A comparative study of beta-adrenoceptors in human and porcine lung parenchyma strip

Effect of histamine, albuterol and deep inspiration on airway and lung tissue mechanics in cynomolgus monkeys

Forced oscillation is a technique that has been used to measure airway and lung tissue impedance. To evaluate airway and lung tissue impedance in a colony of cynomolgus monkeys housed at Schering-Plough Research Institute, a forced oscillation technique was used to measure Newtonian resistance (R(N)), tissue damping (G), tissue elastance (H) and lung hysteresivity (eta). Functional residual capacity (FRC) was also measured to correlate the lung impedance data with FRC. There was no difference in R(N), G, H and eta between Ascaris sensitive allergic monkeys (n=25) and a small cohort (n=5) of non-allergic monkeys under baseline conditions. However, a highly significant (p<0.0001) negative correlation (r=0.71) was found between FRC and H. Significant correlations were also found between FRC and G (r=0.53) and FRC and R(N) (r=0.50). Bronchoprovocation with aerosolized histamine increased R(N), G, H and eta and reduced FRC by 29+/-3% (n=30) from baseline. In monkeys that were hyperreactive to the histamine challenge, an exaggerated increase in lung tissue damping was seen whereas monkeys that were less reactive to the histamine showed greater increases in R(N). Aerosolized albuterol (0.003-3mg/ml) produced a concentration-dependent reversal of the increases in R(N), G, H and eta induced by histamine with the greatest reversal seen on R(N). Deep inspiration, performed after the aerosolized albuterol exposure, also reversed the histamine-induced changes in R(N), G, and H with the complete reversal seen on the increase in H. These results demonstrate that significant correlations exist between airway and lung tissue impedance and FRC and that airway and lung tissue mechanics contribute significantly to inherent bronchoconstrictor reactivity and to the bronchodilator response to a beta-adrenergic agonist and deep inspiration in cynomolgus monkeys.

Relaxin deficiency in mice is associated with an age-related progression of pulmonary fibrosis

Relaxin (RLX) is a peptide hormone with known antifibrotic properties. However, its significance in the lung and its role as a therapeutic agent against diseases characterized by pulmonary fibrosis are yet to be established. In this study, we examined age-related structural and functional changes in the lung of relaxin-deficient mice. Lung tissues of male and female RLX knockout (-/-) and RLX wild-type (+/+) mice at various ages were analyzed for changes in collagen expression and content. We demonstrate an age-related progression of lung fibrosis in RLX -/- mice with significantly increased tissue wet weight, collagen content and concentration, alveolar congestion, and bronchiole epithelium thickening. The increased fibrosis was associated with significantly altered peak expiratory flow and lung recoil (lung function) in RLX -/- mice. Treatment of RLX -/- mice with relaxin in early and developed stages of fibrosis resulted in the reversal of collagen deposition. Organ bath studies showed that precontracted lung strips relaxed in the presence of relaxin. Together, these data indicate that relaxin may provide a means to regulate excessive collagen deposition in diseased states characterized by pulmonary fibrosis.

Effects of salbutamol and Ro-20-1724 on airway and parenchymal mechanics in rats

We investigated the effects of a selective beta(2)-agonist, salbutamol, and of phosphodiesterase type 4 inhibition with 4-(3-butoxy-4-methoxy benzyl)-2-imidazolidinone (Ro-20-1724) on the airway and parenchymal mechanics during steady-state constriction induced by MCh administered as an aerosol or intravenously (iv). The wave-tube technique was used to measure the lung input impedance (ZL) between 0.5 and 20 Hz in 31 anesthetized, paralyzed, open-chest adult Brown Norway rats. To separate the airway and parenchymal responses, a model containing an airway resistance (Raw) and inertance (Iaw), and a parenchymal damping (G) and elastance (H), was fitted to ZL spectra under control conditions, during steady-state constriction, and after either salbutamol or Ro-20-1724 delivery. In the Brown Norway rat, the response to iv MCh infusion was seen in Raw and G, whereas continuous aerosolized MCh challenge produced increases in G and H only. Both salbutamol, administered either as an aerosol or iv, and Ro-20-1724 significantly reversed the increases in Raw and G when MCh was administered iv. During the MCh aerosol challenge, Ro-20-1724 significantly reversed the increases in G and H, whereas salbutamol had no effect. These results suggest that, after MCh-induced changes in lung function, salbutamol increases the airway caliber. Ro-20-1724 is effective in reversing the airway narrowings, and it may also decrease the parenchymal constriction.

