Antioxidant enzyme activity during prolonged exercise in amenorrheic and eumenorrheic athletes

Exogenous 17β-estradiol (E₂) has been shown to be associated with elevated levels of erythrocyte glutathione peroxidase (GPX) activity. The purpose of this study was to examine the influence of endogenous E₂, as defined by menstrual status (amenorrhea v eumenorrhea), on activity of blood antioxidant enzymes at rest and during prolonged exercise. Six amenorrheic (AMc) and six eumenorrheic (EUc) athletes were subjected to a treadmill running test at 60% VO₂max for 90 minutes. Serial blood samples were taken from a forearm vein at rest, 30, 60, and 90 minutes during exercise, and 15 minutes into recovery. Resting estrogen levels were significantly lower in AMc athletes at rest and during exercise as compared with EUc athletes, whereas plasma cortisol levels in AMc were significantly higher. GPX activity was significantly higher in AMc than EUc at rest (46.9 ± 7.7 v 30.2 ± 2.2 nmol/min × mg Hb, P < .05, respectively) and throughout exercise. Glutathione reductase (GR) activity was similar between the two groups at rest and was significantly higher (P < .01) in AMc than EUc during exercise. Plasma lipid peroxidation and catalase activity did not change significantly in response to exercise, nor were they different between AMc and EUc athletes. GPX activity was found to be negatively correlated with E₂ (r = -.64, P < .01) and positively correlated with cortisol (r = .69, P < .01). It is tentatively concluded that the alteration of hormonal status in amenorrhea has an influence on the blood antioxidant enzyme system.