Abstract
Are the different fatty acids mobilized into plasma in proportion to their concentrations in adipose tissue triglyceride? To answer this question, we fed weaning rabbits a special diet to label the fat stores with a variety of dietary fatty acids. The release of adipose tissue fatty acids into the plasma was then induced by ACTH-stimulated lipolysis. The compositions of the resulting plasma free fatty acids and of the adipose tissue triglyceride were then compared. Plasma free fatty acids increased from 625 mumol/L at baseline to 2938 mumol/L after ACTH and represented fatty acids released from adipose tissue. The relative mobilization of these fatty acids from adipose tissue was defined as the ratio between their percentage in the plasma free fatty acid fraction to their percentage in adipose tissue triglyceride. For the 24 fatty acids examined, the relative mobilization ranged from 0.11 for 22:1 n-11 to 5.06 for 20:5 n-3, a 46-fold difference. Relative mobilization correlated positively with unsaturation and negatively with chain length. The relative mobilization for essential fatty acids was in the order of 20:5 n-3 > 20:4 n-6 > 18:3 n-3 > 22:6 n-3 > 18:2 n-6. Saturated fatty acids, along with oleic acid, were much less well mobilized than the entire group of polyunsaturated fatty acids. Our data indicate that the mobilization of fatty acids into plasma was not proportional to their content in adipose tissue, but rather was influenced by their molecular structure. Eicosapentaenoic acid 20:5 n-3 (EPA), and arachidonic acid 20:4 n-6, precursors of two different prostaglandins, were the fatty acids with the highest mobilization into the plasma.
Highlights
Are the different fatty acids mobilized into plasma in proportion to their concentrations in adipose tissue triglyceride?To answer this question, we fed weanling rabbits a special diet to label the fat stores with a variety of dietary fatty acids
Various fatty acids can be incorporated into the adipose tissue from dietary fat, including more unusual fatty acids such as trans fatty acids, erucic acid, cetoleic acid, and the n-3 fatty acids [2,3].In a previous study, we demonstrated that dietary fatty acids were an important source of adipose fatty acids and had a significant effect upon both the composition and quantity of different fatty acids in adipose tissue [4]
The degree of deposition of different dietary fatty acids into adipose tissue varied greatly [4].Because the deposition of dietary fatty acidswas related to their structures rather than to the amounts in the diet, we hypothesized that different fatty acids may have variable rates of mobilization from adipose tissue
Summary
Are the different fatty acids mobilized into plasma in proportion to their concentrations in adipose tissue triglyceride?To answer this question, we fed weanling rabbits a special diet to label the fat stores with a variety of dietary fatty acids. Hollenberg and Angel [10] and Raclot and Groscolas [11]demonstrated that the mobilization of fatty acid from adipose tissue was positively correlated with the unsaturation and negatively with chain length of the fatty acids For most of these studies, in vitro incubation techniques were used with the rat as the animal model supplying epidymal fat pads. The composition of the plasma free fatty acid fraction before and after hormone-induced lipolysis and the fatty acids of adipose tissue triglyceride were analyzed From these data, the relative mobilization rate, defined as the ratio between the percentage of released free fatty acids to the fatty acid composition of adipose tissue, was calculated for 24 different fatty acids.
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