The action of prazosin and propylene glycol on methoxamine-induced bronchoconstriction in asthmatic subjects

Epinephrine evokes shortening of human airway smooth muscle cells following β2 adrenergic receptor desensitization

Epinephrine (EPI), an endogenous catecholamine involved in the body's fight-or-flight responses to stress, activates α1-adrenergic receptors (α1ARs) expressed on various organs to evoke a wide range of physiological functions, including vasoconstriction. In the smooth muscle of human bronchi, however, the functional role of EPI on α1ARs remains controversial. Classically, evidence suggests that EPI promotes bronchodilation by stimulating β2-adrenergic receptors (β2ARs). Conventionally, the selective β2AR agonism of EPI was thought to be, in part, due to a predominance of β2ARs and/or a sparse, or lack of α1AR activity in human airway smooth muscle (HASM) cells. Surprisingly, we find that HASM cells express a high abundance of ADRA1B (the α1AR subtype B) and identify a spontaneous "switch-like" activation of α1ARs that evokes intracellular calcium, myosin light chain phosphorylation, and HASM cell shortening. The switch-like responses, and related EPI-induced biochemical and mechanical signals, emerged upon pharmacological inhibition of β2ARs and/or under experimental conditions that induce β2AR tachyphylaxis. EPI-induced procontractile effects were abrogated by an α1AR antagonist, doxazosin mesylate (DM). These data collectively uncover a previously unrecognized feed-forward mechanism driving bronchospasm via two distinct classes of G protein-coupled receptors (GPCRs) and provide a basis for reexamining α1AR inhibition for the management of stress/exercise-induced asthma and/or β2-agonist insensitivity in patients with difficult-to-control, disease subtypes.

Smooth muscle in tissue remodeling and hyper-reactivity: airways and arteries

Smooth muscle comprises a key functional component of both the airways and their supporting vasculature. Dysfunction of smooth muscle contributes to and exacerbates a host of breathing-associated pathologies such as asthma, chronic obstructive pulmonary disease and pulmonary hypertension. These diseases may be marked by airway and/or vascular smooth muscle hypertrophy, proliferation and hyper-reactivity, and related conditions such as fibrosis and extracellular matrix remodeling. This review will focus on the contribution of airway or vascular smooth dysfunction to common airway diseases.

Airway responsiveness to indirect challenges in COPD

Patients with chronic obstructive pulmonary disease (COPD) demonstrate airway hyperresponsiveness to a number of indirect stimuli. Hyperresponsiveness to cold air hyperventilation, exercise, and drugs like propranalol and methoxamine seem to be able to distinguish patients with COPD from those with asthma, whereas hyperresponsiveness to stimuli like adenosine 5-monophosphate (AMP) and hypertonic saline seem unable to do so. The relationship of airway responsiveness to indirect stimuli and airway inflammation has received little study. The clinical relevance of hyperresponsiveness to an indirect challenge, including the impact on the natural history, relation to types of bronchitis, baseline airway calibre, and response to treatment need to be studied.

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.

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.

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.

Transdermal delivery of the alpha 2-agonist clonidine does not alter airways responses to inhaled histamine or methacholine

Previous studies have reported that the inhalation of the alpha 2-agonist clonidine decreases airways reactivity. Other studies have shown that oral doses of clonidine acutely increase airways reactivity to histamine, but not to methacholine. Recently, a transdermal clonidine delivery system (TTS) has been approved for use, and there is an increasing interest in using this system for management of postmenopausal and smoking cessation symptoms. To our knowledge, the effects of TTS on airways function in asthmatics have not been reported. The purpose of this study was to determine if use of TTS would alter airways reactivity. Six asymptomatic asthmatic subjects underwent a baseline methacholine challenge (M). In a double-blinded randomized crossover fashion, either a placebo or a TTS patch (TTS-1, 0.1 mg/day), was applied to the arm. Four days later, the challenge was repeated. After two to three days of washout, the alternate patch was applied, and a second challenge was performed. Several days later, a second baseline challenge was repeated. This sequence was then repeated using histamine (H). The patch was well tolerated by all subjects. There was no significant change in resting pulse or blood pressure, and for the group no change in airways reactivity to either M or H was noted. In conclusion, while use of TTS-1 does not improve airways function, its short-term use in asthmatics is not associated with an increase in airways reactivity.

