Histamine-induced increase in isometric tension of smooth muscle is mediated by local vagus nerve in human bronchus

Lippia alnifolia essential oil induces relaxation on Guinea-pig trachea by multiple pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Lippia alnifolia Mart. & Schauer, known as "alecrim-do-mato", "alecrim-de-vaqueiro" and "pedrécio", is used in folk medicine as antiseptic and to treat diseases that affect respiratory system, like bronchitis and asthma.

AIM OF THE STUDY

The aim of this work was to investigate the spasmolytic activity and relaxant mechanism of the Lippia alnifolia essential oil (EOLA) on isolated guinea-pig trachea and to correlate with its use in folk medicine.

MATERIALS AND METHODS

Leaves from L. alnifolia were collected in Pico das Almas, Chapada Diamantina, situated in the city of Rio de Contas, Bahia, Brazil. EOLA was extracted by hydrodistillation, analyzed by GC/FID and GC/MS and the volatile constituents were identified. Spasmolytic activity was assayed in isolated guinea-pig trachea pre-contracted with carbachol 1 μM or histamine 10 μM. Relaxant mechanism of EOLA was determined comparing concentration-response curves in the presence or absence of different blockers.

RESULTS

Chemical analysis revealed the presence of carvone (60 ± 0.8%) as major constituent. EOLA (1-243 μg/mL) relaxed isolated guinea-pig trachea pre-contracted with carbachol 1 μM [EC₅₀ = 53.36 (44.75-63.51) μg/mL] or histamine 10 μM [EC₅₀ = 5.42 (4.42-6.65) μg/mL]. The pre-incubation of 4-aminopyridine in histamine-induced contractions did not alter significantly the relaxant effect of EOLA. However, the presence of cesium chloride, glibenclamide, tetraethylammonium, propranolol, indomethacin, dexamethasone, hexamethonium, atropine, L-NAME, methylene blue or ODQ reduced EOLA relaxant effect. EOLA 18 μg/mL pre-incubation in calcium-free medium reduced histamine-evoked contractions, but did not alter histamine contractions in the presence of nifedipine.

CONCLUSIONS

Lippia alnifolia essential oil has spasmolytic activity on isolated guinea-pig trachea and its mechanism of action possibly involves the activation of multiple signal transduction pathways, which culminate in potassium channels activation and cytosolic calcium reduction.

Pharmacological characterisation of the interaction between glycopyrronium bromide and indacaterol fumarate in human isolated bronchi, small airways and bronchial epithelial cells

BACKGROUND

Nowadays, there is a considerable gap in knowledge concerning the mechanism(s) by which long-acting β2-agonists (LABAs) and long-acting muscarinic antagonists (LAMAs) interact to induce bronchodilation. This study aimed to characterise the pharmacological interaction between glycopyrronium bromide and indacaterol fumarate and to identify the mechanism(s) leading to the bronchorelaxant effect of this interaction.

METHODS

The effects of glycopyrronium plus indacaterol on the contractile tone of medium and small human isolated bronchi were evaluated, and acetylcholine and cAMP concentrations were quantified. The interaction was assessed by Bliss Independence approach.

RESULTS

Glycopyrronium plus indacaterol synergistically inhibited the bronchial tone (medium bronchi, +32.51 % ± 7.86 %; small bronchi, +28.46 % ± 5.35 %; P < 0.05 vs. additive effect). The maximal effect was reached 140 min post-administration. A significant (P < 0.05) synergistic effect was observed during 9 h post-administration on the cholinergic tone, but not on the histaminergic contractility. Co-administration of glycopyrronium and indacaterol reduced the release of acetylcholine from the epithelium but not from bronchi, and enhanced cAMP levels in bronchi and epithelial cells (P < 0.05 vs. control), an effect that was inhibited by the selective KCa(++) channel blocker iberiotoxin. The role of cAMP-dependent pathway was confirmed by the synergistic effect elicited by the adenylate cyclase activator forskolin on glycopyrronium (P < 0.05 vs. additive effect), but not on indacaterol (P > 0.05 vs. additive effect), with regard of the bronchial relaxant response and cAMP increase.

CONCLUSIONS

Glycopyrronium/indacaterol co-administration leads to a synergistic improvement of bronchodilation by increasing cAMP concentrations in both airway smooth muscle and bronchial epithelium, and by decreasing acetylcholine release from the epithelium.

