Immediate hypersensitivity reactions in the guinea-pig conjunctiva: studies with a second-generation leukotriene D4 receptor antagonist, MK-571

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Abstract
The role of leukotriene D4 (LTD4) as a mediator of immediate hypersensitivity reactions in the guinea-pig conjunctiva was examined using a potent, second-generation LTD4 receptor antagonist, MK-571 (also known as L-660,711). The microvascular permeability changes in the guinea-pig conjunctiva following challenge with either LTD4 or antigen were measured through accumulation of intravenously administered 99mtechnetium-labeled albumin. Topical application of MK-571 (up to 2 h pretreatment) significantly inhibited the conjunctival responses to LTD4 (ED50 of 18–60 ng/eye) but not to histamine. The responses to a single topical antigen challenge in ovalbumin-sensitized guinea pigs were significantly inhibited (44%) by topical treatment with MK-571, in contrast to the lack of effect previously observed with prototypic antagonists. The inhibitory effects of MK-571 did not involve an action on conversion of [3H]LTC4 to LTD4 and LTE4. Following a second antigen challenge (24 h after the first), MK-571 inhibited the resultant permeability changes by 78%. Specific histamine H1 and H2 antagonists similarly inhibited the responses to the first and second challenges (63 and 74%, respectively). The present study suggests that LTD4 is involved in conjunctival hypersensitivity reactions and that potent LTD4 receptor antagonists may be of therapeutic value in the treatment of allergic conjunctivitis.Key words: allergic conjunctivitis, leukotriene D4, leukotriene D4 antagonists, MK-571, vascular permeability changes.

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