Sodium intake, body sodium, and sodium excretion

Estimation of mean population salt intakes using spot urine samples and associations with body mass index, hypertension, raised blood sugar and hypercholesterolemia: Findings from STEPS Survey 2019, Nepal

Background

High dietary salt intake is recognized as a risk factor for several non-communicable diseases (NCDs), in particular cardiovascular diseases (CVDs), including heart attack and stroke. Accurate measurement of population level salt intake is essential for setting targeted goals and plans for salt reduction strategies. We used a spot urine sample to estimate the mean population salt intake in Nepal and evaluated the association of salt intake with excess weight, hypertension, raised blood sugar and hypercholesterolemia, and a number of socio-demographic characteristics.

Methods

A population-based cross-sectional study was carried out from February to May 2019 using a WHO STEPwise approach to surveillance. Spot urine was collected from 4361 participants aged 15–69 years for the analysis of salt intake. We then used the INTERSALT equation to calculate population salt intake. Student’s ‘t’ test, one-way ANOVA and multivariable linear regression were used to assess the association between salt intake and a number of factors. Statistical significance was accepted at P < .05.

Results

The average (±SD) age of participants was 40 (14.1) years. Mean salt intake, derived from spot urine samples, was estimated to be 9.1g/d. A total of 70.8% of the population consumed more than the WHO’s recommended amount of 5g salt per day, with almost one third of the population (29%) consuming more than 10g of salt per day. Higher salt intake was significantly associated with male gender (β for male = 0.98g; 95%CI:0.87,1.1) and younger age groups (β25–39 years = 0.08; 95%CI:-0.08,0.23) and higher BMI (β = 0.19; 95%CI:0.18,0.21). Participants who were hypertensive and had raised blood cholesterol consumed less salt than people who had normal blood pressure and cholesterol levels (P<0.001).

Conclusions

Salt consumption in Nepal is high, with a total of 70.8% of the population having a mean salt intake >5g/d, well above the World Health Organization recommendation. High salt intake was found to be associated with sex, age group, education, province, BMI, and raised cholesterol level of participants These findings build a strong case for action to reduce salt consumption in Nepal in order to achieve the global target of 30% reduction in population salt intake by 2025.

Biomimetic Chip Enhanced Time-Gated Luminescent CRISPR-Cas12a Biosensors under Functional DNA Regulation

Despite that the currently discovered CRISPR-Cas12a system is beneficial for improving the detection accuracy and design flexibility of luminescent biosensors, there are still challenges to extend target species and strengthen adaptability in complicated biological media. To conquer these obstacles, we present here some useful strategies. For the former, the limitation to nucleic acids assay is broken through by introducing a simple functional DNA regulation pathway to activate the unique trans-cleavage effect of this CRISPR system, under which the expected biosensors are capable of effectively transducing a protein (employing dual aptamers) and a metal ion (employing DNAzyme). For the latter, a time-gated luminescence resonance energy transfer imaging manner using a long-persistent nanophosphor as the energy donor is performed to completely eliminate the background interference and a nature-inspired biomimetic periodic chip constructed by photonic crystals is further combined to enhance the persistent luminescence. In line with the above efforts, the improved CRISPR-Cas12a luminescent biosensor not only exhibits a sound analysis performance toward the model targets (carcinoembryonic antigen and Na⁺) but also owns a strong anti-interference feature to actualize accurate sensing in human plasma samples, offering a new and applicative analytical tool for laboratory medicine.

Holographic Optical Tweezers and Boosting Upconversion Luminescent Resonance Energy Transfer Combined Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas12a Biosensors

Taking advantage of outstanding precision in target recognition and trans-cleavage ability, the recently discovered CRISPR/Cas12a system provides an alternative opportunity for designing fluorescence biosensors. To fully exploit the analytical potential, we introduce here some meaningful concepts. First, the collateral cleavage of CRISPR/Cas12a is efficiently activated in a functional DNA regulation manner and the bottleneck which largely applicable to nucleic acids detection is broken. After selection of a representative aptamer and DNAzyme as the transduction pathways, the sensing coverage is extended to a small organic compound (ATP) and a metal ion (Na⁺). The assay sensitivity is significantly improved by utilizing a bead-supported enrichment strategy wherein emerging holographic optical tweezers are used to enhance imaging stability and simultaneously achieve multiflux analysis. Last, a sandwich-structured energy-concentrating upconversion nanoparticle triggered boosting luminescent resonance energy transfer mode is comined to face with complicated biological samples by skillfully confining the emitters into a very limited inner shell. Following the above attempts, the developed CRISPR/Cas12a biosensors not only present an ultrasensitive assay behavior toward these model non-nucleic acid analytes but also can serve as a formidable toolbox for determining real samples including single cell lysates and human plasma, proving a good practical application capacity.

