The effect of airway epithelium on smooth muscle contractility in bovine trachea

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Abstract
1 In bovine tracheal smooth muscle the presence of airway epithelium significantly reduced the sensitivity and maximum contractile response to histamine, 5-hydroxytryptamine (5-HT) or acetylcholine. 2 Muscle contraction induced by K+ and electrical field stimulation was of similar magnitude both in the presence or absence of adherent epithelium. 3 The effect of epithelium on smooth muscle contractility was unaffected by pretreatment with indomethacin (10−6 M) or mepacrine (5 × 10−5 M). 4 The relaxant response to isoprenaline was enhanced in the presence of epithelium, although this was significant only in the case of precontraction with 5-HT. 5 It is concluded that the bronchial epithelium may produce a relaxant factor which is not a cyclo-oxygenase or lipoxygenase product. The production of this factor may be reduced or lost following epithelial damage and this may be important in the pathogenesis of bronchial hyperresponsiveness in asthma.