Low dietary fish oil threshold for myocardial membrane n-3 PUFA enrichment independent of n-6 PUFA intake in rats
Long chain n-3 PUFA docosahexaenoic acid (DHA) is important for heart and brain function. Investigations of biologically plausible mechanisms using animal models that associate cardioprotection with DHA incorporation into myocardial membranes are derived from supra-physiological fish oil (FO) intakes. We measured the incorporation of DHA into myocardial membranes of rats from low dietary FO intake, within human dietary range and quantitatively assessed the influence of dietary n-6 PUFA. With rats fed diets containing 0.16%-5% FO, equal to 0.12% - 8.7% energy (%en) as eicosapentaenoic acid (EPA) and DHA (EPA+DHA), and either 1.5%en or 7.5%en n-6 PUFA (linoleic acid) for four weeks, dietary n-6:n-3 PUFA ratios ranged from 74 to 0.3. Myocardial DHA concentration increased in a log-linear fashion with a dietary threshold of 0.019%en as EPA+DHA and half maximal dietary [EPA+DHA] equal to 0.29%en (95%CI 0.23-0.35). Dietary linoleic acid intake did not influence myocardial DHA. Myocardial membranes are sensitive to absolute dietary intake of long-chain n-3 PUFA at low %en in the rat, equivalent to a human intake of one meal of fatty fish per week or less. The dietary ratio of n-6:n-3 PUFA has no influence on long chain n-3 PUFA cellular incorporation from dietary fish oil.