Comparison of functional beta-adrenoceptor heterogeneity in central and peripheral airway smooth muscle of guinea pig and man

Rosiglitazone elicits in vitro relaxation in airways and precision cut lung slices from a mouse model of chronic allergic airways disease

Rosiglitazone (RGZ), a peroxisome proliferator-activated receptor-γ (PPARγ) ligand, is a novel dilator of small airways in mouse precision cut lung slices (PCLS). In this study, relaxation to RGZ and β-adrenoceptor agonists were compared in trachea from naïve mice and guinea pigs and trachea and PCLS from a mouse model of chronic allergic airways disease (AAD). Airways were precontracted with methacholine before addition of PPARγ ligands [RGZ, ciglitazone (CGZ), or 15-deoxy-(Δ12,14)-prostaglandin J2 (15-deoxy-PGJ2)] or β-adrenoceptor agonists (isoprenaline and salbutamol). The effects of T0070907 and GW9662 (PPARγ antagonists) or epithelial removal on relaxation were assessed. Changes in force of trachea and lumen area in PCLS were measured using preparations from saline-challenged mice and mice sensitized (days 0 and 14) and challenged with ovalbumin (3 times/wk, 6 wk). RGZ and CGZ elicited complete relaxation with greater efficacy than β-adrenoceptor agonists in mouse airways but not guinea pig trachea, while 15-deoxy-PGJ2 did not mediate bronchodilation. Relaxation to RGZ was not prevented by T0070907 or GW9662 or by epithelial removal. RGZ-induced relaxation was preserved in the trachea and increased in PCLS after ovalbumin-challenge. Although RGZ was less potent than β-adrenoceptor agonists, its effects were additive with salbutamol and isoprenaline and only RGZ maintained potency and full efficacy in maximally contracted airways or after allergen challenge. Acute PPARγ-independent, epithelial-independent airway relaxation to RGZ is resistant to functional antagonism and maintained in both trachea and PCLS from a model of chronic AAD. These novel efficacious actions of RGZ support its therapeutic potential in asthma when responsiveness to β-adrenoceptor agonists is limited.

Beta-adrenoceptor responses of the airways: for better or worse?

Beta2-adrenoceptor agonists are the first-line treatment of asthma and chronic obstructive pulmonary disease (COPD), in which a short-acting beta2-adrenoceptor agonist is used as required for relief of bronchoconstriction. A long-acting beta2-adrenoceptor agonist may be added to an inhaled corticosteroid as step 3 in the management of chronic asthma. Long-acting beta2-adrenoceptor agonists may also be added in treatment of COPD. This review examines the beneficial and detrimental effects of beta2-adrenoceptor agonists. The beneficial effects of beta2-adrenoceptor agonists are mainly derived from their bronchodilator activity which relieves the bronchiolar narrowing and improves air flow. The potential anti-inflammatory actions of stabilizing mast cell degranulation and release of inflammatory and bronchoconstrictor mediators, is considered. Other potential beneficial responses include improvements in mucociliary clearance and inhibition of extravasation of plasma proteins that is involved in oedema formation in asthma. The side effects of beta2-adrenoceptor agonists are primarily related to beta2-adrenoceptor-mediated responses at sites outside the airways. Of major concern has been the development of tolerance and this is discussed in relation to incidence of increased morbidity and mortality to asthma over the past three decades. A clinical aspect of beta2-adrenoceptor pharmacology in recent years has been the recognition of genetic polymorphism of the receptor and how this affects responses to and tolerance to beta2-adrenoceptor agonists. A controversial feature of beta2-adrenoceptor agonists is their stereoisomerism and whether the inactive (S)-isomer of salbutamol had detrimental actions in the commercially used racemate. The consensus is that despite these adverse properties, beta2-adrenoceptor agonist remains the most useful pharmacological agents in the management of asthma and COPD.

Relative resistance of functional β2-adrenoceptor-mediated smooth muscle responses to in vitro desensitization

The effects of in vitro incubation of rat isolated left atria, pulmonary artery rings, and aortic rings with isoprenaline (10-6 M for 6 h) were examined to compare the degree of desensitization of β1- and β2-adrenoceptor-mediated functional responses. The experimental protocols were carefully controlled to exclude influence from persistence of agonist in the tissues after the prolonged exposures, time-dependent changes in tissue sensitivity, and the methods of plotting the data. Concentration-response curves for isoprenaline were constructed before incubation with isoprenaline and, after washout during 1 h, a second curve was obtained. Two protocols were employed: firstly, the preincubation curve was constructed to ensure that a maximum response was obtained (>10-6 M) and, secondly, the preincubation curve was constructed to a maximum isoprenaline concentration of 10-6 M. Preincubation curves were corrected for time-dependent changes in sensitivity from sham-incubation control experiments. There was significant desensitization of the β1-adrenoceptor-mediated positive inotropic responses of the left atria, using both protocols, seen as rightward shifts (dose ratios: 4.48 ± 1.12 and 8.39 ± 2.3) of the concentration-response curves and depression of the maximum responses (77.0 ± 3.2 and 60.8 ± 5.5%). In contrast, the β2-adrenoceptor-mediated relaxations of the noradrenaline-constricted pulmonary artery and aorta did not display a significant loss of sensitivity. When the relaxation responses were plotted as a percentage of the noradrenaline-induced tone, there was no significant rightward shift of the concentration-response curves in the pulmonary artery (dose ratios: 2.82 ± 1.33 and 2.24 ± 0.62) or aorta (dose ratios: 1.43 ± 0.62 and 1.31 ± 0.27) and thus no desensitization.Key words: rat atria, pulmonary artery, aorta, β-adrenoceptors, desensitization.

Childhood asthma--advances in pathogenesis

Increase in morbidity and mortality of asthmatics in the world is a cause of concern. Many researchers have described various aspects of etiopathogenesis which has thrown light on the better understanding of asthma. Our experience with nearly 3 lakhs of asthmatic children, over a period of twenty-five years and our studies in Asthma clinic of ICH & HC, Madras generated new ideas to propose a hypothesis on etiopathogenesis of asthma. "Asthma is a disease caused by a specific infective agent in a genetically predisposed individual resulting in altered cellular response initially leading to hyperactive bronchial tree which on exposure to various aggravating factors manifest clinically as recurrent cough, dyspnoea and wheeze". Category of wheezers who manifest asthma is also discussed.

Noradrenaline-induced relaxation of rat oesophageal muscularis mucosae: mediation solely by innervated beta 3-adrenoceptors

We investigated the effects of cocaine and corticosterone on the noradrenaline-induced relaxation of rat oesophageal smooth muscle in the absence and presence of the selective beta2-antagonist, ICI 111,551. It was found that the concentration-response curve (CRC) of noradrenaline was not shifted by ICI 118,551 at 1 microM, whereas a clear shift to the right was observed at 100 microM of the antagonist. In the presence of corticosterone (10 microM), CRC's were clearly shifted to the left; with cocaine (10 microM) additionally present, a further leftward shift was observed, indicating the involvement of both neuronal and extraneuronal uptake sites. It was concluded that the relaxation of rat oesophageal muscularis mucosae by noradrenaline is solely mediated by beta3-adrenoceptors which are sympathetically innervated.

