noun, plural: prostaglandins
A group of eicosanoids, structurally characterized as 20-carbon unsaturated fatty acids with a five-carbon ring, and extremely potent mediator of a diverse group of physiological processes
Eicosanoid is the generic term to refer to the compounds derived from arachidonic acid or other polyunsaturated fatty acids of 20-carbon length. Some of the prominent eicosanoids include (1) eoxins, (2) leukotrienes, (3) lipoxins, (4) prostacyclin, (5) prostaglandins, (6) resolvins, and (7) thromboxanes.
Prostaglandin is an eicosanoid that is derived from unsaturated 20-carbon fatty acids, such as arachidonic acid, through the cyclooxygenase pathway. In particular, prostaglandin is produced from arachidonic acid by the action of cyclooxygenase that produces cyclic endoperoxides (PGG2 and PGH2) that can give rise to prostacyclin or thromboxanes as well as prostaglandins.
Its name is derived from prostate gland because it was thought of as the tissue producing prostaglandins as they were originally discovered in the semen. Later, it was found out that it was produced by the seminal vesicles and many other tissues.
There are several prostaglandins and they are designated by appending a letter, i.e. from A to I, to indicate the type of substituents found on the hydrocarbon skeleton. A subscript, e.g. 1, 2, 3…, is used to indicate the number of double bonds in the hydro-skeleton. Naturally-synthesized prostaglandins have two double bonds and are synthesized from arachidonic acid (5, 8, 11, 14 eicosatetraenoic acid). The 1- and 3-series are produced in the same pathway with fatty acids having one fewer double bond (8, 11, 14 eicosatrienoic acid or one more double bond (5, 8, 11, 14, 17 eicosapentaenoic acid) than arachidonic acid.
All of the prostaglandins act by binding to specific cell surface receptors causing an increase in the level of the intracellular second messenger cyclic AMP (and in some cases cyclic GMP also). The effect produced by the cyclic aMP increase depends on the specific cell type. In some cases there is also a positive feedback effect. Increased cyclic AMP increases prostaglandin synthesis leading to further increases in cyclic AMP.
Prostaglandins are extremely potent mediators of a diverse group of physiological processes. They are involved in the contraction of smooth muscle. They are also involved in the control of inflammation and body temperature. They have a variety of important roles in regulating cellular activities, especially in the inflammatory response where they may act as vasodilators in the vascular system, cause vasoconstriction or vasodilation together with bronchodilation in the lung and act as hyperalgesics.
Prostaglandins are rapidly degraded in the lungs and will not therefore persist in the circulation. Prostaglandin E2 (PGE2) acts on adenylate cyclase to enhance the production of cyclic AMP. Depending on the receptor it activates, it has various effects. For instance, PGE2 that binds with prostaglandin E2 receptor 1 (EP1) leads to gastrointestinal tract smooth muscle contraction whereas with prostaglandin E2 receptor 2 (EP2), it is involved in gastrointestinal tract smooth muscle relaxation. Other prominent types of prostaglandins naturally produced are prostaglandin D2 and F2α. Prostaglandin D2 (PGD2) is produced by mast cells and works chiefly by recruiting Th2 cells, eosinophils, and basophils. Prostaglandin F2α (PGF2α) is involved in uterus contraction and bronchoconstriction.
Prostaglandins, because of their hormone-like activity, are sometimes referred to as tissue hormones.