Prostaglandin

A variety of hormone-like substances that participate in a wide range of body functions such as the contraction and relaxation of smooth muscle, the dilation and constriction of blood vessels, control of blood pressure, modulation of inflammation, and others. Prostaglandins are derived from a chemical called arachidonic acid. There are numerous naturally occurring prostaglandins in the body. Some drugs act as prostaglandin antagonists — they inhibit the action of prostaglandins.

* * *

Any of a class of physiologically active substances present in many tissues, with effects such as vasodilation, vasoconstriction, stimulation of intestinal or bronchial smooth muscle, uterine stimulation, and antagonism to hormones influencing lipid metabolism. Prostaglandins are prostanoic acid s with side chains of varying degrees of unsaturation and varying degrees of oxidation. Often abbreviated PGA, PGB, PGC, PGD, etc. with numeric subscripts, according to structure. [fr. genital fluids and accessory glands where discovered]

- p. E₁ SYN: alprostadil.

- p. E₂ SYN: dinoprostone.

- p. endoperoxide synthase a protein complex that catalyzes two steps in p. biosynthesis; the cyclooxygenase activity (which is inhibited by aspirin and indomethacin) converts arachidonate and 2O₂ to p. G₂; the hydroperoxidase activity uses glutathione to convert p. G₂ to p. H₂. SYN: cyclooxygenase.

- p. F_2α SYN: dinoprost.

- p. F_2α tromethamine SYN: dinoprost tromethamine.

* * *

pros·ta·glan·din .präs-tə-'glan-dən n any of various oxygenated unsaturated cyclic fatty acids of animals that are formed as cyclooxygenase metabolites esp. from unsaturated fatty acids (as arachidonic acid) composed of a chain of 20 carbon atoms and that perform a variety of hormonelike actions (as in controlling blood pressure or smooth muscle contraction)

* * *

n.

one of a group of hormone-like substances present in a wide variety of tissues and body fluids (including the uterus, brain, lungs, kidney, and semen). Prostaglandins have many actions; for example, they cause contraction of smooth muscle (including that of the uterus), dilation of blood vessels, and are mediators in the process of inflammation (aspirin and other NSAID act by blocking their production). They are also involved in the production of mucus in the stomach, which provides protection against acid gastric juice; use of NSAIDs reduces this effect and predisposes to peptic ulceration, the principal side-effect of these drugs. There are nine classes of prostaglandins (PGA-I), within which individual prostaglandins are denoted by numerals (e.g. PGE₁). Synthetic prostaglandins are used to induce labour or produce abortion (see dinoprostone, gemeprost), to treat peptic ulcers (see misoprostol), and in the treatment of newborn babies with congenital heart disease (see alprostadil) and of glaucoma (see latanoprost).

* * *

pros·ta·glan·din (pros″tə-glanґdin) [prostate gland + -in because they were originally thought to originate in the prostate] any of a group of components derived from unsaturated 20-carbon fatty acids, primarily arachidonic acid, via the cyclooxygenase pathway; they are potent mediators of numerous different physiologic processes. The abbreviation for prostaglandin is PG; specific compounds are designated by adding a letter to indicate the type of ring structure and a numerical subscript to indicate the number of double bonds in the hydrocarbon skeleton (e.g., PGE₂, etc.). Most naturally occurring prostaglandins have two double bonds and are synthesized from arachidonic acid (see illustration). The 1 series and 3 series are produced by the same pathway starting with fatty acids that have one fewer or one more double bond than arachidonic acid. The subscript α or β indicates the three-dimensional configuration of alcoholic groups attached to the ring structures (α denotes a substituent below the plane of the ring, β, above the plane). The naturally occurring PGFs all have the α configuration. Prostaglandins act in the cells in which they are synthesized and on surrounding cells, and their actions and effects vary with concentration, hormonal environment, and cell type.

Cyclooxygenase pathway of prostaglandin and thromboxane synthesis.