Regulation of exercise carbohydrate metabolism by estrogen and progesterone in women

1 Department of Exercise Science, University of Massachusetts, Amherst 01003; 2 Division of Endocrinology, Diabetes and Metabolism and 3 Department of Obstetrics and Gynecology, Baystate Medical Center, Springfield, Massachusetts 01199; and 4 Department of Health and Human Performance, University of Montana, Missoula, Montana 59813 To assess the roles of endogenous estrogen (E 2 ) and progesterone (P 4 ) in regulating exercise carbohydrate use, we used pharmacological suppression and replacement to create three distinct hormonal environments: baseline (B), with E 2 and P 4 low; estrogen only (E), with E 2 high and P 4 low; and estrogen/progesterone (E + P), with E 2 and P 4 high. Blood glucose uptake (R d ), total carbohydrate oxidation (CHO ox ), and estimated muscle glycogen utilization (EMGU) were assessed during 60 min of submaximal exercise by use of stable isotope dilution and indirect calorimetry in eight eumenorrheic women. Compared with B (1.26 ± 0.04 g/min) and E + P (1.27 ± 0.04 g/min), CHO ox was lower with E (1.05 ± 0.02 g/min). Glucose R d tended to be lower with E and E + P relative to B. EMGU was 25% lower with E than with B or E + P. Plasma free fatty acids (FFA) were inversely related to EMGU ( r 2 = 0.49). The data suggest that estrogen lowers CHO ox by reducing EMGU and glucose R d . Progesterone increases EMGU but not glucose R d . The opposing actions of E 2 and P 4 on EMGU may be mediated by their impact on FFA availability or vice versa. ovarian hormones; menstrual cycle; fat oxidation; stable isotope; glycogen