SYNTHESIS OF LINOLEATE AND ALPHA-LINOLENATE BY CHAIN ELONGATION IN THE RAT

The objective was to determine whether rats could synthesize longer ch ain polyunsaturates from hexadecadienoate (16:2n-6) and hexadecatrieno ate (16:3n-3). Rats were gavaged with uniformly C-13-labelled hexadeca dienoate or hexadecatrienoate, euthanized 24 h later, and total lipids were extracted from liver and carcass. Gas chromatograpby/combustion/ isotope ratio mass spectrometry was used to measure C-13 levels in ind ividual liver, carcass, and whole body fatty acids. C-13 Enrichment wa s present in desaturated and chain-elongated polyunsaturates, includin g linoleate, arachidonate, alpha-linolenate, and docosahexaenoate at 1 2-13% of the dose of tracer given. C-13 Enrichment from hexadecatrieno ate was highest in carcass and liver alpha-linolenate, representing 3. 5 and 17.9% of the total alpha-linolenate pool, respectively. For lino leate, arachidonate, or docosahexaenoate, the contribution of C-13 did not exceed 0.2% of the total body pool. Green leafy vegetables common in the human diet were shown to contain up to 1.2% of total fatty aci ds as hexadecadienoate and 11.6% as hexadecatrienoate. Hence, humans c onsuming green vegetables probably synthesize a small proportion of th eir total body content of linoleate and alpha-linolenate.