Beta 2- but not beta 3-adrenoceptors mediate prejunctional inhibition of non-adrenergic non-cholinergic contraction of guinea pig main bronchi

We studied the effects of selective beta-adrenoceptor agonists on the cholinergic and non-adrenergic non-cholinergic (excitatory NANC) contractions elicited by electrical field stimulation of guinea pig main bronchi in vitro. Addition of the selective beta 2-adrenoceptor agonists, fenoterol and salbutamol, and the selective beta 3-adrenoceptor agonist, BRL 37344 (4-[2-[(2-hydroxy-2-(3-chlor-phenyl)ethyl)amino]-propyl]-phenoxyac etic acid), induced a dose-dependent inhibition of the cholinergic contraction (pD2 7.89, 6.71 and 4.56, respectively) and the excitatory NANC response (pD2 9.11, 8.16 and 7.42, respectively). Fenoterol- and BRL 37344-induced inhibition of the excitatory NANC response was blocked with high potency (pKB 8.77 and 9.07, respectively) by the selective beta 2-adrenoceptor antagonist, ICI 118,511 (erythro-1-(7-methylindan-4-yloxy)-3-(isopropylamino)-but an-2-ol). A comparable contraction induced by neurokinin A (2 or 5 nM) was also inhibited by fenoterol, salbutamol and BRL 37344, but at significantly higher concentrations than for the inhibition of the excitatory NANC response (pD2 8.72, 7.56 and 6.66, respectively). Such a preferential inhibition of electrical field stimulation- versus agonist-induced effects was not observed for cholinergic contractions (pD2 versus methacholine-induced tone 7.86, 6.93 and 5.10, respectively). The results clearly exclude the involvement of beta 3-adrenoceptors in these responses. Furthermore they show that beta 2-adrenoceptors are involved in the prejunctional inhibition of excitatory NANC contractions, presumably via modulation of tachykinin release from sensory nerves, and solely in the postjunctional inhibition of cholinergic contractions.

Comparison of the effects of salbutamol and adrenaline on airway smooth muscle contractility in vitro and on bronchial reactivity in vivo

BACKGROUND

The effect of adrenergic agonists in asthma depends on their net effect on microvascular leakage, mucosal oedema, vascular clearance of spasmogens, inhibition of cholinergic neurotransmission, and airway smooth muscle contractility. It has been postulated that adrenaline, by virtue of its alpha effects on the vasculature and cholinergic neurotransmission, may have additional useful properties in asthma compared with selective beta agonists such as salbutamol.

METHODS

The airway effects of adrenaline (a non-selective adrenoreceptor agonist) were compared with the selective beta 2 agonist salbutamol. Their airway smooth muscle relaxant potencies and effect on histamine contraction in human bronchi in vitro were compared with their effects on airway calibre and histamine reactivity in asthmatic subjects in vivo. For the in vitro studies changes in tension were measured in response to these agents in thoracotomy specimens of human airways. In vivo the effects of adrenaline and salbutamol on airway calibre and histamine reactivity were measured in eight subjects with mild to moderate asthma in a randomised crossover study.

RESULTS

Salbutamol and adrenaline had approximately equivalent airway smooth muscle relaxant potencies in vitro and bronchodilator potency in vivo. However, their effects on histamine induced contraction in vitro were significantly different from their effects on histamine reactivity in vivo. Salbutamol was less potent in vitro producing a mean (SE) 2.4 (0.15) doubling dose increase in the histamine EC20 and adrenaline a 5.2 (0.18) doubling dose increase (mean difference between salbutamol and adrenaline 2.8 doubling doses; 95% CI 1.1 to 4.5). Salbutamol had no effect on the maximal response to histamine whereas adrenaline reduced it by 54%. In contrast, salbutamol was more potent in vivo producing a mean (SE) increase in PD20 histamine of 1.84 (0.5) doubling doses whereas adrenaline was without effect increasing PD20 by only 0.06 (0.47) doubling doses (mean difference between adrenaline and salbutamol 1.78, 95% CI 0.26 to 3.29 doubling doses).

CONCLUSIONS

These findings suggest that the alpha adrenergic airway effects of non-selective adrenoreceptor agonists such as adrenaline offer no additional protection against histamine-induced broncho-constriction in vivo than beta 2 selective drugs such as salbutamol, despite adrenaline providing greater protection against histamine-induced contraction in vitro. The differences between the effects of these agents in vitro and in vivo may be related to their opposing vascular effects in vivo.

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.

Cyclic nucleotide phosphodiesterase isoenzymes in guinea-pig tracheal muscle and bronchorelaxation by alkylxanthines

In this study the phosphodiesterase (PDE) isoenzymes in guinea-pig trachealis smooth muscle were separated by DEAE-Sepharose anion exchange chromatography, identified, and characterized. Furthermore the effect of theophylline and 1-n-butyl-3-n-propylxanthine (BPX) on the isolated PDE isoenzymes and on their tracheal relaxant effect were investigated and compared with the nonxanthine PDE inhibitors amrinone and Ro 20-1724. We identified five distinct isoenzymes in guinea-pig tracheal muscle; calcium/calmodulin-stimulated cyclic AMP PDE (PDE I), cyclic GMP-stimulated cyclic AMP PDE (PDE II), cyclic GMP-inhibited and amrinone-sensitive cyclic AMP PDE (PDE III), cyclic AMP-specific and Ro 20-1724-sensitive PDE (PDE IV), and cyclic GMP-specific PDE (PDE V). BPX strongly inhibited the PDE IV isoenzyme with high selectivity, while the inhibitory effect of theophylline was weak. The PDE IV inhibitors BPX and Ro 20-1724 synergistically increased the relaxant effect of the beta 2-adrenoceptor agonist salbutamol in carbachol-contracted trachea much more strongly than theophylline. In contrast, amrinone, a PDE III inhibitor, hardly influenced the relaxant effect of salbutamol, suggesting that the PDE IV isoenzyme is functionally associated with beta 2-adrenoceptors in guinea-pig trachea and that inhibition of this enzyme potentiates the ability of salbutamol to increase the intracellular cyclic AMP content. These results indicate that the PDE IV isoenzyme plays a significant role in alkylxanthine-mediated relaxation of guinea-pig trachea.

Formoterol: pharmacology, molecular basis of agonism, and mechanism of long duration of a highly potent and selective beta 2-adrenoceptor agonist bronchodilator

Formoterol is an innovative, highly potent, beta 2-adrenoceptor-selective agonist combining the clinical advantages of rapid onset of action with a duration of action in excess of 12 h. In vitro, formoterol is a potent airway smooth muscle relaxant with high efficacy, and very high affinity and selectivity for the beta 2-adrenoceptor. Formoterol appears to be retained in airway smooth muscle for extended periods since its relaxant effect on human airway smooth muscle is resistant to repeated washing and formoterol displays 'reassertion' of relaxation after washout of a beta-adrenoceptor antagonist. A model based on the diffusion microkinetics of formoterol into the plasmalemma lipid bilayer is proposed as a basis for these properties. In addition to the release of pro-inflammatory mediators from cells such as the mast cell, several other disease processes probably occur in asthma. Leukocytes, notably eosinophils, adhere to the vascular endothelium and emigrate into airway tissues, which may be damaged by these cells if they are activated to release mediators or their granular contents. Plasma and its component proteins are extravasated from the bronchial microcirculation. Formoterol has been demonstrated to potently inhibit these cells and processes in experimental test systems. Continuing clinical research involving histological examination of tissue reactions may allow a more complete determination of the effects of formoterol on inflammatory processes in humans and the clinical relevance of any such effects.

