Pulmonary physiology: future directions for lung function testing in COPD.

Chronic obstructive pulmonary disease (COPD) is a term that encompasses different pathological conditions having excessive airflow limitation in common. A wide body of knowledge has been accumulated over the last century explaining the mechanisms by which airway (chronic bronchitis) and parenchymal (emphysema) diseases lead to an indistinguishable spirometric abnormality. Although the definition of emphysema is anatomical, early studies showed that its presence can be inferred with good approximation from measurements of lung mechanics and gas exchange, in addition to simple spirometry. Studies using tests of ventilation distribution showed that abnormalities are present in smokers with normal spirometry, although these tests were not predictive of development of COPD. At the beginning of the third millennium, new documents and guidelines for diagnosis and treatment of COPD were developed, in which the functional diagnosis of COPD was restricted, for the sake of simplicity, to simple spirometry. In recent years, there has been a resurgence of interest in separating bronchitic from emphysematous phenotype of COPD. For this purpose, high-resolution computed tomography scanning has been added to diagnostic work-up. At the same time, methods for lung function testing have been refined and seem promising for detection of early small airways abnormalities. Among them are the forced oscillation technique and the nitrogen phase III slope analysis of the multiple-breath washout test, which may provide information on ventilation inhomogeneity. Moreover, the combined assessment of diffusing capacity for nitric oxide and carbon monoxide may be more sensitive than the latter alone for partitioning diffusive components at parenchymal level.

Severity grading of chronic obstructive pulmonary disease: the confounding effect of phenotype and thoracic gas compression.

Current guidelines recommend severity of chronic obstructive pulmonary disease be graded by using forced expiratory volume in 1 s (FEV1). But this measurement is biased by thoracic gas compression depending on lung volume and airflow resistance. The aim of this study was to test the hypothesis that the effect of thoracic gas compression on FEV1 is greater in emphysema than chronic bronchitis because of larger lung volumes, and this influences severity classification and prognosis. FEV1 was simultaneously measured by spirometry and body plethysmography (FEV1-pl) in 47 subjects with dominant emphysema and 51 with dominant chronic bronchitis. Subjects with dominant emphysema had larger lung volumes, lower diffusion capacity, and lower FEV1 than those with dominant chronic bronchitis. However, FEV1-pl, patient-centered variables (dyspnea, quality of life, exercise tolerance, exacerbation frequency), arterial blood gases, and respiratory impedance were not significantly different between groups. Using FEV1-pl instead of FEV1 shifted severity distribution toward less severe classes in dominant emphysema more than chronic bronchitis. The body mass, obstruction, dyspnea, and exercise (BODE) index was significantly higher in dominant emphysema than chronic bronchitis, but this difference significantly decreased when FEV1-pl was substituted for FEV1. In conclusion, the FEV1 is biased by thoracic gas compression more in subjects with dominant emphysema than in those with chronic bronchitis. This variably and significantly affects the severity grading systems currently recommended.

Lung function testing in COPD: when everything is not so simple.

Combined pulmonary fibrosis and emphysema is a condition occurring mainly in male smokers, presenting different lung mechanics and gas exchange abnormalities than emphysema or pulmonary fibrosis alone. We report the case of an elderly man, former heavy smoker, who presented with progressive exertional dyspnea for 1 year. Lung function tests showed near normal spirometry and lung volumes but marked reduction of diffusing capacity for carbon monoxide and even more nitric oxide. The arterial partial pressure of oxygen was reduced with a markedly increased alveolar-to-arterial difference. High-resolution computed tomography of the chest showed a pattern consistent with upper lobe emphysema and lower lobe pulmonary fibrosis. In conclusion, this case report confirms the limitations of a simplistic approach to lung function in the diagnosis of symptomatic smokers.

Dependence of bronchoconstrictor and bronchodilator responses on thoracic gas compression volume.

