Older versus Younger Females Matched for Body Composition Have Lower Sympathetic Transduction at Rest

BACKGROUND: Older female (OF) adults have the highest risk for hypertension and cardiovascular disease among any demographic in America. Therefore, there is a need to better understand the contributors to impaired blood pressure (BP) regulation in female aging. Bursts of spontaneously occurring muscle sympathetic nerve activity (MSNA) contribute to BP regulation on a beat-to-beat basis (i.e., sympathetic transduction). Previous work suggests that OF have attenuated resting sympathetic transduction but there is a need for additional work considering covariates that affect sympathetic transduction (e.g., body mass index (BMI) & sodium intake). We tested the hypothesis that aging attenuates sympathetic transduction in OF (>55 years) compared with young female (YF; 18-35 years) participants matched for body composition and pre-trial sodium intake. METHODS: We studied seven post-menopausal OF (65±6 years) and nine YF (24±4 years; tested in early follicular phase) participants with seated brachial BP <140/90 mmHg after three days of specified sodium intake (target 2300mg/day). We measured mean BP (photoplethysmography) and MSNA (microneurography) during a 10-min rest period in the supine position. We also assessed BMI, body fat % (BF%; bioelectrical impedance), and habitual moderate-to-vigorous physical activity (MVPA) during ≥7 consecutive days using waist-worn accelerometers (ActiGraph). We compared the average change in BP for 10 cardiac cycles after an MSNA burst (i.e., signal-averaged sympathetic transduction) using mixed-effects models (group*time[repeated measure]). We compared other variables using unpaired, two-tailed t-tests for normally distributed data and Mann-Whitney U tests for non-normally distributed data (i.e., failed Shapiro-Wilk test). We compared sodium intake, BMI, BF% and MVPA using equivalence testing. Significance was set to α<0.05. RESULTS: Sodium intake, BMI, BF% and MVPA were equivalent between groups (p>0.06). The following data are presented as OF vs. YF with mean ± SD or median[IQR]. Mean BP (97[22] vs. 77[5] mmHg, p=0.008) and MSNA burst frequency (35±6 vs. 13±4 bursts/min, p<0.0001) were higher in OF. OF had lower mean BP changes following MSNA bursts (time: p<0.0001, group: p=0.013, interaction: p=0.026) with pairwise differences among cardiac cycles 4-10 (post hoc p-values: p≤0.012). Moreover, peak increases in mean BP following MSNA bursts were lower in OF (Δ1.9±0.4 vs. 4.9±2.2 mmHg, p=0.003). CONCLUSION: We found that OF have attenuated sympathetic transduction to BP when compared to YF matched for body composition and sodium intake. This extends past work suggesting that female aging is associated with attenuated sympathetic transduction to BP. National Institutes of Health K01HL160772 (JCW), American Heart Association 23CDA1037938 (JCW), & Florida State University Graduate School Legacy Fellowship, 2023 (CD). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.