慢性盐负荷对血压正常个体体内炎症因子的影响

目的:通过对血压正常个体进行低盐和高盐饮食干预,探索盐负荷对血压正常个体体内炎症因子肿瘤坏死因子α(TNF-α)、高敏C反应蛋白(hs-CRP)和单核趋化蛋白-1(MCP-1)的影响。方法:选取30例年龄在18～60岁的血压正常者参与为期3周的慢性盐负荷试验,包括基线调查3天,低盐饮食、高盐饮食各7天。根据其平均动脉压(MAP)于高盐期较低盐期升高幅度≥10%为标准分为盐敏感者(10例)和盐不敏感者(20例),分别于基线及各期末抽取空腹静脉血标本。血浆TNF-α和MCP-1用酶联免疫吸附(ELISA)法测定,血浆hs-CRP用免疫放射比浊法测定。结果:3O例受试者中盐敏感检出率占33%(10例)。盐敏感者和盐不敏感者干预各期血浆hs-CRP水平无明显变化;而TNF-α水平[盐敏感者:(168.4±67.8) pg/ml vs(42.1±26.7) pg/ml,P0.01;盐不敏感者:(129.8±24.1) pg/ml vs(37.7±15.8) pg/ml,P0.01)]和MCP-1水平[盐敏感者:(205.2±64.2 vs 166.3±48.5) pg/ml,P0.01;盐不敏感者:(212.3±52.2 vs 143.6±55.9) pg/ml,P0.01],两者均为高盐期较低盐期显著增高。盐敏感者和盐不敏感者间同期比较差异无统计学意义。结论:高盐饮食可诱发一种炎症状态,这种炎症状态可能独立于血压的盐敏感性之外。     

高盐饮食对健康人和高血压患者血浆血管内皮生长因子C水平的影响及其与血压的相关性研究

目的:探讨高盐饮食对健康人和高血压患者血浆中血管内皮生长因子-C(VEGF-C)水平的影响以及血浆VEGF-C水平和血压的相关性。方法:选取北京大学首钢医院血管医学中心2013-2014年原发性高血压患者75例(高血压组)和同期体检健康者98例(对照组),按照每天钠盐摄入量是否超过6 g,又分为高盐饮食亚组和低盐饮食亚组。比较高血压组和对照组以及两组中低盐饮食亚组和高盐饮食亚组在年龄、性别构成、肌酐清除率(CCr)、血尿酸(UA)、空腹血糖(FBG)、体重指数(BMI)、总胆固醇(TC)、甘油三酯(TG)、高密度脂蛋白胆固醇(HDL-C)、低密度脂蛋白胆固醇(LDL-C)、收缩压、舒张压、脉压、平均动脉压、心率及颈-股脉搏波传导速度(CF-PWV)等指标上的差异。结果:高血压组与对照组相比,血浆VEGF-C水平升高[(3 940.8±1 141.1)pg/ml vs(2 938.0±987.0)pg/ml,P0.001],两组在年龄、BMI、收缩压、舒张压、脉压、平均动脉压、CF-PWV之间的差异也均有统计学意义(P均0.05)。高血压组中高盐饮食亚组血浆VEGF-C水平显著高于低盐饮食亚组[(4 208.8±113.1)pg/ml vs(3 515.8±1 070.1)pg/ml,P=0.009],两亚组在年龄、收缩压、舒张压、脉压上的差异也均有统计学意义(P均0.05)。对照组中高盐饮食亚组血浆VEGF-C水平也高于低盐饮食亚组[(3 158.7±917.2)pg/ml vs(2 655.7±1 011.3)pg/ml,P=0.012],年龄、BMI、CCr也均存在显著组间差异(P均0.05),但两亚组血压无显著差异。Spearman相关分析显示,无论在所有受试者中还是在高血压组或对照组中,校正潜在混淆因素后,平均动脉压均与血浆VEGF-C水平呈正相关(r=0.536,P0.001;r=0.546,P=0.002;r=0.291,P=0.006)。结论:无论健康受试者还是高血压患者,高盐饮食后血浆VEGF-C水平都升高,且血浆VEGF-C水平和血压呈正相关。     