Factors Influencing Blood Alkalosis and Other Physiological Responses, Gastrointestinal Symptoms, and Exercise Performance Following Sodium Citrate Supplementation: A Review

This review aimed to identify factors associated with (a) physiological responses, (b) gastrointestinal (GI) symptoms, and (c) exercise performance following sodium citrate supplementation. A literature search identified 33 articles. Observations of physiological responses and GI symptoms were categorized by dose (< 500, 500, and > 500 mg/kg body mass [BM]) and by timing of postingestion measurements (in minutes). Exercise performance following sodium citrate supplementation was compared with placebo using statistical significance, percentage change, and effect size. Performance observations were categorized by exercise duration (very short < 60 s, short ≥ 60 and ≤ 420 s, and longer > 420 s) and intensity (very high > 100% VO2max and high 90-100% VO2max). Ingestion of 500 mg/kg BM sodium citrate induced blood alkalosis more frequently than < 500 mg/kg BM, and with similar frequency to >500 mg/kg BM. The GI symptoms were minimized when a 500 mg/kg BM dose was ingested in capsules rather than in solution. Significant improvements in performance following sodium citrate supplementation were reported in all observations of short-duration and very high-intensity exercise with a 500 mg/kg BM dose. However, the efficacy of supplementation for short-duration, high-intensity exercise is less clear, given that only 25% of observations reported significant improvements in performance following sodium citrate supplementation. Based on the current literature, the authors recommend ingestion of 500 mg/kg BM sodium citrate in capsules to induce alkalosis and minimize GI symptoms. Supplementation was of most benefit to performance of short-duration exercise of very high intensity; further investigation is required to determine the importance of ingestion duration and timing.

Sodium, volume and pressure control in haemodialysis patients for improved cardiovascular outcomes

Chronic volume overload is pervasive in patients on chronic haemodialysis and substantially increases the risk of cardiovascular death. The rediscovery of the three-compartment model in sodium metabolism revolutionizes our understanding of sodium (patho-)physiology and is an effect modifier that still needs to be understood in the context of hypertension and end-stage kidney disease. Assessment of fluid overload in haemodialysis patients is central yet difficult to achieve, because traditional clinical signs of volume overload lack sensitivity and specificity. The highest all-cause mortality risk may be found in haemodialysis patients presenting with high fluid overload but low blood pressure before haemodialysis treatment. The second highest risk may be found in patients with both high blood pressure and fluid overload, while high blood pressure but normal fluid overload may only relate to moderate risk. Optimization of fluid overload in haemodialysis patients should be guided by combining the traditional clinical evaluation with objective measurements such as bioimpedance spectroscopy in assessing the risk of fluid overload. To overcome the tide of extracellular fluid, the concept of time-averaged fluid overload during the interdialytic period has been established and requires possible readjustment of a negative target post-dialysis weight. ²³Na-magnetic resonance imaging studies will help to quantitate sodium accumulation and keep prescribed haemodialytic sodium mass balance on the radar. Cluster-randomization trials (e.g. on sodium removal) are underway to improve our therapeutic approach to cardioprotective haemodialysis management.

Rapid weight loss with dietary salt restriction in hospitalized patients with chronic kidney disease

Dietary salt restriction is essential for managing fluid retention in patients with chronic kidney disease (CKD). In this retrospective cohort study, we investigated weight loss from the perspective of fluid status in CKD patients during a 7-day hospitalization period while consuming a low-salt diet (5 g/day). Among 311 patients, the median weight loss (interquartile range, maximum) was 0.7 (0.0–1.4, 4.7) kg on Day 4 and 1.0 (0.3–1.7, 5.9) kg on Day 7. Patients were classified into quartiles based on pre-hospital urinary salt excretion (quartile [Q] 1, 1.2–5.7; Q2, 5.8–8.4; Q3, 8.5–11.3; Q4, 11.4–29.2 g/day). Weight loss was significantly greater in Q3 and Q4 than in Q1. The body mass index (BMI) and urinary salt excretion in the first 24 hours after admission were independently associated with rapid weight loss on Day 4 by multivariate logistic regression analysis. In conclusion, CKD patients with a high salt intake or high BMI exhibit rapid weight loss within a few days of consuming a low-salt diet. Dietary salt restriction is effective for reducing proteinuria in these patients, but long-term observation is needed to confirm the sustained effects.

