Introduction to monoamines Imidazoleamines (part II)

Published Jan. 8, 2021, 8:24 p.m. by Admin

This introductory article is the 2nd of three articles related to monoamines. It is highly recommended that you first read the article before this one, Introduction to monoamines Indolamines (part I)

Imidazoleamines (part II)


Where: Synthesized mostly in the brain and kidneys, used as neurotransmitter and hormone.

Histamine is a neurotransmitter that we humans have a love hate relationship with. It plays a role in over 23 different physiological functions, including the invocation of gastric acid secretion in our stomachs, contributing to allergic reactions, and playing an important role in many of immune responses. The chemical properties of histamine allow it to play a more diverse role within the body, properties such as coulombic (carry a charge), conformationality, and flexibility. Within the stomach histamine acts as a neurotransmitter and stimulates parietal cells to secrete gastric acid. Once stimulated the parietal cells uptake carbon dioxide and water from the blood in order to produce carbonic acid and secrete it into the stomach. During certain types of infections when a sensitized immune cells such as mast cells or basophils encounter a pathogen they will release histamine and other inflammatory chemicals to induce vasodilation. This allows other immune cells and resources from the blood stream to seep into the area of infection giving your immune system a massive advantage. However this is also where histamine sometimes works against us, during an allergic reaction the immune system overreacts to more or less harmless materials such as nuts or pollen. During allergies immune cells induce inflammation via histamine in much the same way which can often lead to swelling or even anaphylaxis. Histamine also impacts the nasal mucous membrane which is why many people that are allergic develop symptoms such as watery eyes, runny nose, sneezing, etc... This is due to the increased vascular permeability induced by histamine.

Typically histamine is released from granules within mast cells, antihistamines work by binding to histamine receptors thereby blocking histamine from binding to it's designated protein receptor. Humans have 4 main types of histamine receptors H1, H2, H3, and H4. When histamine binds to H1 and H2, various effects are possible depending on cell type and tissue location. Note that H3 and H4 are more complex and require an in depth understanding of neurology and immunology respectively, therefore they will not be covered thoroughly within this article.


H1 and H2 receptor binding: (tissues that contain both receptors):




Other fascinating functions of histamine are it's involvement in sleep-wake regulation, sex, arousal, and possibly even the mechanisms related to how memories are forgotten. Additionally I also think it's noteworthy that histamine has also been found in relatively high concentrations in certain animal venoms and insect stings.

Continuation Introduction to monoamines Catecholamines (part III)...