Nasal histamine release following hyperosmolar and allergen challenge.

Allergic rhinitis is characterised by symptoms of sneezing, itching of the nose with watery secretions, and nasal obstruction. We have previously shown that patients can have the diagnosis of allergic rhinitis confirmed by nasal provocation tests and assessment of nasal inspiratory peak flow (NIPF) after specific allergen or hyperosmolar challenge. We now show that histamine is released into the nasal lavage fluid in response to such challenges. Saline lavage alone results in detectable histamine levels in the order of 5 ng/ml, but in the presence of allergen (HDM) there is a significant increase in histamine release in atopics but not in control subjects. With hyperosmolar challenge, atopics showed a biphasic response in that histamine release was increased with 1.8% and 3.6% saline but returned to baseline with 5.4% and 7.2% saline, then showing a further increase with 9.0% saline. This raises the possibility of two populations of responsive mast cells. Hyperosmolar challenge leads to symptoms of nasal itch and sneezing as well as histamine release in atopics but not in controls. This suggests that hyperosmolar challenge can be used as a simple diagnostic test for allergic rhinitis and may provide a model for nasal hyper-reactivity.

Nasal response to allergen and hyperosmolar challenge.

Rhinitis causes both clinical and social discomfort to patients, and in clinical practice is often underdiagnosed. We have examined a simple method for the assessment of a positive nasal provocation test to help in the diagnosis of rhinitis. In patients with histories suggestive of house dust mite (HDM) sensitivity and positive skin-prick tests or specific IgE to Dermatophagoides pteronyssinus, there was a fall in nasal inspiratory peak flow (NIPF) following nasal challenge with allergen. This was not seen in control subjects or in pollen-sensitive patients when challenged with house dust mite. Frequency of sneezing and degree of rhinorrhoea increased in these patients following challenge, and based on these findings we propose a simplified scoring system for the diagnosis of allergic rhinitis. We examined non-specific nasal reactivity using hyperosmolar solutions as a challenge system and found that allergic subjects responded with a fall in NIPF, although the clinical response was not identical to that seen with allergen. Control subjects did not respond to hyperosmolar challenge.