Synthesis of linoleate and α‐linolenate by chain elongation in the rat

AbstractThe objective was to determine whether rats could synthesize longer chain polyunsaturates from hexadecadienoate (16∶2n−6) and hexadecatrienoate (16∶3n−3). Rats were gavaged with uniformly13C‐labelled hexadecadienoate or hexadecatrienoate, euthanized 24 h later, and total lipids were extracted from liver and carcass. Gas chromatogrpahy/combustion/isotope ratio mass spectrometry was used to measure13C levels in individual liver, carcass, and whole body fatty acids.13C Enrichment was present in desaturated and chain‐elongated polyunsaturates, including linoleate, arachidonate, α‐linolenate, and docosahexaenoate at 12–13% of the dose of tracer given.13C Enrichment from hexadecatrienoate was highest in carcass and liver α‐linolenate, representing 3.5 and 17.9% of the total α‐linolenate pool, respectively. For linoleate, arachidonate, or docosahexaenoate, the contribution of13C 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 acids as hexadecadienoate and 11.6% as hexadecatrienoate. Hence, humans consuming green vegetables probably synthesize a small proportion of their total body content of linoleate and α‐linolenate.