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 microl) and physiological challenges (ionic and/or osmotic perturbation in airway lumen, 250 microl). Whereas 250 microl of aerosolized 0.9% saline ca...