Exercise-Induced Vascular Function: The Role of Estrogen and Shear Stress

Abstract

Exercise induces an increase in skeletal muscle blood flow, raises shear stress in the conduit arteries, which in turn leads to their vasodilation. The endogenous production of estrogen has been linked to improvements in vascular endothelial function when measured by flow-mediated dilation (FMD) invoked by a period of cuff occlusion. The interaction between estrogen and shear stress and the effect on vascular function during exercise has not been documented. PURPOSE: The current study sought to determine the exercise-induced FMD response normalized for shear across the menstrual cycle. METHODS: Seven young, sedentary, non-smoking, apparently healthy females (age = 20 ± 1 yrs; BMI = 21.5 ± 3.1) not taking oral contraception reported to the laboratory in a fasted state on days 5±2, 14±2, and 22±2 of their menstrual cycle. Subjects produced a saliva sample via the passive drool technique to confirm the concentration of sexsteroid hormones; estrogen and progesterone. Subjects performed progressive plantar flexion exercise at 2, 4, 6, and 8 Watts. After reaching steady state exercise (3 minutes), measurements of blood velocity and vessel diameter were taken in the popliteal artery via Doppler ultrasound. The slopes of the FMD (% and absolute change) and %FMD normalized for shear rate across work-rates were compared on the three phases of interest. RESULTS: The slope of % FMD to work rate in the ovulation and luteal phases (3.6 ± 0.7 3.3 ± 0.8, respectively) was greater than the menses phase (2.7 ± 0.7), and this was qualitatively reflected by FMD reported in absolute terms. In contrast, the slope of %FMD normalized for shear rate revealed a progressive increase across menstrual phases which peaked in the luteal phase when both estrogen and progesterone levels were elevated (0.041 ± 0.02, 0.055 ± 0.009 0.068 ± 0.02, menses, ovulation, and luteal, respectively). CONCLUSION: Exercise-induced vascular function (FMD) appears to be augmented with increased estrogen concentrations (ovulation and luteal phases), however when FMD is normalized for shear rate there seems to be an effect of increased estrogen alone (ovulation) that is synergistically increased by the concomitant increase in progesterone in the luteal phase of the menstrual cycle.