Abstract
Histamine is considered a principle mediator of several physiological and pathological processes. It induces biological activities through differential expression of four types of histamine receptors (H1R, H2R, H3R and H4R). All the histamine receptors are the G protein-coupled receptor (GPCR) family, are expressed on several histamine responsive target tissues and cells, and suggest a potential role of histamine in cell proliferation, differentiation, hematopoiesis, embryonic development, regeneration, wound healing, aminergic neuron-transmission and several brain functions, secretion of pituitary hormones, regulation of gastrointestinal and circulatory functions, cardiovascular system, inflammatory reactions, immunomodulation, functioning of endocrine system and homeostasis. Since H4R has been discovered very recently and there is paucity of comprehensive literature covering new histamine receptors, their agonists/antagonists and role in various diseases. This has prompted a re-evaluation of the actions of histamine, suggesting a new potential for H4R-agonists/antagonists and a possible synergy between histamine receptors-agonists/antagonists in targeting various patho-physiological conditions. This chapter will highlight the biological and pharmacological characterization of histamine, histamine receptors, and their agonists/antagonists in various biomedical aspects.