A group of natural fatty-acid substances with a wide range of activity; they are so-called because they were first discovered in the SEMEN and thought to arise in the PROSTATE GLAND. Their precise mode of action is not yet clear, but they are potent stimulators of muscle contraction and also effective VASODILATORS. Prostaglandins cause contraction of the UTERUS and have been used to induce labour (see PREGNANCY AND LABOUR); they are also being used as a means of inducing therapeutic abortions (see ABORTION).

Prostaglandins play an important part in the production of PAIN, and ASPIRIN relieves pain because it prevents, or antagonises, the formation of certain prostaglandins. In addition, they play some, although as yet incompletely defined, part in producing inflammatory changes. (See INFLAMMATION; NON-STEROIDAL ANTI-INFLAMMATORY DRUGS (NSAIDS).)

The two most important prostaglandins are PROSTACYCLIN and thromboxane: prostacyclin is a vasodilator (opens the blood vessels) and prevents platelet aggregation, so prevents blood clotting; thromboxanes have the opposite effect and cause vasoconstriction and platelet aggregation. Prostaglandins have been used most successfully to prevent clotting in extra-corporeal haemoperfusion systems (see HEART-LUNG MACHINE). They have to be given intravenously and side-effects tend to be severe, because the drug is usually given at the highest dose the patient can tolerate.