A polyunsaturated fattyacid, CH3(CH2)33(CH2CH:CH)4(CH2)3COOH, that is essential for growth in mammals (see eicosanoid). It can be synthesized from linoleic acid. Arachidonic acid acts as a precursor to several biologically active compounds, including prostaglandins, and plays an important role in membrane production and fat metabolism. The release of arachidonic acid from membrane phospholipids, particularly diacylglycerol, is triggered by certain hormones. See essential fatty acids.