Arachidonic acid is an essential fatty acid and a precursor for all prostaglandins, thromboxanes, and leukotrienes. Virtually all cellular arachidonic acid is esterified in membrane phospholipids where its presence is tightly regulated through multiple interconnected pathways.{3656} Free arachidonic acid is a transient, critical substrate for the biosynthesis of eicosanoid second messengers. Receptor-stimulated release, metabolism, and re-uptake of free arachidonate are all important aspects of cell signaling and inflammation.{314} Arachidonic acid oxidizes spontaneously on exposure to room air, yielding a complex mixture of fatty acid peroxides. Arachidonic acid (peroxide free) contains the antioxidant BHT (Item No. 89910). BHT-free arachidonic acid (Item Nos. 90010 | 10006607) is also available.