Comparison of the effects of selective inhibitors of phosphodiesterase types III and IV in airway smooth muscle with differing beta-adrenoceptor subtypes

1. The relaxant properties of the type IV adenosine 3',5'-cyclic monophosphate phosphodiesterase (cyclic AMP PDE) inhibitor, rolipram and the beta 2-selective and non-selective beta-adrenoceptor agonists salbutamol and isoprenaline, were compared on the guinea-pig, bovine, and mouse trachea and porcine bronchus all precontracted with methacholine (EC30). 2. Rolipram and both beta-agonists produced concentration-dependent reversal of the methacholine-induced tone in the four airway preparations. 3. Isoprenaline and salbutamol were similar in potency on the guinea-pig (-log10IC50:8.43, 8.06) and bovine (-log10 IC50:8.52, 8.40) airways. In contrast, salbutamol was much less potent than isoprenaline on the mouse trachea (> 1000 fold) and the porcine bronchus (> 100,000 fold). 4. The potency of rolipram approached that of isoprenaline on the guinea-pig and bovine trachea (beta 2-adrenoceptors predominate). However, rolipram was significantly less active than isoprenaline on the porcine bronchus (1000 fold) and mouse trachea (> 2000 fold) where beta 2-adrenoceptors predominate. 5. Siguazodan, the type III cyclic AMP PDE inhibitor, produced concentration-dependent relaxations of the porcine bronchus and guinea-pig trachea contracted with methacholine. Siguazodan was 100 fold more active than rolipram in pig tissues indicating the type III isoenzyme may be of greater functional significance in this tissue. In contrast, siguazodan was 15 times less potent that rolipram in guinea-pig airways suggesting a greater role for the type IV PDE. 6. These findings may reflect a possible relationship between the beta 2-adrenoceptor subtype and the functional importance of the type IV PDE isoenzyme. A similar relationship may exist between beta 1-adrenoceptors and the PDE type III isoenzyme.

Beta-adrenoceptors on smooth muscle, nerves and inflammatory cells

Although the bronchodilator action of beta 2-adrenoceptor agonists in asthma is largely due to relaxation of airway smooth muscle, these agents have other effects which may contribute to their anti-asthma action. Human airway smooth muscle contains only beta 2-receptors which, when stimulated, stimulate a rise in intracellular cAMP and activation of PKA (protein kinase A), which in turn phosphorylates several cellular proteins, resulting in relaxation. However, beta-agonists also influence membrane K+ channels and induce smooth muscle relaxation without a rise in cAMP, and this mechanism appears to be the major feature of bronchodilatation in asthma. There is also evidence that beta-agonists may modulate neurotransmission in airways via prejunctional receptors on airway nerves, both sensory and motor. Blockade of prejunctional beta 2-receptors in asthma patients may lead to marked rise in acetylcholine release, with severe bronchoconstriction. Although beta-agonists have little or no effect on the chronic inflammatory response which underlies chronic airway hyper-responsiveness, they do inhibit the release of histamine from mast cells in vitro. The presence of beta-receptors has also been detected not only on mast cells but also on eosinophils, macrophages, lymphocytes and neutrophils, but beta-agonists have little or no inhibitory action on the activities of all these cells due to rapid tachyphylaxis.

Asthma pathogenesis and the implications for therapy in children

Gaining greater insight into the pathogenesis of asthma has redefined the approach to treatment of children with asthma. Clearly, the Expert Panel of the National Heart, Lung, and Blood Institute National Education Program has played a major role in taking the message to a wide audience of health care providers. Although only early trends are evident at this point in time, within several years therapeutic trends underway currently will be more commonplace, and we may observe how asthma continues to impact society and our health care system. The approach to therapy will continue to evolve and most likely be controversial for years to come.

Selective and full beta 1-adrenoceptor agonist action of a catechol derivative of denopamine (T-0509) in the guinea-pig cardiac muscle and trachea: comparison with denopamine, xamoterol and isoprenaline

1. The pharmacological actions of T-0509, a 3-hydroxy derivative of denopamine, were studied in various guinea-pig tissues; these effects were compared with those of isoprenaline, denopamine and xamoterol. 2. The intrinsic activities of the positive inotropic actions of T-0509, denopamine and xamoterol compared with isoprenaline (= 100%) in the papillary muscle were 99%, 83% and 28%, respectively, while their relative potencies (EC50 agonist EC50 isoprenaline) were 0.23, 33 and 1.4, respectively. The intrinsic activities of T-0509, denopamine and xamoterol as positive chronotropic agents in the right atria were 98%, 69% and 48%, respectively, and their equipotent concentrations (isoprenaline = 1) were 0.24, 50 and 4, respectively. 3. The positive chronotropic actions of T-0509 and denopamine were antagonized by bisoprolol (3 x 10(-8) M), but not by ICI 118,551 (3 x 10(-8) M). 4. The intrinsic activity of T-0509 in histamine-contracted tracheae was similar to that of isoprenaline, but its equipotent concentration was 38; the effects of both agents were antagonized by ICI 118,551 (3 x 10(-8) M), but not by bisoprolol (3 x 10(-8) M). Denopamine and xamoterol did not show any agonist activity on guinea-pig trachea. 5. Denopamine and xamoterol antagonized the positive chronotropic (pA2, denopamine: 6.98, xamoterol: 7.75) and tracheal relaxant (pA2, denopamine: 5.39, xamoterol: 6.25) effects of isoprenaline. 6. Isoprenaline, T-0509 and denopamine, but not xamoterol, contracted the guinea-pig aorta in a decreasing order in the presence of propranolol (10(-6) M).7. Based on the above studies, T-0509 appears to be a highly selective betaI-adrenoceptor agonist with full agonist properties, while denopamine and xamoterol appear to be selective, but partial betaI-adrenoceptor agonists.

Resistance of beta 2-adrenoceptor-mediated responses of lung strips to desensitization by long-term agonist exposure--comparison with atrial beta 1-adrenoceptor-mediated responses

In vitro desensitization of beta 2-adrenoceptor-mediated relaxation of guinea-pig isolated parenchymal strips was examined. Concentration-response curves for isoprenaline were obtained and after long-term incubation with isoprenaline, followed by washout, a second curve was obtained. Correction for time-dependent loss of sensitivity was made from time-matched controls. After incubation with 10(-5) M isoprenaline for 0.5, 1, 2, 4 and 8 h, loss of responsiveness of carbachol-contracted lung strips was observed after 4h as a reduced post-incubation maximum response. When the concentration was reduced to 10(-6) M, a 4 h incubation with 1 h washout no longer induced a shift of the post-incubation curve in carbachol-contracted lung strips. In contrast, lung strips with intrinsic tone displayed reduced responsiveness to isoprenaline after 4 h incubation with 10(-6) M isoprenaline. Incubation of the tissue for 4 h with lanthanum (1.4 x 10(-6) M), a relaxant not operating through beta 2-adrenoceptors or their effector coupling, had the same effect upon isoprenaline concentration-response curves as incubation with isoprenaline. This was irrespective of whether intrinsic tone (10(-6) M isoprenaline) or carbachol-contracted (10(-5) M isoprenaline) lung strips were used. It was concluded that the loss of beta 2-adrenoceptor responsiveness after incubation with 10(-6) M isoprenaline was due to the prolonged maximal relaxation of the tissue for 4 h rather than desensitization of the beta 2-adrenoceptor. Indeed, after correction for maximal relaxation and for time, no significant change in beta 2-adrenoceptor sensitivity of the lung occurred after incubation with 10(-6) M isoprenaline for 4 h. This contrasts with significant rightwards shifts of the concentration-response curves for the beta 1-adrenoceptor-mediated increases in rate and tension of guinea-pig right and left atria after identical incubation conditions. Thus whereas beta 1-adrenoceptor-mediated responses displayed desensitization after long-term in vitro agonist exposure, the beta 2-adrenoceptor-mediated responses were resistant.

