Docosahexaenoic acid and n-6 docosapentaenoic acid supplementation alter rat skeletal muscle fatty acid composition

In all muscles of the DAM group, the concentration of 22:5n-6 was significantly lower than 22:6n-3 concentrations. While 22:5n-6 was elevated in the AR-LA group and the AR-DPAn-6 group, 20:4n-6 tended to be higher in the AR-LA muscles and not in the AR-DPAn-6 muscles. The AR-DHA+DPAn-6 had a slight, but non-significant increase in 22:5n-6 content. In the red gastrocnemius of the AR-DPAn-6 group, 22:5n-6 levels (8.1 ± 2.8 wt. %) did not reciprocally replace the 22:6n-3 levels observed in AR-DHA reared rats (12.2 ± 2.3 wt. %) suggesting a specific preference/requirement for 22:6n-3 in red gastrocnemius.Dietary 22:5n-6 is incorporated into skeletal muscles and appears to largely compete with 22:6n-3 for incorporation into lipids. In contrast, 18:2n-6 feeding tends to result in elevations of 20:4n-6 and restrained increases of 22:5n-6. As such, 22:5n-6 dietary comparison groups may be useful in elucidating specific requirements for 22:6n-3 to support optimal health and disease prevention.Docosahexaenoic acid (22:6n-3, DHA) demonstrates health benefits through various physiological systems including neurological [1], cardiovascular [2] and inflammatory systems [3]. These mechanisms are largely derived through 22:6n-3 incorporation in place of other fatty acids into biological membranes and cell signalling mechanisms. The fatty acid composition of muscle has been implicated in obesity and insulin resistance and dietary intake can modify these compositions [4,5]. Feeding rats an essential fatty acid deficient diet results in higher peak twitch tension, reduced twitch contraction and half-relaxation times and quicker fatigability as compared with n-6 and n-3 fatty acid enriched diets in soleus and/or extensor digitorum longus muscles [6].The impact of dietary fatty acid manipulation on the fatty acid composition of rat skeletal muscle has been studied [7-10]. However, only one of these studies, examining a mixed muscle homogenate, [7] employed a traditional two generational