Role of histamine in allergic conjunctivitis

Histamine remains the main mediator released by both specific allergic and non-specific mast cell activation. Histamine is the classic mediator of itc hing, flare and redness, The effects of histamine in allergic conjunctiviti s are mediated by H-1-receptor activation on blood vessels and nociceptive nerves. Histamine effects may be prolonged and exaggerated since a defect i n the histaminase enzymes has been recently demonstrated in VKC. The effect s of histamine on conjunctival tissues may be more complex than those manif ested by the simple symptom of itching. In fact, proinflammatory effects of histamine on conjunctival epithelial cells and fibroblasts have been demon strated. Preliminary results showed that the H-1 antagonist, emedastine, re duces significantly cytokine production from histamine-stimulated fibroblas ts.