HENEICOSAPENTAENOATE (21 5N-3) - ITS INCORPORATION INTO LIPIDS AND ITS EFFECTS ON ARACHIDONIC-ACID AND EICOSANOID SYNTHESIS/

6,9,12,15,18-Heneicosapentaenoic acid (21:5n-3) (HPA), present in smal l amounts in fish oils, has been prepared by chemical elongation of ei cosapentaenoic acid (EPA) and its biological properties compared with EPA and docosahexaenoic acid (DHA). All the double bonds of HPA are di splaced one carbon away from the carboxyl group when compared to EPA. HPA is incorporated into phospholipids and into triacylglycerol in cel l culture to a similar extent as EPA and DHA. HPA is a stronger inhibi tor of the conversion of cr-linoleic acid and dihomo-gamma-linolenic a cid to arachidonic acid (AA) in hepatoma cells than are EPA, DHA, and AA. HPA is a poor substrate for prostaglandin H synthase and for 5-lip oxygenase, but it inactivates prostaglandin H synthase as rapidly as d o AA, EPA, and DHA. HPA inhibits thromboxane synthesis in isolated pla telets as efficiently as EPA. EPA, HPA, and DHA are all weak inducers of acyl-CoA oxidase in hepatoma cells. Therefore, since fish oils cont ain only small amounts of HPA, it is unlikely that this fatty acid is of particular significance for the biological effects of these oils, p ossibly with the exception that it is a strong inhibitor of AA synthes is.