Sodium and blood pressure 2003

Quantifying salt sensitivity

Inner surfaces of blood vessels and outer surfaces of erythrocytes are coated with a negatively charged protective film of proteoglycans, which serves as an effective buffer system for the positively charged sodium ions. If this protective coating is poorly developed or impaired, it loses its buffering capacity. As a consequence, the organism becomes increasingly sensitive to sodium, which in the long run leads to organ damage, especially if daily salt consumption is high. Recently, it has become possible to quantify salt sensitivity using a technically simple method - the salt blood test (SBT). Aim of this mini-review is to explain the physiological concept underlying the SBT and its potential practical relevance in the prevention of cardiovascular disease.

The role of dietary salt and alcohol use reduction in the management of hypertension

Introduction: Despite the improved treatment protocol of hypertension, the magnitude of the disease and its related burden remains raised. Hypertension makes up the leading cause of stroke, kidney disease, arterial disease, eye disease, and cardiovascular disease (CVD) growth. Areas covered: This review provides the overview of the role of dietary salt and alcohol use reduction in the management of hypertension, a brief history of alcohol, the vascular endothelium functions, the effects of alcohol use on blood pressure (BP), the mechanisms of alcohol, brief history of salt, the effects of dietary salt intake on BP, and the mechanisms of salt. Expert opinion: Studies found that high dietary salt intake and heavy alcohol consumption have a major and huge impact on BP while both of them have been identified to increase BP. Also, they raise the risk of hypertension-related morbidity and mortality in advance. On the other way, the dietary salt and alcohol use reduction in the management of hypertension are significant in the control of BP and its related morbidity and mortality. Further, studies suggested that the dietary salt and alcohol use reductions are the cornerstone in the management of hypertension due to their significance as part of comprehensive lifestyle modifications.

Hydrogen Sulfide Inhibits High-Salt Diet-Induced Renal Oxidative Stress and Kidney Injury in Dahl Rats

Background. The study was designed to investigate if H₂S could inhibit high-salt diet-induced renal excessive oxidative stress and kidney injury in Dahl rats. Methods. Male salt-sensitive Dahl and SD rats were used. Blood pressure (BP), serum creatinine, urea, creatinine clearance rate, and 24-hour urine protein were measured. Renal ultra- and microstructures were observed. Collagen-I and -III contents the oxidants and antioxidants levels in renal tissue were detected. Keap1/Nrf2 association and Keap1 s-sulfhydration were detected. Results. After 8 weeks of high-salt diet, BP was significantly increased, renal function and structure were impaired, and collagen deposition was abundant in renal tissues with increased renal MPO activity, H₂O₂, MDA, GSSG, and ^•OH contents, reduced renal T-AOC and GSH contents, CAT, GSH-PX and SOD activity, and SOD expressions in Dahl rats. Furthermore, endogenous H₂S in renal tissues was decreased in Dahl rats. H₂S donor, however, decreased BP, improved renal function and structure, and inhibited collagen excessive deposition in kidney, in association with increased antioxidative activity and reduced oxidative stress in renal tissues. H₂S activated Nrf2 by inducing Keap1 s-sulfhydration and subsequent Keap1/Nrf2 disassociation. Conclusions. H₂S protected against high-salt diet-induced renal injury associated with enhanced antioxidant capacity and inhibited renal oxidative stress.

Dietary sodium influences the effect of mental stress on heart rate variability: a randomized trial in healthy adults

BACKGROUND

Dietary sodium influences intermediate physiological traits in healthy adults independent of changes in blood pressure. The purpose of this study was to test the hypothesis that dietary sodium affects cardiac autonomic modulation during mental stress.

METHOD

In a prospective, randomized cross-over design separated by 1 month between diets, 70 normotensive healthy young adults (F/M: 44/26, aged 18-38 years) consumed a 5-day low (10 mmol/day), normal (150 mmol), and high (400 mmol) sodium diet followed by heart rate variability (HRV) recordings at rest and during 5-min computerized mental arithmetic. Women were studied in the low hormone phase of the menstrual cycle following each diet.