钠钾对血压盐敏感者短时血压变异性的影响

目的观察血压盐敏感者在钠、钾饮食干预后短时血压变异性(BPV)的变化,探讨BPV与盐敏感的关系。方法 2004-04-10对陕西眉县农村正常血压成人93名进行低盐(氯化钠51.3mmol/d)饮食7d,高盐(氯化钠307.7mmol/d)饮食7d的慢性盐负荷试验,之后进行高盐补钾(307.7mmol/d氯化钠基础上口服60mmol/d氯化钾缓释胶囊)干预7d;每个阶段最后一天测3次血压,以血压标准差、变异系数为短时BPV指标。根据高盐饮食后平均动脉压升高幅度是否≥10%,分为血压盐敏感组(n=30)及盐不敏感组(n=63)。结果盐敏感性检出率为32.3%。基线期时,与盐不敏感组比较,盐敏感组收缩压标准差[(4.4±1.1)比(2.5±0.5)mmHg,P<0.01];舒张压标准差[(3.7±1.7)比(2.8±0.9)mmHg,P<0.01];收缩压变异系数[(3.78±1.01)比(2.35±0.55),均P<0.01];舒张压变异系数[(5.06±2.50)比(3.99±1.46),P<0.05]均较高。盐敏感组低盐期及高盐补钾期收缩压、舒张压标准差及变异系数均降低,与盐不敏感组比较,差异无统计学意义;予高盐饮食后,盐敏感组收缩压标准差较低盐期升高,与盐不敏感组比较,差异有统计学意义[(3.7±1.9)比(3.0±1.1)mmHg,P<0.05]。结论高盐摄入、盐敏感是短时BPV增大的重要原因,限盐及补钾具有降低短时BPV的保护作用。     

高盐摄入对盐敏感者血清细胞色素C氧化酶亚单位Ⅱ的影响

目的探讨高盐干预对盐敏感者血清细胞色素C氧化酶亚单位Ⅱ(cytochrome C oxidase subunitⅡ,COX-Ⅱ)水平的影响。方法选取陕西蓝田农村汉族44名成年人参与为期2周的慢性盐负荷试验,试验阶段包括基线期3天,低盐期(每天摄盐3 g,相当于钠51.3 mmol/d)和高盐期(每天摄盐18 g,相当于钠307.8mmol/d)各7天。每个阶段均测量血压,并收集血、尿标本。用ELISA法测定血清COX-Ⅱ浓度。结果盐敏感者中,低盐期血清COX-Ⅱ水平较基线期显著升高[(1.14±0.12)ng/ml比(1.45±0.13)ng/ml,P=0.019];而高盐饮食能够明显降低血清COX-Ⅱ的水平[(1.45±0.13)ng/ml比(1.02±0.13)ng/ml,P=0.003],而在盐不敏感者中未发现此变化。此外,两组血清COX-Ⅱ水平变化与收缩压呈显著负相关。结论膳食盐.的摄人能够影响盐敏感者血清COX-Ⅱ浓度,提示COX-Ⅱ可能参与血压盐敏感性的形成。     