Spot urine samples compared with 24-h urine samples for estimating changes in urinary sodium and potassium excretion in the China Salt Substitute and Stroke Study

Background

The capacity of spot urine samples for detecting changes in population sodium and potassium excretion is unclear.

Methods

Changes in urinary sodium and potassium excretion, over a 6-month to 2-year interval, were measured from 24-h urine samples and estimated from spot urine samples using several published methods in 3270 Chinese. Additional estimates were made by multiplying individual spot sodium and potassium concentrations by a single estimated 24-h urine volume derived from external data.

Results

The measured difference in 24-h urinary excretion between intervention and control groups was -0.35 g (95% CI: -0.68 to -0.02; P = 0.039) for sodium and 0.66 g (95% CI: 0.52 to 0.80; P < 0.001) for potassium, based upon 24-h urine samples. The corresponding estimates of sodium differences for the Tanaka (-0.06 g), Kawasaki (-0.09 g), Intersalt without potassium (-0.09 g) and Intersalt with potassium (-0.14 g) equations were all smaller and identified no reduction in sodium excretion (all P > 0.10). The estimates were -0.65 g for sodium and 1.11 g for potassium using individual spot urine concentrations and an externally derived standard urine volume (both P < 0.01).

Conclusions

The published equations were unable to detect the differences in sodium excretion measured by 24-h urine samples. A method based upon spot urine electrolyte concentrations and a standard urine volume may offer an alternative approach to measuring differences in sodium and potassium excretion between population groups without requiring 24-h urine, but will need further investigation.

Dietary salt regulates uroguanylin expression and signaling activity in the kidney, but not in the intestine

The peptide uroguanylin (Ugn) is expressed at significant levels only in intestine and kidney, and is stored in both tissues primarily (perhaps exclusively) as intact prouroguanylin (proUgn). Intravascular infusion of either Ugn or proUgn evokes well-characterized natriuretic responses in rodents. Furthermore, Ugn knockout mice display hypertension and salt handling deficits, indicating that the Na(+) excretory mechanisms triggered when the peptides are infused into anesthetized animals are likely to operate under normal physiological conditions, and contribute to electrolyte homeostasis in conscious animals. Here, we provide strong corroborative evidence for this hypothesis, by demonstrating that UU gnV (the rate of urinary Ugn excretion) approximately doubled in conscious, unrestrained rats consuming a high-salt diet, and decreased by ~15% after salt restriction. These changes in UU gnV were not associated with altered plasma proUgn levels (shown here to be an accurate index of intestinal proUgn secretion). Furthermore, enteric Ugn mRNA levels were unaffected by salt intake, whereas renal Ugn mRNA levels increased sharply during periods of increased dietary salt consumption. Together, these data suggest that diet-evoked Ugn signals originate within the kidney, rather than the intestine, thus strengthening a growing body of evidence against a widely cited hypothesis that Ugn serves as the mediator of an entero-renal natriuretic signaling axis, while underscoring a likely intrarenal natriuretic role for the peptide. The data further suggest that intrarenal Ugn signaling is preferentially engaged when salt intake is elevated, and plays only a minor role when salt intake is restricted.

The evolution of halophytes, glycophytes and crops, and its implications for food security under saline conditions

The effective development of salt tolerant crops requires an understanding that the evolution of halophytes, glycophytes and our major grain crops has involved significantly different processes. Halophytes (and other edaphic endemics) generally arose through colonization of habitats in severe disequilibrium by pre-adapted individuals, rather than by gradual adaptation from populations of 'glycophytes'. Glycophytes, by contrast, occur in low sodium ecosystems, where sodium was and is the major limiting nutrient in herbivore diets, suggesting that their evolution reflects the fact that low sodium individuals experienced lower herbivory and had higher fitness. For domestication/evolution of crop plants, the selective pressure was human imposed and involved humans co-opting functions of defense and reproductive security. Unintended consequences of this included loss of tolerance to various stresses and loss of the genetic variability needed to correct that. Understanding, combining and manipulating all three modes of evolution are now critical to the development of salt tolerant crops, particularly those that will offer food security in countries with few economic resources and limited infrastructure. Such efforts will require exploiting the genetic structures of recently evolved halophytes, the genetic variability of model plants, and endemic halophytes and 'minor' crops that already exist.

