Metabolism and positional distribution of isomers of 18-carbon dienoic fatty acids containing trans and cis double bonds by developing rat brain.

In addition to dietary linoleic acid (cis,cis-18:2), trans isomers of 18:2 may be ingested as minor components of partially hydrogenated oils. Developing rat brain has significant capacity for conversion of cis,cis-18:2 to more abundant polyenes by desaturation and elongation, but less is known about trans dienes. We have shown that incorporation of 1-14C-labeled cis,cis-,cis,trans-, and trans,trans-18:2 into brain lipids of 10-day-old rats is significant but that metabolism of the isomers between 0.2 and 72 h after intracerebral injection differs markedly. Incorporation of trans,trans-18:2 into phosphoglyceride and triacylglycerol was slower than that for cis,cis diene. Oxidation of all isomers occurred with formation of similar quantities of labeled cholesterol and palmitate. However, metabolism of trans dienes differed in two important respects: (i) desaturation and elongation of trans-containing diene was much less (less than 5 versus greater than 30% for cis,cis-18:2 after 6 h); (ii) trans,trans-18:2 and palmitate appeared to be preferentially esterified to the 1 position, whereas cis,cis-18:2 and its products were mainly in the 2 position of choline and ethanolamine phosphoglycerides. Thus, developing brain does not appear to ensure exclusion of trans dienes from membrane lipids; however, conversion by desaturation and elongation and selectivity for position of acylation differ markedly for the cis- and trans-containing dienoic isomers.