Effects of vitamin E and Lipoic acid on skeletal muscle contractile properties

Initial ex- periments were conducted using an in situ rat tibialis anterior (TA) muscle preparation to assess the influence of di- etary antioxidants on muscle contractile properties. Adult Sprague-Dawley rats were divided into two dietary groups: 1) control diet (Con) and 2) supplemented with vitamin E (VE) and a-lipoic acid (a-LA) (Antiox). Antiox rats were fed the Con rats’ diet (AIN-93M) with an additional 10,000 IU VE/kg diet and 1.65 g/kg a-LA. After an 8-wk feeding period, no differences existed (P > 0.05) between the two dietary groups in maximum specific tension before or after a fatigue protocol or in force production during the fatigue protocol. However, in unfatigued muscle, maximal twitch tension and tetanic force production at stimulation frequencies <40 Hz were less (P < 0.05) in Antiox animals compared with Con. To inves- tigate which antioxidant was responsible for the depressed force production, a second experiment was conducted using an in vitro rat diaphragm preparation. Varying concentra- tions of VE and dihydrolipoic acid, the reduced form of a-LA, were added either individually or in combination to baths containing diaphragm muscle strips. The results from these experiments indicate that high levels of VE depress skeletal muscle force production at low stimulation frequencie