Sympathetic baroreflex sensitivity is enhanced in postmenopausal women

Abstract

The sympathetic nervous system is critical for regulating blood pressure (BP) via the arterial baroreflex and sympathetic transduction in the peripheral vasculature. These mechanisms interact, and both may be altered with aging and impacted by menopause. Although age-related decreases in sympathetic transduction have been demonstrated in women, it remains unclear whether sympathetic baroreflex sensitivity (BRS) is impaired in postmenopausal women (POST). We tested the hypothesis that sympathetic BRS would be enhanced in POST compared with premenopausal women (PRE). We examined beat-by-beat BP and muscle sympathetic nerve activity (MSNA) in 19 PRE (22 ± 2 yr, 22 ± 3 kg/m²) and 12 POST (57 ± 5 yr, 24 ± 2 kg/m²) during 10 min of rest. Spontaneous sympathetic BRS was quantified as the slope of a linear regression between MSNA burst incidence and diastolic BP. Sympathetic transduction to mean arterial pressure (MAP) for the 10 cardiac cycles following spontaneous MSNA bursts was assessed via signal averaging method. Resting MAP was similar (PRE: 82 ± 8 vs. POST: 85 ± 8 mmHg, P = 0.43), whereas resting MSNA was elevated in POST (PRE: 10 ± 6 vs. POST: 45 ± 16 bursts/100 heart beats, P < 0.0001). Spontaneous sympathetic BRS was enhanced in POST (PRE: -2.0 ± 1.2 vs. POST: -5.2 ± 1.9 bursts/beat/mmHg, P < 0.0005). Sympathetic transduction to MAP was attenuated in POST (time: P < 0.001, group: P < 0.001, interaction: P < 0.01). These data suggest that sympathetic BRS may be enhanced in POST. Consistent with recent hypotheses, enhanced sensitivity of the arterial baroreflex's neural arc may signify a compensatory response to reduced efficiency of the peripheral arterial baroreflex arc (i.e., sympathetic transduction) to preserve BP buffering capacity.NEW & NOTEWORTHY Studies examining sympathetic baroreflex function with aging remain equivocal, with some studies showing an increase, decrease, or no change in sympathetic baroreflex sensitivity (BRS) in older adults compared with younger adults. With aging, women experience unique physiological changes due to menopause that influence autonomic function. For the first time, we show that postmenopausal women exhibit a greater sympathetic BRS compared with young premenopausal women.

Keywords: arterial baroreflex; menopause; muscle sympathetic nerve activity; sympathetic transduction.

Graphical abstract

Figure 1.

Spontaneous cardiovagal baroreflex sensitivity in premenopausal and postmenopausal women. White circles denote premenopausal women (n = 19). Black triangles denote postmenopausal women (n = 12). An unpaired t test was used to evaluate a group difference. Values are presented as means ± SD. BRS, baroreflex sensitivity.

Figure 2.

Spontaneous sympathetic baroreflex sensitivity in premenopausal and postmenopausal women. White circles denote premenopausal women (n = 17). Black triangles denote postmenopausal women (n = 10). Four women (2 premenopausal and 2 postmenopausal) were excluded from the larger cohort for this comparison as they did not have a weighted linear regression correlation coefficient above −0.7 in accordance with best practice guidelines (23). An unpaired t test was used to evaluate a group difference. Values are presented as means ± SD. BP, blood pressure; BRS, baroreflex sensitivity; MSNA, muscle sympathetic nerve activity.

Figure 3.

A: signal-averaged sympathetic transduction of mean arterial pressure over the 10 cardiac cycles following a spontaneous MSNA burst in premenopausal and postmenopausal women. Circles denote premenopausal women (n = 18). Triangles denote postmenopausal women (n = 12). A repeated-measures analysis of variance (ANOVA) was used to evaluate the main effects of time and menopausal group. Bonferroni-corrected post hoc analyses were performed when a significant ANOVA interaction was observed. P < 0.05, significant difference pre- and postmenopausal women. B: peak increase in mean arterial pressure over the 10 cardiac cycles following a spontaneous MSNA burst in premenopausal and postmenopausal women. White circles denote premenopausal women (n = 18). Black triangles denote postmenopausal women (n = 12). An unpaired t test was used to evaluate a group difference. Values are presented as means ± SD. MAP, mean arterial pressure; MSNA, muscle sympathetic nerve activity.

Figure 4.

Pearson correlation between spontaneous sympathetic baroreflex sensitivity and peak transduction to mean arterial pressure across both premenopausal and postmenopausal groups (r = 0.55, P = 0.004). Circles denote premenopausal women (n = 17). Triangles denote postmenopausal women (n = 10). BRS, baroreflex sensitivity; MAP, mean arterial pressure.