Abstract
Chemotaxis of guinea-pig eosinophils in vivo has been studied in the guinea-pig conjunctiva. Guinea-pig eosinophils were labelled with 111In oxine and injected i.v. into recipient animals. Circulating radioactivity remained constant over a period of 4 h but dropped transiently in response to a bolus injection (1 nmol) of platelet activating factor (PAF), suggesting that the 111In-labelled eosinophils had retained their responsiveness to PAF. Leukotriene D 4 (LTD 4, 1 nmol/eye) and PAF (10 nmol/eye), but not histamine (5 nmol/eye), induced a significant 2.5-fold increase in conjunctival radioactivity, a measure of eosinophil chemotaxis in vivo, after 17 h. Antigen challenge (250 μg/eye) in ovalbumin-sensitized animals produced larger responses (8-fold increases) at the same time point. A specific LTD 4 receptor antagonist MK-571 (10 μg/eye) completely inhibited in vivo chemotactic responses to LTD 4, and partially inhibited (54%) the responses to ovalbumin (observations subsequently confirmed by histological studies). As eosinophils may play an important role in allergic diseases, the results with MK-571 indicate that selective and potent LTD 4 receptor antagonists may provide a novel therapy for allergic conjunctivitis, rhinitis and asthma.
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