Localization of cAMP in dog and cat trachea: effects of beta-adrenergic agonists

Adenosine 3',5'-cyclic monophosphate (cAMP) is believed to mediate the transport of ions, water, and mucous glycoproteins in the respiratory tract. Because chemical measurements of total tissue levels of cAMP may not always reflect changes in specific cell types, we adapted standard immunocytochemical methods to examine the cellular localization of cAMP in dog and cat tracheae. The beta-adrenergic agonists terbutaline and isoproterenol increased immunoreactive cAMP in ciliated epithelial cells of dog and cat tracheae and in both serous and mucous gland cells of cat tracheae. Epithelial goblet cells did not respond to beta-adrenergic agonists in either species. This study provides information about the location of beta-receptors on individual cells in the trachea that is not available from chemical assays of either cAMP or beta-receptors in these tissues. Our results support the hypothesis that secretory functions in both serous and mucous submucosal gland cells and ciliated epithelial cells, but not goblet cells, may involve cyclic AMP-dependent mechanisms.