GUGLIELMO, C.G.; WILLIAMS, T.D.; ZWINGELSTEIN, G.; BRICHON, G.; WEBER, J-M.: Functional Implications of Fatty Acid Composition of Plasma and Muscle Lipids in Migrant Birds

We report seasonal changes in concentrations and fatty acid (FA) compositions of plasma non-esterified FA, neutral lipids (NL) and phospholipids (PL), and the FA composition of flight muscle PL in western sandpipers (Calidris mauri). The observed changes may have important functional implications for fat deposition during refueling and fat oxidation during flight. Plasma NL and PL levels were greatly elevated during migration, reflecting high rates of fat deposition. The amount of FA in plasma PL was similar to, or in spring as much as twice, that of NL. Further, the NL/PL ratio of plasma may reflect the relative fat stores of invertebrate prey. Thus, measurement of plasma PL and NL/PL may improve methods to assess refueling rates at stopovers. Monounsaturation (MONO) and total unsaturation (UNSAT) of plasma NL and PL increased in migrants. Increased abundance of plasma polyunsaturated FA (especially 20:5, known to stimulate FA oxidation capacity) of migrants was strongly correlated with elevated muscle activities of 3-hydroxyacyl-CoA-dehydrogenase and carnitine palmitoyl transferase. This suggests that 20:5 (probably from the diet) may be a signal to prime the metabolic machinery of flight muscles for high rates of beta-oxidation. Muscle PL MONO increased, but UNSAT was reduced in migrants. Arachidonic acid (20:4 (n-6)) was more abundant in muscle PL in winter (29%) than during migration (19 – 22%), contributing to a reduction in n-6/n-3 FA and suggesting depletion of essential n-6 FA during prolonged flight. We conclude that endogenous or diet-related shifts in plasma FA may regulate the capacity for lipid oxidation of locomotory muscles in long-distance migrant birds.