Pharmacologic modulation of vascular permeability in ocular allergy in the rat

Evans blue (EB) dye extravasation has been used as a reliable and objective parameter of the increased vascular permeability of an allergic conjunctivitis experimental rat model that closely mimics human ocular allergy. Five male Wistar rats, previously immunized (Group 1), had DL-dithiothreitol (DTT) applied topically to one eye 15 min prior to topical challenge with egg albumin (EA). The fellow eye (control) received phosphate buffered saline (PBS) 15 min prior to receiving EA. Immediately prior to challenge, the rats were injected intravenously with EB. After 30 min, the animals were killed and the dye extracted from the eyes. The intensity of EB extravasation was determined by spectrophotometry at 620 nm. EB extravasation was significantly higher in the eyes that received DTT than in those that received PBS. Groups 2, 3 and 4 of nonimmunized rats served as additional controls: Group 2 for DTT toxicity, Group 3 as a proof of the reaginic antibody mediation and Group 4 as a control of EB extravasation under normal conditions. Five additional groups of five rats each were immunized and both eyes of each rat received DTT 15 min before EA challenge. One eye of each rat received 0.1% dexamethasone sodium phosphate topically (Group 5), 0.1% pyrilamine maleate (Groups 6 and 7), and 2% disodium cromoglycate (DSCG) (Groups 8 and 9). The fellow eye received the solvent of each drug topically (control). In the eyes treated with antiallergic drugs, EB extravasation decreased 40% for dexamethasone, 44.1% and 10.4% for pyrilamine, and 51.4% and 51.2% for DSCG.