Quick Facts
Born:
May 21, 1934, Halmstad, Sweden
Died:
July 5, 2024, Mölle (aged 90)
Awards And Honors:
Nobel Prize (1982)
Subjects Of Study:
prostaglandin

Bengt Ingemar Samuelsson (born May 21, 1934, Halmstad, Sweden—died July 5, 2024, Mölle) was a Swedish biochemist who was a corecipient, with fellow Swede Sune K. Bergström and Englishman John Robert Vane of the 1982 Nobel Prize for Physiology or Medicine. The three scientists were honored for their isolation, identification, and analysis of numerous prostaglandins, a family of natural compounds that influence blood pressure, body temperature, allergic reactions, and other physiological phenomena in mammals.

Samuelsson graduated from the University of Lund, where Bergström was one of his professors. He continued his studies at the Karolinska Institute in Stockholm, earning doctorates in biochemistry in 1960 and medicine in 1961. The following year he worked as a research fellow in the chemistry department at Harvard University, subsequently returning to the Karolinska Institute as a member of the faculty the same year. In 1967 Samuelsson taught at the Royal Veterinary College at the University of Stockholm, serving as a professor in veterinary medical chemistry until 1972, when he once again returned to the Karolinska Institute. Samuelsson was a visiting professor at Harvard in 1976 and at the Massachusetts Institute of Technology in 1977. The next year he succeeded Bergström as dean of the medical faculty at the Karolinska Institute, where in 1983 he was named rector, a position he held until 1995.

Samuelsson joined Bergström in research on prostaglandins, and in 1962 they became the first to determine the molecular structure of a prostaglandin. In 1964 they announced that prostaglandins are derived from arachidonic acid, an unsaturated fatty acid that is found in certain meats and vegetable oils. Samuelsson subsequently determined how arachidonic acid combines with oxygen to eventually form prostaglandins. In the 1970s he discovered several new prostaglandins, including thromboxane, which is involved in blood clotting and the contraction of blood vessels. Samuelsson’s later research explored leukotrienes, a group of lipids closely related to prostaglandins that are involved in mediating inflammation. In the 1980s and 1990s he investigated the affects of drugs on leukotriene pathways and studied novel agents capable of inhibiting the actions of leukotrienes.

Samuelsson, Bergström, and Vane received the Albert Lasker Basic Medical Research Award in 1977. Samuelsson published numerous papers and books, among the latter of which were Leukotrienes and Other Lipoxygenase Products (1982; cowritten with Italian biochemist Rodolfo Paoletti), Prostaglandins and Related Compounds (1987), and Trends in Eicosanoid Biology (1990).

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by J.E. Luebering.

prostaglandin, any of a group of naturally occurring lipid compounds that act as chemical messengers, having diverse functions and effects in humans and other animals. Prostaglandins are powerful substances that serve to regulate essential physiological processes and that mediate inflammatory and immune responses. Their role as chemical messengers makes them a valuable target for therapeutic interventions, especially those developed for the treatment of pain and inflammation.

Discovery

Prostaglandins were discovered in human semen in 1935 by Swedish physiologist Ulf von Euler, who named them, thinking that they were secreted by the prostate gland. The understanding of prostaglandins grew in the 1960s and ’70s with the pioneering research of Swedish biochemists Sune K. Bergström and Bengt Ingemar Samuelsson and British biochemist Sir John Robert Vane. The threesome shared the Nobel Prize for Physiology or Medicine in 1982 for their isolation, identification, and analysis of numerous prostaglandins.

Synthesis of prostaglandins

Prostaglandins are made up of unsaturated fatty acids that contain a cyclopentane (5-carbon) ring and are derived from the 20-carbon, straight-chain, polyunsaturated fatty acid precursor arachidonic acid.Chemical Compounds. Carboxylic acids and their derivatives. Classes of Carboxylic Acids. Unsaturated aliphatic acids. Chemical structure of prostaglandin.

Arachidonic acid is a key component of phospholipids, which are themselves integral components of cell membranes. In response to many different stimuli, including various hormonal, chemical, or physical agents, a chain of events is set in motion that results in prostaglandin formation and release. These stimuli, either directly or indirectly, result in the activation of an enzyme called phospholipase A2. This enzyme catalyzes the release of arachidonic acid from phospholipid molecules.