Increased dietary sodium is independently associated with greater mortality among prevalent hemodialysis patients

Dietary sodium is thought to play a major role in the pathogenesis of hypertension, hypervolemia, and mortality in hemodialysis patients; hence, sodium restriction is almost universally recommended. Since the evidence upon which to base these assumptions is limited, we undertook a post-hoc analysis of 1770 patients in the Hemodialysis Study with available dietary, clinical, and laboratory information. Within this cohort, 772 were men, 1113 black, and 786 diabetic, with a mean age of 58 years and a median dietary sodium intake of 2080 mg/day. After case-mix adjustment, linear regression modeling found that higher dietary sodium was associated with a greater ultrafiltration requirement, caloric and protein intake; sodium to calorie intake ratio was associated with a greater ultrafiltration requirement; and sodium to potassium ratio was associated with higher serum sodium. No indices were associated with the pre-dialysis systolic blood pressure. Cox regression modeling found that higher baseline dietary sodium and the ratio of sodium to calorie or potassium were each independently associated with greater all-cause mortality. No association between a prescribed dietary sodium restriction and mortality were found. Thus, higher reported dietary sodium intake is independently associated with greater mortality among prevalent hemodialysis patients. Randomized trials will be necessary to determine whether dietary sodium restriction improves survival.

Sodium balance in pregnancy

Sodium is the major cation in the extracellular fluid volume (ECFV) and as such, is the most important determinant of osmolality and of the volume of this fluid compartment. Hence any alteration in the control of body sodium will be reflected by changes in the ECFV, including the maternal plasma volume. There is no doubt that expansion of the plasma volume is a necessary and desirable event during pregnancy, influencing positively both maternal and fetal outcome. Therefore, studies of sodium balance in pregnancy provide important information relevant to both mother and fetus.

Self-monitoring of home blood pressure with estimation of daily salt intake using a new electrical device

We investigated a simple device to monitor daily salt intake at home and examined the relationship between salt excretion and morning blood pressure in order to enable patients to better manage daily salt intake and hypertension. The correlation between 24-h urinary salt excretion and measured value with salt monitor from overnight urine was significant (n = 224, r = 0.72, P < 0.001). A total of 46 volunteers participated for more than 3 weeks by measuring daily salt intake and morning blood pressure. The relationship between predicted daily salt excretion and blood pressure was examined with use of 3-day moving average. Mean salt excretion and systolic blood pressure (SBP) significantly decreased by the end of the trial (i.e., salt excretion decreased from 158+/-31 to 149+/-30 mmol/day and SBP from 137+/-17 to 133+/-16 mm Hg). Of 46 participants, 18 (39%) had a significant correlation between predicted daily salt excretion and blood pressure (r > 0.4, P < 0.05, n > 21), indicating sodium sensitivity. An additional 17% had a positive correlation that did not reach statistical significance (0.2 < r < or = 0.4), and the remaining 44% had no correlation (r < or = 0.2). Mean decrease in blood pressure per decrease in salt (g) (17 mmol) intake in the 18 participants with a significant correlation was 3.3 mm Hg (SBP) and 1.5 mm Hg (diastolic blood pressure), which was higher than that reported for other studies. Hypertensive patients not using medication showed the largest decrease. We conclude that daily monitoring of salt intake and morning blood pressure will be useful for management of hypertension.

Diagnostic approach to a patient with hyponatraemia: traditional versus physiology-based options

The usual diagnostic approach to a patient with hyponatraemia is based on the clinical assessment of the extracellular fluid (ECF) volume, and laboratory parameters such as plasma osmolality, urine osmolality and/or urine sodium concentration. Several clinical diagnostic algorithms (CDA) applying these diagnostic parameters are available to the clinician. However, the accuracy and utility of these CDAs has never been tested. Therefore, we performed a survey in which 46 physicians were asked to apply all existing, unique CDAs for hyponatraemia to four selected cases of hyponatraemia. The results of this survey showed that, on average, the CDAs enabled only 10% of physicians to reach a correct diagnosis. Several weaknesses were identified in the CDAs, including a failure to consider acute hyponatraemia, the belief that a modest degree of ECF contraction can be detected by physical examination supported by routine laboratory data, and a tendency to diagnose the syndrome of inappropriate secretion of antidiuretic hormone prior to excluding other causes of hyponatraemia. We conclude that the typical architecture of CDAs for hyponatraemia represents a hierarchical order of isolated clinical and/or laboratory parameters, and that they do not take into account the pathophysiological context, the mechanism by which hyponatraemia developed and the clinical dangers of hyponatraemia. These restrictions are important for physicians confronted with hyponatraemic patients and may require them to choose different approaches. We therefore conclude this review with the presentation of a more physiology-based approach to hyponatraemia, which seeks to overcome some of the limitations of the existing CDAs.

