Beta-adrenergic receptors in the lung: an introduction

New phosphodiesterase-4 inhibitors present airways relaxant activity in a guinea pig acute asthma model

Asthma is a disease characterized by chronic inflammation and hyper responsiveness of airways. We aimed to assess the relaxant potential of phosphodiesterase-4 (PDE4) inhibitors N-sulfonilhidrazonic derivatives on non-asthmatic and asthmatic guinea pig trachea. Firstly, guinea pigs were sensitized and challenged with ovalbumin, and then morphological, and contractile changes were evaluated resulting from asthma, followed by evaluation of relaxant effect of derivatives on guinea pig trachea and the cAMP levels measurement by ELISA. It has been evidenced hypertrophy of airway smooth muscle, inflammatory infiltrate, and vascular abnormalities. Moreover, only sensitized tracheal rings were responsive to OVA. Contractile response to histamine, but not to carbachol, was greater in sensitized animals, however the relaxant response to aminophylline and isoprenaline were the same in non-asthmatics and asthmatics. N-sulfonilhidrazonic derivatives presented equipotent relaxant action independent of epithelium, with exception of LASSBio-1850 that presented a low efficacy (< 50%) and LASSBio-1847 with a 4-fold higher potency on asthmatics. LASSBio-1847 relaxant curve was impaired in the presence of propranolol and potentiated by isoprenaline in both groups. Furthermore, relaxation was potentiated 54- and 4-fold by forskolin in non-asthmatics and asthmatics, respectively. Likewise, LASSBio-1847 potentiated relaxant curve of aminophylline 147- and 4-fold in both groups. The PKA inhibitor H-89 impaired the relaxant potency of the derivative. Finally, LASSBio-1847 increased tracheal intracellular cAMP levels similarly to rolipram, selective PDE4 inhibitor, in both animals. LASSBio-1847 showed to be promising to relax guinea pig trachea from non-sensitized and sensitized guinea pigs by activation of β2-adrenergic receptors/AC/cAMP pathway.

Pharmacological identification of β-adrenoceptor subtypes mediating isoprenaline-induced relaxation of guinea pig colonic longitudinal smooth muscle

Object We aimed to identify the β-adrenoceptor (β-AR) subtypes involved in isoprenaline-induced relaxation of guinea pig colonic longitudinal smooth muscle using pharmacological and biochemical approaches. Methods Longitudinal smooth muscle was prepared from the male guinea pig ascending colon and contracted with histamine prior to comparing the relaxant responses to three catecholamines (isoprenaline, adrenaline, and noradrenaline). The inhibitory effects of subtype-selective β-AR antagonists on isoprenaline-induced relaxation were then investigated. Results The relaxant potencies of the catecholamines were ranked as: isoprenaline > noradrenaline ≈ adrenaline, whereas the rank order was isoprenaline > noradrenaline > adrenaline in the presence of propranolol (a non-selective β-AR antagonist; 3 × 10^-7 M). Atenolol (a selective β₁-AR antagonist; 3 × 10^-7-10^-6 M) acted as a competitive antagonist of isoprenaline-induced relaxation, and the pA₂ value was calculated to be 6.49 (95% confidence interval: 6.34-6.83). The relaxation to isoprenaline was not affected by ICI-118,551 (a selective β₂-AR antagonist) at 10^-9-10^-8 M, but was competitively antagonized by 10^-7-3 × 10^-7 M, with a pA₂ value of 7.41 (95% confidence interval: 7.18-8.02). In the presence of propranolol (3 × 10^-7 M), the relaxant effect of isoprenaline was competitively antagonized by bupranolol (a non-selective β-AR antagonist), with a pA₂ value of 5.90 (95% confidence interval: 5.73-6.35). Conclusion These findings indicated that the β-AR subtypes involved in isoprenaline-induced relaxation of colonic longitudinal guinea pig muscles are β₁-AR and β₃-AR.

