Microalbuminuria in salt-sensitive patients. A marker for renal and cardiovascular risk factors

Urinary serine proteases and activation of ENaC in kidney--implications for physiological renal salt handling and hypertensive disorders with albuminuria

Serine proteases, both soluble and cell-attached, can activate the epithelial sodium channel (ENaC) proteolytically through release of a putative 43-mer inhibitory tract from the ectodomain of the γ-subunit. ENaC controls renal Na(+) excretion and loss-of-function mutations lead to low blood pressure, while gain-of-function mutations lead to impaired Na(+) excretion, hypertension, and hypokalemia. We review an emerging pathophysiological concept that aberrant glomerular filtration of plasma proteases, e.g., plasmin, prostasin, and kallikrein, contributes to proteolytic activation of ENaC, both in acute conditions with proteinuria, like nephrotic syndrome and preeclampsia, and in chronic diseases, such as diabetes with microalbuminuria. A vast literature on renin-angiotensin-aldosterone system and volume homeostasis from the last four decades show a number of common characteristics for conditions with albuminuria compatible with impaired renal Na(+) excretion: hypertension and volume retention is secondary to proteinuria in, e.g., preeclampsia and nephrotic syndrome; plasma concentrations of renin, angiotensin II, and aldosterone are frequently suppressed in proteinuric conditions, e.g., preeclampsia and diabetic nephropathy; blood pressure is salt-sensitive in conditions with microalbuminuria/proteinuria; and extracellular volume is expanded, plasma atrial natriuretic peptide (ANP) concentration is increased, and diuretics, like amiloride and spironolactone, are effective blood pressure-reducing add-ons. Active plasmin in urine has been demonstrated in diabetes, preeclampsia, and nephrosis. Urine from these patients activates, plasmin-dependently, amiloride-sensitive inward current in vitro. The concept predicts that patients with albuminuria may benefit particularly from reduced salt intake with RAS blockers; that distally acting diuretics, in particular amiloride, are warranted in low-renin/albuminuric conditions; and that urine serine proteases and their activators may be pharmacological targets.

Effects of sodium citrate on salt sensitivity and kidney injury in chronic renal failure

Metabolic acidosis, which is observed in salt-sensitive hypertension, is also associated with kidney injury. Alkali therapy in chronic renal failure (CRF) may ameliorate the progression of kidney disease; however, few studies have examined the effects of alkali therapy on salt sensitivity and kidney injury in CRF. We randomly administered standard diet (SD), sodium chloride with 20% casein diet (NACL), or sodium citrate with 20% casein diet (NACT) to Sprague-Dawley rats after a CRF or a sham operation. Four weeks after 5/6 nephrectomy, serum bicarbonate levels were higher in the NACT-treated group. On the pressure-natriuresis curve, NACT-treated CRF rats were more salt-resistant than NACL-treated CRF rats. Additionally, the NACT-treated CRF group showed less tubulointerstitial damage than the NACL-treated CRF group. The expression and immunoreactivity of NHE3 in the kidney in the NACT-treated CRF group were lower than those in the NACL-treated CRF group. We observed that dietary NACT as alkali therapy in CRF might improve the altered salt-sensitivity and ameliorate the progression of kidney injury compared to the NACL diet, which may be related to reduced renal NHE3 expression.

Body mass index and body fat distribution as renal risk factors: a focus on the role of renal haemodynamics

Weight excess and/or central body fat distribution are associated with increased long-term renal risk, not only in subjects with renal disease or renal transplant recipients, but also in the general population. As the prevalence of weight excess is rising worldwide, this may become a main renal risk factor on a population basis, even more so because the risk extends to the overweight range. Understanding the mechanisms of this detrimental effect of weight excess on the kidneys is needed in order to design preventive treatment strategies. The increased risk associated with weight excess is partly attributed to associated comorbid conditions, such as hypertension, dyslipidaemia, insulin resistance and diabetes; however, current evidence supports a direct pathogenetic role for renal haemodynamics as well. Weight excess is associated with an altered renal haemodynamic profile, i.e. an increased glomerular filtration rate relative to effective renal plasma flow, resulting in an increased filtration fraction (FF). This renal haemodynamic profile is considered to reflect glomerular hyperfiltration and glomerular hypertension, resulting from a dysbalance between afferent and efferent arterial vasomotor balance. This unfavorable renal haemodynamic profile was found to be associated with renal outcome in experimental models and in human renal transplant recipients, and is associated with a blunted sodium excretion, and reversible by weight loss, renin-angiotensin-aldosterone system blockade or by dietary sodium restriction. More recent evidence showed that a central body fat distribution is also associated with an increased FF, even independent of overall weight excess. In this review, we provide an overview on current literature on the impact of weight excess and central body fat distribution on the renal haemodynamic profile in humans, and its possible role in progressive renal damage.

Infiltrating immune cells in the kidney in salt-sensitive hypertension and renal injury

The importance of the immune system in hypertension, vascular disease, and renal disease has been appreciated for over 50 years. Recent experimental advances have led to a greater appreciation of the mechanisms whereby inflammation and immunity participate in cardiovascular disease. In addition to the experimental data, multiple studies in patients have demonstrated a strong correlation between the observations made in animals and humans. Of great interest is the development of salt-sensitive hypertension in humans with the concurrent increase in albumin excretion rate. Experiments in our laboratory have demonstrated that feeding a high-NaCl diet to Dahl salt-sensitive (SS) rats results in a significant infiltration of T lymphocytes into the kidney that is accompanied by the development of hypertension and renal disease. The development of disease in the Dahl SS closely resembles observations made in patients; studies were therefore performed to investigate the pathological role of infiltrating immune cells in the kidney in hypertension and renal disease. Pharmacological and genetic studies indicate that immune cell infiltration into the kidney amplifies the disease process. Further experiments demonstrated that infiltrating T cells may accentuate the Dahl SS phenotype by increasing intrarenal ANG II and oxidative stress. From these and other data, we hypothesize that infiltrating immune cells, which surround the blood vessels and tubules, can serve as a local source of bioactive molecules which mediate vascular constriction, increase tubular sodium reabsorption, and mediate the retention of sodium and water to amplify sodium-sensitive hypertension. Multiple experiments remain to be performed to refine and clarify this hypothesis.

