Eicosanoids are potent biological effectors
Eicosanoids are fatty acids derivatives with a variety of extremely potent hormonelike actions on various tissues of vertebrate animals. Unlike hormones, they are not transported between tissues in the blood, but they act in the tissue in which they are produced. Thi family of compounds is known to be involved in reproductive function; in the inflammation, fever and pain associated with injury or disease; in the formation of blood clots and blood pressure; in gastric acid secretion; and in a variety of other processes important in human health and disease. More roles for the eicosanoids doubtless remain to be discovered.
Eicosanoids are all derived from the 20-carbon polynsatured fatty acid arachidonic acid, 20:4(Δ5,8,11,14), from which they take their general name (Greek eikos, twenty). There are three classes of eicosanoids: prostaglandins, thromboxanes, and leukotrienes. Various eicosanoids are produced in different cell types by different synthetic pathways, and have different target cells and biological actions.
The prostaglandins (PG) all contain a five-membered ring of carbon atoms originally part of the chain of arachidonic acid. They derive their name from the tissue where they where first recognized (the prostate gland). Two groups were originally derived: PGE, for ether-soluble, and PGF, for phosphate buffer-soluble ( fosfat in Swedish). Each contains numerous subtypes, named PGE1, PGE2, etc,. Prostaglandins are now known to act in many tissues by regulating the synthesis of intracellular messanger molecule 3'-5'-cyclic AMP (cAMP). Because cAMP mediates the action of many hormones, the prostaglandins affect a wide range of cellular and tissue functions. Some prostaglandins stimulate contraction of the smooth muscle of the uterus during labor or menstruations. Others affect blood flow to specific organs, the wake-sleep cycle, and the responsiveness of certain tissues to hormones such epinephrine and glucagon. Prostaglandins in a third group elevate body temperature (producing fever) and cause inflammation, resulting in pain.
The thromboxanes, first isolated from blood platelets (also known as thrombocytes), have a six-membered ring containing a ring containing an ether. They are produced by platelets and act in formation of blood clots and the reduction of blood flow to the site of a clot.
Leukotrienes, found first in leukocytes, contain three conjugated double bonds. They are powerful biological signals; for example, they induce contraction of the muscle lining the airways to the lung. Overproduction of leukotrienes causes asthmatic attacks. The strong contraction of the smooth muscles of the lung that occurs during anaphylactic shock is part of the potentially fatal allergic reaction in individuals hypersensitive to bee stings, penicillin, or various other agents.
Prostaglandin E2 effect
Details of PG synthesis