The anti-asthma herbal medicine ASHMI acutely inhibits airway smooth muscle contraction via prostaglandin E2 activation of EP2/EP4 receptors

Our previous studies have shown that the anti-asthma traditional Chinese medicine herbal formula ASHMI (anti-asthma simplified herbal medicine intervention) inhibits acetylcholine-induced contractions of tracheal rings from ovalbumin-sensitized and naive mice in a β-adrenoceptor-independent manner. We sought to determine whether acute in vivo ASHMI administration inhibits airway hyperreactivity (AHR) in a murine model of allergic asthma and acetylcholine-induced tracheal ring constriction ex vivo and to elucidate the cellular mechanisms underlying these effects. Ovalbumin-sensitized mice received a single oral ASHMI dose 2 h before intravenous acetylcholine challenge. AHR was determined by invasive airway measurements. Myography was used to determine the effects of ASHMI on acetylcholine-induced constriction of tracheal rings from asthmatic mice with or without epithelial denudation. The effect of cyclooxygenase inhibition and EP2/EP4 receptor blockade on ASHMI attenuation of acetylcholine contractions was evaluated. Tracheal cAMP and PGE2 levels were measured by ELISA. A single acute oral dose of ASHMI dramatically reduced AHR in response to acetylcholine provocation in ovalbumin-sensitized mice (P < 0.001). In ex vivo experiments, ASHMI significantly and dose-dependently reduced tracheal ring constriction to acetylcholine (P < 0.05-0.001), which was epithelium independent and associated with elevated cAMP levels. This effect was abrogated by cyclooxygenase inhibition or EP2/EP4 receptor blockade. ASHMI also inhibited contraction to high K(+) (P < 0.001). ASHMI increased tracheal ring PGE2 release in response to acetylcholine or high K(+) (P < 0.05 for both). ASHMI produced direct and acute inhibition of AHR in vivo and blocked acetylcholine-induced tracheal ring constriction via the EP2/EP4 receptor pathway, identifying the mechanism by which ASHMI is an orally active bronchoprotective agent.

Low-dose salbutamol suppresses airway responsiveness to histamine but not methacholine in subjects with asthma

BACKGROUND

Airway hyperresponsiveness is a cardinal feature of asthma. Although the modulation of cholinergic neuroeffector transmission may play a role in airway responsiveness, in vivo evidence remains scarce. It is well known that histamine causes bronchoconstriction partly via vagal reflex, whereas methacholine does not. To investigate the significance of modulating neuroeffector transmission, we compared the effect of low-dose salbutamol-a β2-adrenoceptor agonist-on airway responsiveness to histamine with that to methacholine.

METHODS

We enrolled 12 subjects with stable asthma. After screening confirmed that inhalation of low-dose salbutamol (1μg) did not change their basic pulmonary function, subjects underwent measurement of airway responsiveness to inhaled histamine and methacholine with or without pretreatment with low-dose salbutamol, in a randomized, crossover fashion. Airway responsiveness was measured by an astograph by which respiratory conductance (Grs) was assessed by the forced oscillation method during continuous inhalation of histamine or methacholine in stepwise incremental concentrations. Airway responsiveness was calculated as the cumulative dose of bronchoconstrictors that induced a decrease of 35% in Grs.

RESULTS

Inhalation of 1μg of salbutamol significantly attenuated airway responsiveness to histamine but not methacholine. This selective attenuation was observed irrespective of disease severity or phenotype, namely atopy or non-atopy.

CONCLUSION

Low-dose salbutamol suppresses airway responsiveness to histamine but not methacholine in subjects with asthma. The present study may provide a novel insight into the bronchoprotective mechanism of β2-adorenoceptor agonist in clinical settings.

Low voltage vagal nerve stimulation reduces bronchoconstriction in guinea pigs through catecholamine release

OBJECTIVE

  Electrical stimulation of the vagus nerve at relatively high voltages (e.g., >10 V) can induce bronchoconstriction. However, low voltage (≤2 V) vagus nerve stimulation (VNS) can attenuate histamine-invoked bronchoconstriction. Here, we identify the mechanism for this inhibition.

METHODS

  In urethanea-nesthetized guinea pigs, bipolar electrodes were attached to both vagus nerves and changes in pulmonary inflation pressure were recorded in response to i.v. histamine and during VNS. The attenuation of the histamine response by low-voltage VNS was then examined in the presence of pharmacologic inhibitors or nerve ligation.

RESULTS

  Low-voltage VNS attenuated histamine-induced bronchoconstriction (4.4 ± 0.3 vs. 3.2 ± 0.2 cm H(2) O, p < 0.01) and remained effective following administration of a nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester, and after sympathetic nerve depletion with guanethidine, but not after the β-adrenoceptor antagonist propranolol. Nerve ligation caudal to the electrodes did not block the inhibition but cephalic nerve ligation did. Low-voltage VNS increased circulating epinephrine and norepinephrine without but not with cephalic nerve ligation.

