Epithelial modulation of tracheal smooth muscle response to antigenic stimulation.

The role of the epithelium has been studied in the contractile responses of rat trachea. The different modulations observed are discussed in respect to vagal components of the epithelial layer. Responses of rat trachea to immunologic stimulation are shown to be dependent on the presence of the epithelium, which prolongs the relaxation stage without affecting the contractions. This prolongation is abolished by neonatal capsaicin pretreatment, whereas substance P induces a significantly greater relaxation of serotonin-precontracted intact than deepithelialized trachea. Serotonin concentration-response curves are shifted to the right in intact preparations, which is partly reversed by neonatal capsaicin pretreatment, but a hyporeactivity of the tissue exists. A relaxing factor released by the epithelium is hypothesized, possibly dependent on substance P-ergic innervation. Muscarinic cholinergic innervation slightly modulates the contractions but not the relaxations in antigen-induced responses, independently on the presence of the epithelial layer. 4-Aminopyridine induces epithelium-dependent potentiations of contractions to antigen and to serotonin, which involves acetylcholine at one step of the reaction cascade. Epithelial-dependent contracting and relaxing factors are thus suggested in rat trachea.