810 Xlll. ESSENTIAL FATTY ACIDS 



when linoleate is fed, as compared with the values in control experiments. 

 The supplementation of fat-deficient rats with corn oil (which contains 

 linoleate but no arachidonate) markedly increased the tetraenoic acid 

 content of liver, kidney, heart, and brain in the experiments of Riecke- 

 hoff et al^'^" Even before the spectrophotometric method of analysis for 

 the polyunsaturated acids was available, Ellis and Isbell"^-^'^ found evidence 

 of the appearance of arachidonic acid in the pig upon the ingestion of lino- 

 leic acid. Nunn and Smedley-MacLean,^^ and also Smedley-MacLean 

 and Hume^^^ presented additional evidence of the appearance of arachi- 

 donate in fat-deficient rats following the administration of linoleate. Wid- 

 mer and Holman,^^^ in a study of the effects of fatty acids in the diet on the 

 synthesis of the EFA, confirmed the transformation of linoleate to arachi- 

 donate in the rat. 



Evidence for the synthesis of arachidonic acid from linoleic acid has like- 

 wise been adduced from experiments on chickens. Thus, Reiser and Gib- 

 gQj^i64 reported an increase of tetraenoic acid in the tissues of growing chicks 

 on a fat-free diet when cottonseed oil or ethyl linoleate was fed. The 

 increases were least in the neutral fat of the carcass, more pronounced in 

 the organ neutral fat, and increasingly greater in the carcass and organ 

 phospholipids. In other studies by Reiser and Gibson"'^ and Reiser et 

 al.,^^ it was shown that the polyunsaturated fatty acids reached a minimum 

 value in the yolk of eggs obtained from hens on a fat-free diet. When 

 single unsaturated acids were fed, their interconversion to other unsatu- 

 rated acids in the egg-yolk fat could be followed. It was found that tetra- 

 enoic acid (arachidonic acid) made its appearance in the yolk after ethyl 

 linoleate or cottonseed oil had been fed to the hens. It must be pointed out 

 that spectral eviderce for the interconversions of polyunsaturated acids 

 should be interpreted with caution. The presence of dienoic, trienoic, or 

 tetraenoic acids does not necessarily mean that biologically potent acids 

 have been produced. However, Holman'^^ states that the fact that ara- 

 chidonic acid is not a constituent of plants but is usually a component of 

 animal tissues, and that it may substitute for linoleate in the nutrition of 

 the animal, leads one on a priori grounds to conclude that the transforma- 

 tion of linoleate to arachidonate can actually occur. Finally, probably 

 the most convincing evidence of the change of linoleate to arachidonate is 

 found in the experiments with tagged acids described in the next section. 



i"I. Smedley-MacLean and E. M. Hume, Biochem., J., 35, 996-1002 (1941). 



i"R. Reiser and B. Gibson, J. Nutrition, 42, 325-336 (1950). 



166 R. Reiser and B. Gibson, /. Nutrition, 40, 429-440 (1950). 



"* R. T. Holman, Personal communication to the author (H. J. D.), 1955. 



