Prostaglandins (PGs) are made by virtually all cells from the phospholipids of their cell membranes. They differ from other hormones in that they do not circu-late in the blood to target organs, but rather exert their effects locally, where they are produced.
There are many types of prostaglandins, designated by the letters A through I, as in PGA, PGB, and so on. Prostaglandins have many functions, and we will list only a few of them here. Prostaglandins are known to be involved in inflammation, pain mechanisms, blood clotting, vasoconstriction and vasodilation, contrac-tion of the uterus, reproduction, secretion of digestive glands, and nutrient metabolism. Current research is directed at determining the normal functioning of prostaglandins in the hope that many of them may eventually be used clinically.
One familiar example may illustrate the widespread activity of prostaglandins. For minor pain such as a headache, many people take aspirin. Aspirin inhibits the synthesis of prostaglandins involved in pain mech-anisms and usually relieves the pain. Some people, however, such as those with rheumatoid arthritis, may take large amounts of aspirin to diminish pain and inflammation. These people may bruise easily because blood clotting has been impaired. This too is an effect of aspirin, which blocks the synthesis of prostaglan-dins necessary for blood clotting.