The metabolism of the essential fatty acids. VI. Distribution of unsaturated fatty acids in rats on fat-free and supplemented diets.

In a recent communication (l), indirect evidence was offered for the assertion that a radioactive polybromide, prepared from the unsaturated fatty acids of rats which had been fed methyl linolenate-l-C’*, was derived, not from arachidonic acid, but from a derivative of linolenic acid, possibly an eicosapentaenoic acid. In a further consideration of this problem, it was apparent that an analysis of the fatty acids of animals which had been on a fat-free diet from weaning would reveal a low level of polyunsaturated fatty acids derived only from the mother. Supplementation of the diet with certain acids would then give evidence for the metabolic fate of these acids in the changes which would occur in the distribution of fatty acids on the basic diet. Several methods can conceivably be used for such an analysis. However, the technique which seemed to give the most promise of success with the least difficulty, especially since it has been in use in this Laboratory for some years, is that of reverse-phase chromatography on siliconized Celite, as developed by Howard and Martin (2) and extended by Silk and Hahn (3) and by Crombie et al. (4). In this type of chromatogram, groups of fatty acids are eluted together, depending upon their chain length and degree of unsaturation. Thus myristic (Cl,, saturated), palmitoleic (C&, monounsaturated), and linoleic (Cl,, diunsaturated) acids would be expected to be eluted together. Crombie et al. (4) achieved a partial resolution of these groups by permanganate oxidation of the eluted fatty acids followed by rechromatography, which separated the oxidized unsaturated fatty acids. In this Laboratory, it had been suggested (5) that a complete separation and quantitative estimation of the fatty acids could be achieved by hydrogenation and rechromatography of each fraction. With this treatment, the fatty acids would separate according to chain length, and identification of each would be accomplished by its position in the two chromatograms. Thus, in the case of the mixture described above, after hydrogenation, the resulting myristic,