Estrogen Treatment Decreases Muscle Proglycogen and Total Glycogen at Rest and Following Exercise in Men

Abstract

1216 Women utilize less carbohydrate during endurance exercise as compared with men, however the source of this carbohydrate “sparing” is still not clear. Studies have shown that estradiol (ES) reduces skeletal muscle, liver and cardiac glycogen utilization during exercise in male and female oophorectomized rats. PURPOSE: To determine whether ES reduces skeletal muscle glycogen storage and/or utilization during exercise in young men. METHODS: In a randomized, double-blind, cross-over design, eleven healthy, recreationally active men cycled for 90 min at an intensity of 65% VO2max in the post-absorptive state. They were tested after 8 days of either ES treatment (2mg 17-β-estradiol) or placebo (PL, polycose). Following a two-week washout period, they repeated the test after 8 days on the alternate treatment. Biopsies were obtained prior to and following exercise from the vastus lateralis muscle. The concentrations of muscle pro- (PG) and macro-(MG) glycogen were determined by first extracting MG using a weak acid (PCA) followed by HCl hydrolysis of both fractions and analysis of glucosyl units. Total glycogen was calculated as PG + MG. RESULTS: Exercise significantly decreased muscle PG, MG and total glycogen concentrations, with no effect of ES on PG, MG, or total glycogen utilization during exercise (interaction not significant). ES treatment, as compared with PL, decreased PG and total glycogen, with a trend towards lower MG, at rest and following exercise (see table). CONCLUSIONS: ES does not influence skeletal muscle glycogen utilization during exercise, yet only 8 days of ES treatment in men decreased muscle glycogen content, particularly the PG fraction. We conclude that short-term ES treatment alters skeletal muscle fuel storage but not utilization. (This research was funded by Hamilton Health Sciences Corporation, NSERC and National Institute of Nutrition)TableData are glycogen concentration in mmol glucosyl units/kg dry weight (mean ± SEM, n = 11). Two-way repeated measures ANOVA; * main effect of exercise, P < 0.001; main effect of estrogen, † P = 0.015, ‡ P = 0.09, ¶ P = 0.02.