Plasma phospholipid fatty acid and ex vivo neutrophil responses are differentially altered in dogs fed fish- and linseed-oil containing diets at the same n-6:n-3 fatty acid ratio.

The effect of diets containing either 18-carbon n-3 fatty acids (FA) or 20/22-carbon n-3 FA on canine plasma and neutrophil membrane fatty acid composition, superoxide and leukotriene B₄ and B₅ production when fed at the same n-6:n-3 fatty acid ratio was investigated. Four groups of ten dogs each were fed a low fat basal diet supplemented with safflower oil (SFO), beef tallow (BTO), linseed oil (LSO), or Menhaden fish oil (MHO) for 28 days. Dietary fat provided 40.8% of energy and the n-6:n-3 of the diets were ~100:1, 9.7:1, 0.38:1, and 0.34:1 for the SFO, BTO, LSO and MHO groups, respectively. The MHO and LSO groups had increased incorporation of EPA and DPA in both the plasma and neutrophil membranes compared to the BTO and SFO groups. DHA was observed in the MHO but not in the LSO group. Neutrophils from the MHO diet fed dogs had less LTB₄ and greater LTB₅ than the other three groups. The LSO group also showed a reduction in LTB₄ and greater LTB₅ production compared to the SFO and BTO groups. Both LSO and MHO groups had lower superoxide production compared to the SFO and BTO groups. Diets containing 18 or 20/22 carbon n-3 FA fed at the same n-6:n-3 resulted in differential incorporation of long chain n-3 FA into neutrophil membranes. Thus, fatty acid type and chain length individually affect neutrophil membrane structure and function and these effects exist independent of dietary total n-6:total n-3 FA ratios.