The Effect of Menopause Status on the Skeletal Muscle Metaboreflex.

Abstract

Introduction It is well established that the exercise pressor reflex contributes to cardiovascular control (e.g. mean arterial pressure (MAP)) during exercise. One arm of the exercise pressor reflex includes the metabolically sensitive group IV afferents (i.e. metaboreflex). The metaboreflex‐induced cardiovascular responses to exercise are incompletely understood, especially in women across the aging spectrum. For example, post‐menopausal women have greater increases in MAP and systemic vascular resistance (SVR) during locomotor muscle exercise compared to pre‐menopausal women. However, it is unclear if an exaggerated metaboreflex arising from the locomotor muscles is contributing to these cardiovascular adjustments with exercise in post‐menopausal women. We hypothesized that 1) post‐menopausal women will have an augmented MAP response with isolated metaboreflex activation compared to pre‐menopausal women and 2) the exaggerated increase in MAP in the post‐menopausal women will be primarily due to greater increases in SVR. Methods Pre‐ (n= 10, 25±3yrs, 24±3 kg/m2) and post‐menopausal women (n=12, 58±4yrs, 24±3 kg/m2) performed 2 sessions of cycling exercise at 20 W for 5 min with bilateral upper thigh pressure tourniquets inflated to 90 mmHg. At end exercise, the recovery was randomized to post‐exercise circulatory occlusion (PECO) to isolate the metaboreflex (via bilateral upper thigh pressure tourniquets rapidly inflated to suprasystolic pressure for 2 min) or normal recovery (NR) without intervention. Systolic and diastolic blood pressure were measured via manual sphygmomanometry and MAP was calculated. Cardiac output was measured via open circuit acetylene wash‐in and systemic vascular resistance (SVR) was calculated. Data is reported as the absolute change from rest to recovery. Results MAP was elevated during PECO compared to NR in both groups (p<0.05), while MAP during PECO was greater in post‐ compared to pre‐menopausal women (20±9 vs. 13±5 mmHg, respectively) (p<0.05). Similarly, SVR was elevated during PECO compared to NR in both groups (p<0.05), while SVR was greater during PECO in post‐ compared to pre‐menopausal women (5±3 vs. 3±1 mmHg/L/min, respectively) (p<0.05). In contrast, cardiac output was not different between NR and PECO in either pre‐ (NR: 0.3±1 vs. PECO: −0.2±1 L/min) and post‐menopausal (NR: −0.1±1 vs. PECO: −0.7±0.9 L/min) (all, p>0.05). Conclusion These data demonstrate that isolated metaboreflex stimulation following whole‐body exercise results in exaggerated increases in MAP and SVR in post‐ compared to pre‐menopausal women. These data suggest that exercise pressor reflex‐mediated control of MAP during exercise is accentuated in post‐menopausal women with menopause status.