BACKGROUND AND OBJECTIVE: During forced expiration, alveolar pressure (PALV ) increases and intrathoracic gas is compressed. Thus, 1-s forced expiratory volume measured by spirometry (FEV1-sp ) is smaller than 1-s forced expiratory volume measured by plethysmography (FEV1-pl ). Thoracic gas compression volume (TGCV) depends on the amount of gas within the lung when expiratory flow limitation occurs in the airways. We therefore tested the hypothesis that bronchoconstrictor and bronchodilator responses using FEV1-sp are biased by height and gender, which are major determinants of lung volume. METHODS: We studied 54 asthmatics during methacholine challenge and 55 subjects with airway obstruction (FEV1-sp increase >200 mL and >12% after salbutamol) measuring at the same time FEV1-sp or FEV1-pl . RESULTS: During methacholine challenge, TGCV increased more in males than females, correlated with PALV , total lung capacity (TLC) and height, and the provocative dose was lower using FEV1-sp than FEV1-pl . With salbutamol, FEV1-pl increased <200 mL and <12% in 28 subjects, predominantly tall males, with larger TLC, TGCV and PALV . CONCLUSIONS: Bronchoconstrictor and bronchodilator responses are overestimated by standard spirometry in subjects with larger lungs because of TGCV.

Gz- and not Gi-proteins are coupled to pre-junctional µ-opioid receptors in bovine airways.

We investigated the signal transmission pathway by which activation of µ-opioid receptors attenuates acetylcholine (ACh) release in bovine trachealis. Electrical stimulation (ES)-induced [(3)H]-ACh release was determined in bovine tracheal smooth muscle strips pre-incubated with either the Gi-protein inhibitor pertussis toxin (PTX, 500 ng/ml and 1 µg/ml) or the Gz-protein specific inhibitor arachidonic acid (AA, 10(-6)M and 10(-5)M) and then treated with DAMGO (D-Ala(2),N-MePhe(4),Gly-ol(5)-enkephalin) 10(-5)M. Indomethacin 10(-5)M was used to block AA cascade. The inhibitory effect of DAMGO on ES-induced [(3)H]-ACh release was PTX-insensitive, but, by contrast, ablated by AA in a concentration-dependent manner. AA 10(-5)M alone reduced [(3)H]-ACh release, an effect that was prevented by iberiotoxin 10(-7)M, suggesting an involvement of Ca(2+)-activated K(+)-channels. Western blot analysis consistently showed immunoreactive bands against a specific antibody anti-Gz-α subunit at ∼40 kDa, consistent with the presence of Gz-protein. The present findings suggest that in isolated bovine trachealis, activation of µ-opioid receptors inhibits ACh-release through a signal transmission pathway involving Gz-protein rather than Gi-protein.

Effects of κ- and µ-opioid agonists on cholinergic neurotransmission and contraction in isolated bovine trachealis.

The effects of the selective µ-opioid agonist DAMGO and the selective κ-opioid agonist U-50488H on tritiated acetylcholine release ([(3)H]-ACh) and contractile responses to electrical stimulation (ES) were simultaneously determined in isolated bovine trachealis. The inhibitory effect of DAMGO 10(-5)M on [(3)H]-ACh release was not significantly different from the effect of the non-selective muscarinic agonist pilocarpine 10(-5)M, whereas the effect of U-50488H 10(-5)M was significantly greater. The effects of both opioids were not significantly different when muscles were pre- or co-incubated with the unselective muscarinic antagonist atropine 10(-7)M. Both DAMGO and U-50488H attenuated ES-induced contraction and this effect was significantly correlated with the inhibition of [(3)H]ACh-release (r(2)=0.8552). These data suggest that (1) opioids are important modulators of airway smooth muscle tone, (2) their effect is not altered by the activity of muscarinic autoregulation, and (3) their inhibitory effect of airway smooth muscle contraction can be almost totally explained by inhibition of ACh release.

Pulmonary function and airway responsiveness in young competitive swimmers.

RATIONALE: Strong physical activities are often associated with large lung volumes and relatively reduced flow, which may represent a physiological variant but also an obstructive abnormality. Competitive swimmers have also spirometric values even larger than other athletes, although they are at increased risk for asthma or airway hyperresponsiveness. AIM: We aimed to investigate whether lung volumes increase with duration of swimming training and are related to an obstructive abnormality associated with airway hyperresponsiveness and asthma-like symptoms. METHODS: Forced expiratory volume in 1 sec (FEV(1)), forced vital capacity (FVC), airway responsiveness, and skin prick test were measured in 34 children/adolescents (age: 7-19 yrs old) trained for competitive swimming. Their "lifetime" exposure, i.e., the hours spent in pool was very strongly correlated with their age at the time of study. The effect of swimming activity was therefore estimated from the relationships between lung function data and age. RESULTS: FVC Z-score was positively correlated with age, indicating that absolute values increased more than expected with normal growth, but FEV(1)/FVC was negatively correlated with age. Although the majority of subjects had allergic sensitization to aeroallergens and about one half had asthma-like symptoms and/or airway hyperresponsiveness, these conditions did not alter the relationships between lung function and age. CONCLUSION: Intense swimming activity may cause a greater than normal lung growth, irrespective of the presence of allergic sensitization or airway hyperresponsiveness. The associated reduction of FEV(1) /FVC may represent a physiological variant rather than a true obstructive abnormality.

