IN-SITU VISUALIZATION OF BRONCHIAL SUBMUCOSAL GLANDS AND THEIR SECRETORY RESPONSE TO ACETYLCHOLINE

Airway submucosal glands secrete both macromolecules and liquid, yet t he mechanisms by which these substances are secreted are not well unde rstood. In this study, a video microscope was used to directly visuali ze the submucosal glands in isolated porcine distal bronchi and to obs erve their responses to acetylcholine (ACh), a glandular secretagogue. Submucosal glands were classified as either ''antral,'' ''linear,'' o r ''convoluted'' glands based on the morphology of their terminal coll ecting ducts. Because antral duct glands were most easily visualized, the response to ACh was studied in detail in this gland type. Within 5 -10 s after addition of 10 mu M ACh, the cross-sectional area of the g land duct openings to the airway surface increased severalfold but ret urned to pre-ACh dimensions within 1 min. Between 30 s and 10 min afte r ACh addition, spherical particles (1-10 mu m) entered the antral duc ts from distal acini and exited through the duct openings to the airwa y surface. Some of the particles were retained within the antral duct where they were kept in constant motion by the action of cilia present within the antral duct. The particles, which are likely to contain th e macromolecular secretory products of mucous and/or serous cells, mai ntained their spherical shape within the gland duct, suggesting that t he secretion product was membrane bound. To our knowledge, these studi es provide the first description of airway submucosal gland secretion as viewed in situ.