Dopamine acutely stimulates Na+/H+ exchanger (NHE3) endocytosis via clathrin-coated vesicles: dependence on protein kinase A-mediated NHE3 phosphorylation

Dopamine (DA) is a key hormone in mammalian sodium homeostasis. DA induces natriuresis via acute inhibition of the renal proximal tubule apical membrane Na(+)/H(+) exchanger NHE3. We examined the mechanism by which DA inhibits NHE3 in a renal cell line. DA acutely decreases surface NHE3 antigen in dose- and time-dependent fashion without altering total cellular NHE3. Although DA(1) receptor agonist alone decreases surface NHE3, simultaneous DA(2) agonist synergistically enhances the effect of DA(1). Decreased surface NHE3 antigen, caused by stimulation of NHE3 endocytosis, is dependent on intact functioning of the GTPase dynamin and involves increased binding of NHE3 to the adaptor protein AP2. DA-stimulated NHE3 endocytosis can be blocked by pharmacologic or genetic protein kinase A inhibition or by mutation of two protein kinase A target serines (Ser-560 and Ser-613) on NHE3. We conclude that one mechanism by which DA induces natriuresis is via protein kinase A-mediated phosphorylation of proximal tubule NHE3 leading to endocytosis of NHE3 via clathrin-coated vesicles.

Toward an Integrative Concept of Control of Total Body Sodium

Total body sodium (TBSodium) is a major determinant of body water and arterial pressure. Several observations, in particular that of a "sodium memory," indicate that TBSodium is a controlled variable. Various regulatory elements are involved, e.g., the renin-angiotensin-aldosterone system, atrial receptors, and renal arterial pressure. Balance studies in dogs provide new insights into their contributions to TBSodium control.

Enhanced antinatriuresis in response to angiotensin II in essential hypertension

Angiotensin II regulates sodium homeostasis by modulating aldosterone secretion, renal vascular response, and tubular sodium reabsorption. We hypothesized that the antinatriuretic response to angiotensin II is enhanced in human essential hypertension. We therefore studied 48 white men with essential hypertension (defined by ambulatory blood pressure measurement) and 72 normotensive white control persons, and measured mean arterial pressure, sodium excretion, renal plasma flow, glomerular filtration rate, and aldosterone secretion in response to angiotensin II infusion (0.5 and 3.0 ng/kg/min). Hypertensive subjects exhibited a greater increase of mean arterial pressure (16.7+/-8.2 mm Hg v 13.4+/-7.1 mm Hg in normotensives, P < .05) and a greater decrease of renal plasma flow (-151.5+/-73.9 mL/ min v -112.6+/-68.0 mL/min in controls, P < .01) when 3.0 ng/kg/min angiotensin II was infused. The increase of glomerular filtration rate and serum aldosterone concentration was similar in both groups. Sodium excretion in response to 3.0 ng/kg/min angiotensin II was diminished in both groups (P < .01). However, the decrease in sodium excretion was more pronounced in hypertensives than in normotensives (-0.18+/-0.2 mmol/min v -0.09+/-0.2 mmol/min, P < .05), even if baseline mean arterial pressure and body mass index were taken into account (P < .05). We conclude that increased sodium retention in response to angiotensin II exists in subjects with essential hypertension, which is unrelated to changes in glomerular filtration rate and aldosterone concentration. Our data suggest a hyperresponsiveness to angiotensin II in essential hypertension that could lead to increased sodium retention.

Pressure-dependent renin release: effects of sodium intake and changes of total body sodium

The impact of sodium intake and changes in total body sodium (TBS) for the setting of pressure-dependent renin release (PDRR) was studied in freely moving dogs. An aortic cuff allowed servo control of renal perfusion pressure (RPP) at preset values. Protocols were 1) high sodium intake (HSI), 2) low sodium intake (LSI), 3) TBS moderately increased (+3.1 mmol Na/kg body wt) by 20% reduction of RPP for 2-4 days, 4) large increase of TBS (+8.2) by combining protocol 3 with aldosterone infusion, and 5) TBS reduced (-3.1) by peritoneal dialyses. Twenty-four-hour time courses of arterial plasma renin activity (PRA) revealed that LSI increased PRA for the first 10 h only; afterward PRA did not differ between LSI and HSI. Reduced TBS increased PRA constantly, and the large increase of TBS constantly reduced PRA. PDRR stimulus-response curves (assessed 20 h after last sodium intake) revealed an exponential relationship in each protocol. PDRR was not changed by different sodium intake. Conversely, reduced TBS increased PDRR markedly, whereas the large increase of TBS suppressed it. Thus an inverse relationship between TBS and PRA, i.e., a TBS-dependent renin release, was found. This relationship was enhanced by decreasing RPP. This interplay between TBS-dependent renin release and PDRR allows the organism a differentiated reaction to changes in TBS and arterial pressure.

