Effects of capsaicin desensitization on nasal mucosal secretion in guinea pigs in vivo.

Capsaicin-sensitive mechanisms may contribute to histamine's effects on guinea pig nasal mucosal secretion in vivo. Histamine nasal provocations were performed, secretions were collected, and the following variables were measured: total protein (marker of all secretory processes), alkaline phosphatase (marker of glandular secretion), and albumin (marker of vascular permeability, epithelial permeability, and glandular transport). By challenging only one nostril (ipsilateral), the contralateral responses to these challenges were examined and the nature of "nasonasal" reflexes was determined. Histamine increased albumin and alkaline phosphatase concentrations in lavage fluid on the ipsilateral and contralateral sides. The alkaline phosphatase secretion was reduced by atropine. Capsaicin induced dose-dependent albumin exudation. To determine the roles of capsaicin-sensitive sensory nerves, one nostril was desensitized by topical application of capsaicin to one nostril in increasing doses daily for 5 wk. This led to 1) ablation of all secretory responses to capsaicin, 2) ablation of histamine-induced alkaline phosphatase and total protein secretion, 3) blunted histamine-induced albumin exudation on the desensitized side, and 4) ablation of histamine-induced contralateral reflex-mediated protein secretion. These results indicate that capsaicin stimulates vascular responses, probably by stimulating nociceptive nerve axon responses. Histamine induces vascular responses and albumin exudation by both capsaicin-sensitive sensory neuron axon responses and direct effects on vessels. Histamine stimulates glandular secretion through a capsaicin-sensitive afferent/cholinergic efferent reflex.