816 XIII. ESSENTIAL FATTY ACIDS 



evidence that hexaenoic acid is deposited in increased amounts in the 

 heart and brain, and pentaenoic acid in the liver of rats after supplementa- 

 tion with ethyl arachidonate. However, it is questionable whether or not 

 the tetraenoic acid was converted to the more highly unsaturated fatty 

 acids, since there is some indication that impurities in the preparation of 

 arachidonate were sufficient to account for the newly deposited pentaenoic 

 and hexaenoic acids. Reiser and Gibson'^* noted that a significant increase 

 in dienoic acid, but no augmentation in trienoic acid, occurred in growing 

 chicks fed cod-liver oil which was free from dienoic and trienoic acids. 

 According to Clement and ]\Iay,'^^ conjugated tetraenoic acid can be hydro- 

 genated by rats to yield conjugated trienoic acid. 



Figure 1 presents some known interconversions of the several polyun- 

 saturated acids. 



7. Physiologic Functions Related to the Essential Fatty Acids 



(/) Growth 



The classical demonstration of the necessity of the essential fatty acids 

 in the diet has been their effect on growth when administered to animals 

 on a fat-free diet. When weanling rats are placed on a fat-free diet, they 

 continue to grow noi'mally for two or three weeks, after which the rate of 

 gain-in-weight is decreased below that observed in the case of rats 

 on a diet containing essential fatty acids. Within eight to ten weeks, 

 the body weights usually reach a plateau, and this may be followed 

 by some decrease in body weight."^ When hydrogenated coconut oil 

 is included in the fat-free regimen daring the depletion period, the 

 length of time required for fat depletion is curtailed, and the average body 

 weight at which depletion occurs is reduced.^- Skin symptoms character- 

 istic of the fat-deficiency syndrome invariably develop concomitantly with 

 the retardation in growth. All of these fat-deficiency symptoms can be 

 counteracted when cottonseed oil or other EFA-containing fats are incor- 

 porated in the diet; they can also be prevented or cured by the adminis- 

 tration of the essential fatty acids, either as the free acids or as their esters. 



The above results are best explained on the basis that the EFA provide 

 a necessary factor to permit growth, either by furnishing essential building 

 stones in the form of EFA themselves or by providing retjuired components 

 for certain enzyme systems. Smedley-MacLean and Hume"'^ reported 

 that, when the Walker tumor is implanted in rats receiving a fat-free diet, 



181 G. Clement and P. May, /. physiol. (Paris), 48, 79-83 (1953). 