Urinary kallikrein and salt sensitivity in essential hypertensive males

A strong influence of urinary kallikrein excretion on the salt sensitivity of blood pressure has been recently suggested in normotensive patients. To evaluate the relationship between kallikrein and salt sensitivity in essential hypertension, active kallikrein excretion, plasma renin activity, atrial natriuretic peptide and aldosterone levels were evaluated in 37 male hypertensives (mean age 43.3 +/- 4.7 years) after two weeks on a normal NaCl diet (120 mmol NaCl per day). After kallikrein determination, salt sensitivity was assessed in a randomized cross-over double-blind fashion by evaluating the blood pressure response to a high (240 mmol NaCl per day for two weeks) and a low (40 mmol NaCl per day for 2 weeks) NaCl intake. Blood pressure changes were evaluated considering as baseline blood pressure the measurement taken at the end of the 2 weeks under normal NaCl intake. Patients were classified as salt sensitive when a diastolic blood pressure change of 10 mm Hg or more occurred after both periods of low and high NaCl intake. At the end of the assessment of salt sensitivity, 19 hypertensive patients (mean age 43.0 +/- 4.6 years) were resistant. The urinary excretion of active kallikrein was significantly lower (P < 0.0001) in salt sensitive (0.51 +/- 0.36 U/24 hr) than in salt resistant patients (1.28 +/- 0.48 U/24 hr). Also, plasma atrial natriuretic peptide levels were higher in salt sensitive than in salt resistant hypertensives (P < 0.02), and a significant correlation between urinary kallikrein and plasma atrial natriuretic peptide was demonstrated in salt sensitive hypertensives (r = -0.691, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Na+/H+ exchange in human lymphocytes and platelets in chronic and subacute metabolic acidosis

The effect of acid-base disturbances on sodium/proton (Na+/H+) exchange has been examined in animal models; however, few data are available from human studies. To test the effect of metabolic acidosis on Na+/H+ exchange in man, as well as to examine the relationship between Na+/H+ exchange and cytosolic calcium ([Ca2+]i), we measured both variables in patients with decreased renal function with mild metabolic acidosis (pH 7.34 +/- 0.06), in normal control subjects (pH 7.41 +/- 0.02), and in subjects before (pH 7.40 +/- 0.01), and after (pH 7.26 +/- 0.04) ammonium chloride (NH4Cl) 15 g for 5 d. Lymphocytes and platelets were loaded with the cytosolic pH (pHi) indicator 2'-7'-bis(carboxyethyl)-5,6-carboxyfluorescein and acidified to pH approximately 6.6 with propionic acid. To quantitate Na+/H+ exchange, dpHi/dt was determined at 1 min. [Ca2+]i was measured with fura-2. Na+/H+ exchange was significantly increased only in lymphocytes of patients with renal insufficiency. Neither intracellular pH (pHi) nor [Ca2+]i was different from controls. NH4Cl resulted in a significant increase in Na+/H+ exchange in lymphocytes, but not in platelets of normal subjects. Values of pHi and [Ca2+]i in either cell type remained unaffected. Since metabolic acidosis influenced Na+/H+ only in lymphocytes, but not in platelets, it is possible that protein synthesis may be involved in increasing Na+/H+ exchange.

High salt alone does not influence the kinetics of the Na(+)-H+ antiporter

During a high-salt diet, tubular sodium reabsorption is decreased. This study concerns the effect of a high-salt diet on the proximal tubular (PT) Na+ influx pathways. Brush-border membrane vesicles (BBMV) were prepared from rats on normal-salt (NS) and rats on high-salt (HS) diets. The initial uptake rates of Na+ were the same in NS and HS rats, both in the absence and the presence of 1 mM amiloride. Vmax and Km for the amiloride-sensitive Na+/H+ antiporter were also the same in the NS (Vmax 3.69 +/- 0.31 nmol mg prot-1 10 s-1, Km 6.13 +/- 0.58 mM) and HS groups (Vmax 3.54 +/- 0.28 nmol mg prot-1 10 s-1, Km 6.18 +/- 0.64 mM). There was no difference in the initial uptake rates of the Na(+)-glucose and the Na(+)-alanine symporters in NS and HS. Vmax and Km for the L-dopa-Na+ symporter were also the same in NS (Vmax 72 +/- 2.5 pmol mg prot-1 20 s-1, Km 98 +/- 14 microM) and HS groups (Vmax 78 +/- 6.0 pmol mg prot-1 20 s-1, Km 106 +/- 4 microM). In summary, HS diet does not change the kinetics of the Na+ transporters in the brush-border membrane of PT cells.

