Regulation of exercise carbohydrate metabolism by estrogen and progesterone in women

To assess the roles of endogenous estrogen (E₂) and progesterone (P₄) in regulating exercise carbohydrate use, we used pharmacological suppression and replacement to create three distinct hormonal environments: baseline (B), with E₂ and P₄ low; estrogen only (E), with E₂ high and P₄ low; and estrogen/progesterone (E + P), with E₂ and P₄ 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 (r² = 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 E₂ and P₄ on EMGU may be mediated by their impact on FFA availability or vice versa.