Histamine

Histamine, a decarboxylation product of histidine, is a biochemical substance (C₅H₉N₃) involved in many physiological processes. Histamine functions as a neurotransmitter in the central nervous and has an important role in the immune system.

Histamine is released in almost all tissues of the body when the tissue becomes damaged or inflamed. Histamine is also released when allergic reactions occur. Most of the histamine released comes from mast cells in the damaged tissues and basophil granulocytes in the blood.

Histamine has a great vasodilator effect on the arterioles, which means the blood vessels widen. Aside from that, it also greatly increases capillary porosity, which allowes fluid and plasma proteins to leak into the tissues. A negative side-effect of these characteristics is that edema kan occur in many pathological conditions, as a direct result of the increased blood flow and porosity. These characteristics are most prominent when allergic reactions occur.