RESULTS

Diet did not affect resting blood pressure, but heart rate (HR) (mean ± SE) was 66 ± 1, 64 ± 1, and 63 ± 1 bpm in low, normal, and high sodium conditions, respectively (analysis of variance P = 0.02). For HRV, there was a main effect of sodium on resting SD of normalized RR intervals (SDNN), square root of the mean squared difference of successive normalized RR intervals (RMSSD), high frequency, low-frequency normalized units (LFnu), and high-frequency normalized units (HFnu) (P < 0.01 for all). The response to low sodium was most marked and consistent with sympathetic activation and reduced vagal activity, with increased LFnu and decreased SDNN, RMSSD, and HFnu compared to both normal and high sodium conditions (P ≤0.05 for all). Dietary sodium-by-mental stress interactions were significant for mean NN, RMSSD, high-frequency power, LFnu, and low frequency/high frequency ratio (P < 0.05 for all). The interactions signify that sodium restriction evoked an increase in resting sympathetic activity and reduced vagal activity to the extent that mental stress caused modest additional disruptions in autonomic balance. Conversely, normal and high sodium evoked a reduction in resting sympathetic activity and incremental increase in resting vagal activity, which were disrupted to a greater extent during mental stress compared to low sodium.

CONCLUSION

We conclude that autonomic control of HRV at rest and during mental stress is altered by dietary sodium in healthy normotensive young adult men and women.

Orally active epoxyeicosatrienoic acid analog attenuates kidney injury in hypertensive Dahl salt-sensitive rat

Salt-sensitive hypertension leads to kidney injury. The Dahl salt-sensitive hypertensive rat (Dahl SS) is a model of salt-sensitive hypertension and progressive kidney injury. The current set of experimental studies evaluated the kidney protective potential of a novel epoxyeicosatrienoic acid analog (EET-B) in Dahl SS hypertension. Dahl SS rats receiving high-salt diet were treated with EET-B (10 mg/kg per day) or vehicle in drinking water for 14 days. Urine, plasma, and tissue samples were collected at the end of the treatment protocol to assess kidney injury, oxidative stress, inflammation, and endoplasmic reticulum stress. EET-B treatment in Dahl SS rats markedly reduced urinary albumin and nephrin excretion by 60% to 75% along with 30% to 60% reductions in glomerular injury, intratubular cast formation, and kidney fibrosis without affecting blood pressure. In Dahl SS rats, EET-B treatment further caused marked reduction in oxidative stress with 25% to 30% decrease in kidney malondialdehyde content along with 42% increase of nitrate/nitrite and a 40% reduction of 8-isoprostane. EET-B treatment reduced urinary monocyte chemoattractant protein-1 by 50% along with a 40% reduction in macrophage infiltration in the kidney. Treatment with EET-B markedly reduced renal endoplasmic reticulum stress in Dahl SS rats with reduction in the kidney mRNA expressions and immunoreactivity of glucose regulatory protein 78 and C/EBP homologous protein. In summary, these experimental findings reveal that EET-B provides kidney protection in Dahl SS rats by reducing oxidative stress, inflammation, and endoplasmic reticulum stress, and this protection was independent of reducing blood pressure.

Practical recommendations for treatment of hypertension in older patients

Background:

By the year 2030 the percent of the population over the age of 65 years is projected to range from 3.7% (in sub-Saharan Africa) to almost 22% (in Europe). Accompanying this unprecedented growth will be a significant increase in many of the disease processes or “comorbidities” associated with aging, not the least of which is hypertension. Global health care resources and economies in general will be stressed to breaking point if this condition is not dealt with in an aggressive and timely manner because the consequences of untreated hypertension such as stroke, myocardial infarction, and dementia are exceedingly costly in the long term.

Methods:

To help focus attention on the worldwide epidemic of hypertension, the current literature and guidelines were reviewed, along with information on the various classes of medications indicated in the treatment of hypertension in the elderly.

Results:

Recent, large, randomized trials indicate that hypertension in the elderly can and should be treated to lower the incidence of stroke, myocardial infarction, and chronic kidney disease. Although thiazide-type diuretics are the recommended first-line agents in most cases of uncomplicated hypertension, multiple drug classes have been shown to be useful. In addition, and where feasible, a multidisciplinary team approach has demonstrated the most durable results.

Conclusion:

Thiazide diuretics should be the first-line agents in uncomplicated, isolated systolic hypertension. Starting at low doses and proceeding in a gradual manner, these agents have proven efficacy in decreasing the risk of stroke and cardiovascular events. It is now recommended that these agents be used in low-dose combinations with other antihypertensive drug classes in patients who do not achieve target blood pressure (<140/90 mmHg).

