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Short-term Diets Rich in Arachidonic Acid Influence Plasma Phospholipid Polyunsaturated Fatty Acid Levels and Prostacyclin and Thromboxane Production in Humans^1,2,

Andrew J. Sinclair^*,3 and Neil J. Mann

^* Department of Food Science, Royal Melbourne Institute of Technology, Melbourne 3000, Victoria, Australia School of Nutrition and Public Health, Deakin University, Geelong 3217, Victoria, Australia

Two small-scale dietary intervention studies were conducted to examine the effect of diets rich in arachidonic acid (AA) and n-3 long-chain polyunsaturated fatty acids (n-3 LCP), on the in vivo production of prostacyclin (PGI₂) and thromboxane (TXA₂). The first was a pilot study and contained insufficient numbers for statistical analyses. It involved a 7-d intervention with 10 subjects divided into three groups, consuming diets rich in AA (500 mg/d), rich in AA and docosahexaenoic acid (DHA) (500 mg/d of each), or rich in DHA and eicosapentaenoic acid (EPA) (1500 mg/d of n-3 LCP). Plasma phospholipid (PL) levels of AA increased in all subjects in groups 1 (n = 4) and 2 (n = 3). DHA levels increased in all subjects in Groups 2 and 3 (n = 3), and EPA levels increased in all subjects from Group 3 but fell in all subjects from Group 1. The in vivo production of PGI₂, measured as its urinary metabolite, was increased in two subjects in Group 1 and one subject in Group 2, with all other subjects showing little change. Urinary TXA₂ metabolite increased in all subjects from Group 1. The second study was conducted in seven subjects, who consumed a low fat diet for 2 wk: the 1st wk was a vegetarian diet (no LCP) followed by a 2nd wk where the subjects were required to consume 500 g (raw weight) of kangaroo meat daily (305 mg/d AA, 325 mg/d n-3 LCP). The meat diet was associated with a marked rise in the serum PL levels of AA, EPA and docosapentaenoic acid 22:5(n-3) and with a significant increase in the urinary output of the prostacyclin metabolite, but no effect on TXA₂ production, as measured by its urinary metabolite level. The results of these studies have shown that diets that contain both AA and n-3 LCP are associated with an increase in PGI₂ production, without affecting TXA₂ production. Further studies with purified LCP are warranted.

KEY WORDS: • arachidonic acid • humans • long-chain polyunsaturated fatty acid • prostacyclin • thromboxane

¹ Presented as part of the symposium "Biological Effects of Dietary Arachidonic Acid" given at the Experimental Biology '95 meeting, Atlanta, GA, on April 11, 1995. This symposium was sponsored by the American Institute of Nutrition and was supported by a grant from the Cayman Chemical Company. Guest editors for the symposium were Jay Whelan, University of Tennessee, Knoxville, TN, and J. Bruce German, University of California, Davis, CA.

² Supported by a grant from the Meat Research Corporation, Sydney, NSW, Australia.

³ To whom correspondence should be addressed: Department of Food Science, Royal Melbourne Institute of Technology, GPO Box 2476V, Melbourne 3001, Victoria, Australia.