Salt loading affects cortisol metabolism in normotensive subjects: relationships with salt sensitivity

Is high salt intake inducing obesity via production of cortisol? A novel working hypothesis and pilot study

PURPOSE

Evidence is growing that high salt intake is an independent risk factor for obesity, but the mechanisms are unknown. Our novel working hypothesis is that high salt intake drives cortisol production, which in turn, drives obesity. The current study aimed to demonstrate an acute cortisol response following a single high salt meal.

METHODS

Eight participants (age 30.5 ± 9.8 years [mean ± SD], 50% female), consumed high salt (3.82 g; 1529 mg sodium) and low salt (0.02 g; 9 mg sodium) meals in a randomized cross-over design.

RESULTS

Urinary and salivary cortisol and plasma adrenocorticotropic hormone (ACTH) demonstrated order effects. When high salt was given second, there was a peak above baseline for urinary cortisol (26.3%), salivary cortisol (9.4%) and plasma ACTH (4.1%) followed by a significant decline in each hormone (treatment*time, F[9, 18] = 2.641, p = 0.038, partial η2 = 0.569; treatment*time, F[12, 24] = 2.668, p = 0.020, partial η2 = 0.572; treatment*time, F[12, 24] = 2.580, p = 0.023, partial η2 = 0.563, respectively), but not when high salt was given first (p > 0.05 for all).

CONCLUSION

These intriguing findings provide partial support for our hypothesis and support a need for further research to elucidate the role of high salt intake in cortisol production and, in turn, in the aetiology of obesity.

TRIAL REGISTRATION NUMBER

ACTRN12623000490673; date of registration 12/05/2023; retrospectively registered.

High salt intake activates the hypothalamic-pituitary-adrenal axis, amplifies the stress response, and alters tissue glucocorticoid exposure in mice

AIMS

High salt intake is common and contributes to poor cardiovascular health. Urinary sodium excretion correlates directly with glucocorticoid excretion in humans and experimental animals. We hypothesized that high salt intake activates the hypothalamic-pituitary-adrenal axis activation and leads to sustained glucocorticoid excess.

METHODS AND RESULTS

In male C57BL/6 mice, high salt intake for 2-8 weeks caused an increase in diurnal peak levels of plasma corticosterone. After 2 weeks, high salt increased Crh and Pomc mRNA abundance in the hypothalamus and anterior pituitary, consistent with basal hypothalamic-pituitary-adrenal axis activation. Additionally, high salt intake amplified glucocorticoid response to restraint stress, indicative of enhanced axis sensitivity. The binding capacity of Corticosteroid-Binding Globulin was reduced and its encoding mRNA downregulated in the liver. In the hippocampus and anterior pituitary, Fkbp5 mRNA levels were increased, indicating increased glucocorticoid exposure. The mRNA expression of the glucocorticoid-regenerating enzyme, 11β-hydroxysteroid dehydrogenase Type 1, was increased in these brain areas and in the liver. Sustained high salt intake activated a water conservation response by the kidney, increasing plasma levels of the vasopressin surrogate, copeptin. Increased mRNA abundance of Tonebp and Avpr1b in the anterior pituitary suggested that vasopressin signalling contributes to hypothalamic-pituitary-adrenal axis activation by high salt diet.

CONCLUSION

Chronic high salt intake amplifies basal and stress-induced glucocorticoid levels and resets glucocorticoid biology centrally, peripherally and within cells.

Fluid-induced harm in the hospital: look beyond volume and start considering sodium. From physiology towards recommendations for daily practice in hospitalized adults

PURPOSE

Iatrogenic fluid overload is a potential side effect of intravenous fluid therapy in the hospital. Little attention has been paid to sodium administration as a separate cause of harm. With this narrative review, we aim to substantiate the hypothesis that a considerable amount of fluid-induced harm is caused not only by fluid volume, but also by the sodium that is administered to hospitalized patients.

METHODS

We show how a regular dietary sodium intake is easily surpassed by the substantial amounts of sodium that are administered during typical hospital stays. The most significant sodium burdens are caused by isotonic maintenance fluid therapy and by fluid creep, defined as the large volume unintentionally administered to patients in the form of dissolved medication. In a section on physiology, we elaborate on the limited renal handling of an acute sodium load. We demonstrate how the subsequent retention of water is an energy-demanding, catabolic process and how free water is needed to excrete large burdens of sodium. We quantify the effect size of sodium-induced fluid retention and discuss its potential clinical impact. Finally, we propose preventive measures, discuss the benefits and risks of low-sodium maintenance fluid therapy, and explore options for reducing the amount of sodium caused by fluid creep.

CONCLUSION

The sodium burdens caused by isotonic maintenance fluids and fluid creep are responsible for an additional and avoidable derailment of fluid balance, with presumed clinical consequences. Moreover, the handling of sodium overload is characterized by increased catabolism. Easy and effective measures for reducing sodium load and fluid retention include choosing a hypotonic rather than isotonic maintenance fluid strategy (or avoiding these fluids when enough free water is provided through other sources) and dissolving as many medications as possible in glucose 5%.

Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride

BACKGROUND

Recent cohort studies show that salt intake below 6 g is associated with increased mortality. These findings have not changed public recommendations to lower salt intake below 6 g, which are based on assumed blood pressure (BP) effects and no side-effects.

OBJECTIVES

To assess the effects of sodium reduction on BP, and on potential side-effects (hormones and lipids) SEARCH METHODS: The Cochrane Hypertension Information Specialist searched the following databases for randomized controlled trials up to April 2018 and a top-up search in March 2020: the Cochrane Hypertension Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (from 1946), Embase (from 1974), the World Health Organization International Clinical Trials Registry Platform, and ClinicalTrials.gov. We also contacted authors of relevant papers regarding further published and unpublished work. The searches had no language restrictions. The top-up search articles are recorded under "awaiting assessment."

