Vascular permeability in allergic conjunctivitis in mice lacking histamine H1 receptors

To clarify the role of histamine H1 receptors in allergic conjunctivitis, changes in vascular permeability of the conjunctiva were measured in histamine H1 receptor deficient mice. Wild-type mice showed a significant increase in vascular permeability of the conjunctiva induced by histamine. However, no such increase was found in histamine H1 receptor deficient mice. On the other hand, no differences were observed between wild-type and histamine H1 receptor deficient mice in response to serotonin. A significant increase in vascular permeability was observed in actively sensitized wild-type mice, whereas no increase was observed in histamine H1 receptor deficient mice. Similar findings were noted in passively sensitized animals. Histamine contents of the conjunctiva were significantly decreased by topical application of antigen in both wild-type and histamine H1 receptor deficient mice after active sensitization with antigen. These findings suggested that vascular permeability in the conjunctiva in allergic conjunctivitis is entirely regulated through histamine H1 receptor.