Nasal reactions elicited by unilateral allergen challenge

Nasal reactions to unilateral allergen provocation were studied separately in both nasal cavities of 9 subjects with established seasonal allergic rhinitis. Three tests with the same allergen at the same concentration were performed in the same cavity at 48-h intervals. The parameters observed were clinical symptoms, changes in nasal airway resistance on rhinomanometry, and amount, weight and histamine content of the collected secretion. Nasal obstruction increased significantly on the provoked side but not contralaterally. Secretion increased symmetrically but the histamine content rose only on the provoked side. No priming effect was observed. The results are compatible with the view that the release of histamine has a 2-fold effect. Histamine directly caused vasodilatation of capacitance vessels and capillaries, which resulted in obstruction on the provoked side, and indirectly the histamine release led to stimulation of sensory nerve endings, which by triggering parasympathetic reflexes caused rhinorrhea in both nasal halves.