Isolation and culture of primary equine tracheal epithelial cells

Culture of airway epithelial cells is a useful model to investigate physiology of airway epithelia and airway disease mechanisms. In vitro models of airway epithelial cells are established for various species. However, earlier published method for isolation and culture of equine tracheal epithelial cells requires significant improvements. In this report, the development of a procedure for efficient isolation, characterization, culture, and passage of primary equine tracheal epithelial cells are described. Epithelial cells were isolated from adult equine trachea by exposing and stripping the mucosal epithelium from the adjacent connective tissue and smooth muscle. The tissue was minced and dissociated enzymatically using 0.25% trypsin-ethylenediaminetetraacetic acid (EDTA) solution for 2 h at 37 degrees C. Cells were collected by sieving and centrifugation, and contaminating fibroblasts were removed by differential adhesion. This procedure resulted in a typical yield of 1 x 10(7) cytokeratin-positive epithelial cells per gram tracheal lining tissue. Viability was 95% by trypan blue exclusion and isolates contained approximately 94% cytokeratin-positive cells of epithelial origin. Cells seeded at a density of 6.9 x 10(4) cells/cm2 in serum-free airway epithelial cell growth medium formed monolayers near confluency within a week. Confluent cells were dissociated using dispase II and first passages (P1) and second passages (P2) were successfully established in serum-free medium. Collagen coating of tissue culture flask was not required for cell adhesion, and cultures could be maintained at the level of P2 over 30 d. In the present study, we could establish a high-yield protocol for isolation and culture of equine tracheal epithelial cells that can serve for in vitro/ex vivo studies on the (patho-)physiology of equine airway disease as well as pharmacological and toxicological targets relevant to airway diseases.

Pharmacological characterization of the β-adrenoceptor that mediates the relaxant response to noradrenaline in guinea-pig tracheal smooth muscle

Pharmacological characteristics of beta-adrenoceptors (beta-ARs) mediating noradrenaline-induced relaxation were investigated in guinea-pig tracheal smooth muscle. The inhibitory effects of several types of beta-AR antagonists on noradrenaline-induced relaxation against histamine contraction were scrutinized with Schild plot analysis. The concentration-response curve for noradrenaline obtained in the absence of phentolamine and uptake inhibitors was competitively antagonized by all of the beta-AR antagonists used in this study (propranolol, bupranolol, atenolol, butoxamine and ICI-118,551). However, their pA2 values were markedly less than the expected values for beta1-AR and beta2-AR. On the other hand, pA2 values of ICI-118,551 (6.85) determined in the presence of phentolamine suggested a contribution of a beta1 -AR rather than beta2 -AR. In the presence of phentolamine and uptake inhibitors (desipramine and deoxycorticosterone), the Schild plot for atenolol was a better fit, with two distinct straight lines. The pA2 values of atenolol provided by the regression were: approximately 7.0, which corresponds to the expected beta1-AR value, and approximately 6.5, which was 3 times less than the expected value for beta1 -AR, and thus the possible presence of two classes of beta1 -AR (beta1(Low) and beta1(High)) was suggested. This view was also supported by Schild plot analysis for propranolol, which fit two straight lines each with a slope of 1.0. The present findings indicate that beta1 -ARs contributing to noradrenaline-elicited relaxation in guinea-pig tracheal smooth muscle exhibit diverse pharmacological characteristics and may be subdivided into at least two classes with distinct affinities for atenolol. Under physiological conditions, beta1(Low) rather than beta1(High) seems to play a more significant role in noradrenaline-regulated airway smooth muscle tone.

