Fatty Acid Composition of Vitamin a Esters in Fish Liver Oils.

In order to obtain some information about vitamin A absorption and storage in fish, fatty acid composition of vitamin A esters in fish liver was studied as vitamin A is stored in the liver more concentratedly than any other organs of fish. As early as 1934 Hamano (1-3) showed that a crystalline substance prepared by addition of maleic anhydride to the liver oil of ishinagi (Stereolepis ischinagi), rockfish (Sebastes flammeus) or pollack (Theragra chalcogramma) was palmityl vitamin A dimaleic anhydride adduct derived from vitamin A palmitate naturally present in the oil. Further information on the fatty acid composition was provided by Gray, Hickman and Brown (4) from the study of the distillation curves of rat-liver oils. They concluded that vitamin A given as massive doses of vitamin A alcohol or caproate had been converted to esters composed of the tatty acids occurring naturally in the rat. Later, Gray and Cawley (5) made similar studies on rats receiving smaller doses of fish liver oils or concentrates over a long period and reported that the vitamin A appeared to have been stored in the liver mainly as a single ester, probably palmitate. Sonehara and Yamaguchi (6) came to the same conclusion on the basis of gas chromatographic analysis of molecular distillates of fish liver oils. Though these investigators have assumed the vitamin A ester to be palmitate, they did not succeed in separating the component fatty acids from vitamin A esters. Recently Mahadevan and Ganguly (7), based on partition chromatography, re ported that the vitamin A esters in the liver of rats given various kinds of oils were mostly composed of palmitic acid. Examination of their results, however, raises a doubt as to the integrity of their analytical procedure. Higashi et al. (8) are of the opinion different from the workers mentioned above. They found that after storage for a long time of fish liver containing oil at a low level, only glyceride had been decomposed by the enzyme. This finding enabled them to separate the esters of the unsaponifiable mainly consisting of vitamin A and to determine the fatty acid composition by the addition of bromine. It was found that the esters of the unsaponifiable were not composed of a specific single fatty acid, but of various ones with the composition essentially similar to the component fatty acids of glycerides.