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

To examine the roles of 17 beta -estradiol (E-2) and progesterone (Prog) in lipid metabolism, skeletal muscle enzyme activities were studied in female Sprague-Dawley rats. Groups included sham-operated rats (C) and ovariectom ized rats treated with placebo (O), E-2 (E), Prog (P), both hormones at phy siological doses (P + E), or both hormones with a high dose of E-2 (P + HiE ). Hormone (or vehicle only) delivery was via time-release pellets inserted at the time of surgery, 15 days before metabolic testing. Results demonstr ated that carnitine palmitoyltransferase maximal activity was 19, 21, and 1 9% 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. beta -Hydroxyacyl-CoA dehydrogenase (beta -HAD) maximal a ctivity 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 w ith E-2 returned beta -HAD activity to C levels. These results suggest that E-2 plays a role in lipid metabolism by increasing the maximal activity of key enzymes in the fat oxidative pathway of skeletal muscle.