High-salt diet blunts renal autoregulation by a reactive oxygen species-dependent mechanism

High dietary salt is common in Western countries and is an important contributor to increased cardiovascular disease. Autoregulation of renal blood flow (RBF) and glomerular filtration rate (GFR) is an essential function of the renal microcirculation that could be affected by excessive dietary salt. High salt (HS) increases renal ROS generation partly by the enzyme NADPH oxidase. We hypothesized that a HS diet would impair autoregulation via NADPH oxidase-dependent ROS generation. The role of NADPH-dependent ROS production on the blunted autoregulatory response with a HS diet was assessed in vitro and in vivo using the blood-perfused juxtamedullary nephron preparation and anesthetized rats, respectively. The increase in renal lipid peroxidation and p67(phox) expression induced by HS was prevented by apocynin treatment. Control afferent arterioles exhibited normal autoregulatory behavior in response to acute increases in renal perfusion pressure, whereas arterioles from HS rats exhibited a blunted response. Autoregulatory behavior in HS rats was restored in vitro by acute exposure to the NADPH oxidase inhibitor apocynin. At the whole kidney level, in vivo experiments showed that both RBF and GFR declined in HS rats when left kidney renal perfusion pressure was reduced from ambient to 95 mmHg, whereas control rats maintained stable GFR and RBF consistent with efficient autoregulatory behavior. Apocynin treatment improved in vivo autoregulatory behavior in HS rats and had no detectable effect in normal salt diet-fed rats. These data support the hypothesis that impaired renal autoregulatory behavior in rats fed a HS diet is mediated by NADPH oxidase-derived ROS.

Connecting tubule glomerular feedback in hypertension

In Dahl salt-sensitive rats (Dahl SS), glomerular capillary pressure increases in response to high salt intake and this is accompanied by significant glomerular injury compared with spontaneously hypertensive rats with similar blood pressure. Glomerular capillary pressure is controlled mainly by afferent arteriolar resistance, which is regulated by the vasoconstrictor tubule glomerular feedback (TGF) and the vasodilator connecting TGF (CTGF). We hypothesized that Dahl SS have a decreased TGF response and enhanced TGF resetting compared with spontaneously hypertensive rats, and that these differences are attributable in part to an increase in CTGF. In vivo, using micropuncture we measured stop-flow pressure (a surrogate of glomerular capillary pressure). TGF was calculated as the maximal decrease in stop-flow pressure caused by increasing nephron perfusion, TGF resetting as the attenuation in TGF induced by high salt diet, and CTGF as the difference in TGF response before and during CTGF inhibition with benzamil. Compared with spontaneously hypertensive rats, Dahl SS had (1) lower TGF responses in normal (6.6±0.1 versus 11.0±0.2 mm Hg; P<0.001) and high-salt diets (3.3±0.1 versus 10.1±0.3 mm Hg; P<0.001), (2) greater TGF resetting (3.3±0.1 versus 1.0±0.3 mm Hg; P<0.001), and (3) greater CTGF (3.4±0.4 versus 1.2±0.1 mm Hg; P<0.001). We conclude that Dahl SS have lower TGF and greater CTGF than spontaneously hypertensive rats, and that CTGF antagonizes TGF. Furthermore, CTGF is enhanced by a high-salt diet and contributes significantly to TGF resetting. Our findings may explain in part the increase in vasodilatation, glomerular capillary pressure, and glomerular damage in SS hypertension during high salt intake.

A review of nutritional factors in hypertension management

Hypertension is a major health problem worldwide. Its attendant morbidity and mortality complications have a great impact on patient's quality of life and survival. Optimizing blood pressure control has been shown to improve overall health outcomes. In addition to pharmacological therapies, nonpharmacological approach such as dietary modification plays an important role in controlling blood pressure. Many dietary components such as sodium, potassium, calcium, and magnesium have been studied substantially in the past decades. While some of these nutrients have clear evidence for their recommendation, some remain controversial and are still of ongoing study. Dietary modification is often discussed with patients and can provide a great benefit in blood pressure regulation. As such, reviewing the current evidence will be very useful in guiding patients and their physician and/or dietician in decision making. In this review article of nutritional factors in hypertension management, we aim to examine the role of nutritional factors individually and as components of whole dietary patterns.

