Effects of vitamin E and alpha-lipoic acid on skeletal muscle contractile properties

Initial experiments were conducted using an in situ rat tibialis anterior ( TA) muscle preparation to assess the influence of dietary antioxidants on m uscle contractile properties. Adult Sprague-Dawley rats were divided into t wo dietary groups: 1) control diet (Con) and 2) supplemented with vitamin E (VE) and alpha -lipoic acid (alpha -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 alpha -LA. After an 8-wk feeding period, no differences existed (P > 0 .05) between the two dietary groups in maximum specific tension before or a fter a fatigue protocol or in force production during the fatigue protocol. However, in unfatigued muscle, maximal twitch tension and tetanic force pr oduction at stimulation frequencies less than or equal to 40 Hz were less ( P < 0.05) in Antiox animals compared with Con. To investigate which antioxi dant was responsible for the depressed force production, a second experimen t was conducted using an in vitro rat diaphragm preparation. Varying concen trations of VE and dihydrolipoic acid, the reduced form of <alpha>-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 frequenc ies.