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Background: In vivo, the airways are constantly subjected to oscillatory strain (due to tidal breathing during spontaneous respiration) and (in the event of mechanical ventilation) positive pressure. This exposure is especially problematic for the cartilage-free bronchial tree. The effects of cyclic stretching (other than high-force stretching) have not been extensively characterized. Hence, the objective of the present study was to investigate the functional and transcriptional response of human bronchi to repetitive mechanical stress caused by low-frequency, low-force cyclic stretching., Methods: After preparation and equilibration in an organ bath, human bronchial rings from 66 thoracic surgery patients were stretched in 1-min cycles of elongation and relaxation over a 60-min period. For each segment, the maximal tension corresponded to 80% of the reference contraction (the response to 3 mM acetylcholine). The impact of cyclic stretching (relative to non-stretched controls) was examined by performing functional assessments (epithelium removal and incubation with sodium channel agonists/antagonists or inhibitors of intracellular pathways), biochemical assays of the organ bath fluid (for detecting the release of pro-inflammatory cytokines), and RT-PCR assays of RNA isolated from tissue samples., Results: The application of low-force cyclic stretching to human bronchial rings for 60 min resulted in an immediate, significant increase in bronchial basal tone, relative to non-cyclic stretching (4.24 ± 0.16 g vs. 3.28 ± 0.12 g, respectively; p < 0.001). This cyclic stimulus also increased the affinity for acetylcholine (-log EC50: 5.67 ± 0.07 vs. 5.32 ± 0.07, respectively; p p < 0.001). Removal of airway epithelium and pretreatment with the Rho-kinase inhibitor Y27632 and inward-rectifier K+ or L-type Ca 2+ channel inhibitors significantly modified the basal tone response. Exposure to L-NAME had opposing effects in all cases. Pro-inflammatory pathways were not involved in the response; cyclic stretching up-regulated the early mRNA expression of MMP9 only, and was not associated with changes in organ bath levels of pro-inflammatory mediators., Conclusion: Low-frequency, low-force cyclic stretching of whole human bronchi induced a myogenic response rather than activation of the pro-inflammatory signaling pathways mediated by mechanotransduction.

The role of extracellular acidosis in inflammatory airway diseases is not well known. One consequence of tissue acidification is the stimulation of sensory nerves via the polymodal H(+)-gated transmembrane channels ASICs and TRPV1 receptor. The present study investigated the effect of acidosis on airway basal tone and responsiveness in the guinea pig. Acidosis (pH 6.8, 10 min, 37 degrees C) significantly decreased the basal tone of tracheal rings (p<0.01 vs. paired control). Moreover, pH fall raised the maximal contraction of tracheal rings to acetylcholine (p<0.05 vs. paired control). The pH-induced relaxation of airway basal tone was inhibited by pretreatments with ASIC1a or ASIC3/ASIC2a inhibitors (0.5 mM ibuprofen, 0.1 mM gadolinium), nitric oxide synthase inhibitor (1 mM L-NAME), and guanylate cyclase inhibitor (1 microM ODQ). In contrast, the pH-induced relaxation of airway basal tone was not modified by epithelium removal or pretreatments with a TRPV1 antagonist (1 microM capsazepine), a combination of NK(1,2,3) receptor antagonists (0.1 microM each), a blocker of voltage-sensitive Na(+) channels (1 microM tetrodotoxin), a cyclooxygenase inhibitor with no activity on ASICs (1 microM indomethacin) or ASIC3 and ASIC3/ASIC2b inhibitors (10 nM diclofenac, 1 microM aspirin). Furthermore, acid-induced hyperresponsiveness to acetylcholine was inhibited by epithelium removal, capsazepine, NK(1,2,3) receptor antagonists, tetrodotoxin, amiloride, ibuprofen and diclofenac. In summary, the initial pH-induced airway relaxation seems to be independent of sensory nerves, suggesting a regulation of airway basal tone mediated by smooth muscle ASICs. Conversely, the pH-induced hyperresponsiveness involves sensory nerves-dependent ASICs and TRPV1, and an unknown epithelial component in response to acidosis.