Prostaglandin E2 synthesis elicited by adrenergic stimuli in guinea pig trachea is mediated primarily via activation of beta 2 adrenergic receptors

Prostaglandin (PG) E2 synthesis elicited by adrenergic agonists in the guinea pig trachea has been shown to be mediated via activation of beta-adrenergic receptors. The purpose of this study was to examine arachidonic acid (AA) metabolism and to characterize the subtype of beta receptor involved in PG synthesis. [14C]AA was incubated with guinea pig tracheal rings, and the radiolabelled products were extracted from the medium. Thin layer chromatographic analysis and radioimmunoassay of the extract showed that [14C]AA was incorporated into guinea pig tracheal rings and metabolized mainly into radiolabeled and immunoreactive PGE2 (iPGE2) and smaller amounts into PGF2 alpha. Trace amounts of PGD2, TxB2 and 6-keto-PGF1 alpha but not LTB4 or LTC4 were detected by enzyme immunoassay. Incubation of guinea pig tracheal rings for 10 min with isoproterenol or salbutamol resulted in a significant increase in PGE2 synthesis (optimum concentration 0.1 microM for both compounds). In contrast, dobutamine, BRL 37344, BRL 28410, norepinephrine, phenylephrine, and xylazine (up to 1 microM) did not significantly increase PGE2 production. Isoproterenol-induced iPGE2 production was inhibited by the selective beta 2 receptor antagonist butoxamine (0.1-1.0 microM) and somewhat reduced by the beta 1 receptor antagonist practolol (1 microM). The increase in PGE2 synthesis was diminished with increasing concentrations of isoproterenol (0.5-5.0 microM) or salbutamol (0.5-1.0 microM); but it was reversed by pretreatment of tracheal rings with the protein synthesis inhibitors cycloheximide (0.9 microM) and actinomycin D (2 microM) but not by phenylisopropyl adenosine (0.1-1.0 microM), an inhibitor of adenylyl cyclase. These data suggest that isoproterenol-induced iPGE2 synthesis is primarily via activation of a beta 2 adrenergic receptor. Failure to enhance iPGE2 synthesis by a high concentration of isoproterenol is likely to be due to an induction of new inhibitory protein synthesis.

Pathogenesis of asthma: therapeutic implications

The current knowledge of asthma, specifically an appreciation of the contributing mechanisms leading to its development as well as its clinical features, has increased vastly in recent years. A better understanding of asthma's inflammatory nature has resulted in wider use of antiinflammatory agents. Specific effects of available antiasthma medications have been better elucidated, thereby helping to focus the development of newer drugs and improve the use of currently available therapeutic agents. The purpose of this article is to further understanding of asthma by providing the pathologic and physiologic basis of this disease. This is vitally important information as it is shaping the directions of the therapeutic approach to asthma care.

Control of airway caliber by autonomic nerves in asthma and in chronic obstructive pulmonary disease

Autonomic nerves can influence airway caliber via their effects on airway smooth muscle, bronchial vessels, and mucous glands and may therefore contribute to airway narrowing in asthma or in chronic obstructive pulmonary disease (COPD). Human lungs receive cholinergic, noradrenergic, and peptidergic efferents and several types of afferents. Cholinergic nerve activity contributes to airway narrowing both in asthma and in COPD. Reflex vagal activity may be enhanced because of epithelial damage and exposition of sensory nerve endings to nonspecific irritants. Other possible mechanisms include defects in prejunctional receptors that inhibit acetylcholine release, several postjunctional factors that nonspecifically enhance the effect of a given degree of cholinergic muscle contraction on airway caliber, and interactions between inflammatory mediators and the cholinergic system. The main direct bronchodilating nerve activity in human lungs is nonadrenergic, and scanty data suggest that nonadrenergic inhibitory nerve activity may be variably reduced in asthmatics. Human airway muscle virtually lacks adrenergic innervation, but adrenergic nerves may influence airway caliber by acting on bronchial vessels, mucous glands, and parasympathetic nerves and ganglia. The response of asthmatic airways to beta-agonists seems intrinsically normal, but it may be reduced during severe asthma attacks. There are no convincing data that abnormal adrenergic control is present in the airways of patients with COPD. The physiologic relevance of excitatory neuropeptides in sensory nerves in human airways is uncertain. Tachykinins have proinflammatory and spasmogenic properties and are therefore of potential interest as a factor in the pathogenesis of obstructive airway disease. In conclusion, the data presently available support an abnormal autonomic control of the airways in asthma but not in COPD.

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 2-adrenoceptors in human lung and peripheral mononuclear leukocytes of untreated and terbutaline-treated patients

Beta 2-adrenoceptor agonists act against bronchoconstriction by stimulating beta 2-adrenoceptors in bronchial smooth muscle. However, tachyphylaxis has been argued to occur because of beta 2-adrenoceptor down-regulation following therapy with beta 2-adrenergic agents. To investigate receptor alterations, human peripheral mononuclear leukocytes are frequently used, since human lung tissue is not easily available. In order to study whether beta 2-adrenoceptors in MNL reliably reflect the conditions in the human lung tissue, we compared MNL and human lung tissue of 18 patients who had to undergo lung resection. Ten patients were untreated, and eight had bronchodilator therapy prior to therapy with terbutaline because of bronchoconstriction. Both in human lung and MNL, the beta 2-adrenoceptor subpopulation was characterized by competition experiments with the beta 1-selective antagonist CGP 207.12 A and the beta 2-selective antagonist ICI 118.551. In MNL, a significant decrease in the density of beta 2-adrenoceptors was found in treated but not in untreated patients, while the antagonist affinity of the beta 2-adrenoceptors remained unchanged. However, in lung parenchyma, which was obtained at the very same time from the same patients, no down-regulation of the total amount of beta 2-adrenoceptors could be measured. It is concluded that MNLs are a reliable model for studying properties of beta 2-adrenoceptor regulation. However, the hereby obtained results show that MNLs do not reflect the conditions of beta 2-adrenoceptors in human lung tissue. Human lung tissue is found to be less susceptible than human MNL for beta 2-adrenoceptor down-regulation by terbutaline treatment at therapeutic doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptors in airway disease. Beta-adrenoceptors in lung inflammation

Beta-adrenoceptor dysfunction and increase in airway reactivity can be induced by administration of gram-negative bacteria, endotoxin, viruses, and allergens in laboratory animals. However, the deterioration of lung beta-adrenoceptor function is not invariably associated with lung inflammation. Severe asthmatics, but not asthmatics per se, show a diminished beta-adrenoceptor function of airway smooth muscle. These changes are probably a consequence of the active disease state rather than an intrinsic component of asthma. Mediators released from inflammatory cells such as reactive oxygen species and fatty acid metabolites may directly or indirectly induce beta-adrenoceptor dysfunction. Beta-adrenoceptor function of leukocytes from asthmatic patients can be decreased as well and it is suggested that lymphokines like interleukin-2 and interferon-gamma may affect beta-adrenoceptor function. A disturbed beta-adrenoceptor function on inflammatory cells themselves may have consequences for their immune function, mediator release, and effect on surrounding tissues.

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.

