Effects of platelet-activating factor on vascular permeability and granulocyte recruitment in the rat trachea

Platelet-activating factor (PAF) is a phospholipid mediator known to produce several features of airway inflammation. We examined the effects of intravenous PAF on vascular permeability and granulocyte recruitment in the rat trachea. To assess vascular permeability, anesthetized rats were given injections of Evans blue dye (30 mg/kg, iv) and PAF (1-10 micrograms/kg, iv), and then their tracheas were removed and assayed spectrophotometrically for dye content. We found that a PAF dosage of 6 micrograms/kg increased the tracheal dye content 7-fold compared to controls. The amount of extravasated dye in the tracheas was significantly increased 1 min after PAF injection, was maximal at 5 min, and had returned to control levels by 10 min. To assess granulocyte recruitment, anesthetized rats were given an injection of PAF (6 micrograms/kg, iv), and then their tracheas were removed and stained to reveal myeloperoxidase-containing neutrophils and eosinophils. We found that the number of neutrophils in the tracheal mucosa was increased 7-fold from controls 5 min after PAF injection, but was not significantly increased 6 h later. The number of eosinophils in the tracheal mucosa was not significantly increased from controls at any time after PAF injection. We conclude that intravenous PAF causes a rapid but transient increase in vascular permeability in the rat trachea, and that intravenous PAF also causes a rapid but transient recruitment of neutrophils into the tracheal mucosa without a similar effect on eosinophils.