The prostaglandins (PG) represent a class of substances produced in a wide variety of cells. These act on the cells that produce them, on neighboring cells, or usually over short distances and can be classified as autocrine hormones. Some PGs, such as prostacyclin (PGI2), may be regarded as acting like the more traditional endocrine hormones in the sense that they are synthesized in blood vessel cells, survive in the bloodstream for a period of time, and can exert effects somewhat distant from their sites of synthesis. However, we usually think of PGs and their relatives as being potent local hormones (autocrine and paracrine) acting over a short lifetime. Many of the prostaglandins and relatives are important mediators of inflammatory reactions. Prostaglandins are misnamed for an early activity of semen, presumably originating in the prostate, which contracted uterine smooth muscle.

PGs and their relatives, prostacyclin (PGI2), thromboxanes (TX), leukotrienes (LT), and lipoxins (LP), derive from fatty acids stored in cellular membranes as phospholipids or triglycerides. Fatty acid precursors, typically arachidonic acid, are released by a phospholipase or by a lipase in the cell membranes following a stimulatory event. This event will usually be a signal to activate the enzyme liberating arachidonic acid from hormones, second EDITION

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