Respiratory epithelium inhibits bronchial smooth muscle tone

Abstract

The aim of the present study was to determine whether or not the respiratory epithelium can modulate the responsiveness of bronchial smooth muscle. Paired rings of canine bronchi (4-6 mm OD), in some of which the epithelium had been removed mechanically (by rubbing the luminal surface), were mounted in physiological saline solution, gassed with 95% O2-5% CO2, and maintained at 37 degrees C. The presence or absence of the epithelium was confirmed by histological examination. Removal of the epithelium increased the contractile responses evoked by acetylcholine, histamine, and 5-hydroxytryptamine. Transmural nerve stimulation evoked similar peak responses in the presence and absence of epithelium. In unrubbed preparations, the peak response was followed by a gradual decrease when the stimulation was continued. This decrease, which persisted in the presence of propranolol, was not observed in epithelium-denuded preparations. In bronchial rings contracted with acetylcholine, isoproterenol produced concentration-dependent relaxations which were significantly greater in rings with epithelium compared with denuded rings. These results suggest that respiratory epithelial cells may generate an inhibitory signal to decrease the responsiveness of bronchial smooth muscle to contractile agonists and augment the effectiveness of inhibitory stimuli.

Airway eosinophilic inflammation, epithelial damage, and bronchial hyperresponsiveness in patients with mild‐moderate, stable asthma

“…Besides a direct effect, eosinophils may enhance bronchial reactivity through epithelial damage which has been correlated to airway responsiveness (27). The epithelium may modulate airway responsiveness not only because it acts as a physical barrier to inhaled stimuli (30) but also because it may release relaxing factors (3 1, 32) and inactivate agonists (33).…”

The epithelium and the pharmacology of guinea‐pig tracheal tone in vitro

“…The concentration-response curve for isoprenaline was shifted about 2 fold to the left in epithelium- Taken together, the published effects of epithelium removal on the pharmacology of airway contractions seem confusing. The initial work by Flavahan et al (1985) in dog bronchi suggested that the response to electrical field stimulation, in particular the duration of the contraction, was increased by epithelium removal. However, later work by Barnes et al (1985) in bovine trachea, Holroyde (1986) and Thompson et al (1986) in cat and guinea-pig trachea, demonstrated no effect of epithelium on the response to electrical field stimulation.…”

“…It has had an impact on work with isolated airway preparations where the focus has been on a role for the epithelium in regulation of airway smooth muscle tone. Despite the fact that many of the accumulated observations are negative or contradictory, it has generally been maintained that airway epithelium importantly affects tracheobronchial smooth muscle reactivity (Barnes et al, 1985;Flavahan et al, 1985;Farmer et al, 1986;Finnen et al, 1986;Frossard & Muller, 1986;Goldie et al, 1986;Hay et al, 1986a,b;Holroyde, 1986;Reaburn et al, 1986a,b;Thompson et al, 1986;Tschirhart & Landry, 1986;Nijkamp & Folkerts, 1987). It is understandable that positive results have been searched for and related to the pathology and pharmacology of asthma.…”

Inhibition of airway smooth muscle tone by Chinese herbal medicines

“…First, airway epithelial cells can inhibit bronchoconstriction through a release of the inhibitory prostaglandins and epithelium-derived relaxing factor [10]. However, because mechanical removal of the epithelium did not alter the effects of TJ-17 and TJ-23, involvement of airway epithelial cells in the drug action seems unlikely.…”

“…To test whether the release of epithelium-derived relaxing factor is involved in the effects of TJ-17 and TJ-23 [10], the effects of the drug (100 mg . mL -1 ) on acetylcholine (1310 -5 M)-induced contractions between epithelium-intact tissues and the tissues with their epithelial layer removed were compared.…”