Increased pulmonary alpha-adrenergic and reduced beta-adrenergic receptors in experimental asthma

Effect of Inhaled Alpha-Blocker on Airflow Obstruction in Asthma1

A controlled study of the effect on airflow obstruction of 30 mg of the alpha-blocker thymoxamine given by inhalation is reported in 10 patients with chronic stable asthma. No significant change in peak expiratory flow rate was seen with either thymoxamine or placebo in any patient. Alpha-adrenergic receptors are therefore unlikely to contribute significantly to resting bronchomotor tone in chronic stable asthma.

β2-Adrenoceptor Function in Asthma

β2-adrenoceptor agonists, often used in combination with corticosteroids, have been extensively used for the treatment of asthma. However, concerns have been raised regarding their adverse effects and safety including poor asthma control, life-threatening exacerbations, exacerbations that often require hospitalization, and asthma-related deaths. The question as to whether these adverse effects relate to the loss of their bronchoprotective action remains an interesting possibility. In the chapter, we will review the experimental evidence that describes the different potential factors and associated mechanisms that can blunt the therapeutic action of β2-adrenoceptor agonists in asthma. We show here evidence that various key inflammatory cytokines, growth factors, some respiratory viruses, certain allergens, unknown factors present in serum from atopic asthmatics have the capacity to impair β2-adrenoceptor function in airway smooth muscle, the main target of these drugs. More importantly, we present our latest research describing the role played by mast cells in impairing β2-adrenoceptor function. Although no definitive conclusion could be made regarding the implication of one single mechanism, receptor uncoupling, or receptor desensitization due to phosphorylation represents the main inhibitory pathways associated with a loss of β2-adrenoceptor function in airway smooth muscle. Targeting the pathways leading to β2-adrenoceptor dysfunction will likely provide novel therapies to improve the efficacy of β2-agonists in asthma.

Alteration of airway responsiveness mediated by receptors in ovalbumin-induced asthmatic E3 rats

AIM

Airway hyperresponsiveness is a constant feature of asthma. The aim of the present study was to investigate airway hyperreactivity mediated by contractile and dilative receptors in an ovalbumin (OVA)-induced model of rat asthma.

METHODS

Asthmatic E3 rats were prepared by intraperitoneal injection with OVA/aluminum hydroxide and then challenged with intranasal instillation of OVA-PBS two weeks later. The myograph method was used to measure the responses of constriction and dilatation in the trachea, main bronchi and lobar bronchi.

RESULTS

In asthmatic E3 rats, beta(2) adrenoceptor-mediated relaxation of airway smooth muscle pre-contracted with 5-HT was inhibited, and there were no obvious difference in relaxation compared with normal E3 rats. Contraction of lobar bronchi mediated by 5-HT and sarafotoxin 6c was more potent than in the trachea or main bronchi. Airway contractions mediated by the endothelin (ET)(A) receptor, ET(B) receptor and M(3) muscarinic receptor were augmented, and the augmented contraction was most obvious in lobar bronchi. The order of efficacy of contraction for lobar bronchi induced by agonists was ET-1, sarafotoxin 6c>ACh>5-HT. OX8 (an antibody against CD8(+) T cells) strongly shifted and OX35 (an antibody against CD4(+) T cells) modestly shifted isoprenaline-induced concentration-relaxation curves in a nonparallel fashion to the left with an increased R(max) in asthmatic rats and sarafotoxin 6c-induced concentration-contractile curves to the right with a decreased E(max).

CONCLUSION

The inhibition of airway relaxation and the augmentation of contraction mediated by receptors contribute to airway hyperresponsiveness and involve CD8(+) and CD4(+) T cells.Acta Pharmacologica Sinica (2009) 30: 965-972; doi: 10.1038/aps.2009.61.

Airway vascular reactivity and vascularisation in human chronic airway disease

Altered bronchial vascular reactivity and remodelling including angiogenesis are documented features of asthma and other chronic inflammatory airway diseases. Expansion of the bronchial vasculature under these conditions involves both functional (vasodilation, hyperperfusion, increased microvascular permeability, oedema formation, and inflammatory cell recruitment) and structural changes (tissue and vascular remodelling) in the airways. These changes in airway vascular reactivity and vascularisation have significant pathophysiological consequences, which are manifest in the clinical symptoms of airway disease. Airway vascular reactivity is regulated by a wide variety of neurotransmitters and inflammatory mediators. Similarly, multiple growth factors are implicated in airway angiogenesis, with vascular endothelial growth factor amongst the most important. Increasing attention is focused on the complex interplay between angiogenic growth factors, airway smooth muscle and the various collagen-derived fragments that exhibit anti-angiogenic properties. The balance of these dynamic influences in airway neovascularisation processes and their therapeutic implications is just beginning to be elucidated. In this review article, we provide an account of recent developments in the areas of vascular reactivity and airway angiogenesis in chronic airway diseases.

Autonomic nervous system control of the cardiovascular and respiratory systems in asthma

Patients with asthma have exaggerated bronchoconstriction of their airways in response to certain indirect (e.g. cold air, allergens, dust, exercise) or direct (e.g. inhaled methacholine) stimuli. This 'hyper-reactivity' usually co-exists with airway inflammation, although the pathophysiological mechanisms underlying these changes are not fully understood. It is likely that this hyper-reactivity is associated with abnormal autonomic nervous system (ANS) control. In particular, the parasympathetic (vagal) component of the ANS appears to be implicated in the pathogenesis of asthma. In addition, several studies have suggested the existence of differential alteration in ANS function following exercise in asthmatics compared with non-asthmatic individuals. Several early studies suggested that the altered autonomic control of airway calibre in asthma might be reflected by a parallel change in heart rate. Cardiac vagal reactivity does indeed appear to be increased in asthma, as demonstrated by the cardiac response to various autonomic functions tests. However, other studies have reported a lack of association between bronchial and cardiac vagal tone, and this is in accord with the concept of system-independent ANS control. This review provides a discussion of cardiovascular-autonomic changes associated with either the pathophysiology of asthma per se or with asthma pharmacotherapy treatment. Previous investigations are summarised suggesting an apparent association between altered autonomic-cardiovascular control and bronchial asthma. The full extent of autonomic dysfunction, and its clinical implications, has yet to be fully determined and should be the subject of future investigation.

beta2-Adrenergic receptor polymorphisms and asthma in the North Indian population

INTRODUCTION

The beta(2)-adrenergic receptor (ADRB2) polymorphisms are known to be functionally relevant and disease modifying in subjects with asthma. However, the association of these polymorphisms with asthma remains to be established. Our objective is to investigate the association of the ADRB2 polymorphisms and haplotypes with asthma in North Indian subjects.

METHODS

A subset of 101 unrelated cases and 55 unrelated unaffected individuals were used for a case-control disease-association test.

RESULTS

Ten variable single nucleotide polymorphism (SNP) sites within a span of 2.193 kb were identified in the ADRB2 gene by the sequencing and genotyping of 351 bronchial asthma patients and healthy individuals. The distributions of genotype and allele frequencies for individual SNPs in the ADRB2 gene and ADRB2 haplotype frequencies were estimated in unrelated asthmatics and healthy individuals. No significant association was observed between ADRB2 genotypes and alleles with disease status after Bonferroni correction for multiple testing (reference p value = 0.0083). However, haplotype GGCTTTGCAA was found to be significantly associated with asthma (p = 0.021) in the studied population.

CONCLUSION

Our results suggest that there is likely to be a functional significance of the ADRB2 gene with asthma.