Mechanisms of renal NaCl retention in proteinuric disease

In diseases with proteinuria, for example nephrotic syndrome and pre-eclampsia, there often are suppression of plasma renin-angiotensin-aldosterone system components, expansion of extracellular volume and avid renal sodium retention. Mechanisms of sodium retention in proteinuria are reviewed. In animal models of nephrotic syndrome, the amiloride-sensitive epithelial sodium channel ENaC is activated while more proximal renal Na(+) transporters are down-regulated. With suppressed plasma aldosterone concentration and little change in ENaC abundance in nephrotic syndrome, the alternative modality of proteolytic activation of ENaC has been explored. Proteolysis leads to putative release of an inhibitory peptide from the extracellular domain of the γ ENaC subunit. This leads to full activation of the channel. Plasminogen has been demonstrated in urine from patients with nephrotic syndrome and pre-eclampsia. Urine plasminogen correlates with urine albumin and is activated to plasmin within the urinary space by urokinase-type plasminogen activator. This agrees with aberrant filtration across an injured glomerular barrier independent of the primary disease. Pure plasmin and urine samples containing plasmin activate inward current in single murine collecting duct cells. In this study, it is shown that human lymphocytes may be used to uncover the effect of urine plasmin on amiloride- and aprotinin-sensitive inward currents. Data from hypertensive rat models show that protease inhibitors may attenuate blood pressure. Aberrant filtration of plasminogen and conversion within the urinary space to plasmin may activate γ ENaC proteolytically and contribute to inappropriate NaCl retention and oedema in acute proteinuric conditions and to hypertension in diseases with chronic microalbuminuria/proteinuria.

Association between sodium intake and change in uric acid, urine albumin excretion, and the risk of developing hypertension

BACKGROUND

A high-sodium diet has little short-term effect on blood pressure in nonhypertensive individuals but, for unclear reasons, is associated with hypertension if consumed long term. We hypothesized that a chronically high sodium intake would be associated with increases in biomarkers of endothelial dysfunction, specifically serum uric acid (SUA) and urine albumin excretion (UAE), and that high sodium intake would be associated with incident hypertension among those with higher SUA and UAE.

METHODS AND RESULTS

We prospectively analyzed the associations between sodium intake and the change in SUA (n=4062) and UAE (n=4146) among participants of the Prevention of Renal and Vascular End Stage Disease (PREVEND) study who were not taking antihypertensive medications. We also examined the association of sodium intake with the incidence of hypertension (n=5556) among nonhypertensive participants. After adjustment for confounders, each 1-g-higher sodium intake was associated with a 1.2-μmol/L increase in SUA (P=0.01) and a 4.6-mg/d increase in UAE (P<0.001). The relation between sodium intake and incident hypertension varied according to SUA and UAE. For each 1-g-higher sodium intake, the adjusted hazard ratio for developing hypertension was 0.98 (95% confidence interval, 0.89-1.08) among those in the lowest tertile of SUA and 1.09 (1.02-1.16) among those in the highest tertile. Corresponding hazard ratios were 0.99 (confidence interval, 0.93-1.06) among participants whose UAE was <10 mg/d and 1.18 (confidence interval, 1.07-1.29) among those whose UAE was >15 mg/d.

CONCLUSIONS

Over time, higher sodium intake is associated with increases in SUA and UAE. Among individuals with higher SUA and urine UAE, a higher sodium intake is an independent risk factor for developing hypertension.

Early improvement in albuminuria in non-diabetic patients after Roux-en-Y bariatric surgery

BACKGROUND

Obesity is a growing epidemic in the USA that has been shown to be associated with chronic kidney disease and albuminuria. Bariatric surgery is an effective means of achieving long-term weight loss and improvements in metabolic derangements including albumin excretion over the long term.

METHODS

We report changes in urinary albumin excretion levels in the early post-operative period for a euglycemic, predominantly Hispanic American cohort undergoing Roux-en-Y gastric bypass surgery.

RESULTS

Our cohort of 38 patients was largely female (89.5%) and predominantly Hispanic (76.3%) with a mean BMI of 46 ± 8.0 kg/m(2). Over half (53.3%) of the patients with significant preoperative albumin excretion in our cohort lowered their albumin excretion levels to <20 mg/g of creatinine. This early reduction in albumin excretion in our cohort correlated significantly with the level of albumin excretion preoperatively but not with the degree of weight loss experienced in this early post-operative period.

CONCLUSIONS

Improvements in microalbuminuria in the early post-operative period after Roux-en-Y surgery may result from an interplay between changes in gastrointestinal hormones, insulin sensitivity, blood pressure, and adipose tissue-and needs further study.

Prevention of salt-induced renal injury by activation of NAD(P)H:quinone oxidoreductase 1, associated with NADPH oxidase

NADPH oxidase (NOX) is a predominant source of reactive oxygen species (ROS), and the activity of NOX, which uses NADPH as a common rate-limiting substrate, is upregulated by prolonged dietary salt intake. β-Lapachone (βL), a well-known substrate of NAD(P)H:quinone oxidoreductase 1 (NQO1), decreases the cellular NAD(P)H/NAD(P)(+) ratio via activation of NQO1. In this study, we evaluated whether NQO1 activation by βL modulates salt-induced renal injury associated with NOX-derived ROS regulation in an animal model. Dahl salt-sensitive (DS) rats fed a high-salt (HS) diet were used to investigate the renoprotective effect of NQO1 activation. βL treatment significantly lowered the cellular NAD(P)H:NAD(P)(+) ratio and dramatically reduced NOX activity in the kidneys of HS diet-fed DS rats. In accordance with this, total ROS production and expression of oxidative adducts also decreased in the βL-treated group. Furthermore, HS diet-induced proteinuria and glomerular damage were markedly suppressed, and inflammation, fibrosis, and apoptotic cell death were significantly diminished by βL treatment. This study is the first to demonstrate that activation of NQO1 has a renoprotective effect that is mediated by NOX activity via modulation of the cellular NAD(P)H:NAD(P)(+) ratio. These results provide strong evidence that NQO1 might be a new therapeutic target for the prevention of salt-induced renal injury.

