The selective mobilization of fatty acids is not based on their positional distribution in white-fat-cell triacylglycerols.

Fatty acids have been shown to be selectively mobilized from rat white fat-cells, whatever the dietary manipulations. For convenience, fatty acids have been classified as being highly, weakly and moderately mobilizable. The aim of this study was to examine whether the selective mobilization of fatty acids can be explained, even partly, by their positional distribution in adipose-tissue triacylglycerols (TAG) via the known specificity of hormone-sensitive lipase for the sn-1 and sn-3 positions. Adipose tissue was dietarily manipulated in order to obtain a wide spectrum of fatty acids, including large amounts of either very-long-chain polyunsaturated fatty acids (VLC-PUFA) or very-long-chain monounsaturated fatty acids (VLC-MUFA). The determination of fatty acid distribution in adipose tissue TAG was based on random formation of 1,2-diacyl-rac-glycerols by Grignard degradation, followed by synthesis of phosphatidic acids and hydrolysis in the sn-2 position by phospholipase A2. Regardless of the fatty acid composition and location of fat depots, highly (e.g. 18:4n-3 and some of the VLC-PUFA) and weakly (e.g. VLC-MUFA) mobilizable fatty acids were located mainly in the outer (sn-1 and sn-3) positions of the glycerol moiety (79.5% and 92.5% on average, respectively). Other fatty acids, which are rather moderately mobilizable, were more randomly distributed. We conclude that the selective mobilization of white-fat-cell fatty acids is not based on their positional distribution in TAG.