Mucus secretion by tracheas of ferret and dog.

Mucus secretion, stimulated by nerve excitation or drugs, was measured from the ferret trachea in vitro by two methods: from the whole trachea, and compared with the volume of submucosal glands estimated from histological sections; and from mounted segments of trachea, by displacement of tantalum dust applied to the epithelium and compared with changes in tissue volume estimated by probing the epithelial surface between hillocks. Maximal secretion rates (2-3 microliters X min-1 X cm-2) with tracheal segments were 5-6 times greater per unit area than those with the whole trachea. During secretion the tissue shrank by a volume close to that of the secretion. Similar experiments with the hillock method and dog trachea in vivo gave variable results. Although the ferret submucosal glands can secrete 0.7-5.4 times their volume per minute, any change in tracheal resistance to airflow would be rather small.