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Endothelium-dependent and endothelium- independent vasodilation of skin microcirculation during high salt loading in young healthy women

Introduction: Recent studies have shown that endothelial dysfunction is an early manifestation of adverse effect of high salt (HS) loading (1). In our previous study we have demonstrated that one week of HS diet significantly impaired skin microvascular reactivity in young healthy women independently of changes in blood pressure (BP) (2). The present study was designed to determine if one week of HS diet affects endothelium-dependent and/or endothelium-independent vasodilation of skin microcirculation in young healthy women. Methods: Twenty four young healthy women were assigned to a 7-days low salt (LS) diet (<3.5 g NaCl/day) followed by a 7-days HS diet (~14 g NaCl/day). Skin microvascular blood flow was measured by Laser Doppler Flowmetry in response to iontophoresis of acetylcholine (ACh) and sodium nitroprusside (SNP) before and after LS and HS diet protocols. BP, heart rate (HR), 24h-urine sodium, potassium, urea and creatinine levels were measured before and after diet protocols. Salt intake was estimated based on calculation of 24-hour urinary sodium excretion. The study protocol and procedures conformed to the standards set by the latest revision of the Declaration of Helsinki and the Ethical Committee of Faculty of Medicine University of Osijek approved them. Results: Changes in 24h urinary sodium excretion and calculated salt intake confirmed that subjects conformed to the diet protocols (NaCl, g/day ; baseline 7.2±2.9, LS diet 4.8±1.8, HS diet 13±5.4, P<0.001). Systolic blood pressure (SBP) was unchanged after HS diet, but significantly reduced after LS diet (SBP, mmHg: baseline 114±8, LS diet 106±7, HS diet 108±9, P<0001). HR was not significantly changed after both diet protocols (HR, per minute: baseline 75±12, LS diet 71±9, HS diet 73±0, P=0.377). ACh induced dilation (endothelium-dependent) was unchanged after LS diet, but significantly impaired after HS diet protocol (flow change compared to basic flow: baseline 16.80±7.71, LS diet 17.96±5.23, HS diet 13.08±7.5, P=0.012 baseline and LS diet vs. HS diet). SNP induced dilation (endothelium-independent) was not significantly changed after both LS and HS diet protocols (flow change compared to basic flow: baseline 18.95±7.77, LS diet 19.38±7.49, HS diet 18.98±6.96, P=0.939). Conclusions: This study confirmed our previous findings that one week of HS loading significantly affects skin microvascular reactivity without changes in BP levels in young healthy women. Furthermore, since one week HS diet significantly impaired ACh-, but not SNP-induced dilation, these data suggest that short-term HS intake affects microvascular function in young healthy women through its direct adverse impact on endothelium function. Cavka A, Jukic I, Ali M, Goslawski M, Bian JT, Wang E, Drenjancevic I, Phillips SA. Short-term high salt intake reduces brachial artery and microvascular function in the absence of changes in blood pressure. J Hypertens. 2016 Apr ; 34(4):676-84. doi: 10.1097/ HJH.0000000000000852. Cavka A, Cosic A, Jukic I, Jelakovic B, Lombard JH, Phillips SA, Seric V, Mihaljevic I, Drenjancevic I. The role of cyclo-oxygenase-1 in high-salt diet- induced microvascular dysfunction in humans. J Physiol. 2015 Dec 15 ; 593(24):5313-24. doi: 10.1113/JP271631. This study was supported by project of Faculty of Medicine J.J. Strossmayer University of Osijek VIF2015-MEFOS-05. Where applicable, the authors confirm that the experiments described here conform with the Physiological Society ethical requirements.

high salt diet ; microcirculation ; endothelium ; laser Doppler flowmetry

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