Is There Association between Altered Adrenergic System Activity and Microvascular Endothelial Dysfunction Induced by a 7-Day High Salt Intake in Young Healthy Individuals

Abstract

This study aimed to test the effect of a 7-day high-salt (HS) diet on autonomic nervous system (ANS) activity in young healthy individuals and modulation of ANS on microvascular endothelial function impairment. 47 young healthy individuals took 7-day low-salt (LS) diet (3.5 g salt/day) followed by 7-day high-salt (HS) diet (~14.7 g salt/day). ANS activity was assessed by 24-h urine catecholamine excretion and 5-min heart rate variability (HRV). Skin post-occlusive reactive hyperemia (PORH) and acetylcholine-induced dilation (AChID) were assessed by laser Doppler flowmetry (LDF). Separately, mental stress test (MST) at LS and HS condition was conducted, followed by immediate measurement of plasma metanephrines' level, 5-min HRV and LDF microvascular reactivity. Noradrenaline, metanephrine and normetanephrine level, low-frequency (LF) HRV and PORH and AChID significantly decreased following HS compared to LS. MST at HS condition tended to increase HRV LF/HF ratio. Spectral analysis of PORH signal, and AChID measurement showed that MST did not significantly affect impaired endothelium-dependent vasodilation due to HS loading. In this case, 7-day HS diet suppressed sympathetic nervous system (SNS) activity, and attenuated microvascular reactivity in salt-resistant normotensive individuals. Suppression of SNS during HS loading represents a physiological response, rather than direct pathophysiological mechanism by which HS diet affects microvascular endothelial function in young healthy individuals.

Keywords: autonomic nervous system; catecholamine; endothelium; heart rate variability; high-salt diet; sympathetic nervous system.

Figure 1

Study timeline and protocol. LS—low salt; HS—high-salt; BP—blood pressure; HR—heart rate; BMI—body mass index; WHR—waist-to-hip ratio; hsCRP—high sensitivity C reactive protein; ANS—autonomic nervous system; HRV—heart rate variability; PORH—post-occlusive reactive hyperemia; AChID—acetylcholine-induced dilation; MST—mental stress test.

Figure 2

The effect of mental stress test on plasma metanephrine (A) and normetanephrine (B) concentration at low-salt (LS) and high-salt (HS) diet conditions in young healthy individuals. N = 24 (12 women and 12 men). LS—low salt; HS—high salt; MST—mental stress test; N— number of subjects. Data are presented as average ± SD. One Way ANOVA Repeated Measures, * p < 0.05, LS diet vs. HS diet.

Figure 3

The effect of mental stress test on post-occlusive reactive hyperemia (PORH) (A) and acetylcholine-induced dilation (AChID) (B) of forearm skin microcirculation measured by laser Doppler flowmetry (LDF) at low-salt (LS) and high-salt (HS) diet conditions in young healthy individuals. N = 24 (12 women and 12 men). LS—low salt; HS—high salt; MST—mental stress test; N—number of subjects. Data are presented as average ± SD. One Way ANOVA Repeated Measures, * p < 0.05, LS diet vs. HS diet.