pigs. The effect of naringin on AHR to inhaled methacholine was evaluated 24 h after cough determination. Airway inflammation was assessed via bronchoalveolar lavage fluid (BALF) cytology and lung histopathology. Naringin, given consecutively, significantly reduced ovalbumin-induced enhanced cough and AHR, inhibited the increases in the leukocytes, interleukin-4 (IL-4), IL-5, and IL-13 in BALF compared with the model group. Moreover, the pathologic changes in lung tissues were clearly ameliorated by naringin treatment. These results suggest that naringin may be a beneficial agent for CVA treatment.

Nicotine exaggerates LPS-induced airway hyperreactivity via JNK-mediated up-regulation of Toll-like receptor 4

Tobacco smokers often display increased airway hyperreactivity (AHR) when faced with bacterial infections. The present study uses a murine organ-culture model to dissect the mechanisms involved in this exaggerated smooth muscle response. Nicotine simulates the effects of smoking, and LPS represents bacterial infection. Contractile responses of isolated murine tracheal segments were analyzed in myographs after organ culture with increasing concentrations of LPS and/or nicotine for 4 days with or without specific MAPK inhibitors. Nicotine's effect on the expression of cell surface Toll-like receptors (TLRs), MCP-1, COX-2, and TNF-α were examined by real-time PCR. Increased protein expression was verified by immunohistochemistry. LPS concentration-dependently increased contractile responses to bradykinin and des-Arg(9)-bradykinin. A combination of nicotine and low-dose LPS caused powerful synergistic contractions along with increased kinin receptor expression. Specific kinin B1 and B2 receptor inhibitors blocked this reaction. Nicotine increased mRNA and protein expression of TLR4 and -6 in the epithelium and smooth muscle layer, with MCP-1 and COX-2 mRNA increasing in parallel. Specific inhibition of JNK attenuated nicotine's effects. In conclusion, long-term exposure to nicotine up-regulated the expression of TLR4 and -6 via a JNK-related pathway, causing an exaggeration of the LPS-induced local airway inflammation and increased AHR. This might offer a mechanistic explanation to the increased AHR seen in tobacco smokers confronted with bacterial infections.

Role of prostaglandin D2 /CRTH2 pathway on asthma exacerbation induced by Aspergillus fumigatus

Aspergillus fumigatus is often associated in asthmatic patients with the exacerbation of asthma symptoms. The pathomechanism of this phenomenon has not been fully understood. Here, we evaluated the immunological mechanisms and the role of the prostaglandin D2 / Chemoattractant Receptor-Homologous Molecule Expressed on Th2 Cells (CRTH2) pathway in the development of Aspergillus-associated asthma exacerbation. We studied the effects of A. fumigatus on airway inflammation and bronchial hyper-responsiveness in a rat model of chronic asthma. Inhalation delivery of A. fumigatus conidia increased the airway eosinophilia and bronchial hyper-responsiveness in ovalbumin-sensitized, challenged rats. These changes were associated with prostaglandin D2 synthesis and CRTH2 expression in the lungs. Direct inflammation occurred in ovalbumin-sensitized, challenged animals, whereas pre-treatment with an antagonist against CRTH2 nearly completely eliminated the A. fumigatus-induced worsening of airway eosinophilia and bronchial hyper-responsiveness. Our data demonstrate that production of prostaglandin D2 followed by eosinophil recruitment into the airways via a CRTH2 receptor are the major pathogenic factors responsible for the A. fumigatus-induced enhancement of airway inflammation and responsiveness.

Nicotine impairs cyclooxygenase-2-dependent kinin-receptor-mediated murine airway relaxations

INTRODUCTION

Cigarette smoke induces local inflammation and airway hyperreactivity. In asthmatics, it worsens the symptoms and increases the risk for exacerbation. The present study investigates the effects of nicotine on airway relaxations in isolated murine tracheal segments.

METHODS

Segments were cultured for 24h in the presence of vehicle, nicotine (10 μM) and/or dexamethasone (1 μM). Airway relaxations were assessed in myographs after pre-contraction with carbachol (1 μM). Kinin receptors, cyclooxygenase (COX) and inflammatory mediator expressions were assessed by real-time PCR and confocal-microscopy-based immunohistochemistry.

RESULTS

The organ culture procedure markedly increased bradykinin- (selective B₂ receptor agonist) and des-Arg⁹-bradykinin- (selective B₁ receptor agonist) induced relaxations, and slightly increased relaxation induced by isoprenaline, but not that induced by PGE₂. The kinin receptor mediated relaxations were epithelium-, COX-2- and EP2-receptor-dependent and accompanied by drastically enhanced mRNA levels of kinin receptors, as well as inflammatory mediators MCP-1 and iNOS. Increase in COX-2 and mPGES-1 was verified both at mRNA and protein levels. Nicotine selectively suppressed the organ-culture-enhanced relaxations induced by des-Arg⁹-bradykinin and bradykinin, at the same time reducing mPGES-1 mRNA and protein expressions. α7-nicotinic acetylcholine receptor inhibitors α-bungarotoxin and MG624 both blocked the nicotine effects on kinin B₂ receptors, but not those on B₁. Dexamethasone completely abolished kinin-induced relaxations.

