The airway epithelial lining in guinea pigs is intact promptly after the mucosal crossing of a large amount of plasma exudate.

In the present study of anaesthetized guinea pigs, we have confirmed by chemical analyses that 10 min after topical mucosal provocation with capsaicin 0.4 nmol of platelet-activating factor 8 nmol plasma macromolecular tracers (FITC-dextran, molecular weight 156 kD, previously injected intravenously) have been significantly exuded into airway tissue and lumen. We have also examined the airway mucosa and the mucosal surface material using fluorescence, light, and electron microscopy. Thus we have demonstrated by histological techniques that promptly after the induction of large exudative responses plasma macromolecules are abundant in the lumen as well as in the lamina propria. Furthermore, the exudate is seen on the surface of a mucosa that has an intact epithelial lining. These observations are evidence in favour of the possibility that plasma exudation into the lumen is a first-line defense mechanism of the normal airway mucosa.