Short-term 17{beta}-estradiol decreases glucose Ra but not whole body metabolism during endurance exercise

The female sexhormone 17-estradiol (E₂) has been shown to increaselipid and decrease carbohydrate utilization in animals. Weadministrated oral E₂ and placebo (randomized, doubleblind, crossover) to eight human male subjects for 8 days (~3 mg/day) and measured respiratory variables, plasma substrates, hormones (E₂, testosterone, leptin, cortisol, insulin, andcatecholamines), and substrate utilization during 90 min of enduranceexercise. 6,6-²H]glucose and1,1,2,3,3-²H]glycerol tracers were used to calculatesubstrate flux. E₂ administration increased serumE₂ (0.22 to 2.44 nmol/l, P < 0.05) anddecreased serum testosterone (19.4 to 11.5 nmol/l, P < 0.05) concentrations, yet there were no treatment effects on any of theother hormones. Glucose rates of appearance (R_a) anddisappearance (R_d) were lower, and glycerolR_a-to-R_d ratio was not affected byE₂ administration. O₂ uptake, CO₂production, and respiratory exchange ratio were not affected byE₂; however, there was a decrease in heart rate (P < 0.05). Plasma lactate and glycerol wereunaffected by E₂; however, glucose was significantly higher(P < 0.05) during exercise after E₂administration. We concluded that short-term oral E₂ administration decreased glucose R_a and R_d,maintained plasma glucose homeostasis, but had no effect on substrateoxidation during exercise in men.