CONCLUSION

It is tempting to conclude that a local inflammatory process per se could have a bronchoprotective component by increasing COX-2 mediated airway relaxations and that nicotine could impede this safety mechanism. Dexamethasone further reduced airway inflammation together with relaxations. This might contribute to the steroid resistance seen in some patients with asthma.

MAPK/NF-κB-dependent upregulation of kinin receptors mediates airway hyperreactivity: a new perspective for the treatment

Airway hyperreactivity (AHR) is a major feature of asthmatic and inflammatory airways. Cigarette smoke exposure, and bacterial and viral infections are well-known environmental risk factors for AHR, but knowledge about the underlying molecular mechanisms on how these risk factors lead to the development of AHR is limited. Activation of intracellular mitogen-activated protein kinase (MAPK)/nuclear factor-kappa B (NF-κB) and their related signal pathways including protein kinase C (PKC), phosphoinositide 3-kinase (PI3K) and protein kinase A (PKA) signaling pathways may result in airway kinin receptor upregulation, which is suggested to play an important role in the development of AHR. Environmental risk factors trigger the production of pro-inflammatory mediators such as tumor necrosis factor-α (TNF-α) and interleukins (ILs) that activate intracellular MAPK- and NF-κB-dependent inflammatory pathways, which subsequently lead to AHR via kinin receptor upregulation. Blockage of intracellular MAPK/NF-κB signaling prevents kinin B₁ and B₂ receptor expression in the airways, resulting in a decrease in the response to bradykinin (kinin B₂ receptor agonist) and des-Arg⁹-bradykinin (kinin B₁ receptor agonist). This suggests that MAPK- and NF-κB-dependent kinin receptor upregulation can provide a novel option for treatment of AHR in asthmatic as well as in other inflammatory airway diseases.

Effects of cigarette smoke and chronic hypoxia on airways remodeling and resistance. Clinical significance

Previously we have reported that association of cigarette smoke (CS) and chronic hypoxia (CH) interact positively to physiopathologically remodel pulmonary circulation. In present study we have exposed guinea pigs to CS smoke (four cigarettes/day; 3 months; CS) and to chronic hypoxia (12% O(2), 15 days; CH) alone or in combination (CSCH animals) and evaluated airways remodeling and resistance assessed as Penh (enhance pause). We measured Penh while animals breathe air, 10% O(2) and 5% CO(2) and found that CS and CH animals have higher Penh than controls; Penh was even larger in CSCH animals. A rough parallelism between Penh and thickness of bronchiolar wall and muscular layer and Goblet cell number was noticed. We conclude that CS and CH association accelerates CS-induced respiratory system damage, evidenced by augmented airway resistance, bronchial wall thickness and muscularization and Goblet cell number. Our findings would suggest that appearance of hypoxia would aggravate any preexisting pulmonary pathology by increasing airways resistance and reactivity.

Mechanism of cigarette smoke-induced kinin B(1) receptor expression in rat airways

Pulmonary inflammation is an important pathological feature of tobacco smoke related lung diseases such as chronic obstructive pulmonary disease (COPD). Kinin type 1 and type 2 receptors (B(1)R, B(2)R) are known to be associated with inflammatory responses of the lungs and other organs. In this study, we investigated whether cigarette smoke-induced airway inflammation could up-regulate B(1)R and B(2)R in correlation with IL-1β and TNF-α. Rat lung slices treated with 5 μg/ml total particulate matter (TPM) of cigarette smoke for 24 h showed an enhanced expression of B(1)R and IL-1β by 5-fold and 30-fold, respectively, in comparison to vehicle treatment (dimethyl sulfoxide). However, higher concentrations of TPM failed to induce B(1)R. No significant increase of B(2)R or TNF-α gene induction was observed. IL-1 receptor antagonist (IL-1Ra, 2 ng/ml) significantly blocked B(1)R gene induction by TPM, while 500 μM pentoxifylline, TNF-α inhibitor, reduced it partially. Western blot analysis showed a 2-fold enhanced expression of B(1)R in rat lung slices treated with 5 μg/ml TPM for 24 h and such protein expression was totally blocked by a co-treatment with IL-1Ra but not with pentoxifylline. In addition to the lower airways, rat trachea subchronically exposed to cigarette whole smoke exhibited 11-fold B(1)R gene induction in comparison with those exposed only to air. Our results demonstrate the involvement of B(1)R in cigarette smoke-induced airway inflammation through a mechanism which is mediated by the pro-inflammatory cytokine IL-1β.

