Dietary nitrate supplementation suppresses sympathetic neural responses to mechanoreflex activation during static handgrip exercise in postmenopausal women.

We investigated the impact of short-term dietary nitrate supplementation on sympathetic neural responses to isometric exercise in postmenopausal women. Ten healthy women aged 64±2 (SD) years participated in this randomized, placebo-controlled, double-blind, crossover study. All participants underwent two-week beetroot juice (BRJ: 800 mg nitrate/day) and placebo (nitrate-depleted BRJ) interventions with ≥14 days of wash-out. Before and after each intervention, participants performed static handgrip (SHG) at 40% of maximum voluntary contraction until fatigue, followed by 2-min post-exercise circulatory occlusion (PECO) with an upper-arm cuff inflated to 250 mmHg to isolate metaboreflex activation. Heart rate (HR; electrocardiogram), blood pressure (BP; finger photoplethysmography), and muscle sympathetic nerve activity (MSNA; microneurography) were continuously measured. BRJ increased the time to fatigue more than placebo (79±67 vs. 9±74 sec, p=0.03), which was correlated with decreases in MSNA burst frequency, total activity, and burst incidence at the first 30-sec of SHG when predominately mechanoreflex activation occurs (r=-0.65, -0.62, and -0.68, respectively, all p<0.05). However, BRJ did not alter MSNA responses to peak SHG and PECO. Subsequently, we added 4 postmenopausal women who finished the BRJ intervention only, and categorized all participants into early (n=6) and normal menopause (n=8). The early, but not normal, menopause group showed decreases in MSNA burst frequency and incidence at the first 30-sec of SHG after the BRJ intervention (both p<0.05). Collectively, nitrate supplementation prolonged the time to fatigue during SHG, and this prolongation was likely associated with attenuated sympathetic neural responses to mechanoreflex activation in postmenopausal women, especially those with early menopause.