血压盐敏感者一氧化氮系统与非对称性二甲基精氨酸和补钾的作用

目的 通过观察慢性盐负荷及补钾后血浆非对称性二甲基精氨酸(ADMA)和血、尿一氧化氮(NO)水平的变化及其与血压的关系,探讨血压正常盐敏感者(SS)的血管内皮功能损伤及补钾的保护作用.方法选60例年龄在20～60岁的血压正常者参与为期3周的慢性盐负荷及补钾试验,包括基线调查3 d,低盐(LS)饮食,高盐(HS)饮食,和高盐补钾(HS K)饮食各7 d的研究.每个阶段均测量血压,并收集血、尿标本.血、尿NO用Griess法测量,血浆ADMA用高效液相色谱法测量.结果 受试者60例中共检出SS 13例,检出率为21.6%.盐负荷后,SS血浆ADMA的浓度明显升高[(0.89±0.09 vs 0.51±0.07)μmol/L,P＜0.05],而血浆NO的水平则较LS饮食期显著降低[(41.8±7.6 vs 63.5±7.6)μmol/L,P＜0.01].在HS摄入的基础上大剂量口服补钾可以逆转单纯HS负荷对SS血浆ADMA浓度和血、尿NO水平的作用[(ADMA:0.52±0.09 vs 0.89±0.09)μmol/L;NO:(58.1±7.4 vs 41.8±7.6)μmol/L],血浆ADMA浓度和平均动脉压之间存在正相关关系.结论 血压正常SS于HS负荷后伴随血压升高,血浆ADMA显著升高、NO降低,同时补充钾盐可以逆转前述作用,提示补钾可能通过抑制ADMA的升高降低血压.     

血压盐敏感者一氧化氮系统与非对称性二甲基精氨酸和补钾的作用

目的通过观察慢性盐负荷及补钾后血浆非对称性二甲基精氨酸(ADMA)和血、尿一氧化氮(NO)水平的变化及其与血压的关系,探讨血压正常盐敏感者(SS)的血管内皮功能损伤及补钾的保护作用。方法选60例年龄在20～60岁的血压正常者参与为期3周的慢性盐负荷及补钾试验,包括基线调查3d,低盐(LS)饮食,高盐(HS)饮食,和高盐补钾(HS K)饮食各7d的研究。每个阶段均测量血压,并收集血、尿标本。血、尿NO用Griess法测量,血浆ADMA用高效液相色谱法测量。结果受试者60例中共检出SS13例,检出率为21.6%。盐负荷后,SS血浆ADMA的浓度明显升高[(0.89±0.09vs0.51±0.07)μmol/L,P<0.05],而血浆NO的水平则较LS饮食期显著降低[(41.8±7.6vs63.5±7.6)μmol/L,P<0.01]。在HS摄入的基础上大剂量口服补钾可以逆转单纯HS负荷对SS血浆ADMA浓度和血、尿NO水平的作用[(ADMA:0.52±0.09vs0.89±0.09)μmol/L;NO:(58.1±7.4vs41.8±7.6)μmol/L],血浆ADMA浓度和平均动脉压之间存在正相关关系。结论血压正常SS于HS负荷后伴随血压升高,血浆ADMA显著升高、NO降低,同时补充钾盐可以逆转前述作用,提示补钾可能通过抑制ADMA的升高降低血压。     

盐和左旋精氨酸对血压正常盐敏感者肾血流动力学的影响

目的观察慢性盐负荷和左旋精氨酸对血压正常盐敏感者肾血流动力学的影响。方法以29例血压正常健康自愿者为研究对象,采用慢性盐负荷试验确定血压盐敏感性,观察盐敏感者和盐不敏感者在平衡饮食期、高盐饮食期及低盐饮食期的24h动态血压,同时监测肾小球滤过率（GFR）、有效肾血浆流量（ERPF）滤过分数（FF）及其在静点左旋精氨酸后的变化。结果29例血压正常健康自愿者中,检出盐敏感者（SS）11例（37．93％）,盐不敏感者（SR）18例;与平衡饮食期比较,ss组高盐负荷后ERPF显著减少、FF显著增加,输注左旋精氨酸后,仍存在上述改变;在平衡饮食期和高盐饮食期,SR组输注左旋精氨酸后较输注前ERPF显著增加,但SS组在输注左旋精氨酸前后ERPF无明显变化。结论血压正常盐敏感者高盐负荷时ERPF显著减少,FF显著增加,对左旋精氨酸反应迟钝,提示血压正常盐敏感者存在高盐介导的肾血管内皮功能异常。     

