Hyperosmolar solutions probably induce secretion through a direct action on secretory cells or by release of mediators that secondarily trigger receptor-mediated secretion. Because all central neural connections are severed in the excised ferret trachea, this secretagogue effect could not be due to central reflexes. Although secretion might have been induced by epithelial damage after osmotic challenge, there was no gross morphologic damage to the airway epithelium at the level of light microscopy when comparing KHS to saline solution-treated groups at 3.69 g/dL or 10.69 g/dL. This is consistent with reports that there was no visible injury to the epithelial or endothelial airway barriers after inhalation of 3% saline solution, and consistent with the observation that the proteinase inhibitors studied did not affect saline solution-induced mucin secretion. in detail
Clinical studies show that hypertonic saline solution or mannitol inhalation increases MCC in both healthy and asthmatic subjects, apparently peaking in the first 10 to 15 min with little, if any, residual effect after 1 h.>. Although inhaled hyperosmolar agents can increase ciliary beat frequency (CBF), it is unlikely that this produces a clinically important effect. Hyperosmolar saline solution has been reported to increase, decrease, or have no effect on CBF. A very high concentration saline aerosol (3.4 mol/L, 19.9 g/dL) increased CBF in the canine airway. An increase in CBF was also observed with a 200 to 400 mOsm (0.58 to 1.17 g/dL) of saline solution in the mucus-depleted bovine trachea, but this was not dose dependent even though the MCC increased in a saline solution dose-dependent man-ner. A change of airway surface fluid osmolarity was reported to have no affect on CBF in the human airway. Finally, it has been reported that hypertonic salt solution decreases the CBF of chicken embryo cilia.