Abstract P103: Aberrant Sympathetic Neural Recruitment Strategies During Exercise Pressor Reflex Activation In Postmenopausal Women

Abstract

Age-related elevations in sympathetic nerve activity contribute to numerous deleterious consequences for cardiovascular health, particularly in postmenopausal women (PMW). Aging adversely affects aspects of sympathetic nervous system (SNS) coding to control blood pressure at rest and during physiological stress. Although PMW exhibit greater neural activity at rest, the underlying sympathetic discharge patterns, particularly during sympathoexcitation, remain unknown. This study aimed to test the hypothesis that PMW display aberrant neural coding strategies during physiological stress compared to young women (YW). Efferent muscle sympathetic nerve activity (microneurography) was measured at baseline and during the final minute of both 30% isometric handgrip (HG) and post-exercise ischemia (PEI) in five healthy YW (22 ± 2 y, 20 ± 4 kg/m 2 , mean blood pressure: 82 ± 7 mmHg) and five healthy PMW (60 ± 5 y, 23 ± 3 kg/m 2 , 87 ± 8 mmHg). Sympathetic action potential (AP) discharge patterns were examined using wavelet-based methodology. At baseline, PMW exhibited elevated integrated burst frequency (PMW 30 ± 10 vs YW 9 ± 3 bursts/min; p < 0.01) and increased AP firing (PMW 240 ± 117 vs YW 90 ± 64 APs/min, p = 0.04). Both groups had similar increases in integrated burst frequency during HG and PEI (p < 0.01 vs baseline). AP firing was elevated to a similar extent in both groups during HG (PMW Δ76 ± 60; YW Δ129 ± 146 APs/min; p < 0.01 vs baseline) and PEI (PMW Δ72 ± 51; YW Δ93 ± 64 APs/min; p < 0.01 vs baseline), with no change in the mean AP content per burst (p = 0.86). PMW had reduced recruitment of latent and larger AP subpopulations that were previously silent at baseline (group-by-condition interaction: p < 0.01), as evidenced by an increase in total AP clusters (binned according to peak-to-peak amplitude) during HG and PEI in YW (HG: Δ2 ± 1; PEI: Δ2 ± 2; both p ≤ 0.03 vs baseline) but not PMW (HG: Δ0 ± 1; PEI: Δ0 ± 1; both p ≥ 0.75 vs baseline). These preliminary data suggest that PMW display elevated resting sympathetic AP firing and aberrant reflex AP recruitment, such that the ability of the SNS to recruit subpopulations of previously silent axons during a sympathetic stressor is reduced in PWM compared to YW. These findings extend our knowledge of age-related neural coding strategies in women.