We investigated whether fenoterol was able to enhance contractile responsiveness to neurokinin A (NKA) on the guinea-pig isolated trachea. We then studied the effects of two inhibitors of nuclear factor kappa B (NFkappaB), gliotoxin and pyrrolidine dithiocarbamate, and of the tachykinin NK(1), NK(2) and NK(3) receptor antagonists, SR 140333, SR 48968 and SR 142801 and determined whether tachykinin receptor gene expression was up-regulated in the trachea after exposure to fenoterol. Fenoterol (0.1 microM, 15 h, 21 degrees C) induced an increased contractile response to NKA (mean of difference in maximal tension between control and fenoterol +/- S.E.M; +0.47 +/- 0.14 g, n = 26, P < 0.01). This hyperresponsiveness was strongly reduced by co-incubation with gliotoxin (0.1 microg/ml) or pyrrolidine dithiocarbamate (0.1 mM) and abolished by SR 140333 (0.1 microM) and SR 142801 (0.1 microM). SR 48968 (0.1 microM) diminished the tracheal contractility to NKA but failed to reduce the hyperreactivity induced by fenoterol. Tachykinin NK(1) receptor (NK(1)R), NK(2) receptor (NK(2)R) and NK(3) receptor (NK(3)R) gene expression was analyzed by semiquantitative RT-PCR. Compared to control tissues, NK(1)R and NK(2)R mRNA expression was increased by about 1.6-fold and 1.4-fold, respectively, in tissues treated with fenoterol. We were unable to detect the presence of NK(3)R mRNA in the guinea-pig trachea. In conclusion, fenoterol induces tracheal hyperresponsiveness to NKA and an up-regulation of NK(1)R and NK(2)R gene expression. The hyperresponsiveness implicates the NFkappaB pathway and is abolished by tachykinin NK(1) (SR 140333) and NK(3) (SR 142801) receptor antagonists.

Background and Purpose: Marijuana smoking is widespread in many countries, and the use of smoked synthetic cannabinoids is increasing. Smoking a marijuana joint leads to bronchodilation in both healthy subjects and asthmatics. The effects of Δ(9) -tetrahydrocannabinol and synthetic cannabinoids on human bronchus reactivity have not previously been investigated. Here, we sought to assess the effects of natural and synthetic cannabinoids on cholinergic bronchial contraction.Experimental Approach: Human bronchi isolated from 88 patients were suspended in an organ bath and contracted by electrical field stimulation (EFS) in the presence of the phytocannabinoid Δ(9) -tetrahydrocannabinol, the endogenous 2-arachidonoylglycerol, the synthetic dual CB1 and CB2 receptor agonists WIN55,212-2 and CP55,940, the synthetic, CB2 -receptor-selective agonist JWH-133 or the selective GPR55 agonist O-1602. The receptors involved in the response were characterized by using selective CB1 and CB2 receptor antagonists (SR141716 and SR144528 respectively).Key Results: Δ(9) -tetrahydrocannabinol, WIN55,212-2 and CP55,940 induced concentration-dependent inhibition of cholinergic contractions, with maximum inhibitions of 39, 76 and 77% respectively. JWH-133 only had an effect at high concentrations. 2-Arachidonoylglycerol and O-1602 were devoid of any effect. Only CB1 receptors were involved in the response because the effects of cannabinoids were antagonized by SR141716, but not by SR144528. The cannabinoids did not alter basal tone or contractions induced by exogenous Ach.Conclusions and Implications: Activation of prejunctional CB1 receptors mediates the inhibition of EFS-evoked cholinergic contraction in human bronchus. This mechanism may explain the acute bronchodilation produced by marijuana smoking. [ABSTRACT FROM AUTHOR]

Background and Purpose Marijuana smoking is widespread in many countries, and the use of smoked synthetic cannabinoids is increasing. Smoking a marijuana joint leads to bronchodilation in both healthy subjects and asthmatics. The effects of Δ9-tetrahydrocannabinol and synthetic cannabinoids on human bronchus reactivity have not previously been investigated. Here, we sought to assess the effects of natural and synthetic cannabinoids on cholinergic bronchial contraction. Experimental Approach Human bronchi isolated from 88 patients were suspended in an organ bath and contracted by electrical field stimulation ( EFS) in the presence of the phytocannabinoid Δ9-tetrahydrocannabinol, the endogenous 2-arachidonoylglycerol, the synthetic dual CB1 and CB2 receptor agonists WIN55,212-2 and CP55,940, the synthetic, CB2-receptor-selective agonist JWH-133 or the selective GPR55 agonist O-1602. The receptors involved in the response were characterized by using selective CB1 and CB2 receptor antagonists ( SR141716 and SR144528 respectively). Key Results Δ9-tetrahydrocannabinol, WIN55,212-2 and CP55,940 induced concentration-dependent inhibition of cholinergic contractions, with maximum inhibitions of 39, 76 and 77% respectively. JWH-133 only had an effect at high concentrations. 2-Arachidonoylglycerol and O-1602 were devoid of any effect. Only CB1 receptors were involved in the response because the effects of cannabinoids were antagonized by SR141716, but not by SR144528. The cannabinoids did not alter basal tone or contractions induced by exogenous Ach. Conclusions and Implications Activation of prejunctional CB1 receptors mediates the inhibition of EFS-evoked cholinergic contraction in human bronchus. This mechanism may explain the acute bronchodilation produced by marijuana smoking. [ABSTRACT FROM AUTHOR]