Muscle GSH-Px activity after prolonged exercise,training, and selenium supplementation

A double-blind study of the effects of supplementing with selenium vs. placebo on the physiological responses to acute and chronic exercise was conducted in 24 healthy, nonsmoking males, mean age 22.9±2.1 yr, randomly divided into two groups of 12 (Pla/Sel). After a controlled period in the absence of training, all subjects were put on an individualized endurance training program with the same rules of progression and overload (3 sessions/wk×10 wk). Supplementation, either real (240 μg of organic selenium/d in Sel group) or imaginary (Pla group) was administered during the same period. In each of the conditions Pre- and Post- (training ± sel supplementation), muscle, plasma, and systemic parameters were determined before (BF) and after (AF) acute exercise, involving the repetition of muscle work cycles separated by 5-min recovery periods, combining 20 min at 65% and a maximal duration of 100% VO₂ max of running on a treadmill, leading the subjects to exhaustion between 2 h 40 min and 3 h 30 min. Changes in parameters as a function of three independent variables:

1. Acute exercise (E);
2. Chronic exercise (T); and
3. Selenium supplementing (S)

were tested with ANOVA and the Student\rsst-test on paired series. Among the variables examined, muscle glutathione peroxidase (GPx) presented a remarkable behavior. Enzymatic activity:

1. Decreased significantly (p<0.05,n=24) between the beginning and the end of acute exercise: 29.6±12 vs. 20.8±8.1 IU·g protein^?1 in Pre conditions;
2. Remained at the same level in resting conditions between the beginning and end of training (from Pre to Post) regardless of the group: 33.5±10.8 vs. 32.3±19.8 and 25.7±12.4 vs. 23.5±10.2 IU·g protein^?1 in Pla and Sel subjects, respectively; and
3. Increased from 23.5±10.2 to 37.3±28.5 (P=0.057) during acute exercise in Post-conditions (after training) in supplemented subjects (Sel group).

The situation was as if acute exercise played the role of allosteric stimulator of the GPx reaction in muscle.