Natriuresis after a water load in humans under different sodium body content

The present study was aimed at observing the diuretic and natriuretic responses after a water load (2% body weight) in four groups of young consenting volunteers submitted previously, during three days, to a hypersodic (500 mEq Na/day), hyposodic (35 mEq Na/day), and normosodic (200 mEq Na/day) diet, or treated with furosemide (Lasix, 40 mg/day). During the treatment urine was collected each day. On the fourth day, in the morning, the bladder was emptied, the water load was ingested, and the urine collected during 10 periods of 20 min each. The urinary, sodium, and chloride flows were determined. The four groups displayed diuretic curves following a similar pattern. In contrast, the natriuretic curves of the four groups were completely different; totally flat with low values for the furosemide group and a large initial natriuretic curve for the hypersodic group with a gradual decrease but maintaining high values. The results indicate that the way the organism compensates for the excess of water by means of urinary water loss is independent of the body sodium content, whereas the way in which sodium loss is accomplished is determined by its body content and is independent of the way in which the water is lost.

Atrial natriuretic peptide in pregnancy: response to oral sodium supplementation

1. The control of extracellular fluid volume (ECFV) in normal pregnancy may be related to changes in atrial natriuretic peptide. Previous studies in non-pregnant subjects have suggested that plasma atrial natriuretic peptide (ANP) increases in response to dietary sodium supplementation because of an increase in plasma volume, although this has not been measured directly. 2. Nine women who were pregnant in the third trimester undertook oral sodium supplementation (136 mmol) for 5 days in addition to their usual diet. Twenty-four hour urinary sodium excretion increased by 125 +/- 54 mmol/day (mean +/- s.d.; P less than 0.01). Plasma volume was unchanged, although total ECFV tended to increase (P less than 0.09 and bodyweight increased (1.3 +/- 1.4 kg; P less than 0.01) at the end of these diets. 3. Plasma ANP increased by 30.7 [8.6, 34.5] pmol/L (median [25th, 75th percentile]; P less than 0.05), while plasma renin concentration decreased significantly from 7.3 [6.2, 11.2] to 2.6 [1.7, 3.9] pmol angiotensin I/mL (P less than 0.01), as did plasma aldosterone concentration (1435 [1162, 1722] to 753 [595, 1110] fmol/mL; P less than 0.01). Plasma vasoactive intestinal peptide was unchanged. 4. Pregnant women respond to increased dietary sodium with an increase in plasma ANP in the absence of a significant increase in plasma volume. The acute regulation of plasma ANP in response to increases in dietary sodium in pregnant women does not appear to be mediated by changes in intravascular fluid volume.

Effect of enalapril on body sodium and handling of a sodium chloride load in hypertensive and normotensive rats

1. The effect of enalapril on handling of an Na load and on body Na during 96 h of zero Na intake was measured in hypertensive rats (GH and SHR) and their normotensive controls (N and WKY) by a whole body counting method. 2. Enalapril treatment led to a greater fall in body Na in the first 24 h after the Na load (as expected from the known effect of ACE inhibition on aldosterone production) and thus to a slightly faster excretion of an amount equivalent to the load. 3. Enalapril-treated rats were unable to maintain body Na on a zero Na intake. This was also expected from the known effect on aldosterone production, though other mechanisms are not excluded. The effect was more marked in the SHR and WKY than in GH and N but there was no significant difference in this effect between the hypertensives and their respective control strains.

Definitions and characteristics of salt-sensitivity and resistance of blood pressure: should the diagnosis depend on diastolic blood pressure?

To elucidate the importance of diastolic blood pressure in the definition of salt-sensitive hypertension, we studied 54 male subjects, 36 of whom had untreated, mild essential hypertension. The subjects received a 120 mmol/d Na (as the chloride salt) diet for six days. Thereafter they received a 10 mmol/d Na diet for eight days followed by a 400 mmol/d Na diet for another 8 days. Blood pressure was measured hourly "around the clock" on the last day of each diet; the averaged systolic, diastolic and mean blood pressure values were compared. In 22 subjects diastolic blood pressure increased, when salt intake was increased from 10 to 400 mmol/d. In 18 of these 22 subjects systolic blood pressure increased as well. In 20 subjects, systolic blood pressure increased with salt loading while diastolic blood pressure decreased. In 13 subjects both systolic and diastolic blood pressure decreased with increased salt intake. We defined those subjects showing an increase in diastolic blood pressure as salt-sensitive. If mean blood pressure were used to define salt-sensitivity, 8 of our subjects would have been labeled as salt-sensitive who actually decreased their diastolic blood pressure with salt loading. We suggest that consideration of systolic and diastolic blood pressure responses gives better insight into identifying volume and resistance-related phenomena in salt-sensitive hypertension, than does the consideration of mean blood pressure alone. The definition of salt-sensitivity may require reassessment.