Pharmacology of airway smooth muscle in chronic obstructive pulmonary disease and in asthma

Only a small number of studies investigating the in vitro pharmacologic properties of airway smooth muscle in asthma and well-characterized COPD have been performed. Further detailed studies on well-defined patient groups are required. The majority of available evidence would suggest that once airway smooth muscle is removed from its in vivo milieu, it loses the characteristics of hyperresponsiveness. This would explain why there are no clear differences in the pharmacologic responsiveness of tissue from patients with asthma or COPD and those with no obstructive disease. Future in vitro studies should be directed towards reproducing the in vivo environment. this would entail the establishment of a chronic inflammatory condition created by the continuous presence of neural and humoral factors.

A refractory type asthmatic whose symptoms markedly improved by midaglizole

We present a patient with refractory intrinsic asthma who showed a good response to both a single oral dose and a 4-week period of administration of the selective alpha-2 adrenoceptor antagonist, midaglizole. After the single dose, bronchodilation was immediately observed. With continuous administration, the peak expiratory flow rate (PEFR) was increased and the total daily intake of aerosol was decreased in a dose-dependent fashion. These results suggest that the addition of midaglizole to the usual antiasthmatic agents can be of value in the management of refractory asthma.

Alpha 1-adrenoceptor function and autoradiographic distribution in human asthmatic lung

1. The autoradiographic distribution of alpha 1-adrenoceptors was investigated in non-diseased and asthmatic human lung by use of [3H]-prazosin (H-PZ). To validate binding and autoradiographic methods, H-PZ binding was also measured in rat heart. 2. Significant levels of specific H-PZ binding were detected in sections of rat heart. This binding was associated with a single class of non-interacting sites of high affinity (dissociation constant, Kd = 1.17 +/- 0.26 nM). The maximum binding capacity (Bmax) was 59.5 +/- 4.5 fmol mg-1 protein. 3. In sharp contrast, very low levels of specific H-PZ binding were found in both human nondiseased and asthmatic bronchus, although a high level of binding of [125I]-iodocyanopindolol (I-CYP, 50 pM) to beta-adrenoceptors was detected in these airways. Furthermore, very low levels of autoradiographic grains representing specific H-PZ binding were found in all airway structures in human non-diseased or asthmatic lung parenchyma. 4. Consistent with these data, the alpha-adrenoceptor agonist phenylephrine failed to induce significant increases in tone in bronchi isolated from either non-diseased or asthmatic human lung. Results indicate that asthma does not involve significant increases in airway alpha 1-adrenoceptor function.

Endotracheal diazepam: absorption and pulmonary pathologic effects

We conducted a study to evaluate the absorption of endotracheally administered diazepam and the pulmonary pathologic changes induced by its administration. Six cats received diazepam and five cats received saline endotracheally. Serial blood gases and serum diazepam levels were drawn at intervals for 90 minutes after the administration of diazepam. The cats were sacrificed after two days and their lungs were examined by a pathologist. Mean diazepam levels reached a peak two minutes after the administration of diazepam and remained elevated above therapeutic levels for 90 minutes. There was no significant change in pH, PO2, or PCO2 for either group. Histologic examination of the lungs showed a significantly increased incidence of pneumonitis in the diazepam group as compared to the saline group. This study demonstrates that although diazepam is well absorbed when administered endotracheally, it has adverse effects on the lungs that may preclude endotracheal use in the currently available commercial form.

Inhibition of methoxamine-induced bronchoconstriction by ipratropium bromide and disodium cromoglycate in asthmatic subjects

We compared the effects of pretreatment with saline, ipratropium bromide, and disodium cromoglycate (DSCG) on bronchoconstriction induced by methoxamine--an alpha-adrenoceptor agonist, in asthmatic subjects. All 12 patients bronchoconstricted in response to methoxamine after saline. The PD20 (the dose of methoxamine causing a 20% fall in forced expiratory volume in 1 s [FEV1]) ranged from 0.3-18 mumol. Ipratropium bromide (200 micrograms administered by aerosol) significantly inhibited (P less than 0.05) the response to methoxamine in all patients without producing significant changes in the mean baseline lung function. The mean PD20 for methoxamine after saline was 6.8 mumol and 95% confidence limits (CL) were 3.6, 12.7 mumol. The mean PD20 for methoxamine after ipratropium bromide was 35.4 (95% CL 28.8, 43.6) mumol. DSCG also produced significant (P less than 0.05) shifts to the right in the methoxamine dose response curves, but did not affect resting airway calibre as measured by the FEV1. The mean PD20 for methoxamine increased from 3.3 mumol (95% CL 1.1, 10.0 mumol) after saline to 25.1 mumol (95% CL 14.1, 44.6) after DSCG pretreatment. These findings suggest that alpha-adrenoceptors in the airways of asthmatic subjects may be located at sites other than smooth muscle--possibly on mast cells but more likely on nerve endings and/or parasympathetic ganglia.