COMPARATIVE BIOPOTEXCIES 799 



finding which may possibly explain the divergent results of the several 

 laboratories in regard to the biologic activity of ordinary linolenic acid. 

 Thus, it was observed that ordinary linolenic acid (9,12,15-octadecatrie- 

 noic acid) possesses practically no EFA activity (only 9%). On the other 

 hand, isolinolenic acid (the so-called 7-linolenic acid, which is chemically 

 G,9,12-octadecatrienoic acid) has 100% of the biopotency of linoleic acid. 

 Although 7-linolenic acid is known to occur in the seeds of the evening prim- 

 rose (Oenothera biennis), its distribution is limited. It is uncertain whether 

 or not ordinary linolenate may be activated by being transformed to the 

 7-isomer. More studies are needed to clarify the relationship of the several 

 linolenic acids as possible components of the EFA. Finally, Burr et al.^^ 

 and more recently Deuel and associates'^ proved that another natural 

 trienoic acid, i.e., a-elaeostearic acid (9,11,13-octadecatrienoic acid), which 

 is present in tung oil, is completely devoid of biologic potency. 



(5) The Bioyotency of Arachidonic Acid vs. Linoleic Acid 



In the original report of Burr and collaborators, ^^ methyl arachidonate 

 was listed as being somewhat inferior to linoleate as a source of EFA. 

 These workers were unable to rationalize this observation, since the ara- 

 chidonate content is knowTi to be high in liver fat and in lard, both of which 

 possess a high curative action against the fat-deficiency syndrome. Later 

 workers, Turpeinen,'^ Hume et al.,^^ and Greenberg and co-workers, ^'^ 

 however, assigned to arachidonic acid potencies two or three times that of 

 linoleic acid. On the other hand, Thomasson'^ has ascribed a value of only 

 131% to the tetraenoic acid, as compared with that of linoleate. 



The reasons for the divergence in bioactivity reported by the different 

 groups of workers are not entirely clear. In the original tests of Burr et 

 al.,^^ the low value for arachidonate may have been due to the fact that 

 "some of the purified arachidonic acid which we have fed has been altered 

 in the process of preparation." Even so, Burr et al.^^ were unable to con- 

 firm the high potency of arachidonate reported by Turpeinen'^ when they 

 used the same sample of acid. However, in spite of this single negative 

 finding, the consensus is that arachidonic acid is the most active member of 

 the EFA. 



On the basis of the experimental findings, there appears to be little doubt 



96 E. M. Hume, L. C. A. Nunn, I. Smedley-MacLean, and H. H. Smith, Biochem. J., 

 54,879-883(1940). 



" S. M. Greenberg, C. E. Calbert, H. J. Deuel, Jr., and J. B. Brown, /. Nutrition, 45, 

 521-533(1951). 



98 G. O. Burr, J. B. Brown, J. P. Kass, and W. O. Lundberg, Proc. Soc. Exptl. Biol. 

 Med., 44, 242-244 (1940). 