血压盐敏感者内皮功能损伤及补钾的保护作用研究

目的通过观察血、尿-氧化氮（NO）水平的变化,探讨盐敏感者血管内皮功能损伤及补钾的保护作用。方法选39例年龄16～60岁、血压正常或血压轻度偏高者参与为期3周的慢性盐负荷及补钾试验,包括基线3天,低盐饮食、高盐饮食和高盐加补钾饮食各7天的研究。各个阶段测量体重、血压,并收集血、尿标本。结果盐敏感者血浆NO浓度和尿中NO水平在基线、低盐和高盐阶段均低于盐不敏感者;限盐后血、尿NO浓度增加,而高盐饮食后NO浓度显著减少;盐敏感者在高盐摄入的基础上大剂量口服补钾后血浆NO浓度、尿NO水平显著升高。结论盐敏感者尽管尚处在血压正常或血压轻度偏高阶段已存在一定程度的内皮功能损伤,且这种损伤与盐负荷相关联;大剂量补钾可能通过增加NO水平而改善盐敏感者的血管内皮功能。     

高盐摄入对血压正常人群血浆骨保护素含量的影响

目的:本研究旨在探索高盐摄入对正常血压患者血浆骨保护素(OPG)水平的影响。方法:从农村社区招募18例血压正常的受试者(年龄25～50岁),给予正常饮食3 d,低盐饮食7 d(3g/天,Na Cl),高盐饮食7 d(18 g/d)共17 d饮食干预,采用酶联免疫吸附方法(ELISA方法)测定血浆骨保护素的含量。结果:高盐摄入后受试者体内血浆OPG水平明显升高[(252. 7±13. 9) vs.(293. 4±16. 1) ng/L]。进一步分析显示,OPG浓度与24 h尿钠排泄量呈正相关(r=0. 405,P 0. 01)。结论:盐负荷可以促进血压正常受试者体内OPG的生成,这可能是一种内皮功能自我保护机制。     

慢性盐负荷对血压正常盐敏感性个体胰岛素抗性的影响

目的观察慢性盐负荷对血压正常盐敏感者个体胰岛素抗性的影响。方法对２３例血压正常的健康志愿者，通过３天的平衡饮食期（ＮａＣｌ１４ｇ／ｄ），７天的高盐饮食期（ＮａＣｌ２３ｇ／ｄ）及７天的低盐饮食期（ＮａＣｌ３ｇ／ｄ）在确定盐敏感性的同时，进行口服葡萄糖耐量试验及胰岛素释放试验。结果盐敏感者慢性高盐负荷使空腹血胰岛素水平及胰岛素释放量明显增加，与盐不敏感者差异显著，空腹血胰岛素为１２．２±５．７对７．４±１．７μＵ／ｍｌ，胰岛素曲线下面积分别为７４．６±２１．９对３９．０±１２．４μＵ·ｈ－１·Ｌ－１，Ｐ均＜０．０５；敏感者高盐负荷后与平衡饮食期相比，葡萄糖负荷试验后的１ｈ及曲线下面积亦有升高倾向。结论高盐摄入在升高盐敏感者血压的同时，胰岛素抗性也增加     

Salt loading on plasma asymmetrical dimethylarginine and the protective role of potassium supplement in normotensive salt-sensitive asians

Asymmetrical dimethylarginine (ADMA) is an endogenous inhibitor of NO synthase. Because endothelial NO pathway is compromised in patients with salt-sensitive hypertension, we investigated whether the plasma ADMA can be modulated by chronic salt loading in normotensive salt-sensitive persons and its relationship with NO, and we further determined whether or not dietary potassium supplementation can reverse them. Sixty normotensive subjects (aged 20 to 60 years) were selected from a rural community of Northern China. All of the people were sequentially maintained on a low-salt diet for 7 days (3 g/day, NaCl), then a high-salt diet for 7 days (18 g/day), and high-salt diet with potassium supplementation for another 7 days (4.5 g/day, KCl). After salt loading, the plasma ADMA concentrations increased significantly in salt-sensitive subjects (0.89+/-0.02 micromol/L versus 0.51+/-0.02 micromol/L; P<0.05), whereas the plasma NOx levels reduced considerably (41.8+/-2.1 micromol/L versus 63.5+/-2.1 micromol/L; P<0.01). All of the abnormalities normalized when dietary potassium were supplemented (0.52+/-0.03 micromol/L versus 0.89+/-0.02 micromol/L for ADMA and 58.1+/-0.9 micromol/L versus 41.8+/-2.1 micromol/L for NOx). Statistically significant correlations were found among plasma ADMA level, the mean blood pressure, and the level of NO after salt loading in normotensive salt sensitive individuals. Our study indicates that high dietary potassium intake reduces blood pressure and ADMA levels while increasing NO bioactivity in normotensive salt-sensitive but not salt-resistant Asian subjects after salt loading.     

