Distribution, properties, and functional characteristics of three classes of histamine receptor.

It is clear from the preceding overview of histamine receptor pharmacology that research into the pharmacology of histamine receptors is at an exciting stage of development. The rapid advance of molecular biology should soon see the structural identification and cloning of all three of the major vertebrate histamine receptors. Further work will continue toward enhancing our understanding of the control by histamine of intracellular signaling via H1- and H2-receptors, and the rapid explosion of work on the H3-receptor should begin to unravel the mechanisms underlying its actions, perhaps via effects on ionic channels. The potential role of histamine as an intracellular second messenger raises exciting possibilities, as does the search for a histamine receptor analogous to the ligand-gated ion channel in the invertebrate nervous system.