Ion transport and regulation of respiratory tract fluid output in dogs

To investigate the regulation of respiratory tract fluid output (RTFO), we collected the RTFO in an anesthetized canine model after a series of pharmacological interventions (inhibition of Na+-K+-ATPase or Na+-K+-2Cl(-) cotransporter, 250 mul) and physiological challenges (ionic and/or osmotic perturbation in airway lumen, 250 mul). Whereas 250 mul of aerosolized 0.9% saline caused a transient increase in RTFO, a 250-mul bumetanide-induced increase in RTFO was evident for 18 min and a 250-mul acetylstrophanthidin-induced increase in RTFO persisted for at least 30 min. Dry air ventilation decreased the responses of RTFO to the saline (sham) and acetylysophanthidin intervention but not the bumetanide intervention. Delivery of 250 mosmol/kgH(2)O ion-free mannitol (250 mul) caused marked increases in RTFO that were little affected by the administration of acetylstrophanthidin or bumetanide 30 min before these challenges. A 250-mul 550 mosmol/kgH(2)O ion-free mannitol challenge caused a more marked and prolonged increase in RTFO. Thus aerosol delivery of a low dose of a cardiac glycoside or a near-isosmotic, ion-free, impermeant osmolyte solution may be therapeutically useful by increasing the clearance of secretions from the tracheobronchial airways.