Vascular responses during handgrip exercise in healthy postmenopausal females and older males

Introduction: Aerobic exercise interventions improve peripheral endothelial function in healthy older males. However, this effect is not always observed in healthy postmenopausal females and possible mechanisms underlying this sex-related difference remain unknown. Greater vascular shear stress during acute exercise is a key stimulus mediating longer-term improvements in vascular function. It remains unknown if postmenopausal females display a reduced endothelial sensitivity to exercise-induced shear stress relative to males of similar age. Objective and hypothesis: The objective of this study is to test the hypothesis that healthy postmenopausal females exhibit a lower endothelial sensitivity to exercise-induced shear stress relative to males. Methods: Fourteen healthy postmenopausal females (67 ± 8 years) not under hormone replacement therapy and 9 males of similar age (65 ± 7 years) performed handgrip exercise for 4 minutes at 20%, 40%, 60%, and 80% of their maximal voluntary contraction. Each exercise bout was separated by a 10-min recovery period. Brachial artery diameter and blood velocity were continuously measured 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 stress and compared between groups with an independent t-test. Workload, vascular conductance, diameter dilation, and shear stress were analyzed with mixed-effects models. Results: Males exercised at greater workloads relative to females across all exercise bouts (M: 17 ± 11 vs. F: 9 ± 5 kg, p<0.01). Forearm vascular conductance was greater in males throughout each exercise intensity (M: 2.23 ± 1.70 vs. F: 1.03 ± 0.51 ml/min/mmHg, p=0.02). Despite these differences, arterial dilation (M: 5.32 ± 5.55 vs. F: 5.20 ± 4.80%, p=0.96) and shear stress (M: 142 ± 80 vs. F: 171 ± 86 s−1, p=0.27) did not differ between groups across exercise intensities. Endothelial sensitivity to exercise-induced shear stress did not differ between males (0.02 ± 0.05%/s−1) and females (0.03 ± 0.01%/s−1, p=0.67). Conclusion: These data suggest that a reduced endothelial sensitivity to exercise-induced shear stress may not explain why aerobic exercise interventions do not consistently improve peripheral endothelial function in healthy postmenopausal females. Montreal Heart Institute Foundation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.