EFFECTS OF ESTRADIOL ON SUBSTRATE TURNOVER DURING EXERCISE IN AMENORRHEIC FEMALES

The purpose of this investigation was to determine the effects of tran sdermal estradiol (E2) replacement on substrate utilization during exe rcise. Amenorrheic females (N = 6) performed three exercise trials fol lowing 72 h of placebo (C 72) and 72 and 144 h of medicated transderma l estradiol (E2) treatment (E2 72 and E2 144). Exercise involved 90 mi n of treadmill running at 65% VO2max followed by timed exercise to exh austion at 85% VO2max. Resting blood samples were obtained for glucose , insulin, free fatty acids (FFA), and E2. Exercise blood samples were obtained for E2, lactate, epinephrine, and norepinephrine. Rates of a ppearance and disposal were calculated for glucose and glycerol using a primed, continuous infusion of [6,6-H-2] glucose and [H-2(5)] glycer ol. Medicated transdermal placement increased E2 significantly at rest , before exercise (35.03 +/- 12.3, 69.5 +/- 20.1, and 73.1 +/- 31.6 pg .mL(-1) for the C 72, E2 72, and E2 144 trials, respectively, P < 0.05 ). Resting FFA increased significantly following E2 treatment (0.28 +/ - 0.16, 0.41 +/- 0.27, and 0.40 +/- 0.21 mmol.L-1 for the C 72, E2 72 and E2 144 trials, respectively, P < 0.05). Glucose Ra was significant ly decreased during exercise as a result of E2 replacement (21.9 +/- 7 .7, 18.9 +/- 6.2, and 18.9 +/- 5.6 mu mol.kg(-1).min(-1) for the C 72, E2 72, and E2 144 trials, respectively, P < 0.05). Average glucose Rd also decreased during exercise as a result of E2 replacement (21.3 +/ - 7.8, 18.5 +/- 6.4, and 18.6 +/- 5.8 mu mol.kg(-1).min(-1) for the C 72, E2 72, and E2 144 trials, respectively, P < 0.05). However, the es timated relative contribution of plasma glucose and muscle glycogen to total carbohydrate oxidation was similar among the trials. Epinephrin e values were significantly lower late in exercise during the E2 72 an d E2 144 trials, compared with the C 72 trial (P < 0.05). These result s indicate that elevated E2, levels can alter glucose metabolism at re st and during moderate intensity exercise as a result of decreased glu coneogenesis, epinephrine secretion, and/or glucose transport.