Localisation and expression of beta-adrenoceptor subtype mRNAs in human lung

The cellular localisation and distribution of mRNAs encoding beta-adrenoceptor subtypes in human lung were studied by in situ hybridisation and Northern blot analysis. The 851-bp SmaI/PvuII fragment of human beta 1-adrenoceptor cDNA, the 439-bp SmaI fragment of human beta 2-adrenoceptor cDNA and the 975-bp SmaI fragment of human beta 3-adrenoceptor cDNA bound to single mRNA species of approximately 3.2 kb, 2.2 kb and 2.3 kb in size, respectively. Human lung and heart and rabbit lung expressed both beta 1- and beta 2-adrenoceptor mRNAs with no detectable level of beta 3-adrenoceptor mRNA, while rabbit perirenal adipose tissue expressed beta 1-, beta 2- and beta 3-adrenoceptor mRNAs. Cultured human airway epithelial cells and airway smooth muscle cells expressed only beta 2-adrenoceptor mRNA. In situ hybridisation in human lung, using 35S-labelled antisense RNA probes revealed a high level of expression of beta 1- and beta 2-adrenoceptor mRNAs in the pulmonary blood vessels, high level of expression of beta 2-adrenoceptor mRNA in the alveolar walls with less expression of beta 1-adrenoceptor mRNA. There was a moderate expression of beta 2-adrenoceptor but not beta 1-adrenoceptor mRNA in airway epithelium and smooth muscle of peripheral airways and no detectable beta 3-adrenoceptor mRNA in any lung structures.

High affinity [3H]formoterol binding sites in lung: characterization and autoradiographic mapping

Agonist binding to the beta 2-adrenoceptors and its mapping were studied using the newly developed radioligand [3H]formoterol. The results of [3H]formoterol saturation binding and formoterol inhibition of [3H]formoterol binding were consistent with binding to a single class of receptors (Kd = 1.34 +/- 0.15 nM, Bmax = 154.9 +/- 8.0 fmol/mg protein in guinea pig lung membranes, n = 8; Kd = 1.05 +/- 0.17 nM, Bmax = 67.8 +/- 8.1 fmol/mg protein in human lung membranes, n = 5) and competition assays with other agonists and antagonists disclosed only a single class of site. The nonhydrolyzable GTP analogue GTP gamma S caused a reduction in both Kd and Bmax, indicating that the receptors labelled by [3H]formoterol are coupled to a guanine nucleotide binding regulatory protein. Receptor mapping of [3H]formoterol binding sites shows that beta 2-adrenoceptors were widely distributed in both guinea pig and human lung, with dense labelling over airway epithelium and uniformly over alveolar walls, and sparse labelling of airway and vascular smooth muscle. In addition, submucosal glands were also sparsely labelled in human bronchus. The distribution of beta 2-adrenoceptors was similar to the pattern previously described with non-selective radiolabelled antagonists in the presence of selective beta 1-adrenoceptor antagonists.

Neuronal control of airways smooth muscle

Sensory afferent nerves relay impulses from the airways to the central nervous system so that appropriate changes in bronchomotor tone and breathing patterns may occur. The dominant efferent control of airways smooth muscle is exerted via bronchoconstrictor parasympathetic cholinergic nerves. In some species this is opposed by bronchodilator sympathetic noradrenergic nerves. In addition, there exist both excitatory bronchoconstrictor and inhibitory bronchodilator non-adrenergic, non-cholinergic pathways. This review examines the role of the different branches of the autonomic nervous system in the control of airways smooth muscle tone with particular reference to modulation of these branches and the interactions which may exist between them.

Localization of beta 2-adrenoceptor messenger RNA in human and rat lung using in situ hybridization: correlation with receptor autoradiography