SELECTION CRITERIA

Studies randomizing persons to low-sodium and high-sodium diets were included if they evaluated at least one of the outcome parameters (BP, renin, aldosterone, noradrenalin, adrenalin, cholesterol, high-density lipoprotein, low-density lipoprotein and triglyceride,.

DATA COLLECTION AND ANALYSIS

Two review authors independently collected data, which were analysed with Review Manager 5.3. Certainty of evidence was assessed using GRADE.

MAIN RESULTS

Since the first review in 2003 the number of included references has increased from 96 to 195 (174 were in white participants). As a previous study found different BP outcomes in black and white study populations, we stratified the BP outcomes by race. The effect of sodium reduction (from 203 to 65 mmol/day) on BP in white participants was as follows: Normal blood pressure: SBP: mean difference (MD) -1.14 mmHg (95% confidence interval (CI): -1.65 to -0.63), 5982 participants, 95 trials; DBP: MD + 0.01 mmHg (95% CI: -0.37 to 0.39), 6276 participants, 96 trials. Hypertension: SBP: MD -5.71 mmHg (95% CI: -6.67 to -4.74), 3998 participants,88 trials; DBP: MD -2.87 mmHg (95% CI: -3.41 to -2.32), 4032 participants, 89 trials (all high-quality evidence). The largest bias contrast across studies was recorded for the detection bias element. A comparison of detection bias low-risk studies versus high/unclear risk studies showed no differences. The effect of sodium reduction (from 195 to 66 mmol/day) on BP in black participants was as follows: Normal blood pressure: SBP: mean difference (MD) -4.02 mmHg (95% CI:-7.37 to -0.68); DBP: MD -2.01 mmHg (95% CI:-4.37, 0.35), 253 participants, 7 trials. Hypertension: SBP: MD -6.64 mmHg (95% CI:-9.00, -4.27); DBP: MD -2.91 mmHg (95% CI:-4.52, -1.30), 398 participants, 8 trials (low-quality evidence). The effect of sodium reduction (from 217 to 103 mmol/day) on BP in Asian participants was as follows: Normal blood pressure: SBP: mean difference (MD) -1.50 mmHg (95% CI: -3.09, 0.10); DBP: MD -1.06 mmHg (95% CI:-2.53 to 0.41), 950 participants, 5 trials. Hypertension: SBP: MD -7.75 mmHg (95% CI:-11.44, -4.07); DBP: MD -2.68 mmHg (95% CI: -4.21 to -1.15), 254 participants, 8 trials (moderate-low-quality evidence).   During sodium reduction renin increased 1.56 ng/mL/hour (95%CI:1.39, 1.73) in 2904 participants (82 trials); aldosterone increased 104 pg/mL (95%CI:88.4,119.7) in 2506 participants (66 trials); noradrenalin increased 62.3 pg/mL: (95%CI: 41.9, 82.8) in 878 participants (35 trials); adrenalin increased 7.55 pg/mL (95%CI: 0.85, 14.26) in 331 participants (15 trials); cholesterol increased 5.19 mg/dL (95%CI:2.1, 8.3) in 917 participants (27 trials); triglyceride increased 7.10 mg/dL (95%CI: 3.1,11.1) in 712 participants (20 trials); LDL tended to increase 2.46 mg/dl (95%CI: -1, 5.9) in 696 participants (18 trials); HDL was unchanged -0.3 mg/dl (95%CI: -1.66,1.05) in 738 participants (20 trials) (All high-quality evidence except the evidence for adrenalin).

AUTHORS' CONCLUSIONS

In white participants, sodium reduction in accordance with the public recommendations resulted in mean arterial pressure (MAP) decrease of about 0.4 mmHg in participants with normal blood pressure and a MAP decrease of about 4 mmHg in participants with hypertension. Weak evidence indicated that these effects may be a little greater in black and Asian participants. The effects of sodium reduction on potential side effects (hormones and lipids) were more consistent than the effect on BP, especially in people with normal BP.

Construction of a ceRNA coregulatory network and screening of hub biomarkers for salt-sensitive hypertension

Salt-sensitive hypertension (SSH) is an independent risk factor for cardiovascular disease. The regulation of long non-coding RNAs, mRNAs and competing endogenous RNAs (ceRNAs) in the pathogenesis of SSH is uncertain. An RNA microarray was performed to discover SSH-associated differentially expressed lncRNAs (DElncRNAs) and mRNAs (DEmRNAs), and 296 DElncRNAs and 44 DEmRNAs were identified, and 247 DElncRNAs and 44 DEmRNAs among these RNAs were included in the coexpression network. The coregulatory network included 23 ceRNA loops, and six hub RNAs (lnc-ILK-8:1, lnc-OTX1-7:1, lnc-RCAN1-6:1, GIMAP8, SUV420H1 and PIGV) were identified for further population validation. The ceRNA correlations among lnc-OTX1-7:1, hsa-miR-361-5p and GIMAP8 were confirmed in SSH and SRH patients. A larger-sample validation confirmed that GIMAP8, SUV420H1 and PIGV were differentially expressed between the SSH and SRH groups. In addition, SUV420H1 was included in the SSH screening model, and the area under the curve of the model was 0.720 (95% CI: 0.624-0.816). Our study explored the transcriptome profiles of SSH and constructed a ceRNA network to help elucidate the mechanism of SSH. In addition, SUV420H1 was identified as a hub element that participates in SSH transcriptional regulation and as a potential biomarker for the early diagnosis of SSH.