Airway responsiveness measured by barometric plethysmography in guinea pigs

Barometric plethysmography has become an increasingly used method to indirectly measure respiratory function in unrestrained freely-moving animals. This technique has been criticized because of physiological uncertainty of its major index, the enhanced pause (Penh). Moreover, a recent study raises concerns that during histamine challenges part of the Penh response could be produced by upper airways (nasal) responses. In this study we compared airway responsiveness measured by barometric plethysmography and total lung resistance (RL: ) in guinea pigs, and evaluated the role of upper airways during Penh measurement. Our results showed that intravenous acetylcholine or histamine caused a dose-dependent increase of the Penh values in non-anesthetized guinea pigs, which were correlated with RL: values obtained in separate groups of anesthetized animals. In anesthetized but spontaneously breathing guinea pigs intravenous acetylcholine or histamine also produced a dose-dependent increment of Penh, which was similar regardless if guinea pigs breathed through the nose or through a tracheal tube. Our results suggest that, independently of the physiological meaning of Penh, this index seems to be a useful indirect measurement for evaluating airway responsiveness to intravenous agonists in guinea pigs, and that nasal passage seems not to be involved in this measurement.

Nicotine enhances murine airway contractile responses to kinin receptor agonists via activation of JNK- and PDE4-related intracellular pathways

Background

Nicotine plays an important role in cigarette-smoke-associated airway disease. The present study was designed to examine if nicotine could induce airway hyperresponsiveness through kinin receptors, and if so, explore the underlying mechanisms involved.

Methods

Murine tracheal segments were cultured for 1, 2 or 4 days in serum-free DMEM medium in presence of nicotine (1 and 10 μM) or vehicle (DMSO). Contractile responses induced by kinin B₁ receptor agonist, des-Arg⁹-bradykinin, and B₂ receptor agonist, bradykinin, were monitored with myographs. The B₁ and B₂ receptor mRNA expressions were semi-quantified using real-time PCR and their corresponding protein expressions assessed with confocal-microscopy-based immunohistochemistry. Various pharmacological inhibitors were used for studying intracellular signaling pathways.

Results

Four days of organ culture with nicotine concentration-dependently increased kinin B₁ and B₂ receptor-mediated airway contractions, without altering the kinin receptor-mediated relaxations. No such increase was seen at day 1 or day 2. The airway contractile responses to 5-HT, acetylcholine and endothelin receptor agonists remained unaffected by nicotine. Two different neuronal nicotinic receptor antagonists MG624 and hexamethonium blocked the nicotine-induced effects. The enhanced contractile responses were accompanied by increased mRNA and protein expression for both kinin receptors, suggesting the involvement of transcriptional mechanisms. Confocal-microscopy-based immunohistochemistry showed that 4 days of nicotine treatment induced activation (phosphorylation) of c-Jun N-terminal kinase (JNK), but not extracellular signal-regulated kinase 1 and 2 (ERK1/2) and p38. Inhibition of JNK with its specific inhibitor SP600125 abolished the nicotine-induced effects on kinin receptor-mediated contractions and reverted the enhanced receptor mRNA expression. Administration of phosphodiesterase inhibitors (YM976 and theophylline), glucocorticoid (dexamethasone) or adenylcyclase activator (forskolin) suppressed the nicotine-enhanced airway contractile response to des-Arg⁹-bradykinin and bradykinin.

Conclusions

Nicotine induces airway hyperresponsiveness via transcriptional up-regulation of airway kinin B₁ and B₂ receptors, an effect mediated via neuronal nicotinic receptors. The underlying molecular mechanisms involve activation of JNK- and PDE4-mediated intracellular inflammatory signal pathways. Our results might be relevant to active and passive smokers suffering from airway hyperresponsiveness, and suggest new therapeutic targets for the treatment of smoke-associated airway disease.

Aerosolized polymerized type I collagen reduces airway inflammation and remodelling in a guinea pig model of allergic asthma

Collagen-polyvinylpyrrolidone (Collagen-PVP) has been demonstrated to elicit immunomodulatory properties in different chronic inflammatory diseases. Nevertheless, its effects on asthma are still unknown. We have evaluated whether collagen-PVP could modulate airway inflammation and remodelling in a guinea pig model of allergic asthma. Sensitized guinea pigs were challenged with the allergen (ovalbumin) six times (at 10-day intervals). From the third challenge on, animals were treated every 5 days with saline aerosols containing 0.16, 0.33, or 0.66 mg/ml of collagen-PVP (n = 5, respectively). Some guinea pigs, sensitized and challenged with saline as well as treated with 0 or 0.66 mg/ml collagen-PVP, were included in the study as control (n = 7) and sham groups (n = 5), respectively. From the first challenge on, ovalbumin induced a transient airway obstruction, measured by barometric plethysmography, which was not modified by collagen-PVP treatments. After the last allergen challenge, guinea pigs were anesthetized to obtain bronchoalveolar lavage (BAL) and the left lung caudal lobe. As expected, BAL cell count from allergen-challenged guinea pigs showed abundant neutrophils and eosinophils, as well as numerous tumor necrosis factor (TNF)-alpha-expressing granulocytes and macrophages in airway wall (determined by immunohistochemical assay). Neutrophilia and TNF-alpha-expressing leukocytes, from collagen-PVP treated animals, diminished from 0.16 mg/ml, and eosinophilia from 0.66 mg/ml of collagen-PVP doses. Histological changes induced by allergen challenges include thickening of connective tissue below airway epithelium and vascular wall widening of airway adjacent vessels; these changes were reduced by collagen-PVP treatment. Collagen-PVP seems to have anti-inflammatory and antifibrotic properties in this guinea pig asthma model.