We have used in situ hybridization to study the localization of mRNA encoding the beta 2-adrenoceptor in tissue sections of the human and rat lung and compared this with the distribution of beta 2-receptor binding sites using receptor autoradiography. To localize beta 2-receptor mRNA, a [32P]labeled antisense RNA probe (riboprobe) was generated from human or rat beta 2-receptor cDNA. A similar distribution of beta 2-receptor mRNA was identified in both species. The highest intensity of beta 2-receptor mRNA was detected in smooth muscle of small airways, airway epithelium and pulmonary blood vessels. Lower intensity of beta 2-receptor mRNA was identified in smooth muscle of large airways, and alveolar epithelium (presumably type I and type II pneumocytes). No significant hybridization signal was detected in interstitial tissue. The specificity of the hybridization signal was confirmed with a sense probe (having identical sequence to the mRNA) and preincubation with RNase A, and by Northern blot analysis which revealed a single band of mRNA of 2.2 kb. There was a correspondence between mRNA localization and the distribution of beta 2-receptors visualized by [125I]iodocyanopindolol autoradiographically in the presence of CGP 20712 (a beta 1-selective antagonist). However, alveolar walls that showed a high beta 2-receptor density had relatively low levels of mRNA. This cellular heterogeneity may reflect differences in RNA stability or transcription rate in different lung cells. This approach opens up new options in the investigation of the regulation of pulmonary beta 2-receptor gene expression in health and disease.

Beta-adrenoceptors in human airway tissue: relationship between functional responsiveness and receptor number

Functional organ bath experiments and radiolabelled ligand binding studies were used to investigate the relationship between beta-adrenoceptor-mediated relaxation and the total number of beta-adrenoceptors in human lung parenchymal tissue and bronchial tissue. Sensitivity to the beta-adrenoceptor agonist isoprenaline (pD2) varied almost 10-fold (pD2 values 6.00 to 6.85) for lung parenchymal preparations and 35-fold for bronchial preparations (pD2 values 6.16 to 7.67) between patients. The total number of [3H] DHA labelled beta-adrenoceptors (Bmax) varied almost 6-fold for lung parenchymal membrane preparations (Bmax 164 to 936 fmol/mg protein) and less than 2-fold for bronchial tissue membrane preparations (Bmax 188 to 342 fmol/mg protein) between patients. Comparison of sensitivity to isoprenaline and beta-adrenoceptor number for lung parenchymal tissue from the same patient demonstrated a negative correlation (r = -0.80 [95% confidence intervals: -0.13, -0.96], 6 d.f., P less than 0.05), suggesting that beta-adrenoceptor-mediated sensitivity of lung parenchymal tissue is inversely related to the number of beta-adrenoceptors. However, there was an absence of correlation between sensitivity to isoprenaline and beta-adrenoceptor number in bronchial tissue from the same patient. Thus, the findings of the present study do not support the possibility of a direct relationship between the beta-adrenoceptor-mediated responsiveness and the beta-adrenoceptor number of human airway preparations.

Increased airway reactivity in the guinea-pig follows exposure to intravenous isoprenaline

1. Intravenous infusion of (+/-) isoprenaline (1-100 micrograms kg-1 h-1) enhanced airway responses (resistance, RL; and compliance, Cdyn) to histamine (1.0-1.8 micrograms kg-1) and bombesin (100-240 ng kg-1), whereas airway responses to vagal stimulation remained unchanged. 2. Bilateral vagotomy before intravenous infusion of (+/-)isoprenaline (100 micrograms kg-1 h-1) prevented development of airway hyperreactivity to histamine or bombesin, yet vagotomy after infusion of isoprenaline was without effect. 3. Prior treatment with atropine (1 mg kg-1) did not influence the capacity of (+/-)isoprenaline (100 micrograms kg-1 h-1) to increase airway reactivity to bombesin. 4. Despite a 500-fold difference in spasmolytic potency in vivo, infusion of (+)isoprenaline (100 micrograms kg-1 h-1) or (-)isoprenaline (100 micrograms kg-1 h-1) increased reactivity of the airways to histamine or bombesin to a comparable extent. 5. Neither adrenaline (100 micrograms kg-1 h-1) nor forskolin (600 micrograms kg-1 h-1) increased reactivity of the airways to histamine or bombesin. 6. Intravenous infusion of dopamine (100 micrograms kg-1 h-1) or noradrenaline (100 micrograms kg-1 h-1) increased reactivity of the airways to histamine or bombesin. 7. Intravenous infusion of (+/-) propranolol (100 micrograms kg-1 h-1) increased reactivity of the airways to histamine or bombesin which was partially inhibited by bilateral vagal section. 8. Depletion of circulating platelets by lytic anti-platelet serum or concomitant infusion of an antagonist of platelet-activating factor (PAF), ginkgolide B (1 mg kg-1 h-1) did not diminish the capacity of (+/-)isoprenaline (100 micrograms kg-1 h-1) to induce hyperreactivity of the airways to histamine or bombesin. 9. These observations indicate that (+/-)isoprenaline can induce airway hyper-reactivity by a mechanism unrelated to beta-adrenoceptor activation, but which is dependent upon intact vagus nerves.