Agonist-independent alteration in beta-adrenoceptor-G-protein-adenylate cyclase system in an equine model of recurrent airway obstruction

We examined the inhibitory sympathetic beta-adrenergic mechanisms in peripheral lung, bronchi and trachea of an equine model of recurrent airway obstruction (RAO), to support the hypothesis that the beta-adrenergic receptor dysfunction is not only restricted to cell surface receptor density but rather encompasses a mechanistic defect apart from the receptor, to the intracellular signaling components. The non-asthmatic lung possessed 3.2-fold more beta-adrenergic receptors than bronchi (496 +/- 19.4 vs. 155.1+/- 19.6 fmol/mg protein; P < 0.01) and 6.2-fold higher than in the trachea (79.8 +/- 12.6 fmol/mg protein; P < 0.001) (assessed by radioligand binding assays using (-)-[(125)I]-iodocyanopindolol, ICYP) and in all tissues a greater proportion of the beta(2)- than the beta(1)-subtype (75-80%). The receptor density (B(max)) in lung parenchyma and bronchial membranes was 33 and 42%, respectively, lower (P < 0.001) in RAO than in control animals, attributable to a decrease in the beta(2)-subtype. This receptor down-regulation was accompanied with an attenuated coupling efficiency of the receptor to the stimulatory G(S)-protein (P < 0.05 vs. control). Concomitantly, activation of adenylate cyclase evoked by isoproterenol was significantly reduced in lung and bronchial membranes of animals with RAO, whereas effects of 10 microM GTP, 10mM NaF, 10 microM forskolin and 10 mM Mn(2+) were not altered. There was no difference in beta-adrenergic receptor density, G(S)-protein or adenylate cyclase coupling in the trachea between asthmatic and control animals. In conclusion, in stable asthma the pulmonary beta-adrenergic receptor-G(S)-protein-adenylate cyclase system is impaired, thus the pathologic process involves all signaling components, and due to its close similarity, this animal model seems to serve as a suitable model, at least partly, of chronic asthmatic patients.

Regulation of beta-adrenergic responses in airway smooth muscle

Decreased responsiveness to beta-adrenergic receptor agonists is a characteristic feature of human asthma. This review summarizes data regarding the impact of chronic beta agonist stimulation, cytokines, prostanoids and other factors on beta-adrenergic responses in human airway smooth muscle, as well as the impact of polymorphisms of the beta(2)-adrenergic receptor on these responses. Effects of beta-agonists on both airway smooth muscle relaxation and gene expression are considered. Understanding the regulation of beta-adrenergic responses in airway smooth muscle cells may prove to be an important step in improving the efficacy of beta-agonists for the treatment of asthma.

Airway hyperresponsiveness: a story of mice and men and cytokines

Bronchial hyperresponsiveness (BHR) is an essential part of the definition of asthma. Although our understanding of the allergic inflammatory and immunologic mechanisms of asthma have markedly increased, the mechanism of BHR remains to be elucidated. Increased BHR is associated temporally with exposure to allergens, certain respiratory viruses, pollutants such as ozone, and certain occupational chemicals. An important research use of determining the degree of BHR to direct and indirect challenge is to determine the efficacy of pharmacologic and immunodulatory agents. Beta-adrenergic agents inhibit BHR and certain genetic polymorphisms of the beta-adrenergic receptor are associated with increased BHR. When beta-adrenergic receptors are blocked, sensitivity to allergens is markedly increased in patients with asthma and animal models of asthma. Allergen challenge and clinical asthma are associated with synthesis and release of pro-inflammatory cytokines such as IL-1 and TNF-alpha which have been shown to decrease the response to beta-agonists and increased the reactivity to methacholine and the airways neutrophils and alveolar macrophages. The Th2 cytokine IL-13 is increased in the airways of asthmatics and increases BHR in normal unsensitized animals. The mechanisms of this effect of IL-13 are being intensively investigated. Our group has shown that IL-13 induced BHR persisted for at least 7 days and the soluble receptor IL-13R2alpha protected against their BHR. Other investigators have demonstrated that IL-13 is necessary and sufficient for the induction of BHR and that eosinophilic airway inflammation in the absence of IL-13 fails to induce BHR. These studies indicate that treatment of human asthma with antagonists of IL-13 may be very effective.

Virus associated immune and pharmacologic mechanisms in disorders of respiratory and cutaneous atopy

Anaphylaxis represents non-atopic immediate hypersensitivity, whereas manifestations of atopic immediate hypersensitivity include bronchial asthma, hay fever, allergic rhinitis, chronic urticaria, and atopic dermatitis. In spite similar antigen exposure, only a minority of the population shown some form of atopic disease. Atopic disease with its spontaneous pattern of familial occurrence cannot be induced at will.

The exact pathogenesis of atopy is yet to be elucidated. Two theories prevail: 1) atopy is a primary disorder of the immune system with sequelae in the various effector tissues; and 2) a concept of atopy as a primary autonomic imbalance, essentially beta adrenergic in character, with sequelae in effector cells, including those engaged in the production of antibodies. The autonomic imbalance is perceived as caused not by some disorder of the autonomic nervous system itself but by a defector functioning of its effector cells. These two concepts are not mutually exclusive. The IgE antibody, which mediates allergic reactions, is essentially identical with atopic reagin in various animal species.

The beta adrenergic theory regards atopic disorders (i.e., perennial and seasonal allergic rhinitis, bronchial asthma, and atopic dermatitis) not as immunologic diseases but as unique patterns of altered reactivities to a broad spectrum of immunologic, psychic, infectious, chemical and physical stimuli. The antigen-antibody interaction is given the same role as that of a broad category of nonspecific stimuli that function only to trigger the same defective homeostatic mechanism in the various effector cells involved in immediate hypersensitivities. Current evidence favors the possibility that there are inherited and/or acquired multiple abnormalities in the receptor—adenylate cyclase—cyclic AMP system of all effector cells that are critical in the organization of immune reactivities.

Atopic abnormality may be 1) acquired by functional receptor regulatory shifts caused by hormonal changes, infection (viral, bacterial, etc), allergic tissue injury or other event; 2) genetically determined; or 3) caused by autoimmune disease. One, two or all three of these effector mechanisms may be operative in a particular disease.

There is an important relationship between asthma and viral respiratory infection. A history of childhood viral respiratory illness is a risk factor for the development of chronic obstructive airway syndromes in later life. Asthmatic attacks occurred only when the infection produced fever, malaise, cough or coryza. The dominant role of fever in these episodes immediately suggests the profound involvement of adrenergic effector mechanisms. The presence of autoantibodies to beta-adrenoceptors in patients correlated well with a reduced beta—and an increased alpha-adrenergic responsiveness. Virus infections can elicit autoantibody formation.

In patients with atopic dermatitis an increased susceptibility and abnormal host response to viral infections in general. Defective cytotoxic T cells, abnormally functioning macrophages and natural killer cells, a reduced production of IFNα in children, and of IFNγ in atopic patients with food allergy has recently been demonstrated. Lymphocytic cyclic AMP-phosphodiesterase, that destroys cyclic AMP, is increased in atopic dermatitis and in allergic respiratory disease of adults, and this increased activity correlated closely with histamine release from basophils. Peripheral blood leukocytes and lymphocytes in atopic dermatitis have frequently demonstrated impaired beta adrenergic reactivity.

Allergic tissue injury may be initiated by antigen-specific IgE antibodies that combine with Fcε receptors on various cell types and trigger mediator release upon encounter with the antigen. Various noxious agents that are capable of triggering asthma are capable of releasing inflammatory mediators from the same target cells. Accounting only for those pharmacologic mediators where the cell-type has been identified, the spectrum of mediator-storing, synthesizing, or transporting cells includes neutrophil leucocytes, basophilic leucocytes eosinophilic leucocytes; mast cells, “chromaffin-positive” mast cells, enterochromaffin cells, chromaffin cells; platelets, neurosecretory cells and nerve cells that potentially produce all amine-mediators as well as prostaglandins and kinins.

