P4 and E2 enhance mitochondrial respiratory activity. Oxygen electrode measurements of respiration using isolated rat brain mitochondria. A, Representative traces of mitochondrial oxygen consumption with or without in vivo E2 (30 μg/kg), P4 (30 μg/kg), E2/P4, or sesame oil vehicle control treatment (Ct) in the presence of l-malate (Mal; 5 mm), l-glutamate (Glut; 5 mm), and ADP (410 μm) to initiate state 3 respiration and atractyloside to induce state 4o respiration. The traces are representative of six to eight separate experiments. B, Percent changes in mitochondrial RCR (state 3/state 4o). The data represent mean ± sem of eight separate experiments. *, P < 0.05 compared with control; n = 8.