The role of pain-mediating sensory nerves in histamine-induced inflammation of nasal mucosa.

Topical application of histamine on the nasal mucosa causes an inflammatory reaction with increased mucosal swelling and perfusion. In the nasal mucosa histamine receptors are found in the vascular epithelium and at free sensory nerve endings. The aim of this randomized double-blind placebo controlled study was to investigate if this inflammatory reaction to locally administered histamine was dependent upon the stimuli of pain-mediating sensory nerves, or if it mainly was the result of direct stimuli of the vascular epithelium. Eighteen healthy non-allergic subjects were treated with sprays of lidocaine or saline (placebo) in the nose, followed by challenge with histamine. Using a cross-over design the participants later returned and were allocated to the opposite treatment followed by histamine. Nasal congestion, and concentration, velocity and perfusion of erythrocytes were measured with rhinostereometry and laser Doppler flowmetry. Symptoms of blockage, discharge and itching were scored. When comparing the lidocaine group to the placebo group, we found no significant differences in the reaction to histamine concerning any of the measured parameters or subjective symptoms. In conclusion, our results suggest that the stimuli of pain-mediating sensory nerves do not significantly contribute to the inflammatory effect of histamine on human nasal mucosa.