BACKGROUND: Women remain underrepresented in biomedical research, yet it is agreed that estrogen elicits protection against diseases associated with vascular function. Post-menopausal women may be at an increased risk of disease, which has been supported by attenuated responses of reactive hyperemia (RH) seen in these individuals. Previously, women demonstrated further impairments in RH after ovariectomies. However, little is known concerning the RH responses of naturally post-menopausal women versus those with a hysterectomy. Therefore, our purpose was to identify differences in RH among three groups: pre-menopausal, hysterectomy, and natural menopausal. METHODS: 51 women volunteered to participate: 21 pre-menopausal, 14 post-menopausal, and 16 hysterectomy. A near-infrared spectroscopy (NIRS) device measured skeletal muscle tissue oxygenation (StO2%) in the forearm during a vascular occlusion test. This included 3 min of rest, 5 min of ischemia, and 3 min of reperfusion. The rate of desaturation (downslope), time to maximal saturation, and maximal StO2 (StO2max) were calculated. Separate 1-way ANOVAs were performed, and a p≤0.05 was considered significant. RESULTS: For downslope, the 1-way ANOVA was not significant (p=0.190, =0.067), but for indices of RH (time to StO2max and StO2max), there were significant ANOVAs. For time to StO2max, there was a significant group difference (p<0.014, =0.162) such that pre-menopausal women (43.7 ± 18.3s) exhibited a significantly greater time than post-menopause (32.0 ± 9.3s; p=0.012) and hysterectomy (31.9 ± 7.5s; p=0.015). For StO2max, there was a group difference (p<0.001, =0.292), and the pre-menopausal women (82.1 ± 3.1%) had significantly greater peak values than post-menopausal (77.2 ± 4.7%; p<0.001) and hysterectomy (78.6 ± 2.6%; p=0.005) women. CONCLUSION: Although the women all experienced a similar ischemic vasodilatory stimulus (i.e., downslope), there were differences in measures of RH. These novel findings suggested that a factor other than muscle metabolic rate, perhaps vascular compliance, provoked the observed differences in the ability to rectify the ischemic insult. Notably, there were no differences between post-menopausal and hysterectomy groups. Female-focused clinical trials remain needed to determine strategies to preserve vascular function and to counteract the consequences of estrogen loss, especially trials promoting skeletal muscle.

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