Cloning, pharmacological characterization, and polymorphism screening of the guinea pig beta(2)-adrenoceptor

In asthma, beta(2)-adrenoceptor agonist responsiveness has been associated with Arg16Gly and Gln27Glu polymorphisms of the beta(2)-adrenoceptor. Since the guinea pig is extensively used as an animal model for asthma, we investigated the occurrence of possible polymorphism of the guinea pig beta(2)-adrenoceptor. The guinea pig beta(2)-adrenoceptor coding region was amplified by sequence homology-based cloning. Homology of the translated protein with the human beta(2)-adrenoceptor was 88% with Ala at position 16 and Glu at position 27. Radioligand binding and cAMP- accumulation experiments of Chinese hamster ovary (CHO) cells transfected with the guinea pig beta(2)-adrenoceptor revealed a homogeneous population of functional receptors. Five degenerate single nucleotide polymorphisms were found within the beta(2)-adrenoceptor coding region of outbred Dunkin Hartley guinea pigs, at residues 354, 453, 483, 534 and 642. In conclusion, we have cloned the guinea pig beta(2)-adrenoceptor, which shows to be functional upon expression in a recombinant system and contains five single nucleotide polymorphisms dissimilar to human polymorphisms.

Cytokine regulation of beta-adrenergic responses in airway smooth muscle

Decreased responsiveness to beta-adrenergic receptor agonists is a characteristic feature of human asthma. One explanation for this observation is that cytokines released in the asthmatic airway have direct effects on airway smooth muscle cells that reduce the ability of the cells to relax in response to beta-agonists. This review summarizes data indicating that both inflammatory cytokines, such as IL-1beta and TNF-alpha, and Th2 cytokines, such as IL-13 and IL-5, have the capacity to decrease the ability of cultured airway smooth muscle cells to relax or to generate cyclic AMP in response to beta-agonists, such as isoproterenol. These effects are observed in smooth muscle from human airways and airway smooth muscle of other species. In human airway smooth muscle, the effects of IL-1beta and TNF-alpha appear to be mediated through expression of cyclooxygenase-2, whereas the effect of IL-13 requires activation of the extracellular signal-regulated kinase-mitogen-activated protein kinase pathway. IL-1beta and TNF-alpha also inhibit the ability of beta-agonists to drive airway smooth muscle gene expression through pathways dependent on cyclic AMP response elements. Understanding the mechanistic basis for the effects of these cytokines may prove to be an important step in improving the efficacy of beta-agonists for the treatment of asthma.

Alpha(1L)-, but not alpha(1H)-, adrenoceptor antagonist prevents allergic bronchoconstriction in guinea pigs in vivo

alpha-Adrenoceptors have been classified into alpha(1)- and alpha(2)-adrenoceptors. Recently, the alpha(1)-adrenoceptors were divided into two subtypes: alpha(1L) with low affinity and alpha(1H) with high affinity for prazosin. Little is known concerning the role of each subtype of alpha(1)-adrenoceptor in asthma. We investigated the effects of specific antagonists of alpha(1)- and alpha(2)-, alpha(1H)-, alpha(1L)-, and alpha(2)-adrenoceptors, namely moxisylyte, prazosin, 3-[N-[2-(4-hydroxy-2-isopropyl-5-methylphenoxy) ethyl]-N-methylaminomethyl]-4-methoxy-2, 5, 6-trimethylphenol hemifumarate (JTH-601), and yohimbine, respectively, on antigen-induced airway reactions in guinea pigs. Fifteen minutes after intravenous administration of moxisylyte (0.01, 0.1 or 1 mg/kg), prazosin (0.01, 0.1, 1 or 10 mg/kg), JTH-601 (1, 3, 6 or 10 mg/kg) or yohimbine (0.1 or 1 mg/kg), passively sensitized and artificially ventilated animals received an aerosolized antigen challenge. Bronchial responsiveness to inhaled methacholine was assessed as the dose of methacholine required to produce a 200% increase in the pressure at the airway opening (PC(200)) in non-sensitized animals. JTH-601 and moxisylyte, but not prazosin or yohimbine, dose dependently inhibited antigen-induced bronchoconstriction. None of the tested drugs altered PC(200). JTH-601 significantly reduced leukotriene C(4) levels in bronchoalveolar lavage fluid obtained 5 min after antigen challenge, but prazosin did not. These results indicate that prevention of antigen-induced bronchoconstriction by blockade of alpha-adrenoceptors is due to the inhibition of mediator release via alpha(1L)-adrenoceptor antagonism.

Direct effects of interleukin-13 on signaling pathways for physiological responses in cultured human airway smooth muscle cells

Numerous studies have suggested an important role for the Th2 cytokines interleukin (IL)-13 and IL-4 in the development of allergic asthma. We tested the hypothesis that IL-13 and IL-4 have direct effects on cultured airway smooth muscle cells (HASM). Using RT-PCR, we showed that HASM cells express transcripts for IL-4alpha, IL-13RalphaI, and IL-13RalphaII, but not for the common IL-2Rgamma chain. We then analyzed the capacity of the two cytokines to activate signaling pathways in HASM cells. Both IL-13 and IL-4 caused STAT-6 phosphorylation, but the time course was different between the two cytokines, with peak effects occurring 15 min after addition of IL-4 and 1 h after addition of IL-13. Effects on signaling were observed at cytokine concentrations as low as 0.3 ng/ml. IL-4 and IL-13 also caused phosphorylation of ERK MAP kinase. As suggested by the signaling studies, the biological responses of the two cytokines were also different. We used magnetic twisting cytometry to measure cell stiffness of HASM cells and tested the capacity of IL-4 and IL-13 to interfere with the reductions in cell stiffness induced by the beta-agonist isoproterenol (ISO). IL-13 (50 ng/ml for 24 h), but not IL-4, significantly reduced beta-adrenergic responsiveness of HASM cells, and the MEK inhibitor U0126 significantly reduced the effects of IL-13 on ISO-induced changes in cell stiffness. We propose that these direct effect of IL-13 on HASM cells may contribute at least in part to the airway narrowing observed in patients with asthma.

Association of asthma with beta(2)-adrenergic receptor gene polymorphism and cigarette smoking

Recent studies have suggested that two polymorphisms of the beta(2)-adrenergic receptor (beta(2)AR) gene at codons 16 (arginine to glycine) and 27 (glutamine to glutamate) affect an individual's airway responsiveness, or response to acute or chronic beta(2)-agonist therapy but are not risk factors for asthma. We hypothesize that there is an interaction effect on asthma between the beta(2)AR gene polymorphisms and cigarette smoking. A case-control study was conducted in 128 asthma cases and 136 control individuals identified from 10,014 studied subjects in rural Anqing, China. Allele-specific polymerase chain reaction (PCR) was used to genotype beta(2)AR gene polymorphisms. Multiple logistic regression was used to adjust for potential confounding factors. We found a marginally significant interaction between cigarette smoking and beta(2)AR-16 genotype after adjusting for important confounding factors (p = 0.06). Specifically, we found that compared with never-smoking Gly-16 homozygotes, those ever-smokers who are Arg-16 homozygotes had a significantly increased risk of asthma (odds ratio [OR] = 7.81; 95% confidence interval [CI]: 2.07 to 29.5). This association showed a clear dose-response relationship with the number of cigarettes smoked. However, there was no significant association of asthma with polymorphisms of the beta(2)AR at position 27 (OR = 1.38; 95% CI: 0.69 to 2.73). Our study suggests a gene-environment interaction between the Arg-16 genotype and ever cigarette smoking with respect to the susceptibility of an individual to asthma.