Effects of dietary salt restriction on puromycin aminonucleoside nephrosis: preliminary data

Proteinuria is a major promoter that induces tubulointerstitial injury in glomerulopathy. Dietary salt restriction may reduce proteinuria, although the mechanism is not clear. We investigated the effects of dietary salt restriction on rat kidneys in an animal model of glomerular proteinuria. Male Sprague-Dawley rats were used and divided into 3 groups: vehicle-treated normal-salt controls, puromycin aminonucleoside (PA)-treated normal-salt rats, and PA-treated low-salt rats. PA was given at a dose of 150 mg/kg BW at time 0, followed by 50 mg/kg BW on days 28, 35, and 42. Sodium-deficient rodent diet with and without additional NaCl (0.5%) were provided for normal-salt rats and low-salt rats, respectively. On day 63, kidneys were harvested for histopathologic examination and immunohistochemistry. PA treatment produced overt proteinuria and renal damage. Dietary salt restriction insignificantly reduced proteinuria in PA-treated rats, and PA-treated low-salt rats had lower urine output and lower creatinine clearance than vehicle-treated normal-salt controls. When tubulointerstitial injury was semiquantitatively evaluated, it had a positive correlation with proteinuria. The tubulointerstitial injury score was significantly increased by PA treatment and relieved by low-salt diet. ED1-positive infiltrating cells and immunostaining for interstitial collagen III were significantly increased by PA treatment. These changes appeared to be less common in PA-treated low-salt rats, although the differences in PA-treated normal-salt versus low-salt rats did not reach statistical significance. Our results suggest that renal histopathology in PA nephrosis may potentially be improved by dietary salt restriction. Non-hemodynamic mechanisms induced by low-sodium diet might contribute to renoprotection.

Relapse or worsening of nephrotic syndrome in idiopathic membranous nephropathy can occur even though the glomerular immune deposits have been eradicated

BACKGROUND

Relapse or worsening of nephrotic syndrome (NS) in idiopathic membranous nephropathy (IMN) is generally assumed to be due to recurrent disease. Here we document that often that may not be the case.

SUBJECTS AND METHODS

This is a prospective study of 7 consecutive IMN patients whose renal status improved, then worsened after completing a course of immunosuppressive therapy. Each underwent detailed testing and repeat kidney biopsy.

RESULTS

In 4 patients (group A), the biopsy showed recurrent IMN (fresh subepithelial deposits). Immunosuppressive therapy was begun. In the other 3 patients (group B), the biopsy showed that the deposits had been eradicated. However, the glomerular basement membrane (GBM) was thickened and vacuolated. Immunosuppressive therapy was withheld. Groups A and B were comparable except that group B had very high intakes of salt and protein, based on 24-hour urine testing. Reducing their high salt intake sharply lowered proteinuria to the subnephrotic range and serum creatinine stabilized.

CONCLUSION

This work is the first to demonstrate that relapse/worsening of NS can occur in IMN even though the GBM deposits have been eradicated. High salt and protein intake in combination with thickened and vacuolated GBM appears to be the mechanism.

The associations between G972R polymorphism of the IRS-1 gene, insulin resistance, salt sensitivity and non-dipper hypertension

The aim of this study was to assess the association between G972R polymorphism of the insulin receptor substrate-1 (IRS-1) gene and the circadian variation in blood pressure, insulin sensitivity and salt sensitivity in subjects with uncomplicated, never-treated essential hypertension receiving low-, normal- and high-salt diets. The study was performed on 115 subjects aged 27.48±5.1 years with never-treated, uncomplicated hypertension. In the 7-day consecutive period of time, subjects received a normal-, low- and high-salt diet. At the end of each dietary regimen, the following parameters were recorded: 24-h blood pressure monitoring, lipid profile, insulin level, glucose level, aldosterone level and plasma renin activity. Insulin resistance was evaluated by the homeostasis model assessment (HOMA). In comparison with Gly/Gly carriers, subjects with the G972R polymorphism had higher concentrations of total and LDL cholesterol and triglycerides and HOMA but lower HDL cholesterol. On a high-salt diet, patients with the G972R polymorphism had an increased risk for insulin resistance (odds ratio (OR)=11.42, 95% confidence interval (CI) 7.68-28.44), salt sensitivity (OR=5.38, 95% CI 1.14-25.34) and non-dipper hypertension (OR=3.6, 95% CI 1.07-12.09). Regardless of the dietary salt intake, blood pressure values were similar between G972R and Gly/Gly carriers. In conclusion, the results of our study suggest that the G972R polymorphism of the IRS-1 gene is associated with insulin resistance, salt sensitivity and non-dipper hypertension.

High-NaCl intake impairs dynamic autoregulation of renal blood flow in ANG II-infused rats

The aim of this study was to investigate dynamic autoregulation of renal blood flow (RBF) in ANG II-infused rats and the influence of high-NaCl intake. Sprague-Dawley rats received ANG II (250 ng·kg−1·min−1 sc) or saline vehicle (sham) for 14 days after which acute renal clearance experiments were performed during thiobutabarbital anesthesia. Rats ( n = 8–10 per group) were either on a normal (NNa; 0.4% NaCl)- or high (HNa; 8% NaCl)-NaCl diet. Separate groups were treated with 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (tempol; 1 M in drinking water). Transfer function analysis from arterial pressure to RBF in the frequency domain was used to examine the myogenic response (MR; 0.06–0.09 Hz) and the tubuloglomerular feedback mechanism (TGF; 0.03–0.06 Hz). MAP was elevated in ANG II-infused rats compared with sham groups ( P < 0.05). RBF in ANG II HNa was reduced vs. sham NNa and sham HNa (6.0 ± 0.3 vs. 7.9 ± 0.3 and 9.1 ± 0.3 ml·min−1·g kidney wt−1, P < 0.05). transfer function gain in ANG II HNa was significantly elevated in the frequency range of the MR (1.26 ± 0.50 dB, P < 0.05 vs. all other groups) and in the frequency range of the TGF (−0.02 ± 0.50 dB, P < 0.05 vs. sham NNa and sham HNa). Gain values in the frequency range of the MR and TGF were significantly reduced by tempol in ANG II-infused rats on HNa diet. In summary, the MR and TGF components of RBF autoregulation were impaired in ANG II HNa, and these abnormalities were attenuated by tempol, suggesting a pathogenetic role for superoxide in the impaired RBF autoregulatory response.