Increased salt consumption induces body water conservation and decreases fluid intake

BACKGROUND

The idea that increasing salt intake increases drinking and urine volume is widely accepted. We tested the hypothesis that an increase in salt intake of 6 g/d would change fluid balance in men living under ultra-long-term controlled conditions.

METHODS

Over the course of 2 separate space flight simulation studies of 105 and 205 days' duration, we exposed 10 healthy men to 3 salt intake levels (12, 9, or 6 g/d). All other nutrients were maintained constant. We studied the effect of salt-driven changes in mineralocorticoid and glucocorticoid urinary excretion on day-to-day osmolyte and water balance.

RESULTS

A 6-g/d increase in salt intake increased urine osmolyte excretion, but reduced free-water clearance, indicating endogenous free water accrual by urine concentration. The resulting endogenous water surplus reduced fluid intake at the 12-g/d salt intake level. Across all 3 levels of salt intake, half-weekly and weekly rhythmical mineralocorticoid release promoted free water reabsorption via the renal concentration mechanism. Mineralocorticoid-coupled increases in free water reabsorption were counterbalanced by rhythmical glucocorticoid release, with excretion of endogenous osmolyte and water surplus by relative urine dilution. A 6-g/d increase in salt intake decreased the level of rhythmical mineralocorticoid release and elevated rhythmical glucocorticoid release. The projected effect of salt-driven hormone rhythm modulation corresponded well with the measured decrease in water intake and an increase in urine volume with surplus osmolyte excretion.

CONCLUSION

Humans regulate osmolyte and water balance by rhythmical mineralocorticoid and glucocorticoid release, endogenous accrual of surplus body water, and precise surplus excretion.

FUNDING

Federal Ministry for Economics and Technology/DLR; the Interdisciplinary Centre for Clinical Research; the NIH; the American Heart Association (AHA); the Renal Research Institute; and the TOYOBO Biotechnology Foundation. Food products were donated by APETITO, Coppenrath und Wiese, ENERVIT, HIPP, Katadyn, Kellogg, Molda, and Unilever.

Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride

BACKGROUND

In spite of more than 100 years of investigations the question of whether a reduced sodium intake improves health is still unsolved.

OBJECTIVES

To estimate the effects of low sodium intake versus high sodium intake on systolic and diastolic blood pressure (SBP and DBP), plasma or serum levels of renin, aldosterone, catecholamines, cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL) and triglycerides.

SEARCH METHODS

The Cochrane Hypertension Information Specialist searched the following databases for randomized controlled trials up to March 2016: the Cochrane Hypertension Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL) (2016, Issue 3), MEDLINE (from 1946), Embase (from 1974), the World Health Organization International Clinical Trials Registry Platform, and ClinicalTrials.gov. We also searched the reference lists of relevant articles.

SELECTION CRITERIA

Studies randomising persons to low-sodium and high-sodium diets were included if they evaluated at least one of the above outcome parameters.

DATA COLLECTION AND ANALYSIS

Two review authors independently collected data, which were analysed with Review Manager 5.3.

MAIN RESULTS

A total of 185 studies were included. The average sodium intake was reduced from 201 mmol/day (corresponding to high usual level) to 66 mmol/day (corresponding to the recommended level).The effect of sodium reduction on blood pressure (BP) was as follows: white people with normotension: SBP: mean difference (MD) -1.09 mmHg (95% confidence interval (CI): -1.63 to -0.56; P = 0.0001); 89 studies, 8569 participants; DBP: + 0.03 mmHg (MD 95% CI: -0.37 to 0.43; P = 0.89); 90 studies, 8833 participants. High-quality evidence. Black people with normotension: SBP: MD -4.02 mmHg (95% CI:-7.37 to -0.68; P = 0.002); seven studies, 506 participants; DBP: MD -2.01 mmHg (95% CI:-4.37 to 0.35; P = 0.09); seven studies, 506 participants. Moderate-quality evidence. Asian people with normotension: SBP: MD -0.72 mmHg (95% CI: -3.86 to 2.41; P = 0.65); DBP: MD -1.63 mmHg (95% CI:-3.35 to 0.08; P =0.06); three studies, 393 participants. Moderate-quality evidence.White people with hypertension: SBP: MD -5.51 mmHg (95% CI: -6.45 to -4.57; P < 0.00001); 84 studies, 5925 participants; DBP: MD -2.88 mmHg (95% CI: -3.44 to -2.32; P < 0.00001); 85 studies, 6001 participants. High-quality evidence. Black people with hypertension: SBP MD -6.64 mmHg (95% CI:-9.00 to -4.27; P = 0.00001); eight studies, 619 participants; DBP -2.91 mmHg (95% CI:-4.52, -1.30; P = 0.0004); eight studies, 619 participants. Moderate-quality evidence. Asian people with hypertension: SBP: MD -7.75 mmHg (95% CI:-11,44 to -4.07; P < 0.0001) nine studies, 501 participants; DBP: MD -2.68 mmHg (95% CI: -4.21 to -1.15; P = 0.0006). Moderate-quality evidence.In plasma or serum, there was a significant increase in renin (P < 0.00001), aldosterone (P < 0.00001), noradrenaline (P < 0.00001), adrenaline (P < 0.03), cholesterol (P < 0.0005) and triglyceride (P < 0.0006) with low sodium intake as compared with high sodium intake. All effects were stable in 125 study populations with a sodium intake below 250 mmol/day and a sodium reduction intervention of at least one week.