Asthma, asthma medication and autonomic nervous system dysfunction

Asthma is associated with autonomic nervous imbalance: an increased bronchial sensitivity to cholinergic constrictors and possibly a decreased sensitivity to beta2-adrenergic dilators have been reported in this disease. Also, non-adrenergic and non-cholinergic (NANC) mediators have a small regulatory effect on airway function. These mediators contribute to the pathogenesis of asthma not only by regulating smooth muscle tone in the airways but also by affecting pulmonary blood flow, endothelial permeability and airway secretions. In many studies increased parasympathetic responsiveness has been associated with clinical asthma or the worsening of asthma in adults. However, most of the studies in children have not found association between autonomic dysfunction and asthma. Therefore, the autonomic dysfunction in asthma may be related to more advanced disease or long-term asthma medication in adults. This article briefly reviews the relationships between airway inflammation, beta2-agonist, anticholinergic and glucocorticoid medication as well as autonomic nervous function in asthma.

Adrenergic airway vascular smooth muscle responsiveness in healthy and asthmatic subjects

The purpose of the present study was to determine the responsiveness of airway vascular smooth muscle (AVSM) as assessed by airway mucosal blood flow (Qaw) to inhaled methoxamine (alpha(1)-agonist; 0.6-2.3 mg) and albuterol (beta(2)-agonist; 0.2-1.2 mg) in healthy [n = 11; forced expiratory volume in 1 s, 92 +/- 4 (SE) % of predicted] and asthmatic (n = 11, mean forced expiratory volume in 1 s, 81 +/- 5%) adults. Mean baseline values for Qaw were 43.8 +/- 0.7 and 54.3 +/- 0.8 microl. min(-1). ml(-1) of anatomic dead space in healthy and asthmatic subjects, respectively (P < 0.05). After methoxamine inhalation, the maximal mean change in Qaw was -13.5 +/- 1.0 microl. min(-1). ml(-1) in asthmatic and -7.1 +/- 2.1 microl. min(-1). ml(-1) in healthy subjects (P < 0.05). After albuterol, the mean maximal change in Qaw was 3.0 +/- 0.8 microl. min(-1). ml(-1) in asthmatic and 14.0 +/- 1.1 microl. min(-1). ml(-1) in healthy subjects (P < 0.05). These results demonstrate that the contractile response of AVSM to alpha(1)-adrenoceptor activation is enhanced and the dilator response of AVSM to beta(2)-adrenoceptor activation is blunted in asthmatic subjects.

Effects of inhaled glaucine on pulmonary responses to antigen in sensitized guinea pigs

The alkaloid (S)-(+)-1,2,9,10-tetramethoxyaporphine (glaucine) is a phosphodiesterase 4 inhibitor with bronchodilator and anti-inflammatory activity in vitro. In this study, we examined the in vivo effects of glaucine on an animal model of asthma. In ovalbumin sensitized guinea pigs, inhaled glaucine (10 mg ml(-1), 3 min) inhibited the acute bronchoconstriction produced by aerosol antigen (antigen response was 256+/-42 and 95+/-14 cm H(2)O l(-1) s(-1) in control and glaucine-treated animals, respectively; P<0.05). Pretreatment with glaucine (10 mg ml(-1), 10 min inhalation, 30 min pre- and 3 h post-antigen exposure) markedly reduced airway hyperreactivity to histamine, eosinophil lung accumulation, and increased eosinophil peroxidase activity in bronchoalveolar lavage fluid 24 h after exposure of conscious guinea pigs to aerosol antigen. In addition, inhaled glaucine (5-10 mg ml(-1), 3 min) inhibited the microvascular leakage produced after inhaled antigen at all airway levels. These data support the potential interest of phosphodiesterase 4 inhibitors in asthma treatment.

Role of ERK MAP kinases in responses of cultured human airway smooth muscle cells to IL-1beta

We have previously reported that interleukin (IL)-1beta causes beta-adrenergic hyporesponsiveness in cultured human airway smooth muscle cells by increasing cyclooxygenase-2 (COX-2) expression and prostanoid formation. The purpose of this study was to determine whether extracellular signal-regulated kinases (ERKs) are involved in these events. Levels of phosphorylated ERK (p42 and p44) increased 8.3- and 13-fold, respectively, 15 min after treatment with IL-1beta (20 ng/ml) alone. Pretreating cells with the mitogen-activated protein kinase kinase inhibitor PD-98059 or U-126 (2 h before IL-1beta treatment) decreased ERK phosphorylation. IL-1beta (20 ng/ml for 22 h) alone caused a marked induction of COX-2 and increased basal PGE(2) release 28-fold (P < 0.001). PD-98059 (100 microM) and U-126 (10 microM) each decreased COX-2 expression when administered before IL-1beta treatment. In control cells, PD-98059 and U-126 had no effect on basal or arachidonic acid (AA; 10 microM)-stimulated PGE(2) release, but both inhibitors caused a significant decrease in bradykinin (BK; 1 microM)-stimulated PGE(2) release, consistent with a role for ERK in the activation of phospholipase A(2) by BK. In IL-1beta-treated cells, prior administration of PD-98059 caused 81, 92 and 40% decreases in basal and BK- and AA-stimulated PGE(2) release, respectively (P < 0.01), whereas administration of PD-98059 20 h after IL-1beta resulted in only 38 and 43% decreases in basal and BK-stimulated PGE(2) release, respectively (P < 0.02) and had no effect on AA-stimulated PGE(2) release. IL-1beta attenuated isoproterenol-induced decreases in human airway smooth muscle stiffness as measured by magnetic twisting cytometry, and PD-98059 or U-126 abolished this effect in a concentration-dependent manner. These results are consistent with the hypothesis that ERKs are involved early in the signal transduction pathway through which IL-1beta induces PGE(2) synthesis and beta-adrenergic hyporesponsiveness and that ERKs act by inducing COX-2 and activating phospholipase A(2).

Altered contractile sensitivity of isolated bronchial artery to phenylephrine in ovalbumin-sensitized rabbits

We tested the hypothesis that atopy and/or allergic lung inflammation enhances alpha1-adrenoceptor-mediated contractions of the bronchial artery. Bronchial arterial resistance vessels were isolated from rabbits that had undergone either systemic ovalbumin (OVA) sensitization followed by saline aerosol challenge (OVA/saline rabbits), or OVA sensitization followed by OVA aerosol challenge (OVA/OVA rabbits), or no sensitization followed by saline aerosol challenge (control rabbits). In OVA/OVA rabbits, bronchoalveolar lavage and lung histology revealed lymphocytic and eosinophilic inflammation. Arterial rings were contracted with phenylephrine (PE). In endothelium-intact arteries isolated from OVA/saline and OVA/OVA rabbits, PE responsiveness was enhanced compared with that of arteries isolated from controls. The nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester increased the contractile response to PE in all three experimental groups to a similar degree, suggesting that depressed NOS activity was not involved in the enhanced PE responsiveness in OVA/saline and OVA/OVA rabbits. After endothelium removal, arteries from OVA/saline and control rabbits showed similar PE responsiveness, indicating that the enhancement of PE responsiveness was endothelium dependent, possibly due to an endothelial constricting factor. In OVA/OVA rabbits, endothelium-denuded arteries showed decreased PE responsiveness compared with the other two groups; this difference was abolished by NG-nitro-L-arginine methyl ester. We conclude that systemic sensitization with OVA per se enhances PE-induced contractions of isolated bronchial arteries in rabbits by an endothelium-dependent mechanism and that allergic lung inflammation attenuates this effect by increased nonendothelial NOS activity.