Fetal exposure to maternal type 1 diabetes is associated with renal dysfunction at adult age

OBJECTIVE

In animal studies, hyperglycemia during fetal development reduces nephron numbers. We tested whether this observation translates into renal dysfunction in humans by studying renal functional reserve in adult offspring exposed in utero to maternal type 1 diabetes.

RESEARCH DESIGN AND METHODS

We compared 19 nondiabetic offspring of type 1 diabetic mothers with 18 offspring of type 1 diabetic fathers (control subjects). Glomerular filtration rate ((51)Cr-EDTA clearance), effective renal plasma flow ((123)I-hippurate clearance), mean arterial pressure, and renal vascular resistances were measured at baseline and during amino acid infusion, which mobilizes renal functional reserve.

RESULTS

Offspring of type 1 diabetic mothers were similar to control subjects for age (median 27, range 18-41, years), sex, BMI (23.1 ± 3.7 kg/m(2)), and birth weight (3,288 ± 550 vs. 3,440 ± 489 g). During amino acid infusion, glomerular filtration rate and effective renal plasma flow increased less in offspring of type 1 diabetic mothers than in control subjects: from 103 ± 14 to 111 ± 17 ml/min (8 ± 13%) vs. from 108 ± 17 to 128 ± 23 ml/min (19 ± 7%, P = 0.009) and from 509 ± 58 to 536 ± 80 ml/min (5 ± 9%) vs. from 536 ± 114 to 620 ± 140 ml/min (16 ± 11%, P = 0.0035). Mean arterial pressure and renal vascular resistances declined less than in control subjects: 2 ± 5 vs. -2 ± 3% (P = 0.019) and 3 ± 9 vs. -14 ± 8% (P = 0.001).

CONCLUSIONS

Reduced functional reserve may reflect a reduced number of nephrons undergoing individual hyperfiltration. If so, offspring of type 1 diabetic mothers may be predisposed to glomerular and vascular diseases.

Rise in extracellular fluid volume during high sodium depends on BMI in healthy men

A high sodium (HS) intake is associated to increased cardiovascular and renal risk, especially in overweight subjects. We hypothesized that abnormal sodium and fluid handling is involved, independent of hypertension or insulin resistance. Therefore, we studied the relation between BMI and sodium-induced changes in extracellular fluid volume (ECFV; distribution volume of (125)I-iothalamate) in 78 healthy men, not selected for BMI. A total of 78 subjects with a median BMI of 22.5 (range: 19.2-33.9 kg/m(2)) were studied after 1 week on a low sodium (LS) diet (50 mmol Na(+)/d) and after 1 week on HS (200 mmol Na(+)/d). The change from LS to HS resulted in an increase in ECFV of 1.2 +/- 1.8 l. Individual changes in ECFV were correlated to BMI (r = 0.361, P < 0.01). Furthermore, in response to HS, a higher BMI was associated to a higher rise in filtered load of sodium (FL(Na(+)) = [Na(+)] x GFR, r = 0.281, P < 0.05). Thus, a shift to HS leads to a larger rise in ECFV in healthy subjects with higher BMI, associated with an elevated FL(Na(+)) during HS. Although no hypertension occurred in these healthy subjects, our data provide a potential explanation for the interaction of sodium intake and BMI on cardiovascular and renal risk. Exaggerated fluid retention may be an early pathogenic factor in the cardiorenal complications of overweight.

The V433M variant of the CYP4F2 is associated with ischemic stroke in male Swedes beyond its effect on blood pressure

Cytochrome (CYP) 4A11 and CYP4F2 are responsible for renal production of 20-hydroxyeicosatetraenoic acid, a vasoconstrictor and natriuretic substance. The CYP4A11 F434S and CYP4F2 V433M polymorphisms reduce 20-hydroxyeicosatetraenoic acid production in vitro. The aim of the present study was to evaluate the effect of these polymorphisms on blood pressure (BP) levels, hypertension prevalence, and risk of incident cardiovascular events in middle-aged Swedes. The polymorphisms were genotyped in the cardiovascular cohort of the Malmö Diet and Cancer Study. The incidence of cardiovascular events (coronary events, n=276; ischemic stroke, n=199) was monitored over 10 years of follow-up. The analysis of BP levels was performed twice: either excluding or including subjects under antihypertensive treatment. In the whole population, CYP4A11 S434S homozygotes had higher systolic BP, both crude and adjusted for the number of antihypertensive drugs, and higher prevalence of hypertension with respect to F434 carriers. Male, but not female, CYP4F2 M433 carriers had significantly higher crude and adjusted systolic and diastolic BPs and a trend toward higher hypertension prevalence (P=0.06) with respect to V433V homozygotes. After adjustment for major cardiovascular risk factors, the hazard ratio for incident ischemic stroke in male CYP4F2 M433 carriers was significantly higher with respect to V433V homozygotes (hazard ratio: 1.69; 95% CI: 1.10 to 2.60) even when baseline BP levels and hypertension prevalence were included in the Cox proportional hazard model. A common CYP4F2 V433M polymorphism might increase the risk of incident ischemic stroke in male subjects only partially through its elevating effect on BP. Additional studies are needed to confirm these data.

