INTRACRANIAL CONVERSION OF LINOLEIC ACID TO ARACHIDONIC ACID: EVIDENCE FOR LACK OF Δ8 DESATURASE IN THE BRAIN

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Abstract
Eleven‐day old rats were given intracranial injection of [1‐14C]linoleic acid (all cis 9,12 octadecadienoic acid) and sacrificed after 8 h. Analysis of brain fatty acids showed that 16:0, 18:2, 20:2,20:3 and 20:4 were labeled. Separation by AgN03:Si02 TLC plates followed by reductive ozonolysis characterized thc polyunsaturated fatty acids as 18:2 (Δ9,12), 20:2 (Δ11,14), 20:3 (Δ8,11,14) and 20:4 (Δ5,8,11,14). A smaller amount of 18:3 (Δ6,9,12) was also identified. This initially suggested 20:2 (A1 1,14) as an intermediate in the optional pathway of biosynthesis of arachidonate. However, when [l‐14C]eicosadienoic acid (Δ1 1,141 itself was injected in the brain it was converted to 20:3 (Δ5,11,14) (a non‐methylene interrupted double bond system) rather than the expected 20:3 (Δ8,11,14). Only a small amount of arachidonate was formed from 20:2 (Δ11,14). Thus it was concluded that 20:2 (Δ11,14) was not an intermediate in the pathways of arachidonate biosynthesis due to lack of Δ5 desaturase in thc brain which agrees with the findings of SPKECRER & LEE (1975) in rat liver.