prostaglandin

(prŏs'təglăn`dən), any of a group of about a dozen compounds synthesized from fatty acids in mammals as well as in lower animals. Prostaglandins are highly potent substances that are not stored but are produced as needed by cell membranes in virtually every body tissue. Different prostaglandins have been found to raise or lower blood pressure and regulate smooth muscle activity and glandular secretion. One such substance, which stimulates contraction of the uterus, is used clinically to induce labor; another has been in experimental use as a birth control agent. Prostaglandins also control the substances involved in the transmission of nerve impulses, participate in the body's defenses against infection, and regulate the rate of metabolism in various tissues. Several prostaglandins have been shown to induce fever, possibly by participating in the temperature-regulating mechanisms in the hypothalamus; they also play a part in causing inflammation. The fact that aspirin and other nonsteroidal anti-inflammatory drugs have been shown to inhibit prostaglandin synthesis may account for their usefulness in reducing fever and inflammation. Many naturally occurring prostaglandins as well as many artificial forms have been synthesized in the laboratory.

Prostaglandin

in mammals, a hormone that has a broad spectrum of physiological action. Prostaglandins were discovered in human semen by the Swedish scientist U. Euler in 1936. Initially, they were thought to be secretions of the prostate gland (hence the name). They were obtained in a pure form in 1956–65 by Swedish and American scientists.

About 20 natural prostaglandins are known, including thick liquids and low-melting crystalline substances. All prostaglandins are unsaturated hydroxy fatty acids that have a skeleton of 20 carbon atoms. According to their chemical structure, prostaglandins are divided into four groups—A, B, E, and F—E and F prostaglandins being the most important biologically. The subscripts in the formula below indicate the number of double bonds in the lateral chains of the molecule.

Prostaglandins are found in low concentrations (about 1 μg/g) in almost all organs, tissues, and biological fluids of higher animals. The most important physiological effect that is stimulated by prostaglandins is the ability to contract smooth muscles, especially the muscles of the uterus and fallopian tubes; at childbirth and during menstruation, the concentration of prostaglandins in uterine tissues increases substantially. For this reason, they are used in obstetrics and gynecology to facilitate normal labor and to artificially terminate pregnancy in its early stage.

Prostaglandins are also cardiotonics and bronchodilators. Arterial pressure is lowered by A and E prostaglandins and raised by F prostaglandin. A, E, and F prostaglandins intensify coronary and renal blood flow, inhibit gastric secretion, and affect the endocrine glands, including the thyroid gland; they also affect water-salt metabolism by altering the ratio Na⁺: K⁺ and blood coagulation by inhibiting the aggregation of thrombocytes.

The biosynthesis of prostaglandins occurs in the cells of different tissues. The precursors of prostaglandins are phospholipids; polyunsaturated fatty acids with a linear chain of 20 carbon atoms are released from phospholipids by the enzyme phospholipase. The oxidative cyclization of the carbon atoms, which occurs with the participation of prostaglandin synthetases (a special system of enzymes), results in the synthesis of E and F prostaglandins.

The classification of prostaglandins as local, or cellular, hormones is justified by their varied functions and the absence of a special organ for their biosynthesis. Their mechanism of action is still unclear. It has been established that prostaglandins affect the activity of the enzyme adenyl cyclase, which regulates the concentration of cyclic adenosine 3’: 5’-monophosphate (cyclic AMP) in the cell. Since prostaglandins influence the biosynthesis of cyclic AMP and since cyclic AMP participates in hormonal regulation, a possible mechanism of action of prostaglandins could consist in correcting (intensifying or weakening) the action of other hormones.

Clinical tests have shown prostaglandins to be promising in the treatment of such conditions as gastric ulcer, asthma, hypertonia, thromboses, arthritides, and inflammations of the nasopharynx. For medical and research purposes, prostaglandins are produced: (1) by enzymatic synthesis based on polyunsaturated fatty acids that are produced in the food-processing industry, (2) by complete chemical synthesis in nine to 13 stages chiefly based on cyclopentadiene, and (3) by partial synthesis in three to five stages based on prostaglandin A₂ and E₂ derivatives that are present in high concentrations (reaching 1.4 percent of the raw mass) in several varieties of the soft marine coral Plexaura homomalla.

REFERENCES

Markov, Kh. M. “Prostaglandiny.” Uspekhi fiziologicheskikh nauk, 1970, vol. 1, no. 4.
Prostaglandins. New York, 1971. (Annals of the New York Academy of Sciences, vol. 180.)
The Prostaglandins: Progress in Research. Edited by M. M. Karim. Oxford-Lancaster, 1972.

O. S. RADBIL’ and E. P. SEREBRIAKOV

prostaglandin

[‚präs·tə′glan·dən] (biochemistry) Any of various physiologically active compounds containing 20 carbon atoms and formed from essential fatty acids; found in highest concentrations in normal human semen; activities affect the nervous system, circulation, female reproductive organs, and metabolism.

prostaglandin

[pros″tah-glan´din] any of a group of naturally occurring, chemically related, long-chain hydroxy fatty acids that stimulate contractility of the uterine and other smooth muscle and have the ability to lower blood pressure, regulate acid secretion of the stomach, regulate body temperature and platelet aggregation, and control inflammation and vascular permeability. They also affect the action of certain hormones. First found in semen, they have since been found in cells throughout the body and in menstrual fluid. There are nine types, designated by the letters A to I, the degree of saturation of the side chain of each being designated by subscripts 1, 2, and 3.
Prostaglandins are used clinically to control postpartum hemorrhage, to temporarily manage patent ductus arteriosus, and to treat impotence in men; prostaglandin injections into the amniotic sac, an in-hospital procedure, have been used as an abortion technique in pregnancies after the 16th week. About 30 minutes after an injection of prostaglandin F_2α, contractions begin, and abortion takes place within 19 to 20 hours.

pros·ta·glan·din (PG),

(pros'tă-glan'din), 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 acids 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]

prostaglandin

(prŏs′tə-glăn′dĭn)n. Any of a group of potent hormonelike substances that are produced in various mammalian tissues, are derived from arachidonic acid, and mediate a wide range of physiological functions, such as control of blood pressure, contraction of smooth muscle, and modulation of inflammation.

pros·ta·glan·din

(pros'tă-glan'din) Physiologically active substance 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.

Prostaglandin

A hormonelike chemical produced in the body. Prostaglandins have a wide variety of effects, and may be responsible for the production of some types of pain and inflammation.Mentioned in: Abortion, Therapeutic, Aspirin, Glaucoma

pros·ta·glan·din

(pros'tă-glan'din) 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.

prostaglandin

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prostaglandin

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REFERENCES

prostaglandin

prostaglandin

prostaglandin

pros·ta·glan·din (PG),

prostaglandin

pros·ta·glan·din

Prostaglandin

pros·ta·glan·din

prostaglandin

Words related to prostaglandin

noun a potent substance that acts like a hormone and is found in many bodily tissues (and especially in semen)

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