TRANSACYLASE-MEDIATED AND PHOSPHODIESTERASE-MEDIATED SYNTHESIS OF N-ARACHIDONOYLETHANOLAMINE, AN ENDOGENOUS CANNABINOID-RECEPTOR LIGAND, INRAT-BRAIN MICROSOMES - COMPARISON WITH SYNTHESIS FROM FREE ARACHIDONIC-ACID AND ETHANOLAMINE

The levels of N-arachidonoylethanolamine (anandamide), an endogenous c annabinoid-receptor ligand, and a relevant molecule, N-arachidonoylpho sphatidylethanolamine (N-arachidonoylPtdEtn), in rat brain were invest igated using a newly developed sensitive analytical method, We found t hat rat brain contains small but significant amounts of these two type s of N-arachidonoyl lipids (4.3 pmol/g tissue and 50.2 pmol/g tissue, respectively). Then, we investigated how N-arachidonoylethanolamine (a nandamide) is produced in the brain. We found that anandamide can be f ormed enzymatically via two separate synthetic pathways in the brain: enzymatic condensation of free arachidonic acid and ethanolamine; and formation of N-arachidonoylPtdEtn from PtdEtn and arachidonic acid est erified at the 1-position of phosphatidyl-choline (PtdCho), and subseq uent release of anandamide from N-arachidonoylPtdEtn through the actio n of a phosphodiesterase. We confirmed that rat brain contains both th e enzyme activities and lipid substrates involved in these reactions. Several lines of evidence strongly suggest that the second pathway, ra ther than the first one, meets the requirements and conditions for the synthesis of various species of N-acylethanolamine including anandami de in the brain.