Distribution of beta 1- and beta 2-adrenoceptors in mouse trachea and lung: a quantitative autoradiographic study

1. Binding and quantitative autoradiography were used to detect [125I]-iodocyanopindolol (I-CYP) associated with beta 1- and beta 2-adrenoceptors in mouse tracheal epithelium and airway smooth muscle as well as in lung parenchymal tissue. 2. Specific I-CYP binding to slide-mounted tissue sections of both trachea and parenchyma was of high affinity (KD = 49.0 pM, n = 3, trachea; KD = 118.9 pM, n = 3, parenchyma) and saturable, involving single populations of non-interacting binding sites (Hill coefficient nH = 1.00 +/- 0.02, trachea; nH = 0.99 +/- 0.03, parenchyma). 3. Direct measurement of tissue radioactivity also showed that specific I-CYP binding was competitively inhibited in the presence of the beta-adrenoceptor antagonists (-)-propranolol (non-selective), CGP 20712A (beta 1-selective) and ICI 118,551 (beta 2-selective). Analysis of the competition binding curves for the two selective antagonists revealed mixed populations of beta 1- and beta 2-adrenoceptors in the approximate proportions 33% and 67% respectively in mouse trachea and 28% and 72% respectively in mouse lung parenchyma. 4. Densities of autoradiographic grains derived from specific I-CYP binding to alveolar wall tissue and to tracheal epithelium and airway smooth muscle were quantified by a computer-assisted image analysis system, which allowed the construction of competition binding curves in the presence of the selective beta-adrenoceptor antagonists CGP 20712A and ICI 118,551. Analysis of these data demonstrated that in alveolar wall, beta 1- and beta 2-adrenoceptors co-existed in the proportions 18% and 82%, respectively. 5. Quantitative autoradiographic analyses also showed that beta 1- and beta 2-adrenoceptors were differentially distributed in tracheal epithelium and airway smooth muscle. The beta 2-adrenoceptor subtype accounted for 71% of all beta-adrenoceptors in epithelium. Conversely, beta l-adrenoceptors which mediate relaxant responses of mouse trachea to beta,-adrenoceptor agonists (Henry & Goldie, 1990), accounted for 69% of all beta-adrenoceptors in the airway smooth muscle.

A new approach to the treatment of asthma

Asthma is a chronic inflammatory condition. The previous emphasis on bronchodilator therapy, which does not treat the underlying inflammation, may be misplaced. Earlier introduction of antiinflammatory agents, such as corticosteroids or cromolyn sodium, is strongly recommended. Effective suppression of airway inflammation reduces the need for bronchodilator therapy and may reduce the morbidity and, perhaps, mortality of asthma.

Autoradiographic localization of changes in pulmonary beta-adrenoceptors in an animal model of atopy

Vaccination of guinea pigs with Haemophilus influenzae leads to an impairment of beta-adrenoceptor function in lung. We have used an autoradiographic technique to study the distribution of changes in lung beta-adrenoceptor density. H. influenzae induced a decrease in beta-adrenoceptors in peripheral lung membranes of 22 +/- 5% (mean +/- S.E.M., n = 7), while the affinity of binding was unaffected. Tracheal beta-adrenoceptor binding was not influenced by H. influenzae. Autoradiography revealed a 27% reduction in beta-adrenergic binding sites on alveolar septa. Bronchial epithelial beta-adrenoceptors were decreased for 36%, and vascular smooth muscle and endothelial beta-adrenoceptors were also reduced. beta-Adrenoceptors on airway smooth muscle were unaffected. H. influenzae affected both the beta 1- and beta 2-subtypes of receptors. It is concluded that in this animal model of atopy beta-adrenoceptors may be decreased on several different cell types within the lungs, which may influence overall airway and vascular reactivity.

Neuronally released (-)-noradrenaline relaxes smooth muscle of calf trachea mainly through beta 1-adrenoceptors: comparison with (-)-adrenaline and relation to adenylate cyclase stimulation

The nature of the receptors that mediate the relaxation of smooth muscle by field stimulation, (-)-noradrenaline and (-)-adrenaline was investigated in calf tracheal smooth muscle. The relation between relaxation, stimulation of the adenylate cyclase and density of beta-adrenoceptor subtypes was studied with the help of antagonists of beta 1- and beta 2-adrenoceptors. The question of the existence of catecholamine-containing nerves was also investigated. (1) Nerves with varicosities exhibiting catecholaminergic fluorescence were observed between bundles of smooth muscle cells. (2) Consistent with the existence of adrenergic nerves (-)-noradrenaline was also found. The content of (-)-noradrenaline (1 microgram.g-1 w.w.) was the same in smooth muscle strips from the sublaryngeal region and from the region close to the bifurcation of the calf trachea. (-)-Adrenaline was not detected. (3) Smooth muscle relaxation by low (-)-noradrenaline concentration (0.6-2 nmol/l) was mediated through beta 1-adrenoceptors. Low concentrations of (-)-adrenaline (0.06-1 nmol/l) relaxed through beta 2-adrenoceptors. High concentrations of (-)-noradrenaline and (-)-adrenaline also caused relaxation through beta 2- and beta 1-adrenoceptors respectively. (4) Field stimulation caused relaxation which was half maximal at 0.2-0.8 Hz. Blockade of beta 1-adrenoceptors strongly attenuated the relaxant response to field stimulation and shifted the frequency-relaxation curves to 4 times higher frequencies. These results are consistent with a beta 1-adrenoceptor-mediated relaxation caused by (-)-noradrenaline released from sympathetic nerve endings at low stimulation frequencies. (5) Blockade of beta 2-adrenoceptors failed to reduce smooth muscle relaxation caused by field stimulation at low stimulation frequencies (0.1-1 Hz). However, after beta 1-adrenoceptor blockade, additional blockade of beta 2-adrenoceptors reduced the relaxant effects observed at high frequencies (2-400 Hz). The results suggest that high concentrations of endogenous (-)-noradrenaline cause relaxation through beta 2-adrenoceptors. (6) Binding experiments with 3H-(-)-bupranolol and 3H-ICI 118,551 revealed between 10,000 and 20,000 beta-adrenoceptors per smooth muscle cell of which 3/4 were beta 2 and 1/4 beta 1. The equilibrium dissociation constant of (-)-adrenaline for both beta 1- and beta 2-adrenoceptors and of (-)-noradrenaline for beta 1-adrenoceptors was 1 mumol/l. The affinity of (-)-noradrenaline for beta 2-adrenoceptors was 10 to 20 times lower than for beta 1-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Relaxation of human peripheral airway smooth muscle in vitro does not correlate with severity of chronic airflow limitation in vivo

We tested the hypothesis that a defect in relaxation of peripheral airway smooth muscle contributes to chronic airflow limitation in chronic obstructive pulmonary disease (COPD). Twenty subjects underwent lung function measurements prior to thoracotomy. Lung tissue was obtained during surgery and bronchiolar segments were dissected. Smooth muscle function was measured isotonically in organ baths, using L-isoprenaline and the adenylate cyclase activator forskolin. Segments were precontracted with methacholine. Of the 20 subjects, 10 fulfilled the ATS criteria for COPD and had airflow limitation. There was no significant relationship between the degree of airflow limitation in vivo and the sensitivity or maximal response of peripheral airway muscle to methacholine, L-isoprenaline or forskolin in vitro. Furthermore, we found no differences between the mean contractile- and relaxation responses of airways from subjects with versus those without COPD and airflow limitation. Lung tissue from patients who regularly used beta-adrenergic drugs (n = 3) and/or steroids (n = 3) exhibited responses in vitro similar to those from subjects without medication. These results suggest that airflow limitation in COPD is not associated with an impaired relaxability of peripheral airway smooth muscle.

