The effects of formoterol on plasma exudation produced by a localized acute inflammatory response to bradykinin in the tracheal mucosa of rats in vivo

Beta-adrenergic stimulation contributes to maintenance of endothelial barrier functions under baseline conditions

OBJECTIVES

cAMP signaling within the endothelium is known to reduce paracellular permeability and to protect against loss of barrier functions under various pathological conditions. Because activation of β-adrenergic receptors elevates cellular cAMP, we tested whether β-adrenergic receptor signaling contributes to the maintenance of baseline endothelial barrier properties.

METHODS

We compared hydraulic conductivity of rat postcapillary venules in vivo with resistance measurements and with reorganization of endothelial adherens junctions in cultured microvascular endothelial cells downstream of β-adrenergic receptor-mediated changes of cAMP levels.

RESULTS

Inhibition of β-adrenergic receptors by propranolol increased hydraulic conductivity, reduced both cAMP levels and TER of microvascular endothelial cell monolayers and induced fragmentation of VE-cadherin staining. In contrast, activation by epinephrine both increased cAMP levels and TER and resulted in linearized VE-cadherin distribution, however this was not sufficient to block barrier-destabilization by propranolol. Similarly, PDE inhibition did not prevent propranolol-induced TER reduction and VE-cadherin reorganization whereas increased cAMP formation by AC activation enhanced endothelial barrier functions under baseline conditions and under conditions of propranolol treatment.

CONCLUSIONS

Our results indicate that generation of cAMP mediated by activation of β-adrenergic receptor signaling contributes to the maintenance of endothelial barrier properties under baseline conditions.

Effects of topical formoterol alone and in combination with budesonide in a pollen season model of allergic rhinitis

BACKGROUND

beta(2)-Agonists may exert mast cell stabilizing and anti-plasma exudation effects. While available data suggest no or only marginal effects of beta(2)-agonists on symptoms of allergic rhinitis, little is known about whether these drugs may add to the efficacy of anti-rhinitis drugs.

OBJECTIVE

To examine effects of a beta(2)-agonist, alone and in combination with an intranasal glucocorticosteroid, on symptoms and signs of allergic rhinitis.

METHODS

Patients were examined in a pollen season model. Budesonide 64 microg, alone and in combination with formoterol 9 microg, as well as formoterol 9 microg alone was given in a placebo-controlled and crossover design. After 7 days of treatment, the patients received allergen challenges for 7 days. Symptoms and nasal peak inspiratory flow (PIF) were recorded. Nasal lavages with and without histamine were carried out at the end of each challenge series. These lavages were analysed for tryptase, eosinophil cationic protein (ECP), and alpha(2)-macroglobulin as indices of mast cell activity, eosinophil activity, and plasma exudation, respectively.

RESULTS

Budesonide reduced symptoms of allergic rhinitis and improved nasal PIF in the morning, in the evening as well as post allergen challenge. Formoterol alone did not affect symptoms or nasal PIF and did not affect the efficacy of budesonide. Tryptase, ECP, and alpha(2)-macroglobulin were significantly reduced by budesonide. Formoterol alone did not affect these indices and did not affect the anti-inflammatory effect of budesonide.

CONCLUSION

The present dose of formoterol does not affect symptoms and inflammatory signs of allergic rhinitis and does not add to the efficacy of topical budesonide.

Current issues with beta2-adrenoceptor agonists: pharmacology and molecular and cellular mechanisms

Beta2-adrenoceptors are widely, almost ubiquitously, expressed. Activation of these receptors on bronchial smooth muscle by short- and long-acting beta2-adrenoceptor agonists causes bronchodilation. Here, the beta2-adrenoceptor is linked by the G protein, Gs, to adenylyl cyclase, which increases cyclic adenosine monophosphate (cAMP), thus activating protein kinase A, which affects calcium levels and reduces the efficiency of myosin light-chain kinase, causing relaxation. Activation also entrains numerous acute and longer term downregulation responses affecting the number, location, and net efficiency of signaling of the receptor. Synthetic beta2-agonists are all "partial agonists," incompletely able to optimally stimulate cAMP signal transduction. However, compared with some cells (such as mast cells) involved in exercise- induced asthma induction, airway smooth muscle is privileged in that transduction efficiency is intrinsically high and the tissue is very resistant to complete downregulation. Glucocorticosteroids have broadly beneficial interactions with beta2-adrenoceptors. Researchers have recently discovered that the beta2-adrenoceptor may function as a homodimer and that it can form heterodimers with both the beta1- and beta3-adrenoceptors, and possibly other receptors. This further complicates interpretation of the effect of beta2-adrenoceptor polymorphisms, but it is unknown whether this occurs in humans in vivo. Researchers have known for some time that strong contraction involving receptors coupled to the Gq G protein (e.g., cholinergic and leukotriene receptors via negative biochemical crosstalk), virus infection (via uncoupling), and inflammation (via kinases) can impair relaxation. Most recently, researchers have discovered that the beta2-adrenoceptor can also send potentially adverse signals after "atypical coupling" to Gq rather than Gs. The clinical implications of these uncouplings, crosstalk, and atypical coupling possibilities are not well-understood.