AUTHORS' CONCLUSIONS

Sodium reduction from an average high usual sodium intake level (201 mmol/day) to an average level of 66 mmol/day, which is below the recommended upper level of 100 mmol/day (5.8 g salt), resulted in a decrease in SBP/DBP of 1/0 mmHg in white participants with normotension and a decrease in SBP/DBP of 5.5/2.9 mmHg in white participants with hypertension. A few studies showed that these effects in black and Asian populations were greater. The effects on hormones and lipids were similar in people with normotension and hypertension. Renin increased 1.60 ng/mL/hour (55%); aldosterone increased 97.81 pg/mL (127%); adrenalin increased 7.55 pg/mL (14%); noradrenalin increased 63.56 pg/mL: (27%); cholesterol increased 5.59 mg/dL (2.9%); triglyceride increased 7.04 mg/dL (6.3%).

Effect of sodium intake on renin level: Analysis of general population and meta-analysis of randomized controlled trials

BACKGROUND

We evaluated the association between sodium intake and plasma renin levels in the cross sectional study and meta-analysis of randomized controlled trials, whether there is a persistent elevation of plasma renin by longer-term sodium intake restriction.

METHODS

Plasma renin activity (PRA) and 24-h urine sodium (24HUNa) excretion were measured from individuals randomly selected from a community. Simple and multiple linear regression analyses adjusted for age, 24-h systolic blood pressure, 24-h average heart rate, fasting blood glucose and gender were performed. For meta-analysis, 74 studies published from 1975 to mid-2014 were identified in a systematic literature search using EMBASE, CINAHL, and MEDLINE. Random effects meta-analyses and a meta-regression analysis were performed.

RESULTS

Among the 496 participants recruited, 210 normotensive and 87 untreated hypertensive subjects were included in the analysis. There was no significant association between PRA and 24HUNa in the total population, or hypertensive and normotensive individuals. In the meta-analysis, the standard mean difference (SMD) of renin level by sodium intake reduction was 1.26 (95% CI: 1.08 to 1.44, Z=12.80, P<0.001, I(2)=87%). In the meta-regression analysis, an increase in a day of intervention was associated with a fall in SMD by -0.04 (95% CI: -0.05 to -0.02, Z=-5.27, P<0.001, I(2)=86%), indicating that longer duration of reduced sodium intake would lead to lesser SMD of renin level.

CONCLUSIONS

The present population based cross-sectional study and meta-analysis suggests that prolonged reduction in sodium intake is very unlikely associated with elevation of plasma renin levels.

Systematic review and meta-analysis reveals acutely elevated plasma cortisol following fasting but not less severe calorie restriction

Elevated plasma cortisol has been reported following caloric restriction, and may contribute to adverse effects including stress-induced overeating, but results from published studies are inconsistent. To clarify the effects of caloric restriction on plasma cortisol, and to assess cortisol as an indicator of stress during caloric restriction, we conducted a systematic review and meta-analysis of published studies in which cortisol was measured following caloric restriction without other manipulations in humans. We further compared effects of fasting, very low calorie diet (VLCD), and other less intense low calorie diet (LCD), as well as the duration of caloric restriction by meta-regression. Overall, caloric restriction significantly increased serum cortisol level in 13 studies (357 total participants). Fasting showed a very strong effect in increasing serum cortisol, while VLCD and LCD did not show significant increases. The meta-regression analysis showed a negative association between the serum cortisol level and the duration of caloric restriction, indicating serum cortisol is increased in the initial period of caloric restriction but decreased to the baseline level after several weeks. These results suggest that severe caloric restriction causes activation of the hypothalamic-pituitary-adrenal axis, which may be transient, but results in elevated cortisol which could mediate effects of starvation on brain and metabolic function as well as ameliorate weight loss.

The Expression of RAC1 and Mineralocorticoid Pathway-Dependent Genes are Associated With Different Responses to Salt Intake

BACKGROUND

Rac1 upregulation has been implicated in salt-sensitive hypertension as a modulator of mineralocorticoid receptor (MR) activity. Rac1 could affect the expression of oxidative stress markers, such as hemoxigenase-1 (HO-1) or nuclear factor-B (NF-κB), and the expression of neutrophil gelatinase-associated lipocalin (NGAL), a cytokine upregulated upon MR activation.

AIM

We evaluated RAC1 expression in relation of high salt intake and association with MR, NGAL, HO-1, and NF-κB expression, mineralo- and glucocorticoids levels, and inflammatory parameters.

SUBJECTS AND METHODS

We studied 147 adult subjects. A food survey identified the dietary sodium (Na) intake. RAC1 expression was considered high or low according to the value found in normotensive subjects with low salt intake. We determined the gene expression of RAC1, MR, NGAL, HO-1, NF-κB, and 18S, isolated from peripheral leukocytes. We measured aldosterone, cortisol, sodium, potassium excretion, metalloproteinase (MMP9 y MMP2), and C-reactive protein.

RESULTS

We identified 126 subjects with high Na-intake, 18 subjects had high, and 108 low-RAC1 expression. The subjects with high-RAC1 expression showed a significant increase in MR (P = 0.0002), NGAL (P < 0.0001) HO-1 (P = 0.0004), and NF-κB (P < 0.0001) gene expression. We demonstrated an association between RAC1 expression and MR (R sp 0.64; P < 0.0001), NGAL (R sp 0.48; P < 0.0001), HO-1 (R sp 0.53; P < 0.0001), and NF-κB (R sp0.52; P < 0.0001). We did not identify any association between RAC1 and clinical or biochemical variables.

