BIOSYNTHESIS OF POLYUNSATURATED FATTY-ACIDS IN DEVELOPING BRAIN .1. METABOLIC TRANSFORMATIONS OF INTRACRANIALLY ADMINISTERED 1-C-14 LINOLENIC ACID

Thirteen-day old rats were given intracranial injections of 1-14C linolenic acid (all cis 9,12,15 octadecatrienoic acid) and were sacrificed after 8 h. Analysis of brain fatty acids showed that 16:0, 18:0, 18:1, 18:3, 20:3, 20:4, 20:5, 22:5 and 22:6 were labeled. The total fatty acid methyl esters were separated into classes according to degree of unsaturation on a AgNO3:SiO2 impregnated plate. The bands were scraped off and the eluted fatty acids were first analyzed by GLC and then subjected to reductive ozonolysis to determine double bond position. The saturated acids, 16:0 and 18:0, and the monounsaturated 18:1, must have been formed from radioactive acetate produced by .beta. oxidation of the injected linolenate. Among the polyunsaturated fatty acids, the triene fraction was characterized and identified as 18:3 .omega.3 (.DELTA.9,12,15), the starting material, and 20:3 .omega.3 (.DELTA.11,14,17); the tetraene fraction was identified as 20:4 .omega.3 (.DELTA.8,11,14,17); the pentaene fraction was identified as 20:5 .omega.3 (.DELTA.5,8,11,14,17) and 22:5 .omega.3 (.DELTA.7,10,13,16,19); and, finally, the hexaene fraction was shown to be 22:6 .omega.3 (.DELTA.4,7,10,13,16,19). The biosynthesis of these .omega.3 family fatty acids in the brain in situ is discussed.