Association between alpha-adducin gene polymorphism (Gly460Trp) and genetic predisposition to salt sensitivity: a meta-analysis

Linkage and association studies suggested the relationship between alpha-adducin polymorphism (Gly460Trp; rs4961) and genetic susceptibility to salt-sensitivity. However, the currently available results were inconsistent. This study aimed to define quantitatively the association between salt-sensitivity and alpha-adducin Gly460Trp polymorphism in all published case-control studies. Publications from PubMed and other databases were retrieved. The major inclusion criteria were: (1) case-control design; (2) salt-sensitivity confirmed by sodium loading tests, and (3) the distribution of genotypes given in detail. Seven case-control studies fulfilled the inclusion criteria. In total they involved 820 subjects (454 salt-sensitive and 366 non-salt-sensitive). The meta-analysis shows that Gly460Trp polymorphism in general is not significantly associated with salt-sensitivity [OR (95%CI): 1.40 (0.96, 2.04), P = 0.08]. Subgroup analysis showed that the association is statistically significant in Asian people [OR (95%CI):1.33 (1.06, 1.69), P = 0.02] but not in Caucasian people [OR (95%CI):1.98 (0.57, 6.92), P = 0.28]. This indicates that blood pressure response to sodium varies between ethnical groups. More studies based on a larger population are required to evaluate further the role of alpha-adducin Gly460Trp polymorphism in salt-sensitive hypertension.

Dietary sodium and the incidence of hypertension in the Chinese population: a review of nationwide surveys

BACKGROUND

High dietary salt consumption is considered a risk factor for hypertension.

METHODS

In order to determine the relationship between dietary sodium and blood pressure in the Chinese population, several nationwide epidemiological surveys have been conducted to investigate salt intake and the incidence of high blood pressure.

RESULTS

These surveys found that the residents living in the cold northern and northwestern areas of mainland China consume significantly more sodium than people from the south, that the average blood pressure and prevalence of hypertension are higher in the high-salt-consuming population, and that salt consumption correlates with blood pressure. It was also found that the nationwide prevalence of hypertension increased threefold over the past 30 years, but there was no parallel increase in salt consumption. In the same period, due to improved living standards, the occurrence of overweight or obesity in adults has increased significantly, which might contribute to the elevated prevalence of hypertension.

CONCLUSION

Thus, approaches to preventing hypertension should entail both dietary salt restriction and weight control.

Endogenous cardiotonic steroids and differential patterns of sodium pump inhibition in NaCl-loaded salt-sensitive and normotensive rats

BACKGROUND

Endogenous sodium pump inhibitors promote sodium excretion in normotensives and contribute to vasoconstriction in NaCl-sensitive hypertension. Marinobufagenin (MBG), an endogenous bufadienolide inhibitor of alpha-1 sodium pump, contributes to hypertension in Dahl salt-sensitive rats (DS). We hypothesized that in NaCl-loaded DS and normotensive Sprague-Dawley rats (S-D), MBG would elicit different patterns of sodium pump inhibition.

METHODS

We compared systolic blood pressure (SBP), renal sodium excretion, activity of the sodium pump in aorta and renal medulla, and levels of MBG, atrial natriuretic peptide (ANP), and cyclic guanosine monophosphate (cGMP) in salt-loaded DS and S-D (20% NaCl, 2.5 ml/kg, intraperitoneally).

RESULTS

NaCl loading produced sustained elevations in renal MBG excretion in both DS (2.41 +/- 0.24 vs. 0.79 +/- 0.08 pmol/h/kg, P < 0.01) and S-D (1.97 +/- 0.37 vs. 0.60 +/- 0.07 pmol/h/kg, P < 0.01) vs. that at baseline (n = 10 for each group). In NaCl-loaded DS, SBP rose by 18 mm Hg (P < 0.01) and aortic sodium pump was inhibited by 22% (P < 0.05 vs. control), while in S-D, SBP and activity of aortic sodium pump did not change. NaCl-loaded S-D excreted twice as much sodium as DS; in S-D, renal sodium pump was inhibited by 24% vs. 14% inhibition in DS (P < 0.05). NaCl loading elicited increases in plasma ANP and in renal cGMP excretion in S-D but not in DS.

