Differential effects of epithelium removal on the responsiveness of guinea-pig tracheal smooth muscle to bronchoconstrictors.

1 The influence of the epithelium on contractions produced by the peptidoleukotrienes, 5-hydroxytryptamine (5-HT) and the thromboxane mimetic, U-44069, was examined in trachea from control and ovalbumin-sensitized guinea-pigs. 2 In control tissues removal of the epithelium produced an approximately 2 to 4 fold leftward shift in leukotriene C4 (LTC4) and LTD4 concentration-response curves, but no effect on LTE4-induced contractions. Similar results were obtained in preparations from ovalbumin-sensitized animals. 3 Responses produced by 5-HT or U-44069 were similar in the presence and absence of the epithelium in control guinea-pigs. 4 Indomethacin produced contrasting effects on leukotriene-induced contractions in control guinea-pigs: an increase in sensitivity to LTC4 in the presence but not absence of the epithelium, no effect on LTD4-induced contractions and a decrease in sensitivity to LTE4 in both epithelium-containing and epithelium-free preparations. 5 These results indicate that there is selectivity in the effects of epithelium removal on agonist-induced contractions of the guinea-pig trachea. This provides further evidence for the modulatory influence of the epithelium on the reactivity of mammalian airway smooth muscle and supports the postulated existence of an epithelium-derived inhibitory factor. The observation that in intact trachea indomethacin mimics the effects of epithelium removal on LTC4-induced responses, suggests the involvement of a prostanoid(s) in this phenomenon.