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Stimulation of beta-adrenergic receptors (beta-AR) on the tracheobronchial epithelium elicits a variety of cellular responses which affect the defense of the respiratory tract and which may alter the intensity of the inflammatory response in the airway. Beta-adrenergic agonists acting on the tracheobronchial epithelium affect salt and water exchange across the airway wall, mucus secretion and mucociliary clearance, and release of bronchoactive substances. Studies in a variety of cellular systems have demonstrated that the response to beta-adrenergic agonists is dynamic and may be altered by such agents as beta-agonists and phorbol esters. Furthermore, alterations in adrenergic responsiveness may play an important role in the clinical manifestations and treatment of airway diseases such as asthma. Surprisingly, little is known about the beta-AR receptors on tracheobronchial epithelial cells in man. Moreover, the regulation of the beta-AR receptor-coupled adenylyl cyclase system by beta-agonists and inflammatory mediators present in the airway (e.g. bradykinin, substance P, prostaglandin E2) remains undefined in these cells. This gap in our knowledge is of obvious C3 importance to our understanding of the pathogenesis of airway disease and its response to therapy.

The objectives of this proposal are to characterize the beta-AR-coupled adenylyl cyclase system in isolated tracheobronchial epithelial cells obtained from rabbits and humans. The beta-AR will initially be characterized with regard to density, subtype, coupling to the G protein (Gs) and to adenylyl cyclase . The subtype of the beta-AR in the human epithelial cells will be determined by the polymerase chain reaction. The effects of agents which raise intracellular cAMP levels (e.g. beta-agonists, forskolin, phosphodiesterase inhibitors) on the responsiveness of the adenylyl cyclase system will be assessed. The potential mechanisms involved in any altered regulation will be elucidated by determining receptor distribution, phosphorylation state and mRNA levels. Similar studies will be used to characterize the effects of phorbol esters and inflammatory mediators (e.g. bradykinin, substance P, prostaglandin E2) on the beta-AR-coupled adenylyl cyclase system in isolated epithelial cells. Finally, the effects of aerosolized allergens on this system will be assessed in ragweed-sensitized rabbits and in stable human asthmatics. These studies should help elucidate the mechanisms regulating the beta-AR-coupled adenylyl cyclase system in normal epithelial cells and in cells isolated from inflamed airways.
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