V. BIOGENESIS AND METABOLISM 283 



Linolelaidate (<rans,/rans-9,12-octadeeadienoic) is totally ineffective as an 

 essential acid, and conjugated linoleic acid is deleterious. 



Similar interconversions have been observed to take place in the chicken 

 as evidenced by the analyses of eggs of a laying hen.^^ There appears to be 

 a difference between the hen and the rat in the conversions possible. Reiser 

 reported conversion of dienoic acid to pentaenoic and tetraenoic acids and 

 the conversion of trienoic acid to all acids having from two to six double 

 bonds. However, a word of caution should be spoken concerning the ex- 

 tensive interpretation of spectrophotometric data of the type used for 

 these studies when as yet no analytical standards exist for the determinations 

 of five and six double bonds. It is questionable whether calculations of 

 saturated, oleic, linoleic, and linolenic acid contents are valid when the 

 estimations of four, five, and six double-bonded acids are only relative and 

 proper corrections for their concentrations cannot be made (see p. 287). 



Two studies have been made of the metabolic conversions of conjugated 

 unsaturated fatty acids. It was observed by Miller and Burr^^ that the eleo- 

 stearic acid (9 , 1 1 , 13-octadecatrienoic acid) of tung oil was converted to 

 conjugated dieneoic acid in the rat. Reiser^* has confirmed this finding and 

 studied the metabolism of conjugated dienoic acid in the laying hen. How- 

 ever, the established conversion of conjugated trienoic acid to conjugated 

 dienoic acid in the animal should not be confused Avith similar conversions 

 in the non-conjugated essential fatty acids. The two groups of acids differ 

 markedly in physical and chemical properties and in biological activity, 

 and in their metabolism and in mechanism of in vitro oxidations they bear 

 no relation one to the other. 



A. DIETARY FACTORS AFFECTING METABOLISM 



The first recognized relationship of essential fatty acids to other dietary 

 essentials was that pyridoxine deficiency produces deficiency symptoms in 

 rats very similar to those of fat deficiency.^^"^'^ A double deficiency of fat 

 and pyridoxine results in rapid development of more severe symptoms, and 

 supplementation with either linoleate or pyridoxine reduces the severity 

 of the symptoms (see Fig. 5). Medes et al} studied the relationship of these 

 two dietary essentials, and the results showed that relief from the double 



»2 R. Reiser, J. Nutrition 44, 159 (1951). 



1' E. S. Miller and G. O. Burr, Proc. Soc. Exptl. Biol. Med. 36, 726 (1937). 



" R. Reiser, Arch. Biochem. and Biophtjs. 32, 113 (1951). 



'* L. R. Richardson, A. G. Hogan, and K. F. Itschner, Univ. Missouri Research Bull. 

 333. 



'^ F. W. Quackenhush, H. Steenbock, F. A. Kummerow, and R. R. Platz, /. Nutri- 

 tion 24, 225 (1942). 



'^ R. Jiirgons, II. Pfaltz, and M. Reincrt. Helv. Physiol, et Pharmacol. y{cta 3, 41 

 (1945). 