Mechanical correlates of dyspnea in bronchial asthma.

We hypothesized that dyspnea and its descriptors, that is, chest tightness, inspiratory effort, unrewarded inspiration, and expiratory difficulty in asthma reflect different mechanisms of airflow obstruction and their perception varies with the severity of bronchoconstriction. Eighty-three asthmatics were studied before and after inhalation of methacholine doses decreasing the 1-sec forced expiratory volume by ~15% (mild bronchoconstriction) and ~25% (moderate bronchoconstriction). Symptoms were examined as a function of changes in lung mechanics. Dyspnea increased with the severity of obstruction, mostly because of inspiratory effort and chest tightness. At mild bronchoconstriction, multivariate analysis showed that dyspnea was related to the increase in inspiratory resistance at 5 Hz (R 5) (r (2) = 0.10, P = 0.004), chest tightness to the decrease in maximal flow at 40% of control forced vital capacity, and the increase in R 5 at full lung inflation (r (2) = 0.15, P = 0.006), inspiratory effort to the temporal variability in R 5-19 (r (2) = 0.13, P = 0.003), and unrewarded inspiration to the recovery of R 5 after deep breath (r (2) = 0.07, P = 0.01). At moderate bronchoconstriction, multivariate analysis showed that dyspnea and inspiratory effort were related to the increase in temporal variability in inspiratory reactance at 5 Hz (X 5) (r (2) = 0.12, P = 0.04 and r (2) = 0.18, P < 0.001, respectively), and unrewarded inspiration to the decrease in X 5 at maximum lung inflation (r (2) = 0.07, P = 0.04). We conclude that symptom perception is partly explained by indexes of airway narrowing and loss of bronchodilatation with deep breath at low levels of bronchoconstriction, but by markers of ventilation heterogeneity and lung volume recruitment when bronchoconstriction becomes more severe.

Pre-junctional muscarinic autoreceptors in bovine airways.

UNLABELLED: We searched for pre-junctional inhibitory muscarinic receptors in isolated bovine trachealis strips and bronchial rings. Electric stimulation (ES)-induced tritiated acetylcholine ([(3)H]-ACh)-release and isometric contractions were determined in muscles incubated with the non-selective muscarinic agonist pilocarpine, the non-selective muscarinic antagonist atropine, the selective M(2)-receptor antagonists methoctramine and gallamine, or the selective M(4)-receptor antagonist PD102807. Electric field stimulation (EFS)-induced isometric contractile responses were assessed in trachealis strips and bronchial rings treated with 10(-9)-10(-5)M methoctramine, gallamine or PD102807. Pilocarpine (10(-6) and 10(-5)M) and atropine (10(-7)M) significantly decreased and increased ES-evoked [(3)H]-ACh-release, respectively. The enhancing effect of atropine on [(3)H]-ACh-release prevailed over the inhibitory effect of pilocarpine. M(2)- and M(4)-receptor antagonists did not increase EFS-induced contraction or ES-induced [(3)H]-ACh-release. However, 10(-7)M methoctramine, gallamine or PD102807 significantly attenuated the inhibitory effects of pilocarpine 10(-5)M on ES-induced [(3)H]-ACh-release. CONCLUSIONS: Muscarinic autoregulation is present in bovine airways but is not fully accounted for by M(2)- and M(4)-receptor subtypes.

Outcome measures and rehabilitation treatment in patients affected by Charcot-Marie-Tooth neuropathy: a pilot study.