Modulation of sensory nerve function and the cough reflex: understanding disease pathogenesis

To cough is a protective defence mechanism that is vital to remove foreign material and secretions from the airways and which in the normal state serves its function appropriately. Modulation of the cough reflex pathway in disease can lead to inappropriate chronic coughing and an augmented cough response. Chronic cough is a symptom that can present in conjunction with a number of diseases including chronic obstructive pulmonary disease (COPD) and asthma, although often the cause of chronic cough may be unknown. As current treatments for cough have proved to exhibit little efficacy and are largely ineffective, there is a need to develop novel, efficacious and safe antitussive therapies. The underlying mechanisms of the cough reflex are complex and involve a network of events, which are not fully understood. It is accepted that the cough reflex is initiated following activation of airway sensory nerves. Therefore, in the hope of identifying novel antitussives, much research has focused on understanding the neural mechanisms of cough provocation. Experimentally this has been undertaken using chemical or mechanical tussive stimuli in conjunction with animal models of cough and clinical cough assessments. This review will discuss the neural mechanisms involved in the cough, changes that occur under pathophysiological conditions and and how current research may lead to novel therapeutic opportunities for the treatment of cough.

Effect of TRFK-5 on airway responsiveness in ovalbumin-treated guinea pigs exposed to tobacco smoke

Tobacco smoke (TS) exposure can induce airway hyperresponsiveness, especially in asthma. A feature of asthma is eosinophilia. We hypothesized that tobacco smoke exposure enhances eosinophil responsiveness in sensitized guinea pigs. Tobacco smoke-exposed, ovalbumin (OA)-sensitized guinea pigs were treated with TRFK-5 (1.0 mg/kg, intraperitoneal), an anti-interleukin (IL)-5 agent, or its vehicle. Guinea pigs were challenged with aerosols of OA, capsaicin, histamine, and methacholine. TRFK-5 attenuated airway responsiveness to OA but not to capsaicin, histamine, or methacholine. Bronchial alveolar lavage fluid analysis confirmed TRFK-5 attenuated airway eosinophilia in OA-treated guinea pigs. Therefore, airway responsiveness to OA is enhanced by eosinophils or IL-5 itself.

Tobacco smoke is an adjuvant for maintained airway sensitization in guinea pigs

Tobacco smoke (TS) exposure exacerbates asthma and may induce airway hyperresponsiveness in asymptomatic individuals. We hypothesized that TS exposure is an adjuvant to airway responsiveness. Ovalbumin (OA) sensitized guinea pigs were TS or air exposed. At 30 exposure days OA airway responsiveness was demonstrable in OA-treated animals exposed to either TS or air. After 130 exposure days only TS-exposed guinea pigs demonstrated OA airway responsiveness. Capsaicin airway responsiveness developed in non-sensitized and OA-sensitized guinea pigs exposed to TS. Therefore TS-exposure acts as an adjuvant to antigenic and neurogenic airway responsiveness. Combined antigen and adjuvant avoidance may attenuate or reverse airway responsiveness.

Characterisation of the acute and reversible airway inflammation induced by cadmium chloride inhalation in healthy dogs and evaluation of the effects of salbutamol and prednisolone

The aims of this study were firstly to characterise a model of subclinical and reversible bronchial inflammation induced by cadmium chloride inhalation in healthy dogs and then to examine the effect of prednisolone or salbutamol treatment on the resulting bronchitis. The model characterisation and the effects of treatment were studied using clinical symptoms, haematology, thoracic radiography, bronchoscopy and bronchoalveolar lavage, barometric whole-body plethysmography and histamine broncho-provocation tests. In addition, the activity of matrix metalloproteinases (MMP)-2 and -9 were determined in serum and bronchoalveolar lavage fluid (BALF). Cadmium inhalation induced: (1) a transient bronchial inflammation, dominated by neutrophils; (2) a neutrophilia of the blood that persisted for up to 4 weeks; (3) a transient increased bronchial reactivity, and (4) a significant increase in MMP-9 activity in the BALF. Prednisolone treatment reduced the influx of inflammatory cells into the BALF, but not significantly, had no effect on pulmonary function, and did not reduce of airway hypersensitivity. Salbutamol had almost no effect on any of the parameters investigated.

