Histamine and its receptors, including the recently discovered receptors (H3 and H4), novel
sources of histamine, and the place of histamine in mediator networks continue to be areas
of great interest. The 4 major subtypes of histamine receptors, H1 to H4, differ in their
location, second messengers, and histamine-binding characteristics. In addition, it would
appear that different histamine receptor agonists and antagonists bind to different portions of
the receptor complex. A fifth receptor subtype, the intracellular HIC, has only been defined …