Medroxyprogesterone acetate inhibits the E2 potentiation of the antioxidant profile of brain mitochondria. A, Relative rate of MnSOD activity of isolated whole-brain mitochondria ± in vivo E2 (30 μg/kg), MPA (120 μg/kg), E2+MPA (30 μg/kg + 120 μg/kg), or corn oil vehicle control (OVX). Ovary-intact (shamOVX) rats served as a positive control and were selected on the morning after the estrous cycle by vaginal cytology. The bars represent mean ± sem from five separate experiments with one animal per group for each experiment. *, P < 0.05 vs. OVX; ‡, P < 0.05 vs. E2 (n = 5). Immunoblot data were normalized to loading control and compared relative to OVX. Expression of the mitochondrial antioxidant proteins MnSOD in hippocampus (B) and PrdxV in whole-brain mitochondria (C) was measured using Western blot analysis. The bars represent mean ± sem from five animals per group. *, P < 0.05 vs. OVX; ‡, P < 0.05 vs. E2 (n = 5).