Paradoxical effect of salbutamol in a model of acute organophosphates intoxication in guinea pigs: role of substance P release

Organophosphates induce bronchoobstruction in guinea pigs, and salbutamol only transiently reverses this effect, suggesting that it triggers additional obstructive mechanisms. To further explore this phenomenon, in vivo (barometric plethysmography) and in vitro (organ baths, including ACh and substance P concentration measurement by HPLC and immunoassay, respectively; intracellular Ca2+measurement in single myocytes) experiments were performed. In in vivo experiments, parathion caused a progressive bronchoobstruction until a plateau was reached. Administration of salbutamol during this plateau decreased bronchoobstruction up to 22% in the first 5 min, but thereafter airway obstruction rose again as to reach the same intensity as before salbutamol. Aminophylline caused a sustained decrement (71%) of the parathion-induced bronchoobstruction. In in vitro studies, paraoxon produced a sustained contraction of tracheal rings, which was fully blocked by atropine but not by TTX, ω-conotoxin (CTX), or epithelium removal. During the paraoxon-induced contraction, salbutamol caused a temporary relaxation of ∼50%, followed by a partial recontraction. This paradoxical recontraction was avoided by the M2- or neurokinin-1 (NK1)-receptor antagonists (methoctramine or AF-DX 116, and L-732138, respectively), accompanied by a long-lasting relaxation. Forskolin caused full relaxation of the paraoxon response. Substance P and, to a lesser extent, ACh released from tracheal rings during 60-min incubation with paraoxon or physostigmine, respectively, were significantly increased when salbutamol was administered in the second half of this period. In myocytes, paraoxon did not produce any change in the intracellular Ca2+basal levels. Our results suggested that: 1) organophosphates caused smooth muscle contraction by accumulation of ACh released through a TTX- and CTX-resistant mechanism; 2) during such contraction, salbutamol relaxation is functionally antagonized by the stimulation of M2receptors; and 3) after this transient salbutamol-induced relaxation, a paradoxical contraction ensues due to the subsequent release of substance P.

Vitamin A deficiency increases airway resistance following C-fiber stimulation

Vitamin A deficiency (VAD) remains an important problem in the developing world where environmental air pollution is increasing. Because the coincidence of these factors could increase the prevalence of asthma in these regions, airway reactivity to methacholine (MCh), capsaicin, and sulfur dioxide was studied in VAD rats. The impedance to a small volume oscillation was analyzed to determine airway resistance (R(aw)) and lung elastance (H). VAD rats demonstrated larger increases in R(aw) and H after the administration of methacholine, and in R(aw) after administration of capsaicin or sulfur dioxide. The muscarinic receptor-2 (M2R) selective antagonist AFDX-116 enhanced the effect of capsaicin in vitamin A sufficient (VAS) but not VAD rats and retinoic acid-administration partially restored this enhancement. These data indicate that diminished auto-inhibitory muscarinic receptor-2 function contributed to this increased airway responsiveness to pulmonary C-fiber stimulation in VAD rats. If children with VAD also have diminished M2R function, they may be more prone to develop asthma, particularly in the presence of environmental co-factors such as sulfur dioxide.

Further exploration of the Penh parameter

Unrestrained plethysmography (UP) has been widely used to measure airway reactivity in conscious mice. It is non-invasive, easy to use, suitable for longitudinal studies, and allows a large throughput of animals for screening purposes. A non-dimensional parameter based on a characteristic change in the expiratory waveshape of the UP box signal, Penh, has been used as an indicator of bronchconstriction. Hamelmann et al. [Non-invasive measurement of airway responsiveness in allergen mice using barometric plethysmography. Am J Respir Crit Care Med 1997;156:766-77] presented experimental data showing a correlation between Penh and intrapleural pressure, as well as lung resistance; and Dohi et al. [Non-invasive system for evaluating the allergen-specific airway response in a murine model of asthma. Lab Invest 1999;79:1559-71] showed that Penh tracked the bronchial response to allergen challenge. More recently, papers and letters to the editor have argued against the use of UP and Penh in resistance applications, presenting mathematical and theoretical arguments that the UP waveform, and parameters derived from it (Penh) are dominated by conditioning, and are essentially unrelated to resistance [Lundblad et al. A reevaluation of the validity of UP in mice. J Appl Physiol 2002;93:1198-207; Mitzner and Tankersley. Interpreting Penh in mice. J Appl Physiol 2003;94:828-32]. This paper discusses the mathematics of UP as applied to two types of whole body plethysmographs (WBPs): a sealed chamber (pressure plethysmograph, PWBP); and a chamber with a pneumotachograph in its wall (flow plethysmograph, FWBP). We show that the PWBP waveform is largely dominated by conditioning, and exhibits little effect due to resistance; thus supporting the claim that UP and Penh are unrelated to resistance, when applied to measurements at typical room temperatures. By contrast, the effects of resistance or specific airway resistance (sRaw) are evident in the FWBP waveform, even at room temperature. Penh is derived from the FWBP waveform. We show that the changes in the FWBP waveform which occur in response to methacholine challenge cannot be due to conditioning, and are not simply due to changes in respiratory timing. Finally, we describe how Penh quantifies those changes.

