Physiological roles of 2‐arachidonoylglycerol, an endogenous cannabinoid receptor ligand

2-Arachidonoylglycerol is an arachidonic acid-containing monoacylglycerol isolated from the rat brain and canine gut as an endogenous ligand for the cannabinoid receptors (CB1 and CB2). 2-Arachidonoylglycerol binds to both the CB1 receptor, abundantly expressed in the nervous system, and the CB2 receptor, mainly expressed in the immune system, with high affinity, and exhibits a variety of cannabimimetic activities. Notably, anandamide, another endogenous ligand for the cannabinoid receptors, acts as a partial agonist at these cannabinoid receptors, whereas 2-arachidonoylglycerol acts as a full agonist. The results of structure-activity relationship experiments strongly suggested that 2-arachidonoylglycerol rather than anandamide is the true natural ligand for both the CB1 and the CB2 receptors. Evidence is gradually accumulating which shows that 2-arachidonoylglycerol plays physiologically and pathophysiologically essential roles in various mammalian tissues and cells.