Adrenaline produces the relaxation of guinea-pig airway smooth muscle primarily through the mediation of beta(2)-adrenoceptors

The beta-adrenoceptor subtype that mediates adrenaline-induced relaxation was pharmacologically identified in smooth muscle cells of the isolated guinea-pig trachea. Adrenaline produced a concentration-dependent relaxation with a pD(2) value of 7.1. The concentration-response curve for adrenaline was shifted rightwards in a competitive fashion by the beta(1)-/beta(2)-nonselective antagonists propranolol and bupranolol, with pA(2) values of 8.85 and 8.97, respectively. Adrenaline-induced relaxation was not affected by the beta(1)-selective antagonists atenolol and CGP-20, 712A within the concentration ranges supposed to antagonize the beta(1)-subtype (atenolol, <or=10(-6) M; CGP-20, 712A, <or=10(-8) M). By contrast, the concentration-response curve for adrenaline was shifted rightwards in a competitive fashion by atenolol at concentrations >or=3x10(-6) M with a pA(2) value of 5.77. The concentration-response curve for adrenaline was also competitively antagonized by the beta(2)-selective antagonists butoxamine and ICI-118,551 with pA(2) values of 6.86 and 8.73, respectively. The pA(2) values of beta-adrenoceptor antagonists (propranolol, bupranolol, atenolol, butoxamine and ICI-118,551) tested against adrenaline were consistent with the values when tested against salbutamol, a beta(2)-selective adrenoceptor agonist. The present findings provide evidence that the relaxant response of the smooth muscle of the guinea-pig trachea to the adrenal medulla hormone, adrenaline, is mainly mediated through beta(2)-adrenoceptors.

Evidence showing that beta-adrenoceptor subtype responsible for the relaxation induced by isoprenaline is principally beta2 but not beta1 in guinea-pig tracheal smooth muscle

1. The present study was carried out to pharmacologically identify the beta-adrenoceptor subtype that mediates isoprenaline-elicited relaxation in the isolated guinea-pig tracheal smooth muscle, to answer the question whether it is beta(1)- or beta(2)-subtype? 2. Isoprenaline as well as salbutamol, a well-known beta(2)-selective adrenoceptor agonist, produced a concentration-dependent relaxation with a pD(2) value of 8.12 vs. 7.54 for salbutamol. 3. Isoprenaline-elicited relaxation was not affected by beta(1)-selective antagonists, atenolol and CGP-20,712A, within the concentration ranges supposed to antagonize beta(1)-subtype: atenolol, < or =10(-6) M; CGP-20,712A, < or =10(-8) M. 4. By contrast, the concentration-response curves for isoprenaline as well as salbutamol were shifted rightwards in a competitive fashion by atenolol at the concentrations > or =3 x 10(-6) M. However, pA(2) values of atenolol against isoprenaline (5.86) and salbutamol (5.71) were consistent with the value corresponding to beta(2)- but not to beta(1)-subtype (around 7.00), and these values were not significantly different from each other. 5. Competitive antagonism of the relaxations to isoprenaline and salbutamol were also obtained with beta(2)-selective antagonists, butoxamine and ICI-118,551. Against isoprenaline and salbutamol, the pA(2) values of butoxamine (6.51 vs. 6.81) and ICI-118,551 (8.83 vs. 8.90) were substantially identical. Thus the primary mediation of beta(2)-receptor in the relaxations was strongly supported. 6. The present findings provide evidence that the beta-adrenoceptor which mediates isoprenaline-elicited relaxation of guinea-pig tracheal smooth muscle is essentially beta(2)- but not beta(1)-subtype. The present study also indicates the importance of using multiple receptor antagonists with different pA(2) values to pharmacologically identify the responsible receptor subtype in smooth muscle mechanical responses.

Assessing lung deposition of inhaled medications. Consensus statement from a workshop of the British Association for Lung Research, held at the Institute of Biology, London, U.K. on 17 April 1998