Airway resistance due to alveolar gas compression measured by barometric plethysmography in mice

We developed a method for measuring airway resistance (Raw) in mice that does not require a measurement of airway flow. An analysis of Raw induced by alveolar gas compression showed the following relationship for an animal breathing spontaneously in a closed box: Raw = AbtVb/[Vt (Ve + 0.5Vt)]. Here Abt is the area under the box pressure-time curve during inspiration or expiration, Vb is box volume, Vt is tidal volume, and Ve is functional residual capacity (FRC). In anesthetized and conscious unrestrained mice, from experiments with both room temperature box air and body temperature humidified box air, the contributions of gas compression to the box pressure amplitude were 15 and 31% of those due to the temperature-humidity difference between box and alveolar gas. We corrected the measured Abt and Vt for temperature-humidity and gas compression effects, respectively, using a sinusoidal analysis. In anesthetized mice, Raw averaged 4.3 cmH2O·ml−1·s, fourfold greater than pulmonary resistance measured by conventional methods. In conscious mice with an assumed FRC equal to that measured in the anesthetized mice, the corrected Raw at room temperature averaged 1.9 cmH2O·ml−1·s. In both conscious mice and anesthetized mice, exposure to aerosolized methacholine with room temperature box air significantly increased Raw by around eightfold. Here we assumed that in the conscious mice both Vt and FRC remained constant. In both conscious and anesthetized mice, body temperature humidified box air reduced the methacholine-induced increase in Raw observed at room temperature. The method using the increase in Abt with bronchoconstriction provides a conservative estimate for the increase in Raw in conscious mice.

Respiratory health consequences of environmental tobacco smoke

Over the last several decades there has been a growing interest in examining the health consequences of environmental tobacco smoke (ETS). As a result of a wide body of research, ETS is now considered an unacceptable and entirely preventable public health hazard, and public policy increasingly discourages the presence of tobacco smoke in the public domain. This article provides an overview of the composition of ETS and the major diseases and disorders strongly linked to ETS, emphasizing the effects of ETS on pulmonary function, asthma, and lung cancer.

Spontaneous changes in guinea-pig respiratory pattern during barometric plethysmography: role of catecholamines and nitric oxide

Barometric plethysmography for unrestrained animals is a non-invasive method that allows repetitive measurements of pulmonary function, but habituation of the conscious animal to this technique has not been explored. Respiratory frequency (f(R)) and 'enhanced pause' (P(enh)) were measured by barometric plethysmography for a period of 8 h in guinea-pigs. Compared with basal values, during the first hour of recording a progressive increase in P(enh) (up to 25-50%) and a corresponding decrease in f(R) were recorded, followed by a relative plateau in each for up to 8 h. These changes were avoided by a 30-min pretreatment with propranolol and l-NAME (nitric oxide synthase inhibitor), with P(enh) values as high as this plateau phase since the beginning of recording. Atropine, salbutamol or budesonide did not modify the progressive increment in P(enh). We concluded that catecholamines and nitric oxide are released when guinea-pigs are introduced into the plethysmographic chamber, leading to initial low P(enh) values. These mediators probably diminish owing to habituation of the animal to the new environment, with an apparent progressive increment in P(enh). These spontaneous changes in P(enh) and f(R) must be taken into account during barometric plethysmography in order to avoid misinterpretation of the results.

Nicotine inhibits voltage-dependent sodium channels and sensitizes vanilloid receptors

Nicotine is an alkaloid that is used by large numbers of people. When taken into the body, it produces a myriad of physiological actions that occur primarily through the activation of neuronal nicotinic acetylcholine receptors (nAChRs). We have explored its ability to modulate TRPV1 receptors and voltage-gated sodium channels. The reason for investigating nicotine's effect on sodium channels is to obtain a better understanding of its anti-nociceptive properties. The reasons for investigating its effects on capsaicin-activated TRPV1 channels are to understand how it may modulate this channel that is involved in pain, inflammation, and gustatory physiology. Whole cell patch-clamp recordings from rat trigeminal ganglion (TG) nociceptors revealed that nicotine exhibited anesthetic properties by decreasing the number of evoked action potentials and by inhibiting tetrodotoxin-resistant sodium currents. This anesthetic property can be produced without the necessity of activating nAChRs. Nicotine also modulates TRPV1 receptors inducing a several-fold increase in capsaicin-activated currents in both TG neurons and in cells with heterologously expressed TRPV1 receptors. This sensitizing effect does not require the activation of nAChRs. Nicotine did not alter the threshold temperature (approximately 41 degrees C) of heat-activated currents in TG neurons that were attributed to arise from the activation of TRPV1 receptors. In this regard, its effect on TRPV1 receptors differs from those of ethanol that has been shown to increase the capsaicin-activated current but decrease the threshold temperature. These studies document several new effects of nicotine on channels involved in nociception and indicate how they may impact physiological processes involving pain and gustation.

