Endothelial sensitivity to exercise-induced shear rate in older adults: effect of biological sex and acute folic acid consumption

Aerobic exercise interventions improve peripheral endothelial function in healthy older males. This effect is inconsistently observed in healthy postmenopausal females, and possible mechanisms underlying this sex-related difference remain unknown. We tested the hypothesis that endothelial sensitivity to exercise-induced shear rate is reduced in healthy postmenopausal females and that it can be improved by acute folic acid consumption. Using a double-blind randomized crossover study design, 17 postmenopausal females (66 ± 8 yr) and 14 males (66 ± 6 yr) performed handgrip exercise at 20%, 40%, 60%, and 80% of maximal voluntary contraction after consuming a placebo or 5 mg of folic acid. Brachial artery diameter and blood velocity were measured continuously using high-resolution ultrasound and analyzed using edge-detection software. Endothelial sensitivity to shear rate was quantified as the slope of the linear regression between brachial artery dilation (% change from baseline) and shear rate. During the placebo visit, endothelial sensitivity to exercise-induced shear rate did not differ between females (0.102 ± 0.055%·s^-1) and males (0.091 ± 0.061%·s^-1, <i>P</i> = 0.603). Acute folic acid consumption did not improve endothelial sensitivity to exercise-induced shear rate in females (placebo: 0.102 ± 0.055%·s^-1, folic acid: 0.099 ± 0.062%·s^-1, <i>P</i> = 0.887) or males (placebo: 0.091 ± 0.061%·s^-1, folic acid: 0.102 ± 0.083%·s^-1, <i>P</i> = 0.697). Endothelial sensitivity to exercise-induced shear rate does not differ between healthy postmenopausal females and age-matched males. Acute folic acid consumption does not improve endothelial sensitivity to exercise-induced shear rate in healthy older females or males.<b>NEW & NOTEWORTHY</b> We hypothesized that endothelial sensitivity to exercise-induced shear rate is reduced in healthy postmenopausal females. In contrast to this hypothesis, endothelial sensitivity to increases in shear rate caused by handgrip exercise did not differ between healthy postmenopausal females and males of similar age. These results suggest that a reduced endothelial sensitivity to exercise-induced shear rate may not contribute to the inconsistent effect of aerobic exercise interventions on brachial artery flow-mediated dilation in healthy postmenopausal females.