In vitro measurements of aerosol fine particle fraction (FPF) using particle-sizing apparatus (e.g. the twin impinger, multi-stage liquid impingers, cascade impactors) have a key role to play in the development of new pharmaceutical products and in quality control. However, use of in vitro methodology to attempt to predict lung deposition in vivo is of limited value due, in part, to the inability of current apparatus to mimic upper and lower airway anatomy satisfactorily. Estimates of FPF based on cut-off points ranging from 5-7 microns generally overestimate lung deposition as measured in vivo by gamma scintigraphy. We recommend that: 1. multistage apparatus (minimum five stages) be used to characterize particle size distribution adequately, over the range 0.5-5.0 microns; 2. where possible, measurements should be made at a range of rates and profiles of flow reflecting those likely to be generated using the inhalation device in clinical practice (including use by young and elderly patients with varying degrees of airflow obstruction); 3. encouragement should be given to the further development, standardization, and validation of apparatus with a 'throat' which more closely resembles the human oropharynx and larynx. Pharmacokinetic methods can give a good estimate of total, but not regional, lung deposition, with drugs which are either not absorbed via the gastrointestinal tract, or whose absorption can be blocked by co-administration of charcoal, thus avoiding confounding by absorption of drug substance deposited in the oropharynx and subsequently swallowed. Techniques which rely on evaluation of a timed fractional output of drug substance in the urine are susceptible to the inherent variability of rate of absorption across the respiratory epithelium. We recommend that consideration should be given to the further refinement and validation of PK methods which would more clearly identify the fractional dose deposited in the lung. Lung-imaging methodology, e.g. gamma scintigraphy, employing formulations radiolabelled with gamma-ray-emitting radionuclides such as 99mTc, can measure total lung deposition and oropharyngeal deposition, provided that the radiolabelling process is appropriately validated and suitable corrections are made for attenuation of gamma rays by body tissues. An estimate of regional lung deposition can be made by drawing 'regions of interest' on the scintigraphic image; the precision of this measure is limited by the two-dimensional (2-D) nature of most images which mean that there is an overlay of structures of interest (alveoli, small and large airways), which is most marked centrally. Three-dimensional (3-D) imaging techniques (e.g. single photon emission computed tomography, SPECT, and positron emission tomography, PET) have the potential to give more detailed data on regional lung deposition, but are currently more expensive, employ higher radiation doses, and are less well validated than 2-D (planar) imaging. We consider that, of the available imaging modalities, planar gamma scintigraphy represents current best practice for the assessment of lung deposition from inhaler devices where regional differences may be important. The methodology should be optimized by the adoption of generally accepted standards for radiolabelling, imaging, attenuation correction, and interpretation. It is important that deposition in all sites (device, oropharynx, lungs, stomach) should be quantified. Consideration should be given to refining the concept of regions of interest to coincide more closely with anatomical lung structures. Statistical methods to compare the size distributions of drug and radiolabel in validation experiments should be developed. In the longer term it is envisaged that three-dimensional imaging may play a more important part in evaluating lung deposition; an optimal three-dimensional anatomical model of lung zones of interest needs to be developed.

Ambroxol improves the broncho-spasmolytic activity of clenbuterol in the guinea-pig

The effects of ambroxol on the spasmolytic action of clenbuterol were investigated on acetylcholine-induced bronchospasm in guinea-pigs. Ambroxol (50 mg kg-1 day-1) or vehicle was administered orally for 14 days. Approximately 45 min after the final dose on day 14, the animals were anaesthetized and the spasmolytic effects of clenbuterol (3, 6 or 12 micrograms kg-1 injected intravenously) were determined by use of acetylcholine (40 micrograms kg-1, i.v.)-induced bronchoconstriction. For both vehicle- and ambroxol-treated animals, a positive linear relationship was observed between the log-dose of clenbuterol and the percent inhibition of bronchospasm. The calculated ED25 of clenbuterol (i.e., the dose producing 25% inhibition of the acetylcholine-induced bronchospasm) was 3.98 micrograms kg-1 (3.29 to 4.82 micrograms kg-1, 95% confidence interval) in the presence of ambroxol and 5.81 micrograms kg-1 (4.98 to 6.79 micrograms kg-1) in the absence of ambroxol. The linear regressions with or without ambroxol differed from each other (P < 0.001) but ran parallel (covariance analysis), enabling us to calculate a relative potency, the value of which was 1.46 (1.16 to 1.84). These results demonstrate that the spasmolytic activity of clenbuterol is significantly improved in animals pretreated with ambroxol.