Salt sensitivity in young normotensive subjects is associated with a hyperinsulinemic response to oral glucose.

Insulin resistance associated with a hyperinsulinemic response to oral glucose intake has been found in patients with essential hypertension and is believed to play a role in inducing hypertension by causing renal sodium and water retention. We therefore examined whether salt-sensitive, young normotensives, assumed to be predisposed to essential hypertension, exhibit impaired glucose tolerance in a similar way. The plasma insulin and glucose response to oral glucose intake (75 g) was assessed in 23 healthy, lean, male volunteers ingesting either 20 mmol or 260 mmol NaCl/day for 6 days each in a single-blind randomized crossover study. Salt sensitivity was defined as a significant drop in mean arterial blood pressure greater than 3 mmHg (means of 30 readings in the supine subject; P less than 0.05) under the low-salt diet. Following the glucose load, plasma levels of both glucose and insulin were significantly higher (P less than 0.01) in the salt-sensitive (n = 10) compared with the salt-resistant subjects (n = 13) during the high-salt diet but not during the low-salt diet. Whereas in the salt-sensitive group glucose tolerance improved with dietary salt restriction (P less than 0.01), it deteriorated in the salt-resistant group (P less than 0.05). Following the glucose load under the high-salt diet, there was a significant drop in blood pressure in the salt-sensitive (P less than 0.005) but not the salt-resistant subjects. The hyperglycemic and hyperinsulinemic response in salt-sensitive subjects suggests that insulin resistance is present in these subjects prior to the development of hypertension and that it can be ameliorated by salt restriction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Potassium supplementation ameliorates increased plasma homocysteine induced by salt loading in normotensive salt-sensitive subjects

The mechanism by which high-salt and low-potassium diet contributes to hypertension remains poorly understood. Plasma homocysteine (Hcys) is recognized as a primary mediator of blood pressure (BP) response to some diets. Therefore, the present study tried to investigate whether plasma Hcys and BP could be regulated by salt loading in normotensive salt-sensitive (SS) persons, and further explored whether potassium supplementation could reverse the effect. We enrolled 47 normotensive subjects, aged 29–65 years. The protocol included 7 days on a low-salt diet (3g/day, NaCl), 7 days on a high-salt diet (18g/day), and then a high-salt diet with potassium supplementation (4.5g/day) for 7 days. After high-salt intake, BP was significantly increased and potassium supplementation lowered it in the SS group. Plasma Hcys were higher in SS subjects than in salt-resistant (SR) subjects after salt loading (34.4 ± 17.0 μmol/L versus 19.16 ± 6.4 μmol/L, P < 0.01). Plasma Hcys in SS subjects was increased on a high-salt diet than on a low-salt diet (34.4 ± 17.0 μmol/L versus 16.5 ± 8.3 μmol/L, P < 0.01), but plasma Hcys was ameliorated by potassium supplementation (34.4 ± 17.0 μmol/L versus 20.9 ± 10.4 μmol/L, P < 0.01). In SS subjects, the change of mean arterial blood pressure (MBP) correlated significantly and positively with the alteration of plasma Hcys during low-salt to high-salt intake and high-salt to high-salt with potassium supplementation (r = 0.75, P < 0.001; r = 0.74, P < 0.001, respectively). Our results indicate that Hcys may partly mediate the impact of high-salt intake and potassium supplementation on BP in SS subjects.     

