The effect of platelet activating factor on nasal hypersensitivity.

Platelet activating factor (PAF) is known to have a wide range of biological activities. In the lower airways PAF has been suggested as the biochemical mediator partly responsible for the bronchial hyperreactivity which is a feature of asthma. In order to study whether PAF has a similar effect in the upper airways, we carried out a double blind, placebo-controlled cross-over study in twelve patients with strictly seasonal allergic rhinitis. The study was performed in pollen-free winter months. 26 micrograms PAF or placebo was sprayed into each nasal cavity 8 h and 1 h before a nasal allergen challenge. The nasal response to PAF and the allergen challenge that followed was monitored by repeated measurements of nasal expiratory peak flow rate and symptom scores. PAF induced only minor changes in nasal patency and nasal symptoms as compared to placebo. However, pretreatment with PAF induced an increase in responsiveness of the nasal vasculature to the allergen challenge that followed. This was registered as a small, but statistically significant increase in the symptom scores for nasal blockage, from 1.7 (0.3; SEM) after placebo pretreatment to 2.4 (0.36; SEM) after PAF (p less than 0.05). A similar trend was also noted for the measurements of nasal peak flow. The other response parameters, sneezes and secretion, remained identical. These results suggest that PAF may play a role in human nasal hyperreactivity, but it appears that PAF is not a major mediator involved in the induction of this phenomenon.