CONCLUSIONS

RAC1 expression was associated with an increase in MR, NGAL, NF-κB, and HO-1 expression, suggesting that RAC1 could be a mediator of cardiovascular damage induced by sodium, and may also useful to identify subjects with different responses to salt intake.

Glucocorticoids and renal Na+ transport: implications for hypertension and salt sensitivity

The clinical manifestations of glucocorticoid excess include central obesity, hyperglycaemia, dyslipidaemia, electrolyte abnormalities and hypertension. A century on from Cushing's original case study, these cardinal features are prevalent in industrialized nations. Hypertension is the major modifiable risk factor for cardiovascular and renal disease and reflects underlying abnormalities of Na⁺ homeostasis. Aldosterone is a master regulator of renal Na⁺ transport but here we argue that glucocorticoids are also influential, particularly during moderate excess. The hypothalamic–pituitary–adrenal axis can affect renal Na⁺ homeostasis on multiple levels, systemically by increasing mineralocorticoid synthesis and locally by actions on both the mineralocorticoid and glucocorticoid receptors, both of which are expressed in the kidney. The kidney also expresses both of the 11β-hydroxysteroid dehydrogenase (11βHSD) enzymes. The intrarenal generation of active glucocorticoid by 11βHSD1 stimulates Na⁺ reabsorption; failure to downregulate the enzyme during adaption to high dietary salt causes salt-sensitive hypertension. The deactivation of glucocorticoid by 11βHSD2 underpins the regulatory dominance for Na⁺ transport of mineralocorticoids and defines the ‘aldosterone-sensitive distal nephron’. In summary, glucocorticoids can stimulate renal transport processes conventionally attributed to the renin–angiotensin–aldosterone system. Importantly, Na⁺ and volume homeostasis do not exert negative feedback on the hypothalamic–pituitary–adrenal axis. These actions are therefore clinically relevant and may contribute to the pathogenesis of hypertension in conditions associated with elevated glucocorticoid levels, such as the metabolic syndrome and chronic stress.

HSD11B2 CA-repeat and sodium balance

Type 2 11β-hydroxysteroid dehydrogenase encoded by the HSD11B2 gene converts cortisol to inactive cortisone and thus protects the mineralocorticoid receptor from cortisol exposure. Impaired activity of this enzyme leads to mineralocorticoid excess, suggesting HSD11B2 as a candidate locus for patients at risk of developing low renin or salt-sensitive essential hypertension. In the present study, we searched for frequent polymorphisms in 155 Japanese subjects but detected none in the proximal promoter or coding regions of HSD11B2. Following this result, we genotyped a highly polymorphic CA-repeat polymorphism within the first intron in 848 normotensive and 430 hypertensive Japanese patients, and we then analyzed its association with disease and clinical parameters. We confirmed 12 alleles (12, 15-25 CA repeats) in the population and found no significant difference in the distribution of the allele length between normotensive and hypertensive patients. In 174 normal subjects without medication, urinary cortisol excretion was higher in subjects with more CA repeats in the shorter allele, but the ratio of urinary cortisone to cortisol, a reliable marker of renal HSD11B2 activity, did not differ. However, longer CA-repeat length was positively correlated with 24-h urinary sodium excretion, fractional sodium excretion and potassium clearance, and this observation was confirmed when the longer CA-repeat length was dichotomized. Thus, HSD11B2 CA-repeat genotype is not associated with hypertension itself, but with renal sodium excretion, probably through salt intake/appetite.

Plasma Lp-PLA(2) mass and apoB-lipoproteins that carry Lp-PLA(2) decrease after sodium

BACKGROUND

Lipoprotein-associated phospholipase A(2) (Lp-PLA(2) ) is a novel cardiovascular risk marker, which is predominantly complexed to apolipoprotein (apo) B-containing lipoproteins in human plasma. As increasing dietary sodium intake may decrease plasma apoB-containing lipoproteins, we tested whether a sodium challenge lowers plasma Lp-PLA(2) mass, as well as the levels of apoB-containing lipoprotein particles carrying Lp-PLA(2) (apoB-Lp-PLA(2) ), employing a newly developed enzyme-linked immunosorbent assay.

MATERIALS AND METHODS

In 45 women and 31 men (mean age 44 ± 14 years), plasma Lp-PLA(2) mass (turbidimetric immunoassay), the level of apoB-Lp-PLA(2) , expressed in apoB concentration and lipoproteins were measured in response to a 3-day challenge with 9 g sodium chloride tablets daily.

RESULTS

Urinary sodium excretion increased from 165 ± 60 to 321 ± 70 mmol/24 h (P<0.001) after salt loading. Plasma Lp-PLA(2) mass decreased from 618 (493-719) to 588 (465-698) μg/L (P<0.001), and apoB-Lp-PLA(2) decreased from 0.276 (0.200-0.351) to 0.256 (0.189-0.328) g LDL protein/L (P=0.004) in response to the sodium challenge together with decreases in plasma total cholesterol, nonhigh-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, apolipoprotein B and the total cholesterol/HDL cholesterol ratio (P<0.01 for all). Changes in plasma Lp-PLA(2) mass were correlated positively with changes in total cholesterol, LDL cholesterol and non-HDL cholesterol (r=0.260-0.276, P<0.05 to P<0.02), whereas changes in apoB-Lp-PLA(2) were correlated positively with changes in non-HDL cholesterol and in the total cholesterol/HDL cholesterol ratio (r=0.232-0.385, P<0.05-0.01).

CONCLUSION

Both plasma Lp-PLA(2) mass levels and apoB-Lp-PLA(2) decrease in response to a short-term oral sodium challenge.

