The effect of airflow on mucus secretion into the trachea of the cat

We have investigated the effects of the passage of air and of instillation of hyperosmolal solutions in a segment of trachea of the pentobarbitone-anaesthetized cat on the release of radiolabelled mucus glycoproteins (mucins) into that segment. Ambient air passed through the segment at 11 min-1 increased the output of both 35S- and 3H-labelled mucins. It also stimulated the output of mucins measured chemically. Passage of ambient air warmed to body temperature caused a similar effect on the output of radiolabelled mucins unless the air had also been saturated with water vapour at that temperature. Instillation of cold Krebs-Henseleit solution into the tracheal segment had no effect on the release of radiolabelled mucins. The action of warmed dry air persisted after extrinsic nerves (sympathetic and parasympathetic) to the trachea had been cut. Hyperosmolal solutions placed in the tracheal segment also increased the output of both 35S- and 3H-labelled mucins. We conclude that passage of ambient air through the trachea of the cat increases mucin output. This is probably by its drying action rather than by the mechanical disturbance from the flow or by cooling. The response might occur during eupnoea but is more likely to be important during hyperpnoea such as occurs during exercise. We discuss the relevance of the response to exercise-induced asthma.