Inhibition of beta-adrenergic desensitization by KCa channels in human trachealis

We examined the reduced responsiveness to beta-adrenergic receptor agonists (beta-agonists) after exposure to beta-agonists, and the mechanisms underlying this phenomenon in isolated human tracheal smooth muscle, using isometric tension records to test the hypothesis that repeated inhalation of beta-agonists leads to reduced responsiveness to beta-agonists. The inhibitory effects of isoproterenol (ISO) on contraction by spasmogens participating in asthma attacks diminished markedly after continuous exposure to ISO (0.0003 to 3 microM) for 45 min; moreover, when ISO was repeatedly applied for 10 min to tissues precontracted by methacholine every 30 min, the relaxant effects of ISO gradually attenuated after these repeated applications. In contrast, reduced beta-adrenergic relaxation after continuous and repeated exposure to agonists did not occur when tissues were preincubated with 2 microg/ ml cholera toxin (CTX), which irreversibly activates guanosine triphosphate (GTP)-binding protein (Gs) coupled with beta-adrenergic receptors, for 6 h. However, the CTX inhibition disappeared in the presence of iberiotoxin, a selective inhibitor of large conductance Ca2+-activated K+ (KCa) channels. Our results demonstrate that continuous and repeated exposure to beta-agonists leads to beta-adrenergic desensitization, and that activation of KCa channels by Gs prevents this desensitization.

Role of cyclo-oxygenase-2 induction in interleukin-1beta induced attenuation of cultured human airway smooth muscle cell cyclic AMP generation in response to isoprenaline

Airway smooth muscle (ASM) in human asthma shows reduced relaxation and cyclic AMP generation in response to beta-adrenoceptor agonists. IL-beta attenuates cyclic AMP generation but the underlying mechanism is unclear. We have reported that IL-1beta induces cyclo-oxygenase-2 (COX-2) in human ASM cells and results in a marked increase in prostanoid generation with PGE2 and PGI2 as the major products. We investigated the role of COX-2 induction and prostanoid release (measured as PGE2) in IL-1beta induced attenuation of cyclic AMP generation in response to the beta-adrenoceptor agonist isoprenaline (ISO). Pre-treatment of human ASM cells with IL-1beta significantly attenuated cyclic AMP generation in response to high concentrations of ISO (1.0-10.0 microM) in a time- and concentration-dependent manner. The effect was accompanied by a high concentration of PGE2 release. The non-selective COX inhibitor indomethacin (Ind), the selective COX-2 inhibitor NS-398, the protein synthesis inhibitors cycloheximide (CHX) and actinomycin D and the steroid dexamethasone (Dex) all abolished the PGE2 release and prevented the attenuated cyclic AMP generation. COX substrate arachidonic acid time- and concentration-dependently mimicked IL-1beta induced attenuation and the effect was prevented by the non-selective COX inhibitors Ind and flurbiprofen, but not by NS-398, CHX and Dex. In contrast to IL-1beta, TNFalpha and IFNgamma, which are ineffective in inducing COX-2 and releasing PGE2 from human ASM cells, did not affect the cyclic AMP formation. Our study demonstrates that COX-2 induction and the consequent release of prostanoids plays a crucial role in IL-1beta induced attenuation of human ASM cell cyclic AMP response to ISO.

Role of adrenergic nervous system in cigarette smoke-induced bronchoconstriction in guinea pigs

The goal of this study was to clarify the role of the adrenergic nervous system in bronchoconstriction induced by exposure to cigarette smoke in guinea pigs. Artificially ventilated animals were exposed to 160 puffs of smoke for 8 min. Bronchoconstriction was assessed as a percentage of the baseline total pulmonary resistance (RL). The effects of pretreatment with phentolamine (0.1 mg/kg, i.v.), propranolol (1 mg/kg, i.v.), and/or atropine (1 mg/kg, i.v.) were evaluated. Exposure to cigarette smoke caused significant bronchoconstriction. Phentolamine, an alpha-adrenoceptor antagonist, significantly inhibited cigarette smoke-induced bronchoconstriction, while propranolol, a beta-adrenoceptor antagonist, significantly enhanced it. Combined use of these compounds further enhanced the bronchoconstriction. All of modulations of the bronchoconstriction by adrenoceptor antagonists were completely abolished by pretreatment with atropine. Phentolamine and/or propranolol had no effect on the bronchoconstriction induced by inhaled acetylcholine. Pretreatment with yohimbine (0.5 mg/kg, i.v.), a selective alpha2-adrenoceptor antagonist, showed modulatory effects similar to those of phentolamine on cigarette smoke-induced bronchoconstriction. These results suggest that cigarette smoke-induced bronchoconstriction is regulated by the prejunctional modulation of the cholinergic system via alpha- and beta-adrenoceptors. This mechanism may be modulated by the autoregulation of adrenergic nerves via the alpha2-autoreceptor.

Prostanoids mediate IL-1beta-induced beta-adrenergic hyporesponsiveness in human airway smooth muscle cells

We have previously reported that pretreatment of cultured human airway smooth muscle (HASM) cells with interleukin-1beta (IL-1beta) results in decreased beta-adrenergic responsiveness. The purpose of this study was to determine whether prostanoids released as a result of cyclooxygenase-2 (COX-2) induction by IL-1beta contribute to this effect of the cytokine. Confluent serum-deprived HASM cells were studied in passages 4-7. IL-1beta (20 ng/ml for 22 h) reduced the ability of the beta-agonist isoproterenol (Iso) to decrease stiffness of HASM cells as measured by magnetic twisting cytometry. The effect of IL-1beta on Iso-induced changes in cell stiffness was abolished by nonselective [indomethacin (Indo), 10(-6) M] and selective (NS-398, 10(-5) M) COX-2 inhibitors. Indo and NS-398 also inhibited both the increased basal cAMP and the decreases in Iso-stimulated cAMP production induced by IL-1beta. IL-1beta (20 ng/ml for 22 h) caused an increase in both basal (15-fold) and arachidonic acid (AA)-stimulated (10-fold) PGE2 release. Indo blocked basal and AA-stimulated PGE2 release in both control and IL-1beta-treated cells. NS-398 also markedly reduced basal and AA-stimulated PGE2 release in IL-1beta-treated cells but had no significant effect on AA-stimulated PGE2 release in control cells. Western blot analysis confirmed the induction of COX-2 by IL-1beta. Exogenously administered PGE2 (10(-7) M, 22 h) caused a significant reduction in the ability of Iso to decrease cell stiffness, mimicking the effects of IL-1beta. Cycloheximide (10 microg/ml for 24 h), an inhibitor of protein synthesis, also abolished the effects of IL-1beta on Iso-induced cell stiffness changes and cAMP formation. In summary, our results indicate that IL-1beta significantly increases prostanoid release by HASM cells as a result of increased COX-2 expression. The prostanoids appear to contribute to beta-adrenergic hyporesponsiveness, perhaps by heterologous desensitization of the beta2 receptor.

Effect of phenylephrine on histamine-induced bronchoconstriction in dogs

PURPOSE

Although an α-adrenoceptor has been suggested to be involved in the mechanism of asthma, the effect of α₁-agonist on the airway is still unclear. In this study we evaluated the effect of phenylephrine on the airway with a direct visualization method using a superfine fiberoptic bronchoscope (SFB).

METHODS

Seven mongrel dogs were anesthetized with pentobarbital (30 mg·kg^-1 IV) and paralyzed by pancuronium (0.2mg·kg^-1·h^-1). The trachea was intubated with an endotracheal tube (ID 7 mm) that has a second lumen for insertion of a SFB (OD 2.2 mm) to monitor the bronchial cross-sectional area (BCA) continuously. The tip of a SFB was placed at the level between the second and third bronchial bifurcation. To assess hemodynamics, the direct arterial blood pressure (ABP) and pulmonary arterial pressure (PAP) were monitored via a femoral arterial catheter and Swan-Granz catheter. Bronchoconstriction was elicited by histamine (10 μg·kg^-1+ 500 μg·kg^-1·h^-1_. At 30 min after the histamine was started, saline or phenylephrine (1, 10, and 100μg·kg^-1) was given intravenously. The BCA and hemodynamic variables were assessed before (basal) and 30 min after the histamine was started and 5 min after saline and each phenylephrine dose.

