Neural control of airway submucosal gland secretion

Airway submucosal glands occupy a substantial volume of the large conducting airways and are regulated by vagal muscarinic nerves, alpha- and beta-adrenergic nerves, and nonadrenergic noncholinergic nerves. Vagal nerves modulate various reflexes that increase gland secretion by stimulating release of granules from mucous and serous cells. Stimulated secretions are unaltered from baseline in biochemical and viscoelastic properties. Beta-adrenergic stimulation releases secretions containing relatively little fluid, high concentrations of protein and sulfur, low concentrations of lysozyme and higher viscosity and lower elasticity, and selectively depletes mucous cells. Alpha-adrenergic stimulation causes high fluid flows with low protein and sulfur concentrations, high lysozyme concentrations and low apparent viscosity, and selectively depletes granules from serous cells. Nonadrenergic noncholinergic nerves also stimulate mucin secretion, probably by releasing vasoactive intestinal peptide (VIP).