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

The 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 uniformly 13 C‐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 measure 13 C levels in individual liver, carcass, and whole body fatty acids. 13 C 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. 13 C 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 of 13 C 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.