Influence of dietary arachidonic acid on metabolism in vivo of 8 cis, 11 cis, 14‐eicosatrienoic acid in humans

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Abstract
This study investigated the influence of dietary arachidonic acid (20∶4n‐6) on Δ5 desaturation and incorporation of deuterium‐labeled 8cis, 11cis, 14‐eicosatrienoic acid (20∶3n‐6) into human plasma lipids. Adult male subjects (n=4) were fed diets containing either 1.7 g/d (H120∶4 diet) or 0.21 g/d (LO20∶4 diet) of arachidonic acid for 50 d and then dosed with a mixture containing ethyl esters of 20∶3n‐6[d4] and 18∶1n‐9[d2]. A series of blood samples was sequentially drawn over a 72‐h period, and methyl esters of plasma total lipid, triacylglycerol, phospholipids, and cholesteryl ester were analyzed by gas chromatography‐mass spectrometry. Based on the concentration of 20∶3n‐6[d4] in total plasma lipid, the estimated conversion of 20∶3n‐6[d4] to 20∶4n‐6[d4] was 17.7.±0.79% (HI20∶4 diet) and 2.13±1.44% (LO20∶4 diet). The concentrations of 20∶4n‐6[d4] in total plasma lipids from subjects fed the HI20∶4 and LO20∶4 diets were 2.10±0.6 and 0.29±0.2 μmole/mL plasma/mmole of 20∶3n‐6[d4] fed/kg of body weight. These data indicate that conversion of 20∶3n‐6[d4] to 20∶4n‐6[d4] was stimulated 7‐8‐fold by the HI20∶4 diet. Phospholipid acyltransferase was 2.5‐fold more selective for 20∶3n‐6[d4] than 18∶1n‐9[d2], and lecithin:cholesterol acyltransferase was 2‐fold more selective for 18∶1n‐9[d2] than 20∶3n‐6[d4]. These differences in selectivity were not significantly influenced by diet. Absorption of ethyl 20∶3n‐6[d4] was about 33% less than ethyl 18∶1n‐9[d2]. The sum of the n‐6 retroconversion products from 20∶3n‐6[d4] in total plasma lipids was about 2% of the total deuterated fatty acids. Neither absorption nor retroconversion appears to be influenced by diet.

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