Regulation of exercise carbohydrate metabolism by estrogen and progesterone in women

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 (CHOox), 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), CHOox 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 CHOox 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.