Characteristics of capillary permeability in nasal mucosa.

The transendothelial passage of horseradish peroxidase (HRP) and colloidal carbon and diffusion of HRP in pericapillary space, injected intravenously into rats, was studied at the light microscopic and ultrastructural level in the nasal mucosa. In the lamina propria of the mucosa in the middle third of the nasal septum of rats, the capillaries directly beneath the epithelium were mostly with fenestrae, while the capillaries around the nasal gland were without the fenestrae. The permeability of the capillaries in the lamina propria of the nasal mucosa was very high and some of the endothelial cells were wide open, like liver sinusoid, allowing free passage of carbon pasrticles. Marked transendothelial passage was also noted at ten seconds after HRP infusion through the capillaries without fenestrae located around the nasal gland. On the other hand, no extracapillary leakage of HRP was noted even at 150 seconds after its infusion in the capillaries without fenestrae located in the muscles. The permeability of small venules located in the lamina propria of nasal mucosa also was extremely high. The reasons for the greater permeation of HRP through capillaries of nasal mucosa are as follows. First, the endothelial cell junction was loose in the nasal mucosa and in some capillaries endothelium had holes like liver sinusoid. Second, interstitium surrounding the capillary was loose in nasal mucosa.