ROLES OF HYDRATION, SODIUM, AND CHLORIDE IN REGULATION OF CANINE MUCOCILIARY TRANSPORT-SYSTEM

To gain insight into the homeostatic mechanisms regulating airway ion/ water fluxes and mucociliary transport, the canine tracheobronchial ai rway fluid was perturbed by deposition of hypo-and hyperosmotic aeroso ls for >1 h. Tracheal ciliary beat frequency (CBF) was measured by usi ng heterodyne laser light scattering. Tracheal mucus velocity (TMV) an d bronchial mucociliary clearance (BMC) were measured by using radioae rosols and nuclear imaging. Respiratory tract fluid output (RTFO) was collected by using a secretion-collecting endotracheal tube. In six do gs, CBF increased during water deposition in the airways to 180 +/- 30 mg/min and RTFO increased from 2.2 +/- 0.5 to 18.3 +/- 1.6 mg/min, ac counting for <10% of the fluid deposition. TMV and BMC were unchanged. CBF, TMV, and BMC were markedly increased by inhalation of aerosolize d 3.4 M NaCl. Aerosolized 0.85 M NaCl, in contrast, decreased BMC. In this case, RTFO represented 24% of aerosol deposition. Aerosolized 0.8 5 M choline chloride and 0.85 M sodium gluconate enhanced BMC and TMV concurrent with a decrease in CBF. RTFO of sodium gluconate studies ex ceeded 50% of aerosol deposition. Thus the airways appear to have tran sepithelial compensatory mechanisms that reduce the impact of a modera te increases in NaCl and hydration load, but when these responses cann ot adequately respond because of the delivery of impermeable ions or v ery high tonicity, removal of the challenges are affected by a stimula tion of mucociliary transport.