Inhibition of cigarette smoke-induced oedema in the nasal mucosa by capsaicin pretreatment and a substance P antagonist.

1. The effect of cigarette smoke on vascular permeability in the rat nasal mucosa was studied using the Evans blue extravasation method. Exposure to smoke from cigarettes induced a significant extravasation of Evans blue in the nasal mucosa of normal rats, suggesting an increased vascular permeability to plasma proteins. The oedema response was correlated to tar, nicotine and vapour phase components in the smoke. 2. The smoke-induced permeability effect was abolished in rats pretreated neonatally with capsaicin. Also, systemic or local pretratment with [D-Arg1, D-Pro2, D-Trp7,9, Leu11]Substance P, a substance P antagonist, inhibited the permeability response to cigarette smoke. 3. Insertion of a glass-fibre filter, which removes the particulate phase of the smoke (including nicotine), did not significantly reduce the permeability response. 4. The present findings suggest that the smoke-induced oedema in the rat nasal mucosa is not caused by nicotine but by vapour-phase irritants, which activate capsaicinsensitive C-fibre afferents. These neurons then release agents such as substance P or a related tachykinin which increase permeability to plasma proteins.