Classification of beta-adrenoceptors in ferret tracheal smooth muscle by pharmacological responses

Beta-adrenoceptors in ferret tracheal smooth muscle were classified into beta 1 or beta 2 by determination of (i) the potency rank order for isoprenaline, noradrenaline and adrenaline, and (ii) apparent pA2-values for a specific beta 1-antagonist (practolol) and a specific beta 2-antagonist (ICI 118.551) and (iii) concentration-inhibition curves for procaterol, a beta-agonist showing a biphasic concentration-response curve in organs with a mixed beta 1 and beta 2 adrenoceptor population. We used in vitro tracheal rings and assessed the responses to beta-adrenoceptor agonists as inhibition of phasic contractions elicited by electrical field stimulation (2 Hz for 20 s) or relaxation of tonic contractions elicited by acetylcholine (0.5 microM). The potency rank order for the agonists was isoprenaline greater than noradrenaline approximately adrenaline indicating action through beta 1-receptors. Apparent pA2-values for the antagonists were for 1, 3 and 10 microM practolol 6.0 (SE 0.27), 6.1 (SE 0.21) and 6.3 (SE 0.03), respectively. Apparent pA2 for 0.1, 1 and 10 microM ICI 118.551 were 6.8 (SE 0.25), 6.7 (SE 0.12) and 6.1 (SE 0.14), respectively. These values agree well with published pA2-values for the action of these drugs on beta 1-adrenoceptors. However, the Schild plot for ICI 118.551 was alinear indicating a possible heterogeneity of the beta-adrenoceptors in ferret trachea. The concentration-response curve for procaterol showed the biphasic form typical for organs with a mixed beta 1 and beta 2 population. However, the lower part of the curve, reflecting stimulation of beta 2-adrenoceptors reached only 17.5% (SE 1.4) of the maximally achieved inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Reflex decrease of histamine-induced bronchoconstriction after laryngeal stimulation in asthmatic patients

The aim of this work was to determine if the nonadrenergic noncholinergic nervous system can be reflexly activated in asthmatic patients by stimulating the vocal cords. The stimulation was produced by a cytology brush passed through a bronchoscope previously introduced transnasally and positioned just above the epiglottis. The subjects were premedicated with cholinergic blockers, and bronchoconstriction was induced by inhalation of histamine. In 11 experiments performed on six patients, vocal cords stimulation resulted in a decreased RL from 8.4 +/- 1.0 to 6.3 +/- 0.8 cm H2O.L-1.s (mean +/- SE) (p less than 0.01). To assess the possible contribution of circulating catecholamines to this decrease, plasma epinephrine and norepinephrine levels were measured in six experiments, before and 30 s, 1, 3, and 5 min after the stimulation. Pulmonary resistance fell from 10.0 +/- 1.3 to 7.6 +/- 0.9 cm H2O.L-1.s (mean +/- SE) (p less than 0.05) 30 s and to 7.9 +/- 0.9 cm H2O.L-1.s (p less than 0.05) 60 s after stimulation. Epinephrine and norepinephrine levels increased slightly but not significantly throughout the experiment. We conclude that in asthmatic patients, as in normal subjects, stimulation of the vocal cords produces a reflex decrease in histamine-induced bronchoconstriction which is modulated by the nonadrenergic noncholinergic nervous system.

Beta-adrenoceptor desensitization in guinea-pig isolated trachea

Exposure to (-)-isoprenaline (25 microM, 1 h) caused a stereoselective, time and concentration-related decrease in smooth muscle beta 2-adrenoceptor function in guinea-pig trachea. Furthermore, tracheal relaxant responsiveness to the beta-adrenoceptor agonists (+/-)-fenoterol and (-)-noradrenaline was reduced, while that to theophylline and nitroprusside was unaffected. Responsiveness to forskolin was marginally but significantly reduced. Indomethacin, a cyclooxygenase inhibitor and mepacrine, an inhibitor of phospholipid turnover, had no significant effect on the extent of isoprenaline-induced desensitization. Conversely, cortisol (25 microM) significantly reduced desensitization and enhanced the rate of spontaneous recovery of responsiveness to isoprenaline. Desensitization was not accompanied by a reduction in the density of beta-adrenoceptors in the trachea, as assessed by binding and light microscopic autoradiography using [125I]iodocyanopindolol [( 125I]CYP). Thus, desensitization was probably caused primarily by beta-adrenoceptor/adenyl cyclase uncoupling. This model may be useful in investigations of the effect of glucocorticoids on the beta-adrenoceptor dysfunction recognized in severe asthma.

Nonadrenergic bronchodilation in normal subjects

To investigate whether bronchial C-fiber stimulation induced by capsaicin inhalation evokes nonadrenergic inhibitory (NAI) system bronchodilation, we studied partial and maximal expiratory flow-volume (PEFV and MEFV) curves in 5 normal subjects after inhalation of oxitropium bromide and propranolol. PGF2 alpha (1 mg/ml inhaled for 5 min) was administered to induce bronchoconstriction. Then aerosolized capsaicin was inhaled (2.4 x 10(-9) mol) to stimulate bronchial C-fibers. PGF2 alpha produced significant bronchoconstriction; FEV1 and flow during a PEFV curve at 30% forced vital capacity (V30p) decreased over a 15-min period. Capsaicin induced significant bronchodilation; V30p increased for 2 to 6 min (0.001 less than p less than 0.02), and FEV1 increased for 2 to 4 min (p less than 0.05) when compared with saline-ethanol (vehicle of capsaicin) inhalation. After treatment with the ganglionic blocking agent hexamethonium, the significant bronchodilator response disappeared. These results suggest that the NAI system has a distinct bronchodilator action in human subjects in vivo, and that the bronchial C-fiber receptors may be involved in the reflex pathway for NAI system bronchodilation in humans.

Effects of noradrenaline on the isolated human bronchus. Comparison with the isolated guinea pig trachea

The pharmacodynamic activity of noradrenaline was evaluated comparatively in vitro on isolated human bronchi and on guinea pig tracheal spirals. Noradrenaline exerted a contractile effect on both preparations under resting tone and in the presence of propranolol 10(-6) M; maximal noradrenaline-induced contraction was 15-20% of maximal acetylcholine (ACh)-induced contraction. Without propranolol, the contractile effect of noradrenaline was negligible when the preparations were under resting tone and absent when they were precontracted with ACh. In contrast, noradrenaline exerted a strongly relaxant effect on both human bronchi (-log ED50 5.24 +/- 0.17; N = 5) and guinea pig tracheae (-log ED50 6.15 +/- 0.29; N = 8). With maximal contraction induced by ACh 3.10(-3) M the -log ED50 of both preparations were shifted to the right by functional antagonism and became 4.72 +/- 0.17 and 5.31 +/- 0.11, respectively. The pKD values of noradrenaline, calculated according to Furchgott and Bursztyn (1967), were 4.79 +/- 0.04 in human bronchi (N = 5) and 4.77 +/- 0.16 in guinea-pig tracheae (N = 8). In the presence of cocaine plus phenoxybenzamine these values were not significantly modified in human bronchi and only slightly modified in guinea pig tracheae. It is concluded that noradrenaline induces a strong beta-adrenergic response and a negligible alpha-adrenergic response from both human bronchi and guinea pig tracheae in vitro.

The relationship between exercise-induced asthma and plasma catecholamines

In asthmatics, exercise (E1) is known to induce bronchoconstriction; a second period of exercise (E2) within 30 to 90 min induces a lesser degree of bronchoconstriction. The reason for the "refractory" bronchoconstrictor response to E2 is unclear. We studied 6 normal subjects (Group 1) and 12 stable asthmatics to examine the possible relationship between the refractory period and sympathoadrenal function. The asthmatics were further divided into 2 groups, based on the absence (Group 2, n = 5) or presence (Group 3) of an exercise-induced bronchoconstrictor response. In each subject/patient, after control measurements of spirometry and venous blood sampling, a standard level of treadmill exercise was performed, and blood and spirometry were obtained at 1, 5, 15, and 25 min after the end of exercise. A second period of treadmill exercise, of the same level and duration, was then performed, and blood sampling and spirometry were repeated at the same time intervals after the end of exercise. There was no significant (p less than 0.1) difference in baseline plasma epinephrine (Ep), or norepinephrine (Np) levels; however, plasma dopamine (Dp) levels were significantly (p less than 0.05) higher in Group 3. In Groups 1 and 2, FEV1 did not change significantly after the first (E1) or second (E2) exercise periods, but there were significant (p less than 0.01) changes in Group 3 (maximal percent changes in FEV1, delta FEV1%, E1 = -14.4%, E2 = -8.8%), and the delta FEV1% after E2 was significantly (p less than 0.01) less than after E1.(ABSTRACT TRUNCATED AT 250 WORDS)