Passive smoke effects on cough and airways in young guinea pigs: role of brainstem substance P

Children raised with extended exposure to environmental tobacco smoke (ETS) experience increased cough and wheeze. This study was designed to determine whether extended ETS exposure enhances citric acid-induced cough and bronchoconstriction in young guinea pigs via a neurokinin-1 (NK-1) receptor mechanism at the first central synapse of lung afferent neurons, the nucleus tractus solitarius. Guinea pigs were exposed to ETS from 1 to 6 weeks of age. At 5 weeks of age, guide cannulae were implanted bilaterally in the medial nucleus tractus solitarius at a site that produced apnea in response to the glutamate agonist D,L-homocysteic acid. At 6 weeks of age, either vehicle or a NK-1 receptor antagonist, SR 140333, was injected into the nucleus tractus solitarius of the conscious guinea pigs who were then exposed to citric acid aerosol. ETS exposure significantly enhanced citric acid-induced cough by 56% and maximal Penh (a measure of airway obstruction) by 43%, effects that were attenuated by the NK-1 receptor antagonist in the nucleus tractus solitarius. We conclude that in young guinea pigs extended exposure to ETS increases citric acid-induced cough and bronchoconstriction in part by an NK-1 receptor mechanism in the nucleus tractus solitarius.

Measuring lung function in mice: the phenotyping uncertainty principle

Measuring lung function in mice is essential for establishing the relevance of murine models to human lung disease. However, making such measurements presents particular technical challenges due to the small size of the animal, particularly with regard to the measurement of respiratory flows. In this review, we examine the various methods currently available for assessment of lung function in mice and contrast them in terms of a concept we call the phenotyping uncertainty principle; each method can be considered to lie somewhere along a continuum on which noninvasiveness must be traded off against experimental control and measurement precision. Unrestrained plethysmography in conscious mice represents the extreme of noninvasiveness and is highly convenient but provides respiratory measures that are so tenuously linked to respiratory mechanics that they cannot be considered as meaningful indicators of lung function. At the other extreme, the measurement of input impedance in anesthetized, paralyzed, tracheostomized mice is precise and specific but requires that an animal be studied under conditions far from natural. In between these two extremes lie methods that sacrifice some precision for a reduction in the level of invasiveness, a promising example being the measurement of transfer impedance in conscious, restrained mice. No method is optimal in all regards; therefore, the appropriate technique to use depends on the application.

Immediate sensory nerve-mediated respiratory responses to irritants in healthy and allergic airway-diseased mice

The immediate responses of the upper respiratory tract (URT) to the irritants acrolein and acetic acid were examined in healthy and allergic airway-diseased C57Bl/6J mice. Acrolein (1.1 ppm) and acetic acid (330 ppm) vapors induced an immediate increase in flow resistance, as measured in the surgically isolated URT of urethane-anesthetized healthy animals. Acrolein, but not acetic acid, induced a small URT vasodilatory response. In awake spontaneously breathing mice, both vapors induced a prolonged pause at the start of expiration (a response mediated via stimulation of nasal trigeminal nerves) and an increase in total respiratory specific airway flow resistance, the magnitude of which was similar to that observed in the isolated URT. Both responses were significantly reduced in animals pretreated with large doses of capsaicin to defunctionalize sensory nerves, strongly suggesting a role for sensory nerves in development of these responses. The breathing pattern and/or obstructive responses were enhanced in mice with ovalbumin-induced allergic airway disease. These results suggest that the primary responses to acrolein and acetic acid vapors are altered breathing patterns and airway obstruction, that sensory nerves play an important role in these responses, and that these responses are enhanced in animals with allergic airway disease.

Relationship of age, sex, body weight, and hematologic and respiratory variables with airway reactivity in adult cats

OBJECTIVE

To evaluate the association between airway reactivity and age, sex, body weight, and radiographic findings in cats.

ANIMALS

32 mature cats that constituted 2 age groups (17 young cats that were 1 to 2 years old and 15 old cats that were 12 to 13 years old).

PROCEDURE

Cats were placed in the chamber of a barometric whole-body plethysmograph (volume, 38 L), and box pressure was measured at baseline and after aerosol administration of increasing concentrations of carbachol. Airway reactivity was assessed by monitoring increases in enhanced pause (PENH), a unitless variable that measures bronchoconstriction as derived from dose-response curves. The endpoint chosen was the provocative concentration of carbachol that increased PENH to 300% of the baseline value (PCPENH300).

RESULTS

We did not find a correlation between PCPENH300 and sex, body weight, number of eosinophils, PENH before bronchoconstriction, respiratory frequency, tidal volume, or minute ventilation. Airway reactivity was significantly less in the old cats (mean +/- SD PCPENH300, 0.578 +/- 0.051%), compared with the value for the young cats (0.053 +/- 0.006%). Radiographic patterns differed significantly between groups of cats; a greater proportion of old cats (12/15) had bronchointerstitial patterns, compared with the proportion of young cats (4/17).