Adrenoceptors in airway smooth muscle

This review examines the roles and functional significance of alpha and beta-adrenoceptor subtypes in airway smooth muscle, with emphasis on human airway function and the influence of asthma. Specifically, we have examined the distribution of beta-adrenoceptors in lung and the influence of age, the epithelium, respiratory viruses and inflammation associated with asthma on airway smooth muscle beta-adrenoceptor function. Sites of action, beta 2-selectivity, efficacy and tolerance are also examined in relation to the use of beta 2-agonists in man. In addition, alpha-adrenoceptor function in airway smooth muscle has been reviewed, with some emphasis on comparing observations made in airway smooth muscle with those in animal models.

A study of beta-adrenoceptors in rat lung parenchymal strip

The aim of the present study was to characterize the beta-adrenoceptor population in rat lung strip. For this purpose, Schild plots were obtained for the beta-adrenoceptor antagonists atenolol (beta 1-selective), butoxamine (beta 2-selective) and propranolol (non-selective), using three different agonists:isoprenaline (non-selective), salbutamol (beta 2-selective) and noradrenaline (beta 1-selective). The slopes of these Schild plots were close to the theoretical value of unity, and pA2 values determined with isoprenaline, salbutamol and noradrenaline as agonists were: for propranolol, 7.86 +/- 0.22, 7.72 +/- 0.15 and 7.89 +/- 0.23; for atenolol, 5.19 +/- 0.05, 5.33 +/- 0.07 and 5.47 +/- 0.22 and for butoxamine, 6.31 +/- 0.11, 6.34 +/- 0.03 and 5.99 +/- 0.23, respectively. These data suggest that pharmacological responses of rat isolated lung strip to beta-adrenoceptor agents are mediated by a homogeneous population of beta 2-adrenoceptors, although the presence of a minor population of beta 1-adrenoceptors undetected by the agonists used cannot be excluded.

Autoradiographic localization of beta-adrenoceptors in pig lung using [125I]-iodocyanopindolol

The binding of the beta-adrenoceptor radioligand [125I]-iodocyanopindolol (I-CYP) has been studied in pig lung parenchyma and the distribution of binding sites visualised by light microscopic autoradiography. I-CYP binding was saturable (maximum binding capacity Bmax = 51 +/- 3 fmol mg-1 protein), involving sites with high affinity (dissociation constant KD = 73 +/- 10 pM). Specific I-CYP binding was displaceable both by beta-adrenoceptor agonists ((-)-isoprenaline greater than (-)-adrenaline greater than (+/-)-fenoterol greater than (-)-noradrenaline greater than (+)-isoprenaline greater than (+/-)-RO363) and antagonists ((+/-)-propranolol greater than ICI-118551 greater than atenolol), indicating a predominance of beta 2-adrenoceptors. Further analysis showed that displacement data for the beta 1-selective antagonist atenolol and the beta 2-selective antagonist ICI-118551 were fitted best to a 2 binding site model and that both beta 1- and beta 2-adrenoceptors were present in pig lung in the ratio 28:72 respectively. Autoradiographic grains were localized over tissue and were most dense over alveolar walls greater than vascular endothelium greater than vascular smooth muscle greater than bronchial smooth muscle = bronchial epithelium. Atenolol (10(-5) M) caused a 31% reduction in specific grain density over alveolar wall tissue, while a 10 fold lower concentration of ICI-118551 (10(-6) M) caused a 50% decrease. These results are consistent with binding data in pig lung parenchyma demonstrating a mixed population of beta-adrenoceptors with a predominance of the beta 2 subtype. 6 It is possible that the previously described relaxant responses of the pig lung parenchyma strip to beta-agonists, mediated via beta 2-adrenoceptors, resulted from the sum of reactivities in airway and vascular smooth muscle together with relaxation of alveolar interstitial cells.