OBJECTIVE: : We evaluated the sensitivity of various rehabilitation and lung function scales to detect differences between people with Charcot-Marie-Tooth (CMT) disease and healthy controls. We also studied whether these measurements are sensitive to disclose changes in patients with CMT disease after rehabilitative treatment. DESIGN: : Eight patients with different types of CMT participated in the study. Data were gathered at baseline; at the end of the treadmill training, stretching, respiratory, and proprioceptive exercise (TreSPE) treatment period; and after a washout period of 6 mos. The following instruments were used for data collection: Medical Research Council scale for lower limb strength; Tinetti Balance Scale; Physical Performance Battery; ankle angle, oxygen consumption, and lung function tests; peak treadmill velocity and slope; time to walk 6 m; and CMT Neuropathy Score. The participants underwent TreSPE treatment twice every week for 8 wks. RESULTS: : All rehabilitative measures were significantly worse in subjects with CMT disease than in healthy controls. Lung function was always normal except for the maximum expiratory pressure and maximum inspiratory pressure. No dropouts or worsening in any of the different outcome measures were observed after TreSPE. The ankle angle and the time to walk 6 m were the only measures that significantly improved after treatment. CONCLUSIONS: : The rehabilitative outcome measures used in this protocol are useful in detecting clinical impairment in people with CMT disease. Lung function tests were confirmed to be minimally abnormal in patients with CMT disease. The TreSPE treatment, besides being safe and well tolerated, induced some training effects in CMT neuropathy, in the absence of lung function amelioration and effort tolerance. Follow-up showed that CMT patients should be treated at least twice every year because a regression of all outcome measures to the baseline state was found after a 6-mo washout period.

Formoterol by pressurized metered-dose aerosol or dry powder on airway obstruction and lung hyperinflation in partially reversible COPD.

BACKGROUND: We compared the efficacy and safety of formoterol given by a pressurized metered-dose inhaler (pMDI) (Atimos®, Chiesi Farmaceutici, Italy), using a chlorine-free hydrofluoroalkane (HFA-134a) propellant developed to provide stable and uniform dose delivery (Modulite™, Chiesi Farmaceutici, Italy), with formoterol by dry powder inhaler (DPI) (Foradil® Aerolizer®, Novartis Pharmaceuticals) and placebo, in reducing airflow obstruction and lung hyperinflation, in moderate-to-severe, partially reversible chronic obstructive pulmonary disease (COPD). METHODS: Forty-eight patients were randomized to a 1-week, double-blind, double-dummy, three-period crossover study with 12 µg b.i.d. of formoterol given by pMDI or DPI, or placebo. Spirometry, specific airway conductance, and lung volumes were measured at the beginning and at the end of each treatment period from predose to 4 h postdose. A 6-min walking test was carried out 4 h after the first and the last dose, with dyspnea assessed by Borg scale. Safety was assessed through adverse events monitoring electrocardiography and vital signs. RESULTS: The two formulations of formoterol were significantly superior to placebo but not different from each other in increasing 1-sec forced expiratory volume, specific airway conductance, inspiratory capacity, and inspiratory-to-total lung capacity ratio. The two active treatments were also equivalent and superior to placebo in reducing dyspnea at rest and on exertion. No differences in terms of safety between the two active forms and placebo were detected. CONCLUSIONS: Formoterol given with chlorine-free pMDI was equivalent to DPI in reducing airway obstruction and lung hyperinflation in COPD patients. Both formoterol formulations confirmed the good safety profile similar to placebo.

Acute bronchodilator responsiveness in bronchiolitis obliterans syndrome following hematopoietic stem cell transplantation.

BACKGROUND: The obstructive abnormality of bronchiolitis obliterans syndrome (BOS) after allogeneic hematopoietic stem cell transplantation (HSCT) is deemed to be virtually insensitive to treatment with inhaled bronchodilators. We studied whether nonconventional assessment of bronchodilation may help to detect physiologically meaningful airway responses missed by traditional criteria. METHODS: Standard spirometry, partial and maximal expiratory flow-volume curves, and lung volumes were measured before and 90 min after inhalation of albuterol plus tiotropium in 17 patients who developed mild to very severe BOS following HSCT. RESULTS: After treatment with bronchodilators, the standard criteria of reversibility based on FEV1 and FVC were met in seven out of 17 patients. In eight patients, residual volume (RV) decreased beyond its within-session spontaneous variability, and functional residual capacity (FRC) was reduced in four of them. Partial forced expiratory flow (Vpart) increased beyond its within-session spontaneous variability in nine patients. Out of 10 patients in whom neither FEV1 nor FVC met the standard criteria of reversibility, six had a positive increase in Vpart or a decrease of lung hyperinflation (ie, FRC) or RV. In six patients with limited expiratory flow during tidal breathing, the postbronchodilator increase in Vpart was correlated with a decrease in FRC (R2=0.83; P=.011). CONCLUSIONS: This study suggests that airway smooth muscle tone plays a significant role in BOS after HSCT and that the common knowledge of BOS as an irreversible obstructive disease may stem from the limitation of simple spirometry to detect changes in small airways. TRIAL REGISTRY: ClinicalTrials.gov; No.: NCT01112241 (BOS-01); URL: www.clinicaltrials.gov.

