Synthesis and degradation
The human body synthesizes anandamide from N-arachidonoyl phosphatidylethanolamine (NAPE), which is itself made by transferring arachidonic acid from lecithin to the free amine of cephalin through an N-acyltransferase enzyme. Anandamide synthesis from NAPE occurs via multiple pathways and includes enzymes such as phospholipase A2, phospholipase C and NAPE-PLD.
Endogenous anandamide is present at very low levels and has a very short half-life due to the action of the enzyme fatty acid amide hydrolase (FAAH), which breaks it down into free arachidonic acid and ethanolamine. Studies of piglets show that dietary levels of arachidonic acid and other essential fatty acids affect the levels of anandamide and other endocannabinoids in the brain. High fat diet feeding in mice increases levels of anandamide in the liver and increases lipogenesis. This suggests that anandamide may play a role in the development of obesity, at least in rodents.
Paracetamol (or acetaminophen in the U.S.A.) is metabolically combined with arachidonic acid by FAAH to form AM404. This metabolite of paracetamol is a potent agonist at the TRPV1 vanilloid receptor, a weak agonist at both CB1 and CB2 receptors, and an inhibitor of anandamide reuptake. As a result, anandamide levels in the body and brain are elevated. In this fashion, paracetamol acts as a pro-drug for a cannabimimetic metabolite. This action may be partially or fully responsible for the analgesic effects of paracetamol.