High urinary dopa and low urinary dopamine-to-dopa ratio in salt-sensitive hypertension

Dopamine in urine is derived substantially from renal uptake and decarboxylation of 3,4-dihydroxyphenylalanine (dopa), and increases in excretion of dopa normally parallel increases in excretion of dopamine during salt loading. Since patients with salt-sensitive hypertension may have decreased urinary excretion of dopamine during dietary salt loading, the present study was designed to evaluate the response of dopa to salt loading. Sixteen inpatients with normal-renin essential hypertension ate a constant metabolic diet containing 9 mmol/day sodium for 7 days, followed by the same diet but containing 249 mmol/day sodium for 7 days. Salt sensitivity was defined as an increase in mean arterial pressure of 8 mm Hg between the diets; on this basis, nine patients were salt-sensitive and seven, salt-resistant. The rate of urinary dopa excretion was significantly higher in the salt-sensitive patients throughout the study (mean rates 132 +/- 13 nmol/day in the salt-sensitive group and 78 +/- 9 nmol/day in the salt-resistant group for the 14 days of observation, p less than 0.01). When dietary sodium intake was increased to 249 mmol/day, urinary dopa excretion increased significantly more in salt-sensitive patients than salt-resistant patients. At the end of the high salt diet, dopamine excretion was significantly attenuated in the salt-sensitive patients, despite higher rates of dopa excretion. Thus, the urinary ratio of dopamine to dopa was decreased in salt-sensitive patients, regardless of salt intake.(ABSTRACT TRUNCATED AT 250 WORDS)     

慢性盐负荷对成年人血清肾胺酶的影响

目的 :观察慢性盐负荷对成年人血清肾胺酶浓度的影响。方法 :选取42例28~65岁的成年人参与为期2周的慢性盐负荷试验,包括3 d基线调查及低盐饮食、高盐饮食各7 d的研究。每个阶段均测量血压,并收集血、尿标本,测定24 h尿钠、钾含量;血清肾胺酶采用酶联免疫吸附(ELISA)法测定。结果:与基线期相比,低盐饮食可显著升高受试者血清肾胺酶水平[(5.10±0.18)比(8.12±0.42)mg/L,P     

盐阈、盐摄入量与血压盐敏感性的关系研究

目的探讨盐阈、盐摄入量与血压盐敏感性之间的关系。方法选取203人进行慢性盐负荷试验,确定盐敏感性,并测定其盐阈、收集基线24h尿液,测定尿钠排泄量。结果盐敏感者检出率为19.2%。盐敏感与盐不敏感者之间盐阈、24小时尿钠排泄量差异无统计学意义;无论盐敏感者还是盐不敏感者,盐阈与24h尿钠排泄量有显著相关性。结论盐敏感者钠盐摄入量并不比盐不敏感者高;盐敏感者长期高盐饮食,才可能表现出盐与血压的联系,发生高血压。     

Low sodium/high potassium diet for prevention of hypertension: probable mechanisms of action

20 normotensive subjects (10 with a family history of hypertension) were investigated as to whether moderate salt restriction and/or a high potassium intake had a beneficial effect on blood pressure regulation and prevention of hypertension. In all subjects a moderate reduction of salt intake from 200 to 50 mmol/day over 2 weeks reduced the rise in blood pressure induced by various doses of noradrenaline (0.1, 0.2, and 0.4 microgram/kg/min). Furthermore, of 20 subjects 12 (8 with a family history of hypertension) responded to salt restriction with a fall in systolic or diastolic blood pressure of at least 5 mm Hg. There were no significant differences in plasma renin, aldosterone, vasopressin, and catecholamine levels between responders (salt-sensitive subjects) and non-responders, but salt-sensitive subjects had a mean baseline diastolic blood pressure which was higher than that of salt-insensitive subjects by 13 mm Hg (77.3+/-3.26 vs. 64.6+/-2.06, p less than 0.001). A high potassium intake reduced diastolic blood pressure by at least 5 mm Hg in 10 out of 20 subjects, of the 10 7 had a family history of hypertension and 9 responded to salt restriction. A high potassium intake also improved compliance with a low salt regimen, promoted sodium loss, prevented the rise in plasma catecholamines induced by a low salt diet, and increased the sensitivity of the baroreceptor reflex. These four effects occurred in the group as a whole and were probably the means by which a high potassium intake reduced blood pressure. In all subjects 2 weeks of a combined low sodium/high potassium intake reduced blood pressure rises induced by mental stress or noradrenaline infusion by 10 mm Hg. The results of this study suggest that moderate salt restriction combined with a high potassium intake helps to prevent hypertension, that salt-sensitive subjects exist, and that these individuals would profit most.     

