814 XIII. ESSENTIAL FATTY ACIDS 



and Shorland'^^ reported that linolenate comprised as much as 17% of the 

 fat of pasture-fed horses. In most species, however, linolenate is absent 

 from the depot fat. 



The most striking fact is that the proportion of trienoic acid in the stor- 

 age fat is decreased by feeding polyunsaturated acids and is increased by the 

 administration of fat-free diets. Thus, Reiser et alP observed that, in 

 hens on normal rations, the neutral fat and phospholipid of the egg-yolk 

 fat contained only 0.18% and 0.00%, respectively, of trienoic acids. 

 After fifty-two weeks on a fat-free diet, the trienoic acid contents of the 

 above fractions of egg yolk were found to be 0.42% and 2.3%, respectively. 

 Heart fatty acids, which normally had a content of 22% of trienoic acid, 

 contained only about 4%i after supplementation with corn oil or cod-liver 

 oil.^"^ In 1953 Klein and Johnson^ noted that the trienoic acid content of 

 the mitochondria, poorly sedimentable layer, and microsomes of the livers 

 of senescent rats and of rats on a fat-free diet, was increased over the con- 

 trol level in both cases. Smedley-]\IacLean,'^^ Avho had also reported an 

 increase in trienoic acid in fat deficiency, expressed the opinion that the 

 trienoic acid present may be a partially hydrogenated arachidonic acid, 

 resulting from the attempt on the part of the animal to make the most of 

 its stores of arachidonate. Mead and Slaton^^^ confirmed this finding. 



b. Transformations of Administered Linolenate. Reiser and co-workers*^ 

 reported that the hen is able to convert ingested linolenic acid into dienoic, 

 tetraenoic, pentaenoic, and hexaenoic acids and to deposit these poljam- 

 saturated acids in egg-yolk fat. On the other hand, Holman^^^ is of the 

 opinion that the rat converts trienoic acid mainly to hexaenoic acid, al- 

 though in another report this author^^ did note the formation of unsaturated 

 acids containing four, five and six double bonds in the rat after the adminis- 

 tration of linolenic acid. 



It is difficult to harmonize the above data with the information avail- 

 able on the nutritional value of linolenic acid. A number of workers, 

 including Burr^ and Greenberg et al.,^^-"^ have adduced evidence to show 

 that linoleic and linolenic acids have different functions. Whereas lino- 

 leic acid and arachidonic acid can support growth and also alleviate skin 

 symptoms, it is suggested that linolenic acid only supports growth. Hol- 

 man,'^'^" believes that the tetraenoic acid produced in the animal as a result 



"5 E. G. Brooker and F. B. Shorland, Biochem. J., 46, 80-85 (1950). 



1^8 1. Smedley-MacLean, The Metabolism of Fat, Methuen, London, 1943. 



"' R. T. Holman, Proc. Third Conf. on Research, Am. Meat Inst., Chicago, 1951, pp. 

 1-10. 



"8 S. M. Greenberg, H. J. Deuel, Jr., and J. B. Brown, Abst. Twenty-fourth Fall Meeting, 

 Am. Oil Chemists' Soc, San Francisco, Sept. 26-29 (1951). 



