To date, four RvEs (RvE1, 18S-RvE1, RvE2, and RvE3) have been discovered. COX-2, acetylated by aspirin in hypoxic endothelial cells, introduces oxygen groups into 18R-hydro (peroxy)-eicosapentaenoic acid (18R-HEPE). Activated PMN uses 5-LOX to convert 18R-HEPE to 5S (6)-epoxy-18R-HEPE, which is further hydrolyz