Reduced sympathetic inhibition in salt-sensitive Japanese young adults

The purpose of our study was to investigate the sympathetic response to excess salt loading of 54 normotensive young adults with and without a family history of hypertension. We examined muscle sympathetic nerve activity, plasma concentration and urinary excretion of catecholamines, and ambulatory blood pressures during low (4 g NaCl) and high (16 g NaCl) salt diet intake. Ambulatory blood pressure and urinary excretion of catecholamines are known to be reduced during sleep. These parameters were therefore calculated during waking and sleeping periods. The subject was defined as salt-sensitive when mean ambulatory systolic pressure during the waking period was ≥3mm Hg higher during high salt intake than during low salt intake (n = 26: 21.4 ± 0.3 years old). When mean systolic pressure was either lower or equal during high salt intake than during low salt intake, the subject was defined as salt-resistant (n = 24: 21.3 ± 0.3 years old). Muscle sympathetic nerve activity, plasma concentration and urinary excretion of norepinephrine in salt-resistant subjects were significantly reduced (P < .05) by salt intake, wheras plasma concentration of epinephrine was unchanged and urinary excretion of epinephrine was reduced. In contrast, urinary excretion of epinephrine in salt-sensitive subjects was significantly elevated (P < .05) during high salt intake, whereas muscle sympathetic nerve activity and urinary excretion of norepinephrine remained unchanged despite a significant increase (P < .01) of ambulatory blood pressure. Of the salt-sensitive subjects, 73% (19 of 26) had a positive family history of hypertension, whereas only 5 of 24 salt-resistant subjects had a positive family history. These data indicate that the inhibition of sympathetic activity during a high salt intake did not occur in salt-sensitive young adults, and this may be linked with a hereditary predisposition to hypertension.     

Lack of validation of a same-day outpatient protocol for determination of salt sensitivity of blood pressure

Salt sensitivity of blood pressure has been studied in humans with a 48-hour inpatient protocol of salt loading and depletion or with longer outpatient protocols using high- and low-salt diets. Results have been reproducible, but both methods are laborious and costly. A 6-hour protocol of intravenous salt loading and furosemide has been reported but never validated. We studied 14 normal volunteers (39±2 years old; 86% women and 21% black) with the inpatient and 6-hour protocols, separated by 30 days. Four subjects (29%) were salt sensitive in the inpatient protocol. They had higher systolic blood pressure, higher body mass index, and somewhat lower plasma renin activity than salt-resistant subjects. Baseline systolic blood pressure before both protocols was highly reproducible (r=0.90; P<0.0001; limits of agreement: +6.2 to -8.0 mm Hg), whereas the response to salt depletion was not (r=0.09). Three salt-sensitive and 4 salt-resistant subjects were misclassified by the short protocol. Three-hour natriuresis by furosemide in the short protocol (344±15 mmol) was not different from the 12-hour natriuresis in the inpatient protocol (357±19). However, stimulation of plasma renin activity and aldosterone was significantly less in the short (+0.10±0.07 ngA(I)/L/sec and -61±44 pmol/L) than in the inpatient protocol (+1.80±0.60 ngA(I)/L/sec and +256±88 pmol/L; P<0.03 for both). Activation of hormonal changes that regulate depressor responses to salt depletion may not have occurred with the 3-hour natriuresis of the short protocol. This methodology cannot be used to study salt sensitivity of blood pressure, because the phenotype, mechanisms, and prognosis of the latter have been defined with the inpatient protocol.