Histamine, a useful transmitter, which is in the nervous system and immune system and plays a central role in innate and acquired immunity in allergy and inflammation, closely associated with mast cell functions.1 British scientists Henry and Laidlaw first described properties of histamine for imidazolethylamine, which indicates an amine occurring in tissues. It is an organic nitrogenous compound involved in local immune responses and regulating physiological function in the gut and acting as a neurotransmitter for the uterus. It is also involved in the inflammatory response and has a main role as a mediator of pruritus. It is produced by basophils and by mast cells found in nearby connective tissues. It is a hydrophilic vasoactive amine, which released into synapses in the central nervous system. Histamine has two basic centers. Histamine is normally protonated to a singly charged cation, most because of the aliphatic amino group (having a pKa around 9.4). Histamine has a special chemical structure, including the base, obtained as a mineral oil mull, melts at 83–84 °C. Which are easily dissolved in water or ethanol. The nitrogen farthest away from the side chain is the 'tele' nitrogen and is denoted by a lowercase tau sign. The nitrogen closest to the side chain is the 'pros' nitrogen and is denoted by the pi sign. The position of the nitrogen with the hydrogen on it determines how the tautomer is named. If the nitrogen with the hydrogen is in the tele position, then histamine is in the tele-tautomer form. The tele-tautomer is preferred in solution. This structure make the histamine a monoamine neurotransmitter and also make so many sense in the effect on the nervous system. Most of them generated in granules in mast cells and white blood cell, it has an important roles in the body, such as causing vasodilation and a fall in the blood pressure2, effects on nasal mucous membrane, sleep-wake regulation, gastric acid release, multiple sclerosis and protective effects. As recent research of RE Brown3 demonstrated that neuronal histamine system was a danger response system. Which means many central nervous system functions, such as arousal, anxiety, activation of the sympathetic nervous system, the stress-related release of hormones from the pituitary and of central aminergic neurotransmitters, antinociception, water retention and suppression of eating are all involved in the histamine system. As a transmitter in the nervous system and a signaling molecule in the gut, skin and immune system. Histamine are effect on the brain (such as sensory systems, anxiety, aversion, pleasure, cognition, learning and memory). The main receptors are H1 and H2 receptors of histamine. Also, H3 receptors act as inhibitory auto- and heteroreceptors. What’s more, there are other receptors, like H4, ionotropic receptors including NMDA. With the research of histamine, more and more antihistamine drug were found to protect human from disease. Antihistamine H1 receptor drug can greatly improve sleep-wake cycle, body temperature, anaphylactic reaction and so on. Antihistamine H2 receptor drug protect human from stomach disease, which like cimetidine is widely used in the clinical.
1 “Histamine in the Nervous System”, HELMUT L. HAAS, OLGA A. SERGEEVA, AND OLIVER SELBACH, Physiol Rev 88: 1183–1241, 2008;doi:10.1152/physrev.00043.2007.
2 "The physiological action of beta-iminazolylethylamine.". Dale, HH; Laidlaw, PP the Journal of Physiology. 41 (5): 318–44, 1910. doi:10.1113/jphysiol.1910.sp001406.