CONCLUSIONS

Our present observations demonstrate that in NaCl-loaded S-D and DS, a comparable MBG response is associated with preferential inhibition of the sodium pump in the kidney and in vascular smooth muscle, respectively, resulting in an adaptive natriuresis in S-D but sodium retention and pressor response in DS.

Are all individuals equally sensitive in the blood pressure to high salt intake? (Review article)

It has been reported that only one-third of normotensive subjects and half of hypertensive patients are salt-sensitive. Many causes of salt-sensitivity have been proposed. Our suggestion is that a reduced urinary kallikrein level may be one cause, since mutant kininogen-deficient rats, which cannot generate kinin in the urine, are salt-sensitive. Renal kallikrein is secreted by the connecting tubule cells of the kidney, which are located just distal to the macula densa or the tubuloglomerular feedback system. Excess amounts of sodium taken overflow into the distal tubules and are reabsorbed in the collecting ducts. Kinins generated inhibit sodium reabsorption in the collecting ducts. Both blacks and whites with essential hypertension excrete less urinary kallikrein than do their normotensive counterparts, but the mean value in "normotensive blacks" were not different from that in "hypertensive whites". African-Americans consume less potassium than whites. Potassium and ATP-sensitive potassium channel blockers are releasers of renal kallikrein. In a small-scale study, sodium loading caused more increase in the systolic blood pressure in urinary low-kallikrein group than in urinary high-kallikrein group. Large-scale clinical studies, under strict control of potassium intake, are needed to elucidate the relationship between salt-sensitivity and urinary kallikrein levels.

Recombinant adeno-associated virus-mediated human kallikrein gene therapy prevents high-salt diet-induced hypertension without effect on basal blood pressure

AIM

To investigate the effects of the expression of human kallikrein (HK) on basal level blood pressure and high-salt diet-induced hypertension.

METHODS

We delivered the recombinant adeno-associated viral (rAAV)-mediated HK (rAAV- HK) gene and rAAV-LacZ (as the control) to normal, adult Sprague-Dawley rats. The animals were administered a normal diet in the first 4 weeks, followed by a high-salt diet. The expression of HK in the rats was assessed by ELISA and RT- PCR. Blood pressure and Na+ and K+ urinary excretion were monitored.

RESULTS

Under the normal diet, no obvious changes in blood pressure and Na+ and K+ urinary excretion were observed. When the high-salt diet was administered, systolic blood pressure in the control animals receiving rAAV-LacZ increased from 122.3+/-1.13 mmHg to a stable 142.4+/-1.77 mmHg 8 weeks after the high-salt diet. In contrast, there was no significant increase in the blood pressure in the rAAV-HKtreated group, in which the blood pressure remained at 121.9+/-1.73 mmHg. In the rAAV-HK-treated group, Na+ and K+ urinary excretion were higher compared to those of the control group. The morphological analysis showed that HK delivery remarkably protected against renal damage induced by a high-salt intake.

CONCLUSION

Our study indicates that rAAV-mediated human tissue kallikrein gene delivery is a potentially safe method for the long-term treatment of hypertension. More importantly, it could be applied in the salt-sensitive population to prevent the occurrence of hypertension.

Dietary salt restriction and blood pressure in clinical trials

Dietary salt has long been recognized as a major factor affecting blood pressure such that sodium intake is a component of lifestyle modification guidelines for control of high blood pressure. These recommendations are based on results from epidemiologic observational studies and clinical trials of various sodium diets among normotensives and hypertensives. Nonetheless, results from the different studies vary such that specific recommendations regarding sodium intake are difficult to interpret. The results from several recent major trials indicated greater associations of blood pressure and sodium intake than earlier studies as well as meta-analyses of numerous clinical trials. The studies of sodium intake and blood pressures are complicated by measurements of intake, salt sensitivity, hypertension treatment, effects of sodium independent of blood pressure, and length of interventions. Limitations in the methodology of different studies have reduced the value of the results to provide specific and reliable sodium intake levels essential for clinical and lifestyle guidelines.

