Docosahexaenoic acid varies in rat skeletal muscle membranes according to fibre type and provision of dietary fish oil

Background: Dietary fish oil provides polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA) and is associated with modified oxygen consumption, contractile fatigue and physiological responses to ischaemia or hypoxia in striated muscle. This study systematically investigated the membrane incorporation of fatty acids, with a focus on DHA, into skeletal muscle in relation to functional/metabolic differences and their responsiveness to fish oil doses.

Methods: Male Sprague-Dawley rats were randomised to isoenergetic diets (10% fat by weight). Human Westernstyle diets were simulated with 5.5% tallow, 2.5% n-6 PUFA sunflower seed oil and 2% olive oil (Control). HighDHA tuna oil exchanged for olive oil provided a Low (0.32%) or moderate (Mod) (1.25%) fish oil diet. Membrane phospholipid fatty acid composition was analysed in samples of five skeletal muscles selected for maximum variation in muscle fibre-type.

Results: Concentrations of DHA varied according to muscle fibre type, very strongly associated with fast oxidative glycolytic fibre population (r ² = 0.93; P < 0.01). No relationship was evident between DHA and fast glycolytic or slow oxidative fibre populations. Fish oil diets increased membrane incorporation of DHA in all muscles, mainly at the expense of n-6 PUFA linoleic and arachidonic acid.

Conclusion: The exquisite responsiveness of all skeletal muscles to as little fish oil as the equivalent of 1–2 fish meals per week in a human diet and the selective relationship to fatigable muscle fibre-types supports an integral role for DHA in muscle physiology, and particularly in fatigue resistance of fast-twitch muscles.

Summary: Skeletal muscle fibres vary according to structural, metabolic and neurological characteristics and ultimately influences contractile function. This study sort to determine if the composition of phospholipid polyunsaturated fatty acids (PUFA), incorporated in their membranes, might also differ according to fibre type and when omega-3 PUFA are made available in the diet. We systematically demonstrated that the omega-3 PUFA, docosahexaenoic acid (DHA), incorporated into skeletal muscle membranes well above its provision in the diet and without competitive influence of high omega-6 PUFA concentrations, typical to the Western-style human diet. Notably, incorporation preferentially occurred according to metabolic characteristics of each muscle, supporting the notion that DHA plays an integral role in fast oxidative glycolytic muscle fibres.