Variations in erythrocyte antioxidant glutathione peroxidase activity during the menstrual cycle

OBJECTIVE: Antioxidant enzymes are an important part of the defence mechanisms against free radical damage. Little is known, however, about the relationship between sex steroid hormones and cellular antioxidant systems. We have investigated the effect of physiological sex steroid changes on the erythrocyte antioxidant glutathione peroxidase (GSH-Px) activity during the menstrual cycle in a population of healthy normomenorrhoic women. DESIGN: Prospective, controlled. PATIENTS: Ten normally cycling women (age range: 19-28 years; mean: 23.3 years) were recruited for alternate-day blood sampling from the first day of one menstrual bleed until the first day of the subsequent menstrual phase. MEASUREMENTS: Plasma was analysed for LH, FSH, oestradiol (E2) and progesterone (P4) concentrations. Erythrocyte GSH-Px activity was evaluated on the same days in all subjects. Pyruvate-kinase (PK) activity, as an index of red blood cell population age, was also determined. RESULTS: All the women examined had a normal ovulatory cycle, as indicated by the hormone plasma pattern. Cycle length was standardized on the basis of the preovulatory E2 peak. Significant cycle phase-related changes in GSH-Px (P < 0.03) were observed, with higher GSH-Px activity levels being found from the later follicular to early luteal phase as compared to early follicular phase (chi 2 = 8.53, P < 0.001 and chi 2 = 5.54, P < 0.002, respectively). A significant positive correlation was observed between mean E2 and GSH-Px cycle-related changes (r = 0.78, P = 0.001). Conversely, no significant cycle phase-dependent variations were detected in PK. CONCLUSIONS: The findings support the hypothesis that physiological ovarian E2 production during the menstrual cycle may play an important role in regulating erythrocyte glutathione peroxidase activity.