Acute and sustained changes in sodium balance during nifedipine treatment in essential hypertension

PURPOSE

To assess the changes in sodium excretion and sodium balance after initiation of nifedipine treatment and after withdrawal of nifedipine.

PATIENTS

Eight patients with uncomplicated mild to moderate essential hypertension were entered in a single-blind, placebo-controlled study of 39 days' duration.

METHODS

Two 7-day periods while on a fixed sodium intake of 150 mmol/day approximately 3 weeks apart. After 4 days of a placebo and fixed sodium intake, patients were given nifedipine GITS (gastrointestinal therapeutic system) once a day and carefully studied for the following 4 days. Thereafter, patients continued to receive nifedipine GITS, and approximately 3 weeks later they were studied again for a week while on a fixed sodium intake. Nifedipine administration was stopped and changes occurring after withdrawal were studied.

RESULTS

Nifedipine caused a significant increase in sodium excretion with a cumulative loss of sodium of 38 mmol per subject within the first 4 days of treatment. The withdrawal of nifedipine treatment caused a significant decrease in sodium excretion and a cumulative retention of sodium of 42 mmol per subject within the first 4 days of withdrawal.

CONCLUSION

Nifedipine causes an acute and a sustained reduction in sodium balance in patients with essential hypertension. This prolonged effect may contribute to the mechanism whereby nifedipine lowers blood pressure.

Biohistory of slavery and blood pressure differences in blacks today. A hypothesis

Genetic factors are known to play an important role in the variations in blood pressure levels. However, genetic factors that explain the higher average blood pressure levels of western hemisphere blacks when compared with African blacks have not been seriously considered. Because the genetic makeup of a population is largely determined by biological and ecological forces in the past, an examination of the biohistory of blacks, specifically the slavery era, was conducted. An overview of the salient findings of that investigation is included in this article. The published historical evidence on the transatlantic slave trade and New World slavery (from the 16th century to the 19th century) reveals that conditions existed for "natural selection," and therefore, genetic changes were virtually inevitable in the slave populations. During this period of history, mortality was extremely high, and fertility (or reproductive success) was so low among the survivors that most plantation societies in the western hemisphere depended on a constant importation of captives (over 12 million) from Africa for the viability of the plantation communities. Because the major causes of death were salt-depletive diseases such as diarrhea, fevers, and vomiting, it is argued that individuals with an enhanced genetic-based ability to conserve salt had a distinct survival advantage over others and were, therefore, more likely to bequeath their genotype to subsequent generations of Western hemisphere blacks. Thus, it is predicted that blacks in the Americas have a greater frequency of individuals with an enhanced genetic-based ability to conserve salt than African blacks.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics of renal sodium excretion during changes in dietary sodium intake in man--an exponential process?

The kinetics of urinary sodium excretion was studied during sodium restriction and sodium supplementation in normal subjects. Eight were studied on a normal sodium intake (24 h urinary sodium: 133.3 + 9.6 mmol) and then during 6 days on a low sodium intake of 10 mmol/day. Six other subjects were studied after equilibration on the low sodium intake for 7 days and then during 5 days on a high sodium intake of 350 mmol/day. 24 h urinary sodium excretion during sodium restriction was consistent with a first-order exponential process with an estimated half-life of 21.8 + 2.4 hours. During sodium supplementation there were corresponding increases in urinary sodium excretion reaching the new steady-state within 3 days but the behaviour of the urinary sodium excretion during the transition period was not consistent with a mono-exponential process. These observations support the concept that the control of sodium balance, during sodium restriction at least, is consistent with a first order proportional feed-back system. This kinetic approach should provide a useful framework for further studies on the dynamics of sodium excretion.

Effect of enalapril on handling of a sodium chloride load by genetically hypertensive and normotensive rats

1. Enalapril was given in the drinking water (300 mg/L) for 4.5 days to normotensive (N) and genetically hypertensive (GH) rats on zero sodium intake. An intraperitoneal NaCl load was given 12 h after enalapril was started. 2. Enalapril did not increase the maximum rate of sodium excretion, but caused the rats to excrete more than the load in the first 24 h and then to have a slow fall in body sodium while on a sodium-free diet. 3. In terms of the Strauss et al. (1958) concept of body sodium, enalapril appears to lower the basal level. However, in addition it causes a slow leak of sodium which becomes apparent when sodium intake is very low.