SOURCES OF FAT IN ANIMAL BODY 533 



presence of arachidonic acid in thyroid, spleen, and suprarenal lipids, in 

 which it comprised 0.4, 4.0, and 5.5% of the total fatty acids. However, 

 the highest concentration of this C 2 o-unsaturated acid is in the suprarenal 

 glands, in which it makes up 11.2% of the total fatty acids 76 and as much as 

 22% of the suprarenal phospholipids. 7778 According to Holman, 79 the 

 best practical source of arachidonic acid in animal tissue is bull testicle. 



Arachidonic acid is presumably a component of most animal fats. 

 The acid has been shown to be present to the extent of 2.2% in the rat, 51 

 and 2.0% in pig depot fat. 8081 It has likewise been found to occur in the 

 fat of fowl (duck, goose, chicken), 82 of the dog (as cited earlier), 74 and of 

 man 65,66,33 s ma ll amounts of arachidonic acid have been reported in egg 

 lecithin 84 and in butterfat. 85 



When weanling rats were kept on a fat-free diet, the arachidonate con- 

 tent was found by Longenecker 51 to be extremely low (0.2-0.3%). On the 

 other hand, when the diet contained a source of arachidonate (dog chow), 

 considerable amounts of this acid were observed (2.2%). When these 

 animals were fasted, the arachidonate was spared to a considerable extent. 

 Smedley-MacLean and Hume 86 reported very little change in the arachi- 

 donate content of the fat-free dry weight of rats kept on a fat-free diet for 

 from six to eleven months. It was very low in the subcutaneous tissue, 

 and only after ten weeks of dosing with methyl arachidonate was a definite 

 increase in the arachidonate content noted in this tissue. However, an 

 immediate increase occurred in the liver when curative doses of this acid 

 were given. When large Walker tumors were implanted in rats, and the 

 animals were maintained on a fat-free diet over a period of 97 days, a 

 marked decrease was noted in the highly unsaturated acid in the subcu- 

 taneous fat, but not in the carcass fat. 87 It has been suggested that the 

 arachidonate is reduced when new tissue is being formed; however, its 

 constant value when new tissue is not being laid down indicates that it is 

 not required for the normal maintenance of the cell. 86 



76 J. B. Brown, unpublished data, cited by W. C. Ault and J. B. Brown, J. Biol. 

 Chem., 107, 607-614 (1934), p. 607. 



77 W. C. Ault and J. B. Brown, J. Biol. Chem., 107, 607-614 (1934). 



78 G. Y. Shinowara and J. B. Brown, /. Biol. Chem., 134, 331-340 (1940). 



79 R. T. Holman, personal communication to the author, 1953. 



80 H. K. Dean and T. P. Hilditch, Biochem. J., 27, 1950-1956 (1933). 



81 A. Banks and T. P. Hilditch, Biochem. J., 26, 298-308 (1932). 



82 J. B. Brown and C. C. Sheldon, J. Am. Chem. Soc., 56, 2149-2151 (1934). 



83 D. L. Cramer and J. B. Brown, /. Biol. Chem., 151, 427-438 (1943). 



84 P. A. Levene and I. P. Rolf, /. Biol. Chem., 51, 507-513 (1922). 



86 A. W. Bosworth and E. W. Sisson, /. Biol. Chem., 107, 489-496 (1934). 



86 I. Smedlev-MacLean and E. M. Hume, Biochem. J., 35, 990-995 (1941). 



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



