THE HUMAN NASAL RESPONSE TO CAPSAICIN

Airway sensory nerves play a role in reactions to inhaled allergens, irritants, and physical stimuli. Capsaicin, the pungent principle of hot peppers, stimulates a subcategory of sensory nerves. To study the consequences of selective activation of airway sensory nerves in the human nose, we administered capsaicin nasal challenges to eight volunteers (four normal subjects and four subjects with perennial allergic rhinitis). Capsaicin (20 mu mol/L), when sprayed into the nose, induced burning, rhinorrhea, and lacrimation. Capsaicin also induced a significant increase in total protein content of nasal lavage fluid after challenge compared with vehicle (increase from before challenge to 1 minute after challenge, 172 +/- 55 vs 46 +/- 29 mu g/ml, p < 0.001). In contrast to many animal studies, capsaicin did not increase vascular permeability in the airway, because albumin content of nasal lavage fluid was not increased (p = 0.86). On the other hand, lactoferrin, a marker of glandular secretion, was increased (p < 0.005). Repetitive capsaicin challenge every 10 minutes led to tachyphylaxis of symptoms, total protein secretion, and lactoferrin secretion. Compared with vehicle, unilateral capsaicin (6 mmol/L) disk challenge induced significant secretion both ipsilateral (21.3 +/- 4.2 vs 4.9 +/- 2.2 mg, p < 0.01) and contralateral (18.2 +/- 4.4 vs 7.4 +/- 1.9 mg, p < 0.04) to challenge. Thus we have shown that capsaicin challenge to the human nose leads to airway sensory nerve activation. Further, we have demonstrated that capsaicin stimulates a predominantly central neuronal response and that the induced secretory response is of glandular rather than vascular origin.