Eicosanoids, prostaglandins, thromboxanes,leucotrienes and anandamide
The discovery of transmitters deriving from fatty acids, in particular from arachidonic acid, goes back to the years 1970. These transmitters, sometimes called autacoids, are eicosanoids such as prostaglandins and leukotrienes.
Classified under the term of eicosanoids are, prostaglandins, prostacyclin, thromboxanes, leukotrienes and lipoxins.
They are derived from arachidonic acid which is also called eicosatetraenoïc acid because it is constituted of 20 carbon atoms (eicosa means twenty). Arachidonic acid has 4 double bonds, the first being placed in omega-6 position from the terminal methyl group. The so called dihomolinolenic acid, also called eicosatrienoïc acid and eicosapentaenoic acid which is present in fish oil can also lead to the formation of prostaglandins.
The term PG indicates a prostaglandin, the capital letters E, F, I, H etc, depend on substituents fixed on the cyclopentanic cycle and the figure which follows indicates the number of double bonds present in two chains fixed on the cycle. The letters has and ß characterizes isomers.
Thromboxanes, TX, are constituted of an oxane, a cyclohexanic cycle where a carbon atom is replaced by an oxygen atom. The letters A, B, depend on the substituents fixed at the cycle. The figures indicate the number of double bonds present in the two aliphatic chains.
The term leukotrienes, LT, means that they were found initially in leukocytes and that, chemically, they involve three double bonds separated by a simple bond. They are not cyclic.