Plasma glutathione peroxidase in healthy young adults: influence of gender and physical activity

Objectives Oxidative stress is implicated in the pathophysiology of many cardiovascular diseases. Plasma glutathione peroxidase (pl•GPx, GPx3) is an antioxidant enzyme found in the extracellular fluid. This study aimed to determine reference values for serum GPx3 concentration and GPx activity in young healthy males and females of similar aerobic fitness and to determine the impact of acute physical activity on serum GPx. Design and methods 52 young, healthy but not physically trained subjects (24 male, 28 female; AGE = 20.4 ± 0.7 yr, cycling VO2 max = 39.2 ± 1.6 mL/kg/min; mean ± SE) participated in this study. An independent group of 18 subjects participated in an acute, 90 min bout of 50% VO2 max cycling exercise. Serum GPx activity and GPx3 protein levels, as well as estradiol and 8-iso- prostaglandin F2α (8-iso-PGF2α; an index of lipid peroxidation) were determined. Results Females had significantly higher serum GPx3 concentration (29.1 ± 1.6 vs. 24.2 ± 1.3 mg/L, p< 0.01) and serum GPx activity (256.4 ± 10.4 vs. 222.8 ± 15.6 U/L, p< 0.05) than males; specific activity (U/mg) was not different between genders. There was no significant gender difference in 8-iso-PGF2α. No significant correlation was found between either GPx activity or GPx3 concentration and serum estradiol or VO2 max. The acute, prolonged, mild intensity exercise did not affect serum GPx activity or 8-iso-PGF2a levels in males or females. Conclusions The results of this study suggest that in a young, healthy but not physically well-trained population females are endowed with slightly higher serum GPx3 concentrations and GPx activities than males, but the functional significance of this has not been established. Furthermore, the results indicate that serum GPx levels are not associated with aerobic fitness level, or serum estradiol concentration and that acute, prolonged, mild exercise does not affect the activity of serum GPx in this population.