[The effect of bronchial epithelium on bronchial contractility].

Removal of the epithelium increases the sensitivity of mammalian airway smooth muscle to several bronchoactive agents. An epithelium derived relaxing factor (EpDRF) of unknown identity has been postulated to modulate smooth muscle tone in the airways. Rings or segments of porcine third order bronchi, from some of which the epithelium had been removed mechanically, were mounted in organ baths for isometric tension recording. Removal of the epithelium affected bronchial reactivity. Metacholine produced concentration-dependent contractions of porcine bronchi. In the absence of epithelium the concentration response curve was shifted to the left (p less than 0.01). The effect of epithelium removal was not inhibited by diclofenac (100 microM), propranolol (5 microM), the inhibitor of endothelium-derived relaxing factor gossypol (10 microM). These observations suggest that the epithelium of porcine bronchi relaxes the tone of the subjacent smooth muscle. The EpDRF probably responsible for this effect is neither a cyclooxygenase product nor a stimulator of soluble guanylate cyclase.