Renoprotection by statins is linked to a decrease in renal oxidative stress, TGF-beta, and fibronectin with concomitant increase in nitric oxide bioavailability

Clinical and experimental studies have provided evidence suggesting that statins exert renoprotective effects. To investigate the mechanisms by which statins may exert renoprotection, we utilized the hypertensive Dahl salt-sensitive (DS) rat model, which manifests cardiovascular and renal injury linked to increased angiotensin II-dependent activation of NADPH oxidase and decreased nitric oxide (NO) bioavailability. DS rats given high salt diet (4% NaCl) for 10 wk exhibited hypertension [systolic blood pressure (SBP) 200 +/- 8 vs. 150 +/- 2 mmHg in normal salt diet (0.5% NaCl), P < 0.05], glomerulosclerosis, and proteinuria (158%). This was associated with increased renal oxidative stress demonstrated by urinary 8-F(2alpha)-isoprostane excretion and NADPH oxidase activity, increased protein expression of transforming growth factor (TGF)-beta (63%) and fibronectin (181%), increased mRNA expression of the proinflammatory molecules monocyte chemoattractant protein-1 (MCP-1) and lectin-like oxidized LDL receptor-1 (LOX-1), as well as downregulation of endothelial NO synthase (eNOS) activity (-44%) and protein expression. Return to normal salt had no effect on SBP or any of the measured parameters. Atorvastatin (30 mg.kg(-1).day(-1)) significantly attenuated proteinuria and glomerulosclerosis and normalized renal oxidative stress, TGF-beta1, fibronectin, MCP-1 and LOX-1 expression, and eNOS activity and expression. Atorvastatin-treated rats showed a modest reduction in SBP that remained in the hypertensive range (174 +/- 8 mmHg). Atorvastatin combined with removal of high salt normalized SBP and proteinuria. These findings suggest that statins mitigate hypertensive renal injury by restoring the balance among NO, TGF-beta1, and oxidative stress and explain the added renoprotective effects observed in clinical studies using statins in addition to inhibitors of the renin-angiotensin system.

Albuminuria, expression of nicotinamide adenine dinucleotide phosphate oxidase and monocyte chemoattractant protein-1 in the renal tubules of hypertensive Dahl salt-sensitive rats

In chronic renal diseases, experimental and human data suggest that excess albumin filtered through the glomerular capillary barrier is over-reabsorbed by proximal tubular cells, thereby activating these cells and upregulating the expression of chemokines. On the other hand, a high-salt diet has been shown to induce proteinuria in hypertensive Dahl salt-sensitive (DSS) rats, accompanied with the expression of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase in the kidney. In the current study, we therefore examined albuminuria and the expressions of NADPH oxidase and monocyte chemoattractant protein-1 (MCP-1) in the renal tubular cells in hypertensive DSS rats, as well as the effects of the antioxidant N-acetylcysteine (NAC) on each of these parameters. DSS rats were fed a normal-salt diet (0.24% NaCl), a high-salt diet (8% NaCl), or a high-salt diet plus NAC supplementation (15 mg/mL drinking water) for 4 weeks. The high-salt diet provoked an increase in glomerular injuries accompanied with albuminuria and in urinary H2O2 and MCP-1 excretion. Immunohistochemical analysis showed the prominent expression of MCP-1 in the dilated tubular cells, where the NADPH oxidase subunit p47phox was also expressed. The current results suggest that albuminuria caused expression of NADPH oxidase and MCP-1 in the dilated renal tubules, resulting in interstitial inflammation and migration of mononuclear cells in DSS rats, because blockade of albuminuria by NAC counteracted the p47phox and MCP-1 expression.

Salt: its role in chronic kidney disease

Few controversies in medicine have such a long history as that of whether salt is identifiably dangerous or not dangerous. The most common reported association between excess dietary salt intake and clinical outcome has been in the field of hypertension, but dietary sodium intake mediates effects that go far beyond, and are independent of, extracellular fluid expansion and elevation in blood pressure. For nephrologists, clinical trials that demonstrate no negative outcome of a high salt diet in the general population are thus not particularly assuasive, because patients with chronic kidney disease (CKD) represent an entity that is by no means comparable to the general population. This review takes a look at the challenges associated with salt balance in CKD patients (particularly at K/DOQI stage 5), followed by a summary of current concepts believed to play a part in salt-mediated pathophysiology, and the conclusion, based on the present state of scientific knowledge, that it appears advisable to advocate low dietary salt intake in this patient population.

Renal response to angiotensin II is blunted in sodium-sensitive normotensive men

BACKGROUND

In hypertension, sodium sensitivity (SS) of blood pressure is associated with renal hemodynamic abnormalities related to increased activity of the renal renin-angiotensin aldosterone system (RAAS). The renal mechanisms of SS in normotensives are unknown. Therefore, we studied whether SS is related to renal hemodynamics and renal responsiveness to angiotensin II (AngII) in young healthy adults.

METHODS

Blood pressure (mean arterial pressure (MAP)) and renal function were measured in 34 healthy men after 1-week low-sodium diet (LS; 50 mmol Na(+)/24 h), 1-week high-sodium diet (HS; 200 mmol Na(+)/24h), and 1-week HS-ACEi (enalapril 20 mg/day). The responses of effective renal plasma flow (ERPF; (131)I-Hippuran clearance) to graded infusion of AngII were assessed during each condition.

