INDEPENDENT MODULATION OF HORSE AIRWAY SMOOTH-MUSCLE BY EPITHELIUM AND PROSTANOIDS

The effects of epithelial removal and cyclooxygenase inhibition on con tractions induced by exogenous acetylcholine (ACh) and electrical fiel d stimulation (EFS) were evaluated in horse tracheal strips and bronch ial rings. Epithelial removal potentiated the response to ACh but had no influence on the response to EFS. The effect of epithelial removal was not altered by pretreating the tissues with meclofenamate, a cyclo oxygenase inhibitor. In trachealis strips, meclofenamate augmented con tractions induced by EFS but not by ACh. In bronchial rings, meclofena mate augmented EFS-induced contraction to a greater extent than ACh-in duced contraction. These effects of meclofenamate were epithelium-inde pendent. We conclude that horse airway epithelium produces a relaxant factor that is not a prostanoid. Endogenous prostanoids originating fr om non-epithelial sites inhibit only cholinergic nerves in the trachea but both parasympathetic nerves and smooth muscle in the bronchi.