Failure to downregulate the epithelial sodium channel causes salt sensitivity in Hsd11b2 heterozygote mice

In vivo, the enzyme 11β-hydroxysteroid dehydrogenase type 2 influences ligand access to the mineralocorticoid receptor. Ablation of the encoding gene, HSD11B2, causes the hypertensive syndrome of apparent mineralocorticoid excess. Studies in humans and experimental animals have linked reduced 11β-hydroxysteroid dehydrogenase type 2 activity and salt sensitivity of blood pressure. In the present study, renal mechanisms underpinning salt sensitivity were investigated in Hsd11b2(+/-) mice fed low-, standard-, and high-sodium diets. In wild-type mice, there was a strong correlation between dietary sodium content and fractional sodium excretion but not blood pressure. High sodium feeding abolished amiloride-sensitive sodium reabsorption, consistent with downregulation of the epithelial sodium channel. In Hsd11b2(+/-) mice, the natriuretic response to increased dietary sodium content was blunted, and epithelial sodium channel activity persisted. High-sodium diet also reduced renal blood flow and increased blood pressure in Hsd11b2(+/-) mice. Aldosterone was modulated by dietary sodium in both genotypes, and salt sensitivity in Hsd11b2(+/-) mice was associated with increased plasma corticosterone levels. Chronic administration of an epithelial sodium channel blocker or a glucocorticoid receptor antagonist prevented salt sensitivity in Hsd11b2(+/-) mice, whereas mineralocorticoid receptor blockade with spironolactone did not. This study shows that reduced 11β-hydroxysteroid dehydrogenase type 2 causes salt sensitivity of blood pressure because of impaired renal natriuretic capacity. This reflects deregulation of epithelial sodium channels and increased renal vascular resistance. The phenotype is not caused by illicit activation of mineralocorticoid receptors by glucocorticoids but by direct activation of glucocorticoid receptors.

Effects of low-sodium diet vs. high-sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride (Cochrane Review)

BACKGROUND

The question of whether reduced sodium intake is effective as a health prophylaxis initiative is unsolved. The purpose was to estimate the effects of low-sodium vs. high-sodium intake on blood pressure (BP), renin, aldosterone, catecholamines, and lipids.

METHODS

Studies randomizing persons to low-sodium and high-sodium diets evaluating at least one of the above outcome parameters were included. Data were analyzed with Review Manager 5.1.

RESULTS

A total of 167 studies were included. The effect of sodium reduction in: (i) Normotensives: Caucasians: systolic BP (SBP) -1.27 mm Hg (95% confidence interval (CI): -1.88, -0.66; P = 0.0001), diastolic BP (DBP) -0.05 mm Hg (95% CI: -0.51, 0.42; P = 0.85). Blacks: SBP -4.02 mm Hg (95% CI: -7.37, -0.68; P = 0.002), DBP -2.01 mm Hg (95% CI: -4.37, 0.35; P = 0.09). Asians: SBP -1.27 mm Hg (95% CI: -3.07, 0.54; P = 0.17), DBP -1.68 mm Hg (95% CI: -3.29, -0.06; P = 0.04). (ii) Hypertensives: Caucasians: SBP -5.48 mm Hg (95% CI: -6.53, -4.43; P < 0.00001), DBP -2.75 mm Hg (95% CI: -3.34, -2.17; P < 0.00001). Blacks: SBP -6.44 mm Hg (95% CI: -8.85, -4.03; P = 0.00001), DBP -2.40 mm Hg (95% CI: -4.68, -0.12; P = 0.04). Asians: SBP -10.21 mm Hg (95% CI: -16.98, -3.44; P = 0.003), DBP -2.60 mm Hg (95% CI: -4.03, -1.16; P = 0.0004). Sodium reduction resulted in significant increases in renin (P < 0.00001), aldosterone (P < 0.00001), noradrenaline (P < 0.00001), adrenaline (P < 0.0002), cholesterol (P < 0.001), and triglyceride (P < 0.0008).

CONCLUSIONS

Sodium reduction resulted in a significant decrease in BP of 1% (normotensives), 3.5% (hypertensives), and a significant increase in plasma renin, plasma aldosterone, plasma adrenaline, and plasma noradrenaline, a 2.5% increase in cholesterol, and a 7% increase in triglyceride.

Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride

BACKGROUND

In spite of more than 100 years of investigations the question of reduced sodium intake as a health prophylaxis initiative is still unsolved.

OBJECTIVES

To estimate the effects of low sodium versus high sodium intake on systolic and diastolic blood pressure (SBP and DBP), plasma or serum levels of renin, aldosterone, catecholamines, cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL) and triglycerides.

SEARCH METHODS

PUBMED, EMBASE and Cochrane Central and reference lists of relevant articles were searched from 1950 to July 2011.

SELECTION CRITERIA

Studies randomizing persons to low sodium and high sodium diets were included if they evaluated at least one of the above outcome parameters.

DATA COLLECTION AND ANALYSIS

Two authors independently collected data, which were analysed with Review Manager 5.1.