On the assessment of the beta-adrenoceptor blocking activity of propranolol using the rat isolated right ventricle

Two methods for determining pA2 values, the Schild regression and the use of the formula pA2 = pAx + log(x - 1), have been reassessed. The effects of propranolol on the contractile responses of the rat isolated right ventricle to isoprenaline were studied. The inhibitory effect with the lower concentrations of propranolol tested (3 X 10(-9) -10(-7) M) was solely competitive. Thus there was a parallel dextral displacement of the concentration-response curves to isoprenaline with no depression of the maximal responses. Dual antagonism was observed with the higher concentrations of propranolol tested (10(-6) and 3 X 10(-6) M), thereby showing a parallel displacement of the concentration-response curve to the lower concentrations of isoprenaline with a depression of the maximal responses. Without analysis of data for individual concentrations of propranolol on concentration-response curves to isoprenaline, Schild regression did not clearly illustrate that the antagonism was not solely competitive with the higher concentrations of propranolol. We suggest that data for individual concentrations of antagonist should always be analyzed to ascertain whether there has been a parallel shift of the concentration-response curves to agonist prior to determining pA2 values.

Responsiveness to tyramine in isolated lung parenchymal strip of guinea-pig and rat

The effects of alpha/beta-adrenoceptor agonists in isolated lung parenchymal strip are well characterized but information related to indirectly acting sympathomimetic agents is scarce. In the present study the response to tyramine was analyzed in lung strips from guinea-pig and rat. Tyramine elicited a dose-related contraction of the lung strip with an EC50 of 1.12 X 10(-4) M in the guinea-pig and 4.28 X 10(-4) M in the rat. Incubation with propranolol did not modify the tyramine-induced contraction but blocked the relaxation which occasionally appeared at low concentrations of tyramine. No tachyphylaxis to tyramine was detected. Cocaine (3 X 10(-5) M) and reserpine significantly increased the EC50 values of tyramine. In reserpine-treated animals, phentolamine (both animal species), clemizole (guinea-pig) and methysergide (rat) displaced to the right the concentration-response curve to tyramine but the dose ratios were significantly lower than those obtained for their specific agonists. These results suggest that in addition to the adrenergic component (catecholamine release and direct alpha-adrenoceptor activation) there is an important contribution of other receptor systems such as histamine (guinea-pig) and 5-hydroxytryptamine (rat) to the contractile response to tyramine in lung tissue.

Nature of the beta-adrenoreceptors in the tracheal smooth muscle of the adult pig

Relaxant responses to isoprenaline (ISO), adrenaline (ADR) and noradrenaline (NA) were investigated on carbachol-contracted, isolated tracheal smooth muscle preparations of the adult pig to determine the nature of the beta-adrenoreceptors present. The order of relaxant potencies of the catecholamines on this preparation was ISO greater than ADR greater than NA. The potency ratio at 37 degrees C was 1:0.06:0.005. This suggests that beta 2-adrenoreceptors predominate in isolated tracheal smooth muscle of the adult pig. Though the order of potency for the above catecholamines did not change, at the lower temperatures of 29 degrees and 33 degrees C, the potency ratios were slightly modified to 1:0.0.98:0.004 and 1:0.07:0.004 respectively. pA2 values on pig tracheal smooth muscle were 8.65 and 9.13 respectively, for the non-selective beta-blockers propranolol and alprenolol, and 5.63, 5.20 and 6.26 respectively, for the beta 1 selective blockers practolol, atenolol and metoprolol and 6.82 for the beta 2 selective beta-blocker, H 35/25. The results suggest the existence and predominance of beta 2-adrenoreceptors in tracheal smooth muscle of the adult pig.

Classification of beta-adrenoceptors in isolated bronchus of the pig

1 (+/-)-Isoprenaline (Iso), (-)-adrenaline (Ad), (-)-noradrenaline (NA), the beta 2-selective adrenoceptor agonist (+/-)-fenoterol (Fen) and the beta 1-selective adrenoceptor agonist (+/-)-RO363 caused concentration-dependent relaxation of preparations of pig bronchus pre-contracted with carbachol 40-ng/ml (0.22 microM). Iso, Ad, NA and Fen caused complete relaxation of carbachol-induced tone, but RO363 caused relaxation equivalent to only 59% of the maximal response to Iso. 2 When relaxation responses to these amines were plotted as a % of their maximal effects, comparison of EC50 values showed that the order of potency was RO363 greater than Iso greater than NA greater than Fen greater than Ad (14.4:4.6:1:0.4:0.3). 3 pA2 values determined for the beta-adrenoceptor antagonists propranolol (non-selective) and atenolol (beta 1-selective), or the partial agonist salbutamol (beta 2-selective) using Iso as agonist were 8.3, 7.3 and 4.4 respectively. The pA2 value for atenolol using RO363 as the agonist was 7.6. 4 These results indicate that porcine bronchus contains a homogeneous population of beta 1-adrenoceptors.