Reflex decrease of histamine-induced bronchoconstriction after laryngeal stimulation in humans

The aim of this work was to determine whether the nonadrenergic, noncholinergic, inhibitory nervous system can be reflexly activated in humans by laryngeal stimulation. The stimulation was achieved with a cytology brush passed through a bronchoscope previously introduced transnasally and positioned just above the epiglottis. In one series of experiments, subjects were premedicated with beta-adrenergic and cholinergic blockers, and bronchoconstriction was induced by histamine inhalation. The results showed that mechanical irritation of the vocal cords with the cytology brush produced a sharp, short-lasting (less than 1 min) decrease in RL from (mean +/- SE) 6.8 +/- 2.1 to 4.8 +/- 1.5 cm H2O.L-1.s, and in the absence of parasympathetic blockade, laryngeal irritation produced a fall in RL from (mean +/- SE) 9.0 +/- 3.7 to 5.4 +/- 2.0 cm H2O.L-1.s (p less than 0.0001) (ANOVA). This decrease in RL was independent of the slight cough produced by laryngeal stimulation and reflects a change in lower and not upper airway resistance. Adequacy of the beta-adrenergic and cholinergic blockade was checked with an intravenous infusion of isoproterenol and inhaled methacholine, respectively. In 2 subjects, the fall in RL was abolished by a block of the superior laryngeal nerves and direct local anesthesia of the vocal cords. We conclude that mechanical irritation of the larynx produces a partial reversal of histamine-induced bronchoconstriction that is mediated through nervous pathways that are neither beta-adrenergic nor cholinergic in origin. We suggest that this decrease in bronchoconstriction is modulated by the nonadrenergic, noncholinergic, inhibitory nervous system.

Electrophysiological and other aspects of excitation-contraction coupling and uncoupling in mammalian airway smooth muscle

In this article the electrophysiological events which are believed to underly agonist-induced contraction and relaxation of airway smooth muscle are reviewed, with special emphasis on the indispensable role of the Ca ion. The contribution made by Na, K, Ca and Cl to, and the role that the electrogenic Na:K-dependent ATPase plays in, the maintenance of the resting membrane potential in both normal and sensitised airway smooth muscle cells is described together with the permeability changes that occur in the plasmalemma in response to excitatory and inhibitory agonists. In addition, the currently available evidence for the existence of potential-sensitive and receptor-operated Ca channels in respiratory smooth muscle, and how such channels may be involved in the regulation of airway calibre, is critically assessed.

Beta-adrenoceptors in human tracheal smooth muscle: characteristics of binding and relaxation

Specific binding of [125I]-(-)-cyanopindolol to human tracheal smooth muscle membranes was saturable, stereo-selective and of high affinity (Kd = 5.3 +/- 0.9 pmol/l and RT = 78 +/- 7 fmol/g tissue). The beta 1-selective antagonists atenolol and LK 203-030 inhibited specific [125I]-(-)-cyanopindolol binding according to a one binding site model with low affinity in nearly all subjects, pointing to a homogeneous beta 2-adrenoceptor population. In one subject using LK 203-030 a small beta 1-adrenoceptor subpopulation could be demonstrated. The beta-mimetics isoprenaline, fenoterol, salbutamol and terbutaline recognized high and low affinity agonist binding sites. Isoprenaline's pKH- and pKL-values for the high and low affinity sites were 8.0 +/- 0.2 and 5.9 +/- 0.3 respectively. In functional experiments isoprenaline relaxed tracheal smooth muscle strips having intrinsic tone with a pD2-value of 6.63 +/- 0.19.

Innervation of airway smooth muscle. Efferent mechanisms

The classical view, with one excitatory (cholinergic) and one inhibitory (noradrenergic) component, of the innervation of airway smooth muscle is incomplete and at least two other, possibly peptidergic, types of innervation must be included when the innervation of airways is considered. A summary of these neuronal components is given in Fig. 1 and their possible origin is outlined. Besides the inhibitory noradrenergic innervation of the airways observed in some species, an inhibitory NANC (i-NANC) innervation has been demonstrated. The polypeptide, VIP, seems to be the most likely candidate for the neurotransmitter in the i-NANC innervation of the airways. The excitatory cholinergic innervation is present in the airways from the trachea down to the peripheral bronchi. In the guinea-pig bronchi an excitatory NANC (e-NANC) innervation has been demonstrated as well. The e-NANC nerves may correspond to chemosensitive primary afferent nerves with substance P or a related tachykinin as transmitter. When the innervation of airway smooth muscle of different mammalian species is compared it is evident that all nerve components except the cholinergic, show a considerable variability among species. The cholinergic innervation seems to be present in all mammalian species whereas the other components may be completely absent from some species. Distinct regional variations in the innervation of the airways may occur, which is exemplified by the distribution of the autonomic innervation in the guinea-pig tracheo-bronchial tree. Cholinergic neurotransmission in for example the guinea-pig and human airways can be modulated by NA via prejunctional inhibitory alpha 2-adrenoceptors. Furthermore, the e-NANC neurotransmission in the guinea-pig airways may be modulated by NA or by selective alpha 2-adrenoceptor agonists, acting via prejunctional inhibitory alpha 2-adrenoceptors. The clinical importance of the NANC innervation in relation to asthma is discussed. The i-NANC nerves may exert a modulating effect on bronchoconstriction, and a functional defect would presumably lead to an exaggerated response to constrictor stimuli. The e-NANC nerves in the airways may also be clinically relevant since the transmitter (tachykinins) from these nerves can produce bronchoconstriction and promote inflammation of the airway epithelium, either by direct mechanisms or indirectly by activation of mast cells, and thus contribute to the features of asthma.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparative study on the ventilatory and haemodynamic effects of xamoterol and atenolol in asthmatic patients

The effects of single oral doses of atenolol 50 mg and xamoterol 200 mg (a recently developed partial beta 1-adrenoceptor agonist) on lung function, heart rate and blood pressure were investigated in 11 patients with asthma. Xamoterol caused a significant increase in heart rate and systolic blood pressure, which changes are consistent with the partial beta 1-adrenoceptor agonist activity of this drug. Atenolol induced a significant decrease in FEV1 and the forced vital capacity (FVC); there was a non-significant change in FEV1 and FVC after xamoterol. There was no significant difference between the effects of atenolol and xamoterol of FEV1 and FVC. Bronchospasm induced by atenolol 50 mg and xamoterol 200 mg was completely reversed by inhalation of the beta 2-adrenoceptor agonist terbutaline to a cumulative dose of 4.0 mg.

Human small airway smooth muscle responses in vitro; actions and interactions of methacholine, histamine and leukotriene C4

The in vitro contractile responses to methacholine, histamine and leukotriene C4 (LTC4) were measured in human bronchiolar strips obtained after surgery. LTC4 was approximately 100 times more potent than both methacholine and histamine (mean pD2 values were 8.01, 6.18 and 5.87 respectively). All three agonists produced the same maximum contractile response (Tmax) and no difference was found in the time course of methacholine-, histamine- and LTC4-induced responses. When methacholine, histamine and LTC4 were applied in succession on one airway preparation, no interactions between these agonists were demonstrated for pD2. However, interactions were found concerning Tmax. The sensitivity (pD2) could be measured accurately and reproducibly and showed a relatively small within-patients variation (coefficients of variation 4-5%). In contrast, Tmax showed a considerable within-patients variation (coefficients of variation 47-91%), which limits its usefulness when small numbers of airway preparations are studied.