RESULTS

The sodium-induced change in MAP ranged from -7 to +14 mm Hg. SS (a sodium-induced increase in MAP >3 mm Hg) was present in 13 subjects. ERPF was lower in SS subjects during LS and during HS-ACEi. The AngII-induced decrease in ERPF was blunted in SS on LS (-25 +/- 6 vs. -29 +/- 7% in sodium-resistant (SR) subjects, P < 0.05) and on HS (-30 +/- 5 vs. -35 +/- 6%, P < 0.05). The blunting was corrected by angiotensin-converting enzyme inhibitors (ACEi) (-36 +/- 6 vs. -37 +/- 7%).

CONCLUSION

SS normotensive subjects have a blunted renal response to exogenous AngII. This is ameliorated by ACEi, supporting a role for inappropriately high intrarenal RAAS activity. As these findings cannot be attributed to subclinical renal hypertensive damage, high intrarenal RAAS activity and altered renal hemodynamics may be primary phenomena underlying SS.

Age- and sodium-sensitive hypertension and sex-dependent renal changes in rats with a reduced nephron number

We have demonstrated that the reduction of angiotensin II effects during the nephrogenic period reduces the nephron number and induces the development of hypertension. The hypotheses examined are that this reduction of angiotensin effects leads to the development of an age-dependent sodium sensitive hypertension and that the hypertension is angiotensin II dependent. Newborn rats were treated with an angiotensin II type 1 receptor antagonist during the first 2 weeks of age. At 3 to 4 and 11 to 12 months of age, changes in systolic blood pressure, proteinuria, and renal function in response to a prolonged high sodium intake were examined. The basal blood pressure response to the administration of the angiotensin II receptor antagonist was also evaluated at both ages. Basal blood pressure was similarly elevated (P<0.05) in male and female treated rats, and the increment was age dependent. High sodium intake only elicited a blood pressure elevation (136+/-1 to 154+/-3 mm Hg; P<0.05) and a decrease in glomerular filtration rate (28%; P<0.05) at 11 to 12 months in treated rats. Blockade of angiotensin II receptors during renal development induced an increase (P<0.05) in proteinuria that was age and sex dependent, but high sodium intake only induced an elevation in proteinuria in the younger rats (50%; P<0.05). Hypertension was maintained by angiotensin II at both ages because blood pressure decreased to normal levels after treatment with an angiotensin II type 1 receptor antagonist. This study shows that the reduction of angiotensin II effects during the nephrogenic period modifies renal function and induces the development of an angiotensin II-dependent hypertension that becomes sodium sensitive during aging.

Racial differences in microalbumin excretion in healthy adolescents

It has been suggested that "normal" levels of urine albumin excretion rate (AER) may be predictive of an increased risk for progression of hypertension, cardiovascular morbidity, and mortality. No data are available on the effect of race and gender on AER in normal youth. We evaluated AER in timed urine samples in subjects participating in a study of stress-induced pressure natriuresis. A total of 317 healthy, normotensive adolescents aged 15 to 18 years (155 males and 162 females; 216 blacks and 101 whites) participated in a 5-hour testing protocol, which included a 1-hour period of mental stress preceded and followed by a 2-hour rest period. AER (micrograms per minute) was determined after 60 minutes of rest, and log transformation was used to normalize the data. AER was significantly higher in blacks as compared with whites (P=0.006). We also found a race-by-sex interaction, which was driven by the low albumin excretion in white females (P=0.036). Indexing urine albumin to creatinine excretion revealed the same pattern. Among blacks, AER was also higher in subjects who demonstrated impaired stress-induced pressure natriuresis versus those with normal sodium excretion (P=0.024). AER was related to blood pressure only in African-American males. The relative elevation of AER in normotensive black adolescents and the association with impaired pressure natriuresis and blood pressure is noteworthy. These findings suggest that albumin excretion may be a marker for a population at increased risk for the development of vascular and renal injury even before the manifestation of hypertension.

Insulin resistance is the major determinant for microalbuminuria in severe hypertriglyceridemia: implication for high-risk stratification

OBJECTIVE

The significance of high triglyceride levels as a risk factor for coronary heart disease is uncertain. We hypothesized that oral glucose tolerance test (OGTT) and certain novel markers may help to identify high-risk patients.

PATIENTS AND METHODS

We recruited 80 subjects with severe hypertriglyceridemia (age 27-73 years) without clinical proteinuria and diabetes mellitus (DM) which were diagnosed by fasting glucose <126 mg/dL from Hyperlipidemia Clinic of National Taiwan University Hospital for this study. We applied OGTT to evaluate occult DM and homeostasis model assessment (HOMA)-insulin resistance (IR) score to evaluate insulin resistance, and the measurements of microalbuminuria as a marker of vascular damage. In addition, serum or plasma markers of inflammation and fibrinolysis, fasting glucose and insulin as well as traditional cardiovascular risk factors were also evaluated.

RESULTS

The serum level of triglyceride was higher in patients with microalbuminuria than in those without (14.1+/-5.7 vs. 9.6+/-3.9 mmol/L, p=0.025). Patients with microalbuminuria had higher fasting blood glucose and insulin, higher post-OGTT glucose and insulin, higher prevalence of newly developed diabetes mellitus (DM) (39% vs. 11%, p=0.007) and higher HOMA-IR (6.2+/-4.4 vs. 3.3+/-2.0, p<0.001). Among all the inflammatory and fibrinolytic markers, only soluble intercellular adhesion molecule showed significant different between these two groups. Multiple logistic regression analysis showed that among the serum markers, only HOMA-IR level was significantly related to microalbuminuria.

CONCLUSIONS

HOMA-IR is the major determinant for microalbuminuria in patients with severe hypertriglyceridemia. Impaired glucose metabolism is evident in patients with both severe hypertriglyceridemia and microalbuminuria.