MAIN RESULTS

A total of 167 studies were included in this 2011 update.The effect of sodium reduction in normotensive Caucasians was SBP -1.27 mmHg (95% CI: -1.88, -0.66; p=0.0001), DBP -0.05 mmHg (95% CI: -0.51, 0.42; p=0.85). The effect of sodium reduction in normotensive Blacks was SBP -4.02 mmHg (95% CI:-7.37, -0.68; p=0.002), DBP -2.01 mmHg (95% CI:-4.37, 0.35; p=0.09). The effect of sodium reduction in normotensive Asians was SBP -1.27 mmHg (95% CI: -3.07, 0.54; p=0.17), DBP -1.68 mmHg (95% CI:-3.29, -0.06; p=0.04). The effect of sodium reduction in hypertensive Caucasians was SBP -5.48 mmHg (95% CI: -6.53, -4.43; p<0.00001), DBP -2.75 mmHg (95% CI: -3.34, -2.17; p<0.00001). The effect of sodium reduction in hypertensive Blacks was SBP -6.44 mmHg (95% CI:-8.85, -4.03; p=0.00001), DBP -2.40 mmHg (95% CI:-4.68, -0.12; p=0.04). The effect of sodium reduction in hypertensive Asians was SBP -10.21 mmHg (95% CI:-16.98, -3.44; p=0.003), DBP -2.60 mmHg (95% CI: -4.03, -1.16; p=0.0004).In plasma or serum there was a significant increase in renin (p<0.00001), aldosterone (p<0.00001), noradrenaline (p<0.00001), adrenaline (p<0.0002), cholesterol (p<0.001) and triglyceride (p<0.0008) with low sodium intake as compared with high sodium intake. In general the results were similar in studies with a duration of at least 2 weeks.

AUTHORS' CONCLUSIONS

Sodium reduction resulted in a 1% decrease in blood pressure in normotensives, a 3.5% decrease in hypertensives, a significant increase in plasma renin, plasma aldosterone, plasma adrenaline and plasma noradrenaline, a 2.5% increase in cholesterol, and a 7% increase in triglyceride. In general, these effects were stable in studies lasting for 2 weeks or more.

Characteristics of sodium sensitivity in Korean populations

Sodium sensitivity (SS) is a variable response of blood pressure (BP) to changes in sodium intake. The present study evaluated the existence and the characteristics of subjects with SS in Koreans. One hundred one subjects with (n = 31, 57.7 ± 9.8 yr) or without hypertension (n = 70, 40.8 ± 16.5 yr) were given a low-sodium dietary approache to stop hypertension (DASH) diet (LSD) for 7 days and a high-sodium DASH diet (HSD) for the following 7 days. The prevalence of SS in the present study population was 27.7% (17.6% in the non-hypertensive subjects and 51.6% in the hypertensive subjects). Analysis of the non-hypertensive subjects showed that systolic BP, diastolic BP, and mean arterial pressure at baseline and after HSD were higher in the subjects with SS than the subjects without SS, and there were no differences after LSD. In the hypertensive subjects, there was no difference in the BP at baseline and after HSD whether or not the subjects had SS. However, the systolic BP of hypertensive subjects with SS was lower than hypertensive subjects without SS after LSD. In the present study population, subjects with SS have distinctive BP features unlike to subjects without SS.

Hsd11b2 haploinsufficiency in mice causes salt sensitivity of blood pressure

Salt sensitivity of blood pressure is an independent risk factor for cardiovascular morbidity. Mechanistically, abnormal mineralocorticoid action and subclinical renal impairment may blunt the natriuretic response to high sodium intake, causing blood pressure to rise. 11β-Hydroxysteroid dehydrogenase type 2 (11βHSD2) controls ligand access to the mineralocorticoid receptor, and ablation of the enzyme causes severe hypertension. Polymorphisms in HSD11B2 are associated with salt sensitivity of blood pressure in normotensives. In this study, we used mice heterozygote for a null mutation in Hsd11b2 (Hsd11b2(+/-)) to define the mechanisms linking reduced enzyme activity to salt sensitivity of blood pressure. A high-sodium diet caused a rapid and sustained increase in blood pressure in Hsd11b2(+/-) mice but not in wild-type littermates. During the adaptation to high-sodium diet, heterozygotes displayed impaired sodium excretion, a transient positive sodium balance, and hypokalemia. After 21 days of high-sodium feeding, Hsd11b2(+/-) mice had an increased heart weight. Mineralocorticoid receptor antagonism partially prevented the increase in heart weight but not the increase in blood pressure. Glucocorticoid receptor antagonism prevented the rise in blood pressure. In Hsd11b2(+/-) mice, high-sodium feeding caused suppression of aldosterone and a moderate but sustained increase in corticosterone. This study demonstrates an inverse relationship among 11βHSD2 activity, heart weight, and blood pressure in a clinically important context. Reduced activity causes salt sensitivity of blood pressure, but this does not reflect illicit activation of mineralocorticoid receptors by glucocorticoids. Instead, we have identified a novel interaction among 11βHSD2, dietary salt, and circulating glucocorticoids.

The effect of polyphenol-rich dark chocolate on fasting capillary whole blood glucose, total cholesterol, blood pressure and glucocorticoids in healthy overweight and obese subjects

Numerous studies indicate that polyphenol-rich chocolate reduces fasting blood glucose, blood pressure (BP) and total cholesterol in healthy individuals and hypertensives with or without glucose intolerance. The aim of the present study was to investigate the effect of two doses of polyphenol-rich dark chocolate (DC) on fasting capillary whole blood glucose, total cholesterol and BP and to examine whether improvements in these parameters are associated with changes in adrenocorticoid excretion in overweight and obese individuals. The study used a randomised, single-blind, cross-over design where fourteen overweight and obese subjects were randomised to either take 20 g DC with 500 mg polyphenols then 20 g DC with 1000 mg polyphenols or vice-versa. Participants followed each diet for 2 weeks separated by a 1-week washout period. It was observed that the 500 mg polyphenol dose was equally effective in reducing fasting blood glucose levels, systolic BP (SBP) and diastolic BP (DBP) as the 1000 mg polyphenol dose suggesting that a saturation effect might occur with increasing dose of polyphenols. There was also a trend towards a reduction in urinary free cortisone levels with both groups although it did not reach statistical significance. No changes in anthropometrical measurements were seen. We suggest that more research is required to investigate the mechanism(s) by which polyphenol-rich foods influence health.