Species differences in bradykinin receptor-mediated responses of the airways

1. Bradykinin (BK) is a nine amino acid peptide (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) formed from the plasma precursor kininogen during inflammation and tissue injury. The actions of BK are mediated by G protein-coupled cell surface receptors, designated B1 and B2. 2. BK has a plethora of effects in the airways including bronchoconstriction, bronchodilation, stimulation of cholinergic and sensory nerves, mucus secretion, cough and oedema resulting from promotion of microvascular leakage. These airway effects are mediated in the main by the B2 receptor subtype. 3. BK acts mainly indirectly, primarily through airway nerve activation, but also by the release of prostanoids, thromboxanes and nitric oxide (NO). 4. Airway responses to BK have been studied in detail in guinea-pigs, mice, sheep and rats. This review describes the effects of BK in these species and draws comparison with its effects in normal humans and patients with respiratory diseases. 5. Despite its many and varied effects in the airways of animals and man, the exact contribution of BK to airways disease remains unclear.

Sodium cromoglycate on plasma protein exudation to topically-applied substance P in the tracheal airways of rats or guinea-pigs in vivo

Sodium cromoglycate (SCG) was examined against substance P(SP)-induced plasma protein exudation in the trachea of anaesthetized rats and guinea-pigs in vivo to determine whether SCG is a tachykinin receptor antagonist in the airways. A segment of trachea was prepared in situ for continuous perfusion with normal saline. Plasma-derived protein in the perfusion fluid (airway lumen) was increased after topical application of SP (1 microM, 5 min contact). In rats, the SP response was not attenuated by iv SCG but was inhibited (29%) by topical SCG under certain experimental conditions and using a high concentration of SCG (500 microM, 5 min contact, 30 min before SP and with SP). The NK(1)receptor antagonist, RP 67 580 (67 microM) abolished the SP response in rats. Sodium cromoglycate did not inhibit the SP response in guinea-pigs (same protocol as in rats). Thus, SCG attenuates plasma protein exudation (and presumably microvascular leak) induced by SP in rat tracheal airways but, if SCG is a tachykinin receptor (NK(1)) antagonist, it not only lacks potency but is species-selective, i.e. more effective in rats than in guinea-pigs.

Effects of formoterol on histamine induced plasma exudation in induced sputum from normal subjects

BACKGROUND

A number of studies have shown that beta 2 agonists, including formoterol, inhibit plasma exudation induced by the inflammatory stimulus in animal airways. Whether clinical doses of beta 2 agonists inhibit plasma exudation in human bronchial airways is unknown.

METHODS

In order to explore the microvascular permeability and its potential inhibition by beta 2 agonists in human bronchial airways a dual induction method was developed: plasma exudation induced by histamine inhalation followed by sputum induction by hypertonic saline (4.5%) inhalation. Sixteen healthy subjects received formoterol (18 micrograms) in a placebo controlled, double blind, crossover study. Sputum was induced on five occasions: once at baseline and four times after histamine challenge (30 minutes and eight hours after both formoterol and placebo treatments). Sputum levels of alpha 2-macroglobulin were determined to indicate microvascular-epithelial exudation of bulk plasma.

RESULTS

Histamine induced plasma exudation 30 minutes after placebo was considerably greater than at baseline (median difference 11.3 micrograms/ml (95% confidence interval 0.9 to 90.0)). At 30 minutes after formoterol the effect of histamine was reduced by 5.1 (0.9 to 61.9) micrograms/ml compared with placebo. At eight hours histamine produced less exudation and inhibition by formoterol was not demonstrated.

CONCLUSION

This study shows for the first time an anti-exudative effect of a beta 2 agonist in healthy human bronchial airways. Through its physical and biological effects, plasma exudation is of multipotential pathogenic importance in asthma. If the present findings translate to disease conditions, it suggests that an anti-exudative effect may contribute to the anti-asthmatic activity of formoterol.