186 III. OXIDATION AND METABOLISM 



linolenate in the storage fat is decreased by feeding polyunsaturated acids, 

 and is increased by the administration of fat-free diets. Thus, Reiser 

 et al.^^^ reported that, on usual diets, the neutral fat and phospholipid of the 

 egg-yolk fat of hens contained only 0.18% and 0.00%, respectively, of 

 trienoic acids. After fifty-two weeks on a fat-free diet, the values of the 

 above fractions were found to have increased to 0.42% and 2.3%, respec- 

 tively. In contradistinction to the augmentative effect of fasting, the 

 administration of corn oil decreased the proportion of trienoic acids in 

 heart fatty acids from 22.2% to 4.8%.«i» More recently, Klein and 

 Johnson®" observed that the trienoic acid content of mitochondria, 

 "poorly sedimentable layer" and microsomes of the livers of senescent rats, 

 and of rats on a fat-free diet, was increased over the control level in both 

 cases. Smedley-MacLean®^^ reported an increase in trienoic acid in fat 

 deficiency; it was suggested that this "trienoic acid fraction" may rep- 

 resent partially-hydrogenated arachidonate, resulting from the attempt on 

 the part of the rat to make the most of its stores of arachidonate. 



The metabolic fate of ingested hnolenic acid apparently varies with 

 species. Reiser and co-workers®-^ reported that Hnolenic acid is converted 

 into dienoic, tetraenoic, pentaenoic, and hexaenoic acids in the hen; 

 these polyunsaturated acids are deposited in the egg-yolk fat in increased 

 amounts after linolenate feeding. On the other hand Holman®^* believes 

 that linolenic acid is converted chiefly to hexaenoic acid. In another 

 paper,®^* he also reported its conversion to unsaturated acids having four, 

 five, and six double bonds. 



The data recorded above are difficult to reconcile with the information 

 available on the nutritional value of linolenic acid. A number of 

 workers®^®"" have adduced e\ddence to show that linoleic and linolenic 

 acids have different fimctions. While linoleic and arachidonic acid 

 support growth and also alleviate skin symptoms, linolenic acid apparently 

 supports growth to only a slight extent, unless "sparked" with linoleic 

 acid, and has no effect upon the dermatitis.®^^ It has been further demon- 

 strated that linolenic acid is only slightly active in protecting rats from 



"2 p. D. Klein and R. M. Johnson, Federation Proc., 12, 231 (1953). 



"' I. Smedley-MacLean, T'he Metabolism of Fat, Methuen, London, 1943. 



^^^ R. T. Holman, Proc. Third Conference on Research, Amer. Meat Inst., Chicago, 1951, 

 pp. 1-10. 



«35 R. T. Holman, Proc. Soc. Exptl. Biol. Med., 76, 100-102 (1951). 



^^^ G. O. Burr, Federation Proc, 1, 224-233 (1942). 



"' S. M. Greenberg, C. E. Calbert, E. E. Savage, and H. J. Deuel, Jr., /. Nutrition, U, 

 473-486 (1950). 



