Sympathetic Baroreflex Sensitivity is Enhanced in Postmenopausal Women.

Abstract

The sympathetic nervous system is critical for regulating blood pressure (BP) via the arterial baroreflex as well as 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 to 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 minutes 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 mm Hg, P=0.43), whereas resting MSNA was elevated in POST (PRE: 10±6 vs. POST: 45±16 bursts/100 heartbeats, P<0.0001). Spontaneous sympathetic BRS was enhanced in POST (PRE: -2.0±1.2 vs. POST: -5.2±1.9 bursts/beat/mm Hg, 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.