INTERCONVERSIONS OF POLYUXSATURATED FATTY ACIDS 813 



When the linoleate is altered by conjugation or elaidinization, it cannot 

 l)e converted to biologically active tetraenoic acids. Thus Reiser '^^ 

 reported that, when conjugated trilinolein was fed to hens, the conjugated 

 dienoic acids appeared in the egg-yolk fat, but that no more highly con- 

 jugated a(rids were oljserved. Holman'^ noted that, when elaidinized lino- 

 leic acid was fed to rats, it was (converted to spectrophotometrically detect- 

 able tetraenoic acid, as demonstrated l\y alkali isomerization. The tetra- 

 enoic acid, however, was reported to be biologically inert. 



b. Conversion to Polyunsaturated Acids Other Than Tetraenoic Acid. 

 Although the experimental data are exceedingly fragmentary, the present 

 indication is that a species difference obtains in the possible transformations 

 of the dienoic acids. Thus, on the one hand, Reiser and Gibson^®^ and 

 Reiser et al.^^ found that the laying hen could convert ingested linoleate 

 into pentaenoic acid as well as into tetraenoic acid. Plowever, neither 

 trienoic nor hexaenoic acid was formed in this species. In contradistinc- 

 tion to these results, Rieckehoff et al.^^° and Widmer and Holman'"^ found 

 that hexaenoic and pentaenoic acids, as well as tetraenoic acid, were 

 derived from dienoic acid in the case of rats; hexaenoic acid was present 

 in the greatest amount. Although these workers failed to observe the 

 formation of pentaenoic or hexaenoic acids, after supplementation, when 

 selected tissues were used, evidence for the synthesis of both 

 types of acids was obtained when the whole animal was analyzed. 



(2) Interconversions of Linolenic Acid 



a. Factors Altering the Trienoic Acid Content of Tissues. The metabo- 

 lism of linolenic acid shows certain interesting ^-ariations as compared with 

 that of linoleic acid. One of the earliest observations w^as that this trienoic 

 acid was present in exceedingly small quantities, even when a considerable 

 amount was present in the ration. This led Bloor"^ to postulate that lino- 

 lenic acid is preferentially utilized, and is not deposited. 



However, it now appears that the deposition of linolenic acid in the tissues 

 is dependent upon the species of animal. On the one hand, Ellis and Is- 

 I^g]jii3,ii4 reported that only small amounts of trienoic acids were to be 

 found in the case of pigs, even when they were fed large amounts of soy- 

 beans. However, Beadle et al.'^''* did find as much as 11.4% of this acid in 

 the "yellow" fat of swine. Rats which had received a linseed oil diet were 

 found to have as much as 25.6% of linolenate in their fat depots. ^'''* Brooker 



"3 W. R. Bloor, Biochemistry of the Fatty Acids, Reinhold, New York, 1943. 

 "< B. W. Beadle, O. H. M. Wilder, and H. R. Kraybill, /. Biol. Chem., 175, 221-229 

 (1948). 