Dietary sodium effects on heart rate variability in salt sensitivity of blood pressure

High dietary sodium intake is a risk factor for hypertension, and heart rate variability (HRV) is decreased in hypertension. Effects of dietary sodium intake on HRV of normotensive persons have not, however, been investigated to date. The present study examined effects of low and high sodium diets on blood pressure, heart rate, and HRV in 36 healthy, normotensive women, ages 40-70. Each was placed on a low sodium diet for 6 days followed by a high sodium diet for 6 days. The high salt diet increased mean systolic blood pressure, decreased heart rate, and increased high frequency HRV (HF). Cardiac vagal tone, estimated at baseline from heart period and a time domain estimate of respiratory sinus arrhythmia, was higher in salt-sensitive than salt-insensitive subjects. The finding of increased vagal tone in normotensive persons on high salt intake indicates that dietary sodium status should be considered in behavioral studies of HRV.

A missing link between a high salt intake and blood pressure increase

It is widely accepted that a high sodium intake triggers blood pressure rise. However, only one-third of the normotensive subjects were reported to show salt-sensitivity in their blood pressure. Many factors have been proposed as causes of salt-sensitive hypertension, but none of them provides a satisfactory explanation. We propose, on the basis of accumulated data, that the reduced activity of the kallikrein-kinin system in the kidney may provide this link. Renal kallikrein is secreted by the distal connecting tubular cells and all kallikrein-kinin system components are distributed along the collecting ducts in the distal nephron. Bradykinin generated is immediately destroyed by carboxypeptidase Y-like exopeptidase and neutral endopeptidase, both quite independent from the kininases in plasma, such as angiotensin converting enzyme. The salt-sensitivity of the blood pressure depends largely upon ethnicity and potassium intake. Interestingly, potassium and ATP-sensitive potassium (K(ATP)) channel blockers accelerate renal kallikrein secretion and suppress blood pressure rises in animal hypertension models. Measurement of urinary kallikrein may become necessary in salt-sensitive normotensive and hypertensive subjects. Furthermore, pharmaceutical development of renal kallikrein releasers, such as K(ATP) channel blockers, and renal kininase inhibitors, such as ebelactone B, may lead to the development of novel antihypertensive drugs.

Early Socioeconomic Position and Blood Pressure in Childhood and Adulthood

Studies have found an association between low socioeconomic position in childhood and high adult blood pressure. It is unclear whether this association is explained by a pathway directly linking disadvantage to elevated blood pressure in childhood and adolescence, which then tracks into adulthood. We assessed parental socioeconomic position and systolic blood pressure in 1807 children and adolescents ages 3 to 18 years at baseline. Adult systolic blood pressure was measured 21 years later at ages 24 to 39 years. There was strong tracking of blood pressure from childhood to adulthood. Lower parental socioeconomic position was associated with higher blood pressure in childhood, adolescence ( P <0.01), and adulthood ( P <0.0001), with the mean age- and sex-adjusted systolic pressure differences between the highest and lowest socioeconomic groups varying between 2.9 and 4.3 mm Hg. With adjustment for blood pressure in childhood and adolescence, the regression coefficient between parental socioeconomic position and adult blood pressure attenuated by 32%. A similar level of attenuation (28%) occurred with adjustment for adult body mass index (BMI). With adjustment for both preadult blood pressure and adult BMI, the association between parental socioeconomic position and adult blood pressure was attenuated by 45%. Other factors, including birth weight and BMI in childhood and adolescence, had little impact on the association between parental socioeconomic position and adult blood pressure. These data suggest that early socioeconomic disadvantage influences later blood pressure in part through an effect on blood pressure in early life, which tracks into adulthood, and in part through an effect on BMI.

Testosterone supplementation in aging men and women: possible impact on cardiovascular-renal disease

Treatment of aging men and women with testosterone supplements is increasing. The supplements are given to postmenopausal women mainly to improve their libido and to aging men to improve muscle mass and bone strength, to improve libido and quality of life, to prevent and treat osteoporosis, and, with the phosphodiesterase-5 inhibitors, such as sildenafil, to treat erectile dysfunction. The increased use of testosterone supplements in aging individuals has occurred despite the fact that there have been no rigorous clinical trials examining the effects of chronic testosterone on the cardiovascular-renal disease risk. Studies in humans and animals have suggested that androgens can increase blood pressure and compromise renal function. Androgens have been shown to increase tubular sodium and water reabsorption and activate various vasoconstrictor systems in the kidney, such as the renin-angiotensin system and endothelin. There is also evidence that androgens may increase oxidative stress. Furthermore, the kidney contains the enzymes necessary to produce androgens de novo. This review presents an overview of the data from human and animal studies in which the role of androgens in promoting renal and cardiovascular diseases has been investigated.