RESULTS

Histamine reduced BCA by 40.3±6.3%. Phenylephrine at 10 and 100 μg·kg^-1 significantly increased the ABP and PAP; and it significantly decreased the BCA, by 6.5±6.9% and 14.2±7.9%, respectively. Plasma epinephrine and norepinephrine were also significantly reduced following phenylephrine 100 μg·kg^-1 IV.

CONCLUSION

The dose of phenylephrine that produced vasopressive actions worsened the histamine-induced bronchoconstriction slightly but significantly. Therefore, phenylephrine should be used with caution in asthmatic patients.

Genetic factors in lung disease: atopy and bronchial asthma

Atopy defined as high IgE responsiveness has now been subject to genetic studies at the molecular level owing to the development of a great number of DNA markers over the human genome. Either by linkage analysis or by association study strong candidate genes of atopy have been proposed to be located on chromosome 11q13 and 5q31 where high-affinity IgE Fc receptor beta subunit and allergy-associated cytokines, respectively, have been mapped. Meanwhile, we found a novel association between one of alleles of D11S97, an anonymous DNA marker on 11q13, and high total serum IgE in a large number of Japanese general population and atopic family members. However, failure to replicate linkage or association studies by different investigators suggest polygenic nature of atopy. In addition to the genes regulating IgE synthesis, the requirement of local (pulmonary) genetic factors in the development of bronchial asthma have been speculated. Linkage analysis suggested possible existence of gene(s) regulating susceptibility and/or clinical characteristics of bronchial asthma also on chromosome 5q. One of the candidate is beta 2-adrenergic receptor gene polymorphism. Mutated gene transfection studies suggested functional significance of some polymorphisms and clinical evaluations have revealed their contribution to airway responsiveness and severity of asthma.

Stereoselective synthesis and biodistribution of potent [11C]-labeled antagonists for positron emission tomography imaging of muscarinic receptors in the airways

Quantitation of muscarinic receptors in the lungs in vivo with positron emission tomography (PET) is of clinical interest. For that purpose we decided to develop [11C]-labeled ligands with a high affinity (KD < 0.1 nM). Three quaternary muscarinic antagonists, racemic N-methylpiperidin-4-yl 2-cyclohexyl-2-hydroxy-2-phenylacetate methiodide 1a (pKB = 10.39), its (R)-isomer 1b (pKB = 11.08), and (R,R)-quinuclidin-3-yl 2-cyclohexyl-2-hydroxy-2-phenylacetate methiodide 2 (pKB = 11.28), were labeled by reacting [11C]CH3I with their tertiary amine precursors. The enantiomerically pure tertiary amine precursors were prepared by stereoselective synthesis starting from (R)-(-)-mandelic acid. In vitro binding assay of 1b and 2 demonstrated that both ligands bind with very high affinity to the muscarinic receptor subtypes M1, M2, and M3. They are more potent than the muscarinic antagonist (R)-N-methylquinuclidinyl benzilate ((R)-MQNB). Distribution studies with 1a, 1b, and 2 in control and atropine-treated male Wistar rats demonstrated significant specific binding (90-99% of total issue uptake) in tissues containing cholinoceptors (heart, intestine, lung, pancreas, spleen, stomach, submandibular gland). Because the tissue/plasma concentration ratios of 1b are most favorable, this ligand was used for further evaluation. Analysis of plasma samples showed a very rapid clearance (t1/2 = 0.3 min) of the radioligand 1b and a relatively slow appearance of a hydrophilic metabolite. At 15 min postinjection of 1b, analysis of heart, lungs, and liver showed that respectively 99%, 88%, and 8% of the tissue radioactivity corresponded with the parent compound. Ligand 1b appears to be an excellent candidate for PET studies of mAChR receptors in heart and lungs.

Binding of [3H][D-Ala2, MePhe4, Gly-ol5] enkephalin, [3H][D-Pen2, D-Pen5]enkephalin, and [3H]U-69,593 to airway and pulmonary tissues of normal and sensitized rats

The role of endogenous opioid peptides in the regulation of bronchomotor tone, as well as in the pathophysiology of asthma is uncertain. We have studied the binding of highly selective [3H]labeled ligands of mu-([D-Ala2, MePhe4, Gly-ol5]enkephalin; DAMGO), delta ([D-Pen2, D-Pen5]enkephalin; DPDPE), and kappa-(U-69,593) opioid receptors to membranes of trachea, main bronchus, lung parenchyma and pulmonary artery obtained from normal (unsensitized) and actively IgE-sensitized rats acutely challenged with the specific antigen. [3H]DAMGO, [3H]DPDPE and [3H]U-69,593 bound to membranes of normal and sensitized tissues at a saturable, single high-affinity site. The rank order of receptor densities in normal tissues was delta- > or = kappa- > or = mu-, with lung parenchyma exhibiting the greatest binding capacity for delta- and mu- receptors compared to the other regions examined. The Kd values showed small differences between ligands and regions tested. The mu- and delta-opioid receptor densities were decreased in sensitized main bronchus and lung parenchyma, respectively, compared to normal tissues. By contrast, kappa-opioid receptor density was augmented in sensitized lung parenchyma but an increase in Kd values was also observed. These differential changes in the density and affinity of opioid receptor types may be related to alterations in endogenous opioid peptides during the process of sensitization.

In-vitro bronchorelaxing effects of novel nitric oxide donors GEA 3268 and GEA 5145 in guinea-pigs and rats

Endogenously released nitric oxide (NO) in airways might contribute to physiological bronchodilation; induced production of NO might play a role in the pathogenesis of asthma, although it could also be a compensatory mechanism to other factors that cause bronchoconstriction or inflammation. To investigate the efficacy of NO donors on bronchial tone, the bronchorelaxing efficacies of NO donors, new experimental GEA compounds 3268 and 5145 (oxatriazole sulphonylamides) were compared with those of sodium nitroprusside and SIN-1 (3-morpholinosydnonimine) and to the standard beta 2-adrenergic agonist, salbutamol, in bronchi of guinea-pigs and rats in-vitro. Their relaxing effects were also studied in rat mesentery arteries to compare the selectivity for airways. The capacity of the NO donors to produce nitrites and nitrates was assayed by the Griess reaction. The novel NO donors GEA 3268 and GEA 5145 were more potent bronchorelaxing agents than the old NO donors sodium nitroprusside and SIN-1. In guinea-pig bronchi, however, salbutamol was most potent. In rat bronchi the GEA compounds induced the strongest relaxation effect when compared with the old NO donors or with salbutamol. The airway selectivity of the drugs studied decreased in the order of salbutamol, SIN-1, GEA 5145, GEA 3268, sodium nitroprusside. The nitrites and nitrates produced spontaneously did not correlate with the efficacy of the relaxants. The results obtained suggest that NO is only partly responsible for the relaxation and the potency is dependent on the animal species and constricting agents used.

Effects of in vitro mast cell degranulation on human lung beta-receptor binding parameters

BACKGROUND

Numerous studies have demonstrated that subjects with allergic asthma have beta-adrenergic hyporesponsiveness, predisposing these individuals toward bronchospasm, mucous production, and mast cell degranulation. Since sympathetic innervation of the human respiratory tract is sparse, reduced beta-responsiveness probably results from alterations at or beyond the receptor level.

OBJECTIVE

We therefore examined whether anaphylaxis of human lung tissue acutely modulated the human lung beta-receptor system in ways that might lead to decreased beta-adrenergic responsiveness.

