Medroxyprogesterone acetate inhibits the E2 potentiation of PDH activity and COX activity. A, Relative rate of PDH activity from 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 of estrus by vaginal cytology consisting primarily of anucleated cornified cells. The bars represent mean ± sem from five separate experiments with one animal per group for each experiment. *, P < 0.05 vs. OVX; (n = 5). B, Relative rate of COX activity of isolated whole-brain mitochondria. 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).