Depending on the type of stimulus and the enzymes present, arachidonic acid may diverge down one of several possible pathways. One enzyme, lipoxygenase, catalyzes the conversion of arachidonic acid to one of several possible leukotrienes, which are important mediators of the inflammatory process. Another enzyme, cyclooxygenase, catalyzes the conversion of arachidonic acid to one of several possible endoperoxides. The endoperoxides undergo further modifications to form prostaglandins, prostacyclin, and thromboxanes. The thromboxanes and prostacyclin have important functions in the process of blood coagulation.

Biological activities of prostaglandins

Prostaglandins have been found in almost every tissue in humans and other animals. Plants synthesize molecules similar in structure to prostaglandins, including jasmonic acid (jasmonate), which regulates processes such as plant reproduction, fruit ripening, and flowering. Prostaglandins are very potent; for example, in humans some affect blood pressure at concentrations as low as 0.1 microgram per kilogram of body weight.

The structural differences between prostaglandins account for their different biological activities. Some prostaglandins act in an autocrine fashion, stimulating reactions in the same tissue in which they are synthesized, and others act in a paracrine fashion, stimulating reactions in local tissues near where they are synthesized. In addition, a given prostaglandin may have different and even opposite effects in different tissues. The ability of the same prostaglandin to stimulate a reaction in one tissue and inhibit the same reaction in another tissue is determined by the type of receptor to which the prostaglandin binds.

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Vasodilation and blood clotting

Most prostaglandins act locally; for instance, they are powerful locally acting vasodilators. Vasodilation occurs when the muscles in the walls of blood vessels relax so that the vessels dilate. This creates less resistance to blood flow and allows blood flow to increase and blood pressure to decrease. An important example of the vasodilatory action of prostaglandins is found in the kidneys, in which widespread vasodilation leads to an increase in the flow of blood to the kidneys and an increase in the excretion of sodium in the urine. Thromboxanes, on the other hand, are powerful vasoconstrictors that cause a decrease in blood flow and an increase in blood pressure.

Thromboxanes and prostacyclins play an important role in the formation of blood clots. The process of clot formation begins with an aggregation of blood platelets. This process is strongly stimulated by thromboxanes and inhibited by prostacyclin. Prostacyclin is synthesized in the walls of blood vessels and serves the physiological function of preventing needless clot formation. In contrast, thromboxanes are synthesized within platelets, and, in response to vessel injury, which causes platelets to adhere to one another and to the walls of blood vessels thromboxanes are released to promote clot formation. Platelet adherence is increased in arteries that are affected by the process of atherosclerosis. In affected vessels the platelets aggregate into a plaque called a thrombus along the interior surface of the vessel wall. A thrombus may partially or completely block (occlude) blood flow through a vessel or may break off from the vessel wall and travel through the bloodstream, at which point it is called an embolus. When an embolus becomes lodged in another vessel where it completely occludes blood flow, it causes an embolism. Thrombi and emboli are the most common causes of heart attack (myocardial infarction). Therapy with daily low doses of aspirin (an inhibitor of cyclooxygenase) has had some success as a preventive measure for people who are at high risk of heart attack.

Inflammation

Prostaglandins play a pivotal role in inflammation, a process characterized by redness (rubor), heat (calor), pain (dolor), and swelling (tumor). The changes associated with inflammation are due to dilation of local blood vessels that permits increased blood flow to the affected area. The blood vessels also become more permeable, leading to the escape of white blood cells (leukocytes) from the blood into the inflamed tissues. Thus, drugs such as aspirin or ibuprofen that inhibit prostaglandin synthesis are effective in suppressing inflammation in patients with inflammatory but noninfectious diseases, such as rheumatoid arthritis.

Smooth muscle contraction

Although prostaglandins were first detected in semen, no clear role in reproduction has been established for them in males. This is not true in women, however. Prostaglandins play a role in ovulation, and they stimulate uterine muscle contraction—a discovery that led to the successful treatment of menstrual cramps (dysmenorrhea) with inhibitors of prostaglandin synthesis, such as ibuprofen. Prostaglandins also play a role in inducing labor in pregnant women at term, and they are given to induce therapeutic abortions.

The function of the digestive tract is also affected by prostaglandins, with prostaglandins either stimulating or inhibiting contraction of the smooth muscles of the intestinal walls. In addition, prostaglandins inhibit the secretion of gastric acid, and therefore it is not surprising that drugs such as aspirin that inhibit prostaglandin synthesis may lead to peptic ulcers. Prostaglandin action on the digestive tract may also cause severe watery diarrhea and may mediate the effects of vasoactive intestinal polypeptide in Verner-Morrison syndrome, as well as the effects of cholera toxin.

Robert D. Utiger