CONCLUSION

  These results indicate that low-voltage VNS attenuates histamine-induced bronchoconstriction via activation of afferent nerves, resulting in a systemic increase in catecholamines likely arising from the adrenal medulla.

Effect of Inhaled Histamine on Airway Epithelial Cell Swelling in Ozone-Exposed Guinea Pigs

BACKGROUND

It has been reported that histamine stimulates ion channels on airway epithelial cells and induces changes in osmolarity and the ion composition of the periciliary field of airway epithelia.

OBJECTIVE

To investigate the effect of inhaled histamine on epithelial cell swelling, we studied the role of airway epithelial cells under histamine inhalation challenge in an animal model of airway inflammation using ozone exposure.

METHOD

After exposure to 3.0 ppm ozone for 2 h, guinea pigs were anesthetized and tracheostomized, and then, lung resistance (R(L)) was measured. Histamine inhalation challenge and histological examination were performed.

RESULT

The values of R(L) before histamine inhalation in the control group and the ozone-exposed group were 0.26 +/- 0.11 and 0.45 +/- 0.34 cm H(2)O/s, respectively. R(L) increased significantly after histamine inhalation both in the control and the ozone-exposed groups. The threshold of histamine (PC(200)) in the ozone-exposed group was significantly lower than that in the control group. A significant swelling of the epithelial cells after histamine inhalation was observed both in the control and the ozone-exposed groups, with a greater increase in the ozone-exposed group compared with the control group. However, no change in wall thickness was observed in the histamine/antihistamine or the ozone/histamine/antihistamine group.

CONCLUSION

Our results suggest the possibility that the airway epithelial cell swelling plays a role in the increase in R(L) after histamine inhalation, especially in the presence of airway inflammation.

Rapid inhibitory effect of glucocorticoids on airway smooth muscle contractions in guinea pigs

The common disease asthma is characterized by the obstruction, inflammation and increased sensitivity of the airways. Glucocorticoids (GCs) are one of the most potent anti-inflammatory agents available for treating allergic disease. In this study, we report that the GC budesonide (BUD) can rapidly inhibit the histamine-induced contractions of airway smooth muscle in a process mediated by non-genomic mechanisms. The tracheas of albino Hartley guinea pigs were used. We measured the effects of BUD on the increased isometric tension of trachea segment rings and the shrinking of single airway smooth muscle cells (ASMCs) induced by histamine. With the application of each reagent, the changes in the isometric tension of the segment rings upon maximum contraction and at four time points were recorded. We found that BUD significantly suppressed the increase in isometric tension induced by histamine in guinea pigs within 15 min. We also observed that BUD can reduce the histamine-induced shrinking of single ASMCs in an even shorter time. Mifepristone (RU486) and actidione did not depress the inhibitory effect of BUD. The results preclude action via genomic-mediated responses that usually take several hours to occur. We conclude therefore that GCs have a rapid non-genomic inhibitory effect on guinea pig airway smooth muscle contractions, and provide a new way to investigate this non-genomic mechanism. Further study can provide theoretical evidence for the clinical application of GCs in asthma and other allergic diseases.

The Non-neuronal cholinergic system: an emerging drug target in the airways

The non-neuronal cholinergic system is widely expressed in human airways. Choline acetyltransferase (ChAT) and/or acetylcholine are demonstrated in more or less all epithelial surface cells (goblet cells, ciliated cells, basal cells), submucosal glands and airway smooth muscle fibres. Acetylcholine is also demonstrated in the effector cells of the immune system (lymphocytes, macrophages, mast cells). Epithelial, endothelial and immune cells express nicotinic and muscarinic receptors. Thus the cytomolecule acetylcholine can contribute to the regulation of basic cell functions via auto-/paracrine mechanisms (proliferation, differentiation, ciliary activity, secretion of water, ions and mucus, organization of the cytoskeleton, cell-cell contact). Acetylcholine also modulates immune functions (release of cytokines; proliferation, activation and inhibition of immune cells). Preliminary experimental evidence suggests that mucosal inflammation may be associated with raised acetylcholine levels, impairing cell and organ homeostasis. It should be considered that anti-muscarinic drugs which are applied for the treatment of chronic airway diseases antagonize the effect of both neuronal and non-neuronal acetylcholine. Non-neuronal acetylcholine, however, is still active, possibly directly within the cell cytosol and also via nicotinic receptors localized on various non-neuronal cells. It is an essential task to clarify the pathophysiological role of the non-neuronal cholinergic system in more detail to develop new drugs which can target the synthesis, release, inactivation and cellular activity of non-neuronal acetylcholine.