Effect of ovarian hormones on mitochondrial enzyme activity in the fat oxidation pathway of skeletal muscle

To examine the roles of 17β-estradiol (E₂) and progesterone (Prog) in lipid metabolism, skeletal muscle enzyme activities were studied in female Sprague-Dawley rats. Groups included sham-operated rats (C) and ovariectomized rats treated with placebo (O), E₂ (E), Prog (P), both hormones at physiological doses (P+E), or both hormones with a high dose of E₂ (P+HiE). Hormone (or vehicle only) delivery was via time-release pellets inserted at the time of surgery, 15 days before metabolic testing. Results demonstrated that carnitine palmitoyltransferase maximal activity was 19, 21, and 19% lower (P < 0.01) in O, P, and P+E rats, respectively, compared with C rats. Conversely, activity in E and P + HiE rats was 14 and 19% higher (P < 0.01) than in C. β-Hydroxyacyl-CoA dehydrogenase (β-HAD) maximal activity was 20% lower (P ± 0.01) in O than in C rats; similarly, P and P+E rats were 18 and 19% lower, respectively (P ± 0.01); however, treatment with E₂ returned β-HAD activity to C levels. These results suggest that E₂ plays a role in lipid metabolism by increasing the maximal activity of key enzymes in the fat oxidative pathway of skeletal muscle.