METHODS

Fresh thoracotomy peripheral lung samples from 26 patients were incubated with (anaphylaxis) or without (control) anti-IgE (1:100) for up to 90 minutes and histamine release was documented. Lung fragments were quick frozen at various times after anti-IgE for analyses of beta-receptor binding parameters. Antagonist Kd (dissociation constant) and receptor concentration values were determined using (-)[125I]pindolol and agonist IC50 values were determined using isoproterenol.

RESULTS

In comparison with time O, neither anaphylaxis nor control samples had differences in receptor binding parameters with time. There were also no differences between anaphylaxis and control lung samples at any time point, and ratios of log control binding parameter/log anaphylaxis binding parameter ranged from 0.96 to 1.01.

CONCLUSIONS

Anaphylaxis of lung does not lead to acute changes in antagonist or agonist affinity for beta-receptors or changes in receptor concentration. Under the conditions studied, lung mast cell degranulation does not acutely alter the human lung beta-receptor system in ways that might account for the beta-adrenergic hyporesponsiveness found in allergic asthma.

Droperidol inhibits tracheal contraction induced by serotonin, histamine or carbachol in guinea pigs

PURPOSE

Droperidol (D) is effective in the treatment of patients with status asthmaticus. It has been reported that D inhibits the bronchoconstriction induced by serotonin (5-HT) but not that by histamine (H) or acetylcholine. However, haloperidol, another butyrophenone, is known to interact with and inhibit calmodulin, an intracellular Ca(++)-binding protein which is important in the contraction of smooth muscles. The present study was designed to investigate the effects of D on tracheal contractions induced by 5-HT, H or carbachol (C) and to determine the contribution of alpha-adrenoceptors to the relaxant effect of D in vitro.

METHODS

Tracheas of female guinea pigs were cut spirally into strips and mounted in water-jacketed organ baths in Tyrode's solution, aerated with a mixture of 95% O2 and 5% CO2 at 37 degrees C. The changes in isometric tension induced by each spasmogen in the strips were measured with a transducer and a polygraph.

RESULTS

We found that D inhibited the tracheal contractions induced by 5-HT, H or C in a concentration-dependent manner. At 1.25 x 10(-6) M D blocked the effect of 10(-4) M 5-HT by 44.1 +/- 4.3% and at 2.5 x 10(-6) M by 63.8 +/- 3.8%. Similarly, at 5.0 x 10(-6) M concentration, D blocked the effect of 10(-5) M H by 27.7 +/- 5.3% and at 10(-5) M by 56.2 +/- 2.6%. Furthermore, 5 x 10(-6) M of D reduced the contractions produced by 10(-7) M C by 37.1 +/- 3.0% and 10(-5) M of D by 76.1 +/- 3.2%. The inhibiting effect of D was strongest on contractions induced by 5-HT. Prazosin (10(-6) M) affected neither 5-HT-induced contractions nor the inhibition by D.

CONCLUSION

Our data indicate that D partially blocks the contractile responses not only to 5-HT, an effect which would be mediated through a blockade of the 5-HT receptors, but also to H or C, probably through inhibition of calmodulin. Our data support previous reports indicating that droperidol may be an important therapeutic agent in the treatment of patients with hyperreactive airways.

Dissociation between bronchial hyperreactivity in vivo and reduced beta-adrenoceptor sensitivity in vitro in allergen-challenged guinea pigs

In a recently developed guinea pig model of allergic asthma, we investigated the relationships between allergen-induced bronchial hyperreactivity in vivo, tracheal smooth muscle function in vitro, and the number of inflammatory cells in the bronchoalveolar lavage. At 6 h after allergen provocation (after the early asthmatic reaction) bronchial hyperreactivity to histamine aerosol was observed, which was still present, but reduced, at 24 h after the challenge (after the late asthmatic reaction). The severity of bronchial hyperreactivity at 6 h and at 24 h after each of four daily allergen provocations was progressively reduced. The contractile properties of tracheal smooth muscle preparations in response to methacholine or histamine were not changed at 6 h and 24 h after a single allergen provocation, as well as at 24 h after the fourth of the repeated provocations. However, the sensitivity to isoprenaline-induced relaxation of a half-maximal contraction obtained with methacholine or histamine was significantly reduced at 24 h after either a single or the fourth of the repeated provocations. The time course of the reduced beta-adrenoceptor sensitivity in vitro did not correlate with that of bronchial hyperreactivity in vivo. However, it was parallelled by a progressive infiltration of inflammatory cells in the airways, suggesting that mediators from these cells may decrease airway smooth muscle beta-adrenoceptor sensitivity.

Effects of sensitization on vasoactive intestinal polypeptide-induced relaxation and its concentration and binding in guinea-pig airways

We investigated the relaxant effect of vasoactive intestinal polypeptide (VIP) in trachea and lung parenchyma from normal and sensitized guinea-pigs. A technique by which drug access was restricted to either the mucosal or the adventitial surface of tracheal rings was used. In intact trachea, concentration-response curves for VIP entering from the mucosal surface (pD2 = 6.61 +/- 0.06) were displaced to the right compared with those for adventitial entry (pD2 = 6.78 +/- 0.04). Epithelium removal produced a leftward shift (approximately 2.8-fold) in the mucosal VIP concentration-response curve. Sensitization did not alter the responsiveness (maximal effect) or sensitivity (pD2 values) of tracheal rings to VIP irrespective of the surface of drug entry and of the absence or presence of epithelium. VIP-induced relaxation of normal and sensitized lung strips was also similar. Sensitization resulted in a significant decrease in tracheal VIP content (from 2.16 +/- 0.07 in normal to 0.60 +/- 0.08 nmol/mg protein in sensitized trachea; P < 0.05; n = 7) whereas the affinity of both high- and low-affinity binding sites for VIP increased as compared to that of normal trachea. Differences were not found in the binding capacities of normal and sensitized trachea. VIP content and binding did not differ in normal and sensitized lung. In conclusion, immunological sensitization produced changes in VIP tracheal content and binding but neither VIP-induced relaxation of isolated airways nor the influence of epithelium in this response was altered.

Alpha 1-adrenergic and muscarinic receptors in adult and neonatal rat type II pneumocytes

Binding characteristics of the alpha 1-adrenergic radioloigand [3H]prazosin, and the muscarinic cholinergic radioligand, [3H]quinuclidinyl benzilate, were determined both in intact cell preparations of rat alveolar type II pneumocytes (TIIPs) and in membrane preparations of rat lung tissue. Binding in adult and neonatal (< 24 h postnatal age) rats was also compared. Binding affinities for both receptor classes on TIIPs and whole lung membrane preparations alike did not vary significantly with age. In lung membrane preparations, the concentrations of both receptor classes were higher in neonates than adults. In TIIPs, the alpha 1-adrenergic receptor concentration was higher in neonates, but muscarinic receptor concentration was higher in adults. To begin investigation of the functional significance of these receptors, the effects of alpha 1-adrenergic and muscarinic agonists on intracellular calcium ion concentration ([Ca2+]i) were also measured. Both agonists induced consistent increases in [Ca2+]i, which were blocked by respective antagonists. These data indicate the presence of receptors on TIIPs for alpha 1-adrenergic and muscarinic agonists that may influence cellular function via modulation of [Ca2+]i.