Does a low-density gas mixture or oxygen supplementation improve exercise training in COPD?

BACKGROUND: Low-density gas mixtures and oxygen (O2) supplementation are known to improve physical performance and ventilatory adaptation during incremental maximal exercise in COPD. We investigated whether their combined use during intense physical training is also effective in ameliorating exercise tolerance in patients affected by moderate to severe COPD. METHODS: Thirty patients (FEV1 < 60% of predicted) underwent a 2-month rehabilitation program. Leg-cycle training was conducted thrice weekly at 80% of the initial peak work rate for at least 20 min breathing room air, a 60% helium and 40% O2 mixture, or supplemental O2 (40%) inhaled from a Douglas bag. The study was randomized with a double-blind design. Before and at the end of the training period the subjects were tested for spirometry, arterial gas tension, diffusing lung capacity for CO, and incremental and constant work rate exercise test on a cycle ergometer. RESULTS: Physical training resulted in a significant improvement in peak oxygen consumption and power output (P < .01 for both) and in exercise endurance time (P < .05) independently of the kind of inhaled gas during the rehabilitation program (P ≥ .42). No changes were observed in lung function tests or gas exchange. CONCLUSIONS: We concluded that the use of a low-density gas mixture or O2 supplementation does not contribute to improved exercise performance in patients with moderate to severe COPD without a significantly decreased diffusion lung capacity for CO who are able to tolerate intense physical training.

Beta-Adrenergic Agonists.

Inhaled ß2-adrenoceptor (ß2-AR) agonists are considered essential bronchodilator drugs in the treatment of bronchial asthma, both as symptoms-relievers and, in combination with inhaled corticosteroids, as disease-controllers. In this article, we first review the basic mechanisms by which the ß2-adrenergic system contributes to the control of airway smooth muscle tone. Then, we go on describing the structural characteristics of ß2-AR and the molecular basis of G-protein-coupled receptor signaling and mechanisms of its desensitization/ dysfunction. In particular, phosphorylation mediated by protein kinase A and ß-adrenergic receptor kinase are examined in detail. Finally, we discuss the pivotal role of inhaled ß2-AR agonists in the treatment of asthma and the concerns about their safety that have been recently raised.

Noninflammatory mechanisms of airway hyper-responsiveness in bronchial asthma: an overview.

Airway hyper-responsiveness (AHR) is a cardinal feature of asthma. Its absence has been considered useful in excluding asthma, whereas it may be present in other diseases such as atopic rhinitis and chronic obstructive pulmonary disease. AHR is often considered an epiphenomenon of airway inflammation. Actually, the response of airways to constrictor stimuli is modulated by a complex array of factors, some facilitating and others opposing airway narrowing. Thus, it has been suggested that AHR, and perhaps asthma, might be present even without or before the development of airway inflammation. We begin this review by highlighting some terminological and methodological issues concerning the measurement of AHR. Then we describe the neurohumoral mechanisms controlling airway tone. Finally, the pivotal role of airway smooth muscle and internal and external modulation of airway caliber in vivo are discussed in detail.

Bronchodilator effects of exercise hyperpnea and albuterol in mild-to-moderate asthma.

In asthmatic patients, either bronchodilatation or bronchoconstriction may develop during exercise. In 18 patients with mild-to-moderate asthma, we conducted two studies with the aims to 1) quantify the bronchodilator effect of hyperpnea induced by incremental-load maximum exercise compared with effects of inhaled albuterol (study 1, n=10) and 2) determine the time course of changes in airway caliber during prolonged constant-load exercise (study 2, n=8). In both studies, it was also investigated whether the bronchodilator effects of exercise hyperpnea and albuterol are additive. Changes in airway caliber were measured by changes in partial forced expiratory flow. In study 1, incremental-load exercise was associated with a bronchodilatation that was approximately 60% of the maximal bronchodilatation obtainable with 1,500 microg of albuterol. In study 2, constant-load exercise was associated with an initial moderate bronchodilatation and a late airway renarrowing. In both studies, premedication with inhaled albuterol (400 microg) promoted sustained bronchodilatation during exercise, which was additive to that caused by exercise hyperpnea. In conclusion, in mild-to-moderate asthmatic individuals, hyperpnea at peak exercise was associated with a potent yet not complete bronchodilatation. During constant-load exercise, a transient bronchodilatation was followed by airway renarrowing, suggesting prevalence of constrictor over dilator effects of hyperpnea. Finally, the bronchodilator effect of hyperpnea was additive to that of albuterol.