Effects of relaxants on electrical and mechanical activities in the guinea-pig tracheal muscle

In isolated tracheal muscles of the guinea-pig, effects of several relaxants were studied by simultaneously recording the membrane potential and mechanical response. Intracellular recordings showed regular slow waves in most preparations. There was a close correlation between membrane potential and slow wave amplitude. The linear regression line of the slow wave amplitude (Y mV) on the membrane potential (X mV) could be expressed by Y = -0.35X-5.9. The mean values of resting potential and slow wave amplitude were -50.6 +/- 0.6 mV and 11.9 +/- 0.5 mV, respectively. Relaxant drugs used (isoprenaline, terbutaline, adrenaline, noradrenaline, theophylline, forskolin and dibutyryl cyclic AMP) all produced hyperpolarization of the membrane and abolished the slow wave. The degree of relaxation was closely related to these electrical responses, although the recovery of electrical responses was faster than the mechanical response. It was concluded that the relaxation caused by the agents, which are known to increase the intracellular cyclic AMP level, was accompanied by a clear hyperpolarization and suppression of slow waves.

A physiological basis for subclassifying beta-adrenoceptors examined by chemical sympathectomy of guinea-pigs

Chemical sympathectomy of guinea-pigs was induced by chronic pretreatment with 6-hydroxydopamine over a 20 day period. Control animals were sham injected with vehicle at the same times. Isolated tissues were removed from the animals and beta-adrenoceptor sensitivity assessed from cumulative concentration-response curves for isoprenaline, followed after wash-out by a partial agonist (salbutamol, ritodrine or prenalterol). The following responses were measured: increases in force and rate of contraction of left and right atria respectively, inhibition of carbachol-induced ileal contractions, relaxation of intrinsic tone of lung strips and tracheal spirals, inhibition of contractions of vas deferens and soleus muscle induced by field stimulation. Left and right atria and ileum from 6-hydroxydopamine-pretreated guinea-pigs exhibited supersensitivity to beta-adrenoceptor stimulation. This was measured as a leftwards shift of the concentration-response curve for isoprenaline and as an elevation of the partial agonist maximum response (relative to isoprenaline), when compared with tissues from sham-injected controls. The supersensitivity was assumed to be due to the loss of endogenous neurotransmitter release by chemical sympathectomy and specific for the beta-adrenoceptor. In contrast, lung strips, vas deferens and soleus muscle were not supersensitive. The responses of these tissues are thought to be mediated via beta 2-adrenoceptors whereas cardiac and ileal responses are beta 1-adrenoceptor mediated. The latter receptor subtype would therefore appear to be under the influence of sympathetic innervation, but since no supersensitivity occurred at beta 2-adrenoceptors these were presumed to be non-innervated but stimulated by circulating adrenaline. These results obtained by use of chemical sympathectomy with 6-hydroxydopamine support the contention that the physiological basis of beta-adrenoceptor subclassification is that the beta 1-subtype are innervated whereas the beta 2-subtype are non-innervated.

Measurement of human small airway smooth muscle function in vitro with the bronchiolar strip preparation

The technique by which human bronchiolar strips are prepared is described in detail. The biological viability of the preparations after storage at 4 degrees C overnight and the reproducibility of contractile responses to KCl and methacholine were examined in lung tissue from six patients. Measurements were performed on the first and second day after surgical resection. On both days, most bronchioles showed an increase in contractility. The responses on the first day were not different from those on the second day. No significant changes in time were found for pD2 and slope of the methacholine dose-response curves. The variability of responses between patients was significantly larger than between strips within patients. The pD2 was the best reproducible parameter.

Selectivity of bevantolol hydrochloride, a beta 1-adrenoceptor antagonist, in asthmatic patients

Bevantolol hydrochloride, a new beta-adrenoceptor antagonist, has been shown to be cardioselective in animals. To evaluate its selectivity in humans, a double-blind, crossover study was conducted in 8 asthmatics. Following a single oral dose of placebo, bevantolol 75 or 150 mg or propranolol hydrochloride 40 mg, forced expiratory volume in 1 second (FEV1), heart rate, blood pressure and skeletal muscle tremor were measured before and after 4 increasing intravenous doses of terbutaline sulfate to establish terbutaline dose-response curves. The FEV1 decreased after all active treatments. During terbutaline infusions there was an increase in FEV1 after both bevantolol doses and placebo. The terbutaline dose-response curve after bevantolol shifted to the right, however. After propranolol, there was no increase in FEV1 during terbutaline stimulation. Heart rate and skeletal muscle tremor showed a similar pattern during the experiment. In dosages that have previously been shown to produce at least the same degree of blockade of exercise-induced tachycardia, bevantolol has less influence on terbutaline-induced bronchodilation, heart rate increase and skeletal muscle tremor than did propranolol. Thus bevantolol has relative beta 1-adrenoceptor antagonist selectivity. Drawing upon the results of a previous study in the same patients, we believe bevantolol, atenolol and metoprolol have similar beta 1-selectivity.

Is there any evidence of beta 1-adrenoceptors mediating relaxation of guinea-pig lung parenchyma?

We tried to find functional evidence for the existence of beta 1- and beta 2-adrenoceptors in the isolated guinea-pig lung parenchymal strip preparation, using potent and selective beta 1- and beta 2-adrenoceptor stimulation. To obtain potent beta 1-adrenoceptor stimulation the nonselective beta-adrenoceptor agonist isoprenaline was combined with a highly selective beta 2-adrenoceptor antagonist--ICI 118,551. Potent beta 2-adrenoceptor stimulation was obtained by procaterol. Practolol (beta 1-adrenoceptor antagonist) and ICI 118,551 were used as antagonists. ICI 118,551, 10(-7) mol/l, shifted the concentration response (C/R) curve of isoprenaline to a higher concentration range. The C/R curve of procaterol was shifted in the same way and to the same degree by this concentration of ICI 118,551. The C/R curve of isoprenaline was not further shifted after blockade with a combination of ICI 118,551, 10(-7) mol/l, and practolol, 10(-6). However, in the trachea preparation, a tissue containing both beta 1- and beta 2-adrenoceptors, there was a further shift of the C/R curve of isoprenaline to a higher concentration range after blockade with a combination of ICI 118,551 and practolol in the concentrations given above. In this preparation the shift of the C/R curve of procaterol was ten times greater than that of isoprenaline after blockade with ICI 118,551, 10(-7) mol/l. We conclude that it is possible to characterize small fractions of beta 1-adrenoceptors coexisting with beta 2-adrenoceptors with the technique used. Furthermore there is still no functional evidence of the existence of beta 1-adrenoceptors in the lung parenchyma.

Beta-adrenoceptor heterogeneity in guinea-pig airways: comparison of functional and receptor labelling studies

The distribution of beta-adrenoceptor subtypes in guinea-pig airways has been studied by radioligand binding assays and analysis of mechanical responses. Binding studies with the ligands [3H]-dihydroalprenolol and [125I]-cyanopindolol, revealed that beta-adrenoceptors were unevenly distributed throughout the airways with the highest density located in the parenchyma and the lowest density in the trachea. The relative proportion of beta 1:beta 2-adrenoceptor binding sites was assessed by computer-assisted analysis of the inhibition curves generated by selective agents. It was virtually identical in each region and in the order of 15:85%. beta-Adrenoceptor agonists caused concentration-dependent relaxations of both tracheal spirals and parenchymal lung strips. This response appeared to be mediated by both beta 1- and beta 2-adrenoceptors in tracheal spirals as the pA2 value for the beta 1-selective antagonist, atenolol, varied depending upon which agonist was used, and, in the presence of the beta 2-adrenoceptor antagonist ICI 118,551, noradrenaline and isoprenaline produced biphasic concentration-effect curves. In parenchymal lung strips only the one subtype was involved as antagonist pA2 values were not dependent on the agonist used and the properties were consistent with those expected for a beta 2-adrenoceptor.