THE HUMAN NASAL RESPONSE TO CAPSAICIN

Airway sensory nerves play a role in reactions to inhaled allergens, i rritants, and physical stimuli. Capsaicin, the pungent principle of ho t peppers, stimulates a subcategory of sensory nerves. To study the co nsequences of selective activation of airway sensory nerves in the hum an nose, we administered capsaicin nasal challenges to eight volunteer s (four normal subjects and four subjects with perennial allergic rhin itis). Capsaicin (20 mu mol/L), when sprayed into the nose, induced bu rning, rhinorrhea, and lacrimation. Capsaicin also induced a significa nt increase in total protein content of nasal lavage fluid after chall enge compared with vehicle (increase from before challenge to 1 minute after challenge, 172 +/- 55 vs 46 +/- 29 mu g/ml, p < 0.001). In cont rast to many animal studies, capsaicin did not increase vascular perme ability in the airway, because albumin content of nasal lavage fluid w as not increased (p = 0.86). On the other hand, lactoferrin, a marker of glandular secretion, was increased (p < 0.005). Repetitive capsaici n challenge every 10 minutes led to tachyphylaxis of symptoms, total p rotein secretion, and lactoferrin secretion. Compared with vehicle, un ilateral capsaicin (6 mmol/L) disk challenge induced significant secre tion both ipsilateral (21.3 +/- 4.2 vs 4.9 +/- 2.2 mg, p < 0.01) and c ontralateral (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 c apsaicin stimulates a predominantly central neuronal response and that the induced secretory response is of glandular rather than vascular o rigin.