Activation of PAF receptors results in enhanced synthesis of 2-arachidonoylglycerol (2-AG) in immune cells

The endocannabinoid signaling system is believed to play a down-regulatory role in the control of cell functions. However, little is known about the f actors activating endocannabinoid synthesis and which of two known endocann abinoids, 2-arachidonoylglycerol (2-AG) or N-arachidonoylethanolamine (20:4 n-6 NAE, anandamide), is of physiological importance. We approached these q uestions by studying a possible link between cell activation with 1-O-alkyl -2-acetyl-sn-glycero-3-phosphocholine (platelet-activating factor, PAF) and the generation of 2-AG and anandamide in human platelets and mouse P388D1 macrophages. Human platelets responded to stimulation with the production o f various 1- and 2-monoacylglycerols, including 2-AG, whereas stimulation o f P388D1 macrophages induced the rapid and selective generation of 2-AG, wh ich was immediately released into the medium. The effect of PAF was recepto r mediated, as PAF receptor antagonist BN52021 blocked the effect. The trea tment did not change the content of anandamide in either macrophages or pla telet-rich plasma. The inhibitors of PI- and PC-specific phospholipases C ( U73122 and D609) as well as PI3-kinase inhibitor (wortmannin) attenuated PA F-induced 2-AG production in macrophages. These data suggest a direct role for the endocannabinoid system in controlling immune cell activation status and indicate that 2-AG rather than anandamide is the endocannabinoid rapid ly produced in response to proinflammatory stimulation of immune cells.