The name ‘prostaglandin’ was coined after it was found that semen contracted the smooth muscle of the uterus. It was considered that the substance in the semen responsible for this effect came from the prostate gland. There are many different prostaglandins and related substances, and the nomenclature is complex. All are derived from a membrane lipid called arachidonic acid, which has 20 carbon atoms and 4 double bonds. The substances derived from this acid are more properly called eicosanoids (eicosa-20; enoic-double bonds). There are three main groups of eicosanoids — prostaglandins, thromboxanes, and leukotrienes. The first two, prostaglandins and thromboxanes, are sometimes called prostanoids.
Arachidonic acid is part of some membrane phospholipids. Phospholipase enzymes liberate the arachidonic acid from its linkage to the phospholipid. (Anti-inflammatory steroids, such as cortisol, prevent this liberation and hence relieve inflammation.) The free arachidonic acid then undergoes a complex series of biochemical transformations, to produce the prostanoids (PGE2, PGD2, PGF2a, PGI2 (prostacyclin)) and the thromboxanes (TXA2 and others). The cyclo-oxygenase enzymes are involved at this stage, and it is these that are inhibited by NSAIDs, including aspirin.
Bergstrom and Samuelsson, in Sweden, worked out the complex chemistry of arachidonic acid and its products, and Vane and colleagues, in England, showed that aspirin inhibited the cyclo-oxygenase system. Together they shared a Nobel Prize in 1982 for their work on the prostanoids. There is an alternative pathway for metabolism of arachidonic acid using lipoxygenase enzymes, rather than cyclo-oxygenase; the end products are a family of leukotrienes (B4, C4, D4, E4, and F4).
The whole eicosanoid cascade is set off by a great variety of different types of stimuli. Three examples are these: following the action of thrombin on platelets during the clotting process; by the actions of kinins released on injury; and following the reaction of antibodies with antigens on the surface of cells, as in an allergic response.
Not all eicosanoids are produced in all tissues. For example, prostacyclin is produced predominantly from the cells lining blood vessels: this causes vasodilatation and inhibits platelet aggregation. On the other hand, the thromboxane TXA2 is formed in platelets and causes vasoconstriction and platelet aggregation. Because the enzymes used in the production of prostacyclin and TXA2 are different, a small daily dose of aspirin is able to prevent TXA2 formation without affecting prostacyclin formation. This is therefore an effective way of preventing intravascular thrombosis, and thus reducing the risk of strokes and heart attacks. Many people now follow this simple routine. The prostanoid PGE2 is effective in inhibiting gastric secretion and stimulates mucus secretion in the stomach; it is also a mediator of fever. Many prostaglandins have bronchoconstrictor actions. Leukotrienes generally cause bronchoconstriction and vasodilatation (except for the coronary arteries, which are constricted); they are important mediators in all types of inflammation, and responsible for the slow, second, histamine-resistant phase of anaphylaxis.
Alan W. Cuthbert
See also allergy; aspirin; fever; inflammation.
"prostaglandins." The Oxford Companion to the Body. . Encyclopedia.com. (June 17, 2019). https://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/prostaglandins
"prostaglandins." The Oxford Companion to the Body. . Retrieved June 17, 2019 from Encyclopedia.com: https://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/prostaglandins
Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).
Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.
Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:
Modern Language Association
The Chicago Manual of Style
American Psychological Association
- Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
- In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.