Effect of the ovarian hormones on GLUT4 expression and contraction-stimulated glucose uptake

This study examined the roles of the female sex steroids, 17β-estradiol (E₂) and progesterone (Prog), on glucose uptake and GLUT4 protein expression. Female Sprague-Dawley rats were either sham operated (C) or ovariectomized and treated with placebo (O), E₂ (E), Prog (P), or both hormones at physiological doses (P + E) or the same dose of Prog with a high dose of E₂ (P + HiE) via timed-release pellets inserted at the time of surgery, 15 days before metabolic testing. On the morning of day 15, animals received a 300-μCi injection (ip) of 2-deoxy-[¹⁴C]glucose and then either exercised on a motorized treadmill for 30 min at 0.35 m/s or remained sedentary in their cages for the same period. Basal glucose uptake was not different between the treatment groups in either the red or white quadriceps. However, glucose uptake was decreased (P < 0.05) in O, P, and P + E rats during exercise in the red quadriceps compared with C rats, whereas E and P + HiE treatment restored glucose uptake. Glycogen content in skeletal muscle followed similar trends, with no differences seen in resting animals. Postexercise red quadriceps glycogen levels were higher (P < 0.05) in the E and P + HiE rats compared with O and P. Treatment of ovariectomized rats with progesterone (P rats) decreased (P < 0.05) GLUT4 content in the red quadriceps by 21% compared with C rats. These data demonstrate that estrogen-deficient animals have a decreased ability for contraction-stimulated glucose uptake and increased glycogen use during aerobic exercise. However, changes in contraction-stimulated glucose uptake could not be explained by altered transporter protein content, since the absence of E₂ had no effect on GLUT4 protein.