CONCLUSIONS AND CLINICAL RELEVANCE

These data support the notion that age exerts a strong influence on airway reactivity in adult cats, and radiographic differences suggest that structural changes in older cats may contribute to this effect. These findings have important implications for interpretation of results of airway reactivity tests in cats.

A reevaluation of the validity of unrestrained plethysmography in mice

Presently, unrestrained plethysmography is widely used to assess bronchial responsiveness in mice. An empirical quantity known as enhanced pause is derived from the plethysmographic box pressure [P(b)(t), where t is time] and assumed to be an index of bronchoconstriction. We show that P(b)(t) is determined largely by gas conditioning when normal mice breathe spontaneously inside a closed chamber in which the air is at ambient conditions. When the air in the chamber is heated and humidified to body conditions, the changes in P(b)(t) are reduced by about two-thirds. The remaining changes are thus due to gas compression and expansion within the lung and are amplified when the animals breathe through increased resistances. We show that the time integral of P(b)(t) over inspiration is accurately predicted by a term containing airway resistance, functional residual capacity, and tidal volume. We conclude that unrestrained plethysmography can be used to accurately characterize changes in airway resistance only if functional residual capacity and tidal volume are measured independently and the chamber gas is preconditioned to body temperature and humidity.

Tobacco smoke exposure and bombesin-like peptides in guinea pigs

Bombesin-like peptides (BLPs) are associated with tobacco smoke (TS)-induced diseases. We sought to determine if acute TS exposure releases BLPs into the pulmonary circulation. Sensitized and non-sensitized guinea pigs were chronically exposed to TS or compressed air. Thereafter, the lungs were acutely challenged with TS while perfused. Perfusates were analyzed for BLPs. TS increased BLPs in non-sensitized guinea pigs. A separate study determined daily bombesin exposure increased lung cell counts but not airway hyperresponsivensess. TS exposure releases BLPs into the pulmonary circulation but can be modified by host factors and bombesin itself does not induce airway hyperresponsiveness.

Enhanced lung C-fiber responsiveness in sensitized adult guinea pigs exposed to chronic tobacco smoke

Tobacco smoke (TS) exposure induces bronchoconstriction and increases airway secretions and plasma extravasation in certain sensitive individuals, particularly those with asthma. C-fiber activation also induces these effects. Although the mechanism by which chronic TS exposure induces airway dysfunction is not well understood, TS exposure may enhance C-fiber responsiveness. To investigate the effect of chronic TS exposure on C-fiber responsiveness to capsaicin and bradykinin, especially in atopic individuals, we exposed ovalbumin (OA)-sensitized guinea pigs to TS (5 mg/l air, 30 min/day for 7 days/wk) or to compressed air. Nonsensitized guinea pigs were also exposed to either compressed air or TS. Beginning after 120 days of exposure, C fibers and rapidly adapting receptors (RARs) were challenged with capsaicin and bradykinin. TS exposure enhanced sensory receptor and airway responsiveness to both intravenous capsaicin and bradykinin challenge. C-fiber, RAR, and airway responsiveness to capsaicin challenge was greatest in OA-sensitized guinea pigs exposed to TS. OA alone induced capsaicin hyperresponsiveness at 5 microg. Airway responsiveness to bradykinin was also greatest in OA-sensitized guinea pigs exposed to TS. OA alone enhanced C-fiber responsiveness to bradykinin at 5 and 10 microg. C-fiber activation by either agonist appeared direct, whereas RAR activation appeared indirect. Therefore, a mechanism of airway hyperirritability induced by the combination of OA sensitization and chronic TS exposure may include hyperirritability of lung C fibers.

Chronic tobacco smoke exposure increases cough to capsaicin in awake guinea pigs

Chronic exposure to irritants such as tobacco smoke (TS) can induce spontaneous and enhanced irritant-induced coughing, especially in asthma. To determine if the mechanism of enhanced coughing involves activation of capsaicin-sensitive sensory receptors (C-fibers), we exposed both non-sensitized (NS) and ovalbumin-sensitized guinea pigs to TS (5 mg/L air, 30 min exposure, and 7 days/week). Similar groups were exposed to compressed air. After 90 days of exposure, we challenged the airways with capsaicin, bradykinin, histamine and methacholine. Capsaicin induced coughing as well as bronchoconstriction in guinea pigs exposed to TS. In ovalbumin (OA) guinea pigs coughing and bronchoconstriction were enhanced. Tachykinin receptor antagonists attenuated coughing to both capsaicin and acute TS challenge. Bradykinin also induced coughing and bronchoconstriction in guinea pigs exposed to TS. There was no statistical separation between the two TS groups however. Histamine and methacholine induced similar bronchoconstriction but fewer coughs in all four experimental groups. In conclusion, chronic TS exposure induced coughing to capsaicin and bradykinin challenge. The effect of capsaicin was further enhanced in OA guinea pigs. Enhanced coughing induced by TS exposure likely involves activation of capsaicin-sensitive sensory C-fibers and neuropeptide release with possible subsequent activation of rapidly-adapting receptors.