Genetic polymorphism of the beta-2 adrenergic receptor in atopic and non-atopic subjects

To investigate a possible genetic basis for reported differences in beta-2 receptor expression in atopic subjects, DNA from 42 atopic children (22 asthmatics and 22 with allergic rhinitis) and 30 non-atopic subjects was Southern blotted and Ban-1 restriction fragment polymorphisms (RFLPS) were studied using a 2.6 kb probe of the human beta-2 receptor gene. Two alleles 3.1 kb and 2.9 kb were identified. Homozygotes and heterozygotes for the two alleles were found with equal frequency in the atopic patients who had asthma and in those who had allergic rhinitis only. The gene frequencies for the upper and lower alleles were 0.45 and 0.55 respectively. Our studies do not provide evidence for an association between a particular polymorphic form of the human beta-2 receptor gene and atopy.

Effect of salbutamol on histamine induced bronchoconstriction in healthy infants

BACKGROUND

The effect of inhaled beta 2 adrenergic drugs on infants with wheezing disorders remains controversial. Salbutamol inhibits the bronchial responsiveness of infants to histamine and nebulised water but whether or not it acts as a bronchodilator in this age group is unclear. The aim of the present study was to determine whether salbutamol can hasten the reversal of histamine induced bronchoconstriction in infants.

METHODS

Bronchial challenge with histamine was performed in 40 infants aged 12 months or less with no previous history of respiratory symptoms. Response to histamine was assessed by forced partial expiratory flow/volume curves to measure maximal flow at functional residual capacity (VmaxFRC). After a fall of 40% or more from baseline VmaxFRC, each infant was randomly assigned to receive either salbutamol 0.5% or saline 0.9% solution by nebuliser. The rate of recovery of VmaxFRC and the time to reach baseline VmaxFRC were derived by linear regression.

RESULTS

Infants who received salbutamol had a significantly faster rate of recovery (geometric mean 8.5 ml/s/min) than those who received saline (4.1 ml/s/min). Considerable interindividual variation was observed in the time from maximum bronchoconstriction to recovery of baseline VmaxFRC in both groups of subjects.

CONCLUSIONS

Salbutamol significantly speeds the reversal of histamine induced bronchoconstriction in infants during the first 12 months of life. This observation provides further evidence to support the presence of functional beta adrenergic receptors in the airways of infants.

Mutations in the gene encoding for the beta 2-adrenergic receptor in normal and asthmatic subjects

It has long been hypothesized that a defective beta 2-adrenergic receptor (beta 2AR) may be a pathogenic factor in bronchial asthma. We examined the gene encoding the beta 2AR to assess the frequency of polymorphisms in 51 patients with moderate to severe asthma and 56 normal subjects. Nine different point mutations were found in both heterozygous and homozygous forms at nucleic acid residues 46, 79, 100, 252, 491, 523, 1053, 1098, and 1239. No mutations resulting in large deletions or frame shifts were detected. Of these nine polymorphisms, four were found to cause changes in the encoded amino acids at residues 16, 27, 34, and 164. The most frequent polymorphisms were arginine 16 to glycine (Arg16-->Gly) and glutamine 27 to glutamic acid (Gln27-->Glu). The other two polymorphisms, valine 34 to methionine, and threonine 164 to isoleucine, occurred in only four subjects. The incidence of beta 2AR homozygous polymorphisms was no greater in asthmatic patients as compared with controls (Arg16-->Gly: 53% versus 59%, Gln27-->Glu: 24% versus 29%, respectively; P = NS). Some subjects were found to have both of these polymorphisms simultaneously, but there was no difference in incidence between the two groups, with 23% of asthmatics and 28% of normal subjects being homozygous for both polymorphisms. The apparently normal subjects with both polymorphisms did not have subclinical hyperreactive airways disease as determined by methacholine challenge testing. In the asthma group, one mutation (Arg16-->Gly) identified a subset of patients with a distinct clinical profile.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional disturbances of the autonomic nerve in nasal hyperreactivity: an up-date review

During the 1980s, our view of airway hypersensitivity was altered significantly. Advances in biochemical techniques revealed involvement of several nonspecific events in nasal hyperreactivity: Autonomic dysfunction involving primary and/or secondary receptor disorders, epithelial damage by cytotoxic proteins in eosinophil, which is stimulated by inflammatory mediators, and an axonal reflex of sensory C fibers. Since 1983, we have neurobiochemically investigated the autonomic nerve dysfunction in the nasal mucosa of patients with nasal allergy and guinea pigs with experimentally-induced nasal hypersensitivity. We propose the following mechanisms as potential contributors to the disturbance of the beta receptor function in airway hyperreactivity: i) Down-regulation caused by excess endogenous norepinephrine stimulation, ii) down-regulation and uncoupling to adenylate cyclase, produced by the inflammatory mediator-induced activation of protein kinase C, iii) the action of beta receptor inhibitory factor, presumably anti beta receptor autoantibodies, and iv) dysfunction of beta receptor kinase, which is known to cause short-term desensitization of beta receptors after exposure to beta agonists. This review provides the anatomical and neurobiochemical background for the autonomic regulation and dysfunction in the nose. We also introduce our series of experiments and the above updated hypotheses of how functional disturbances of the autonomic nerve in the nasal mucosa may occur.

Beta adrenergic receptor inhibitory factor in serum of patients with nasal allergy

Sera obtained from patients with perennial mite nasal allergy and Japanese cedar pollinosis were examined to identify "beta receptor inhibitory factor". This was done by evaluating the inhibition of 3H-dihydroalprenolol binding to guinea pig cerebral membrane. beta receptor binding was inhibited by preincubation with sera from 8 of 44 (18.1%) perennial allergy patients, whereas sera from 2 of 41 (4.9%) controls showed this inhibition. Sera from 6 of 41 pollenosis patients (14.6%) showed this inhibitory effect in the pollen season but not in other seasons. Serum from one such patient (2.4%) demonstrated this effect both in and out of the pollen season. Sera from 2 pollenosis patients inhibited the beta receptor function not in the pollen season, but in the off season. This inhibitory effect was eliminated by immunodepletion from the positive-inhibition serum. These findings identified circulating beta receptor inhibitory factor in a limited population of patients with nasal allergy indicating the possible pathogenetic role of this factor in the disturbance of the sympathetic nerve function. This beta receptor inhibitory effect may correspond to the anti beta receptor autoantibody which Venter postulated in 1980.

Subcellular distribution of beta 2-adrenergic receptors delineated with quantitative ultrastructural autoradiography of radioligand binding sites

beta-Adrenergic receptors play a critical role in signal transduction in the cardiovascular system. Regulation of beta-adrenergic receptor expression depends on multiple factors, including rates of synthesis and degradation of receptor protein and trafficking of receptors between the cell surface and putative intracellular compartments. To characterize the subcellular distribution of beta-adrenergic receptors and to delineate the ultrastructure of intracellular compartments in which adrenergic receptors reside in the steady state, we studied Chinese hamster fibroblast cells transfected with the human beta 2-adrenergic receptor gene. beta 2-Adrenergic receptors of these cells were covalently labeled with the lipophilic photoactivatable antagonist [125I]iodocyanopindolol diazarine, and specific radioligand binding sites were localized at the ultrastructural level of resolution with quantitative electron microscopic autoradiography. The density of beta 2-adrenergic receptors was approximately 100-fold greater in the plasmalemma than in any other compartment. Approximately 50% of total cellular receptors were identified on the cell surface in an apparently random, nonclustered distribution and without association with clathrin-coated pits or other cell surface structural specializations. The remaining receptors were distributed among intracellular membranous compartments, including smooth vesicles, rough endoplasmic reticulum, and the Golgi apparatus, organelles presumably involved in stages of receptor synthesis, degradation, or trafficking. In the basal state, there was no association of beta 2-adrenergic receptors with coated intracellular vesicles typical of the endocytotic pathway of selected cell surface receptors that function to internalize their extracellular ligands. These results are the first to rigorously quantify the subcellular distribution of beta-adrenergic receptors and unequivocally establish the presence of a substantial pool of intracellular receptors.