Effects of a low-salt diet on flow-mediated dilatation in humans

BACKGROUND

The effect of salt reduction on vascular function, assessed by brachial artery flow-mediated dilatation (FMD), is unknown.

OBJECTIVE

Our aim was to compare the effects of a low-salt (LS; 50 mmol Na/d) diet with those of a usual-salt (US; 150 mmol Na/d) diet on FMD.

DESIGN

This was a randomized crossover design in which 29 overweight and obese normotensive men and women followed an LS diet and a US diet for 2 wk. Both diets had similar potassium and saturated fat contents and were designed to ensure weight stability. After each intervention, FMD, pulse wave velocity, augmentation index, and blood pressure were measured.

RESULTS

FMD was significantly greater (P = 0.001) with the LS diet (4.89 +/- 2.42%) than with the US diet (3.37 +/- 2.10%), systolic blood pressure was significantly (P = 0.02) lower with the LS diet (112 +/- 11 mm Hg) than with the US diet (117 +/- 13 mm Hg), and 24-h sodium excretion was significantly lower (P = 0.0001) with the LS diet (64.1 +/- 41.3 mmol) than with the US diet (156.3 +/- 56.7 mmol). There was no correlation between change in FMD and change in 24-h sodium excretion or change in blood pressure. No significant changes in augmentation index or pulse wave velocity were observed.

CONCLUSIONS

Salt reduction improves endothelium-dependant vasodilation in normotensive subjects independently of the changes in measured resting clinic blood pressure. These findings suggest additional cardioprotective effects of salt reduction beyond blood pressure reduction. The trial is registered with the Australian and New Zealand Clinical Trials Registry (unique identifier: ANZCTR12607000381482; http://www.anzctr.org.au/trial_view.aspx?ID=82159).

Salt-sensitive men show reduced heart rate variability, lower norepinephrine and enhanced cortisol during mental stress

Salt sensitivity (SS) represents a risk factor for essential hypertension, which has been related to enhanced cardiovascular stress reactivity possibly mediated by increased noradrenergic susceptibility. We investigated biophysiological responses to mental stress in salt-sensitive (ss) and salt-resistant (sr) subjects, hypothesizing lower heart rate variability (HRV) and higher cortisol in the ss. A total of 48 healthy normotensive Caucasian men (age 25.6+/-2.6, body mass index 22.9+/-2.3) were phenotyped for SS (defined as significant drop in mean arterial pressure>3 mm Hg under the low-salt diet) by a 2-week high- versus low-salt diet. Subjects underwent a standardized mental stress task with continuous cardiovascular monitoring before, during and after the test (Finapres; Ohmeda, Louisville, CO, USA). Blood samples were drawn to examine cortisol and catecholamines before, after and 20 min after stress. The task elicited significant increases of systolic blood pressure (SBP), diastolic BP (DBP) and heart rate (HR) and a significant decrease of HRV (all time effects P<0.0001). The ss subjects showed lower norepinephrine (NE) and higher cortisol, indicated by significant group effects (P=0.009 and 0.025, respectively). HR increased and HRV decreased more in the ss under the stress, shown by significant time by group interactions (P=0.045 and 0.003, respectively). The observation of a more pronounced HR rise coupled with a greater decrease of HRV in healthy ss men under the influence of brief mental stress confirms their enhanced physiological stress reactivity. The lower peripheral NE may represent an effort to compensate for increased noradrenergic receptor sensitivity. The enhanced cortisol levels are backed by recent genetic findings on HSD11B2 polymorphisms and may promote hypertension.

Angiotensin administration stimulates renal 11 beta-hydroxysteroid dehydrogenase activity in healthy men

BACKGROUND

We examined whether acute administration of angiotensin modulates the activity of 11 beta-hydroxysteroid dehydrogenase (11 beta HSD), the intracellular enzyme catalyzing the interconversion between the hormonally active cortisol and inactive cortisone.

METHODS

Twenty-one male healthy subjects were examined after 1 week of a low- and high-salt diet (50 and 200 mmol/day, respectively). Separate infusions of angiotensin I (Ang I) and II (Ang II) were administered, both at rates of 4 and 8 ng/kg/min. The ratios of tetrahydrocortisol + allotetrahydrocortisol/tetrahydrocortisone (THF + allo-THF/THE) and of free cortisol/free cortisone (UFF/UFE) in urine were measured as indices of overall 11 beta HSD set point and activity of renal 11 beta HSD type 2, respectively. Glomerular filtration rate (GFR) was measured by constant infusion of (125)I-iothalamate.

RESULTS

Ang I and Ang II infusion dose-dependently increased mean arterial blood pressure (MAP) and plasma aldosterone, and decreased plasma renin activity (PRA) and GFR at both diets. Ang I and Ang II infusion resulted in a dose-dependent decrease in the excretion of UFF, UFE, and of the UFF/UFE ratio at both diets, without changing the urinary (THF + allo-THF)/THE ratio. Salt restriction did not affect these 11 beta HSD variables, but was accompanied by a decrease in UFF and UFE excretion.

CONCLUSION

This study suggests that acute angiotensin administration stimulates the activity of 11 beta HSD type 2 in human kidney. Angiotensin might therefore exert a dual effect on the mineralocorticoid receptor (i.e., an indirect agonistic effect by increasing aldosterone availability and a direct or indirect antagonistic effect by stimulation of renal 11 beta HSD type 2 activity).