The impact of menstrual phase on lower limb microvascular function, ERα, eNOS, and p-eNOS protein in premenopausal females

There is variability in the impact of the menstrual phase on microvascular function with some studies reporting an increase from the early follicular (EF) to late follicular (LF) phase. Estradiol (E2) may increase nitric oxide bioavailability and thereby microvascular function through increasing estrogen receptor α (ERα), endothelial nitric oxide synthase (eNOS), and phosphorylated eNOS (p-eNOS) protein. It is unknown whether variability in ERα, eNOS, and p-eNOS protein levels drives menstrual cycle-related changes in microvascular endothelial function. We hypothesized that microvascular function would be positively related to ERα, eNOS, and p-eNOS protein across the menstrual cycle. Premenopausal females (21 ± 3 yr) completed two visits (EF and LF phase) to assess leg microvascular function (<i>n</i> = 23) and protein levels (<i>n</i> = 17). Microvascular function was quantified by passive leg movement hyperemia leg blood flow area under the curve (LBF AUC) and change to peak (LBF Δpeak). eNOS, p-eNOS, and ERα content were quantified from quadricep muscle biopsies. E2 increased from the EF to LF phase (<i>P</i> = 0.002). There were no phase differences in LBF AUC (<i>P</i> = 0.252) and LBF Δpeak (<i>P</i> = 0.477), or eNOS (<i>P</i> = 0.722), p-eNOS (<i>P</i> = 0.079), and ERα (<i>P</i> = 0.182) protein assessed via immunoblotting, or eNOS (<i>P</i> = 0.610) and p-eNOS (<i>P</i> = 0.510) assessed via immunofluorescence. E2, eNOS, and p-eNOS proteins were positively related to microvascular function (<i>P</i> < 0.05). This study does not support a group-level role of the EF to LF menstrual phase transition in influencing leg microvascular function or ERα, eNOS, and p-eNOS protein. Rather, it highlights that individual quantification of E2 and eNOS protein may be more indicative of microvascular function.<b>NEW & NOTEWORTHY</b> This study provides the first parallel assessments of microvascular function and estrogen-related protein content across the early to late follicular phases of the menstrual cycle in humans. Both microvascular function assessed via passive leg movement hyperemia and estrogen-related protein (eNOS, p-eNOS, and ERα) from skeletal muscle biopsies did not differ across phases; however, correlation analysis suggests a mechanistic link between estradiol, eNOS, and p-eNOS protein levels and peripheral microvascular function in premenopausal females.