Biosynthesis of polyunsaturated fatty acids in the developing brain: I. Metabolic transformations of intracranially administered 1-¹⁴C linolenic acid

Abstract

Thirteen-day old rats were given intracranial injections of 1-¹⁴C linolenic acid (allcis 9,12,15 octa decatrienoic acid) and were sacrificed after 8 hr. 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 radiogas liquid chromatography and then subjected to reductive ozonolysis to determine double bond position. The saturated acids, 16∶0, and 18∶0, as well as the mono-unsaturated 18∶1, must have been formed from radioactive acetate produced by β oxidation of the injected linolenate. Among the polyunsaturated fatty acids, the triene fraction was characterized and identified as 18∶3 ε3 (Δ^9,12,15), the starting material, and 20∶3 ω3 (Δ^11,14,17); the tetraene fraction was identified as 20∶4 ω3 (Δ^8,11,14,17); the pentaene fraction was identified as 20∶5 ω3 (Δ^5,8,11,14,17) and 22∶5 ω3 (Δ^{7,10,13,16,19}); and, finally, the hexaene fraction was shown to be 22∶6 ω3 (Δ^{4,7,10,13,16,19}). The biosynthesis of these ω3 family fatty acids in the brain in situ is discussed.