A type of prostaglandin (see next entry).

Prostaglandins

Short-acting hormone-like unsaturated fatty acids produced from precursor fatty acids found in the phospholipids of cell membranes. The enzymes prostaglandin synthetase and cyclo-oxygenase are required for this purpose. Together with similar substances known as prostacyclins, thromboxanes and leukotrienes, prostaglandins act locally and are involved in many body processes including blood clotting, blood pressure, pain, water balance, inflammation, uterine contractions, transmission of nerve impulses, immune assistance, hormone responses and control of sodium, potassium and chloride ions across cell membranes. By controlling capillary permeability, the prostaglandins may promote the exchange of nutrients for waste products at this level.

The prostaglandins, prostacyclins, thromboxanes and leukotrienes should collectively be referred to as 'eicosanoids' or 'prostanoids' but the term prostaglandins is often used for all of them.

The body uses its enzymes to oxidize the precursor fatty acids in specific ways to make specific prostaglandin molecules. About 30 prostaglandins have been identified to date, and are categorized into three series (families) according to which fatty acid they are made from.

Series 1 and 2 prostaglandins are produced from linoleic acid, and have one and two double bonds, respectively. Series 3 prostaglandins are made from from alpha-linolenic acid and have three double bonds. (See Fats for information on fatty acid metabolism.)

Linoleic acid is metabolized to DGLA, which can itself be metabolized to either series 1 prostaglandins, or to another fatty acid known as arachidonic acid. Series 2 prostaglandins are derived from arachidonic acid.

Alpha-linolenic acid is metabolized to EPA, which gives rise to series 3 prostaglandins.

Individual prostaglandins do not have names but are referred to as PG plus a letter of the alphabet and the number of the series they belong to.

Some prostaglandins and their functions

The reputed anti-inflammatory properties of flavonoids such as quercetin, rutin, curcumin, silymarin and green tea polyphenols may be related to their ability to inhibit the enzymes cyclo-oxygenase and lipoxygenase, which are required for prostaglandin synthesis. The popular medication aspirin also works in the same way, which accounts for its effectiveness in treating problems such as headaches and joint pains caused by the over-production of  pro-inflammatory prostaglandins from arachidonic acid.