Airway smooth muscle as a model for new investigative drugs in asthma.

Bronchial asthma as such exists because airway smooth muscle (ASM) contracts excessively in response to various stimuli. After several decades during which research was mainly focused on airway inflammation, increasing attention is now being paid to a possible abnormal behaviour of ASM. Thus, ASM is regarded as a major target for anti-asthma treatments. This review first describes the mechanisms of ASM contraction and airway hyperresponsiveness, through cellular, animal and human models. The developments of new drugs targeting extra and/or intracellular pathway of ASM contraction are discussed.

Airway responsiveness to methacholine and deep inhalations in subjects with rhinitis without asthma.

BACKGROUND: Airway hyperresponsiveness in asthma is believed to be caused in part by the inability of deep inspirations to modulate airway narrowing. OBJECTIVE: We investigated whether deep inspirations taken before or after methacholine inhalation attenuate bronchoconstriction in subjects with rhinitis. The results were compared with a group of healthy subjects. METHODS: Ten subjects with rhinitis without asthma and 10 healthy subjects were studied on 3 different occasions at random. Bronchial challenges were performed with a single dose of methacholine known to decrease the FEV(1) by 17% to 40%. Challenges were performed with avoidance of deep inspirations, or with 5 deep inspirations preceding or following the inhalation of methacholine. Lung function measurements were specific airway conductance, forced expiratory flow at 30% to 40% of vital capacity on a maneuver started from end-tidal inspiration (partial flow), and residual volume (partial residual volume). RESULTS: In healthy subjects, deep inspirations taken after methacholine caused less changes in specific airway conductance, partial flow, and partial residual volume (P < .005 for all) than deep inspirations taken before methacholine or avoidance. In subjects with rhinitis, methacholine produced similar functional changes independently of the presence or absence of any deep inspirations. Compared with normal subjects, the attenuating effects of deep inspirations after methacholine on partial flow and partial residual volume were blunted in the subjects with rhinitis (P = .02 and P = .05, respectively). CONCLUSION: The ability to dilate methacholine-constricted airways by deep inspirations is impaired in subjects with rhinitis, possibly because of an abnormal behavior of airway smooth muscle.

Cysteinyl-leukotrienes in the regulation of beta2-adrenoceptor function: an in vitro model of asthma.

BACKGROUND: The response to beta2-adrenoceptor agonists is reduced in asthmatic airways. This desensitization may be in part due to inflammatory mediators and may involve cysteinyl-leukotrienes (cysteinyl-LTs). Cysteinyl-LTs are pivotal inflammatory mediators that play important roles in the pathophysiology of asthma, allergic rhinitis, and other inflammatory conditions. We tested the hypothesis that leukotriene D4 (LTD4) and allergen challenge cause beta2-adrenoceptor desensitization through the activation of protein kinase C (PKC). METHODS: The isoproterenol-induced cAMP accumulation was evaluated in human airway smooth muscle cell cultures challenged with exogenous LTD4 or the PKC activator phorbol-12-myristate-13-acetate with or without pretreatments with the PKC inhibitor GF109203X or the CysLT1R antagonist montelukast. The relaxant response to salbutamol was studied in passively sensitized human bronchial rings challenged with allergen in physiological salt solution (PSS) alone, or in the presence of either montelukast or GF109203X. RESULTS: In cell cultures, both LTD4 and phorbol-12-myristate-13-acetate caused significant reductions of maximal isoproterenol-induced cAMP accumulation, which were fully prevented by montelukast and GF109203X, respectively. More importantly, GF109203X also prevented the attenuating effect of LTD4 on isoproterenol-induced cAMP accumulation. In bronchial rings, both montelukast and GF109203X prevented the rightward displacement of the concentration-response curves to salbutamol induced by allergen challenge. CONCLUSION: LTD4 induces beta2-adrenoceptor desensitization in human airway smooth muscle cells, which is mediated through the activation of PKC. Allergen exposure of sensitized human bronchi may also cause a beta2-adrenoceptor desensitization through the involvement of the CysLT1R-PKC pathway.