Pathophysiological Mechanisms of Salt-Dependent Hypertension

Changes in salt intake are associated in general with corresponding changes in arterial blood pressure. An exaggerated increment in blood pressure driven by a salt load is characteristic of salt-sensitive hypertension, a condition affecting more than two thirds of individuals with essential hypertension who are older than 60 years. In the last decade, significant insight was gained about the role of the kidney in the increment in blood pressure induced by sodium retention. The present review focuses on the pathophysiological characteristics of the blood pressure increase driven by expansion of extracellular fluid and the increment in plasma sodium concentration. In addition, we discuss systemic and renal conditions that result in decreased urinary sodium excretion and were implicated in the development of salt-sensitive hypertension.

Salt, the kidneys, and arterial hypertension

The kidneys play a major role in the regulation of the salt balance and thereby regulate blood pressure. Salt sensitivity is acquired or genetically-induced and is noted in about 50% of patients with essential hypertension. This property leads to a high cardiovascular risk. In this situation, the benefit of salt restriction is significant, and this dietary change should be associated with a high potassium intake. In patients treated by antihypertensive drugs, salt restriction improves the blood pressure control, which can permit a reduction of the number of drugs required to achieve a normal blood pressure. The recommended maximal salt intake should not exceed 6 grams/day (NaCl). Because most dietary salt comes from processed foods, the help of the food industry is crucial for a long-term compliance with a reduced salt intake, which could yield an additional important benefit in the reduction of cardiovascular risk.

Effects of the renin-angiotensin system genes and salt sensitivity genes on blood pressure and atherosclerosis in the total population and patients with type 2 diabetes

Most studies on the genetic determinants of blood pressure and vascular complications of type 2 diabetes have focused on the effects of single genes. These studies often have yielded conflicting results. Therefore, we examined the combined effects of three renin-angiotensin system (RAS) genes and three salt sensitivity genes in relation to blood pressure and atherosclerosis in the total population and type 2 diabetic patients. The study was a part of the Rotterdam Study, a population-based cohort study. We have genotyped three RAS gene polymorphisms and three salt sensitivity gene polymorphisms. Diabetic patients with three risk genotypes of the RAS genes had a 6.9 mmHg higher systolic blood pressure (P for trend = 0.04) and a 6.0 mmHg higher pulse pressure (P for trend = 0.03) than those who did not carry any risk genotypes. Diabetic patients with three risk genotypes of the salt sensitivity genes had a 9.0 mmHg higher systolic blood pressure (P = 0.19) and a 13.1 mmHg higher pulse pressure (P = 0.02). Diabetic patients who carried three risk genotypes for the RAS genes had a higher mean intima-media thickness than those with two risk genotypes (mean difference 0.04 mm, P = 0.02). We found that among type 2 diabetic patients, mean systolic blood pressure, pulse pressure, and risk of hypertension increased with the number of risk genotypes for the RAS genes and the salt sensitivity genes.

Renal hemodynamics in overweight and obesity: pathogenetic factors and targets for intervention

Weight excess is a risk factor for progressive renal function loss, not only in subjects with renal disease or renal transplant recipients, but also in the general population. Considering the increasing prevalence of obesity worldwide, weight excess may become the main renal risk factor on a population basis, all the more so because the risk is not limited to morbid obesity, but is already apparent in the overweight range. The mechanism of the renal risk is multifactorial. In addition to the role of comorbid conditions such as hypertension and diabetes, current evidence supports a pathogenetic role for renal hemodynamics, specifically glomerular hyperfiltration, and also glomerular hypertension. Weight excess is associated with an elevated glomerular filtration rate and a less pronounced rise in renal plasma flow, resulting in an elevated filtration fraction. This suggests glomerular hypertension due to afferent-efferent dysbalance, which impairs glomerular protection from systemic hypertension. Data in renal transplant recipients support the pathogenetic role of elevated glomerular pressure for long-term renal prognosis. Blockade of the renin-angiotensin-aldosterone system can reverse the renal hemodynamic abnormalities. The obesity-associated renal risk is unfavourably affected by high sodium intake. This may be due to the effects of sodium on blood pressure, which is often sodium-sensitive in obesity, but direct renal effects are also present. Interestingly, sodium restriction ameliorates overweight-associated hyperfiltration in overweight subjects. More focus on weight excess as a renal risk factor is warranted. Preventive measures should focus on weight excess as well as on specific protection against renal damage, by renin-angiotensin-aldosterone system-blockade and moderate sodium restriction.

IL6 suppression provides renal protection independent of blood pressure in a murine model of salt-sensitive hypertension

Impaired cytochrome P450 epoxygenase enzyme (Cyp2c) regulation contributes to renal damage in angiotensin salt-sensitive hypertension (ANG/HS). We hypothesized that interleukin-6 null mice (IL6-/-) would improve Cyp2c regulation and reduce renal damage in hypertensive mice fed a high salt diet. Systolic blood pressure increased to a greater extent in ANG/HS hypertension as compared to angiotensin (ANG) hypertension but blood pressure did not differ between WT and IL6-/- hypertensive groups. Albuminuria, a marker for renal injury, increased significantly in ANG/HS hypertension in WT mice (5,113 +/- 1,050 mug/day) and was attenuated in the ANG/HS IL6-/- group (1,306 +/- 385 mug/day). Renal Cyp2c protein expression significantly decreased with ANG/HS hypertension in WT mice as compared to high salt alone. However, the ability to upregulate Cyp2c expression in response to a high salt diet was restored in the ANG/HS IL6 deficient hypertensive mice. Renal expression of soluble epoxide hydrolase, which inactivates protective epoxygenase metabolites, was significantly reduced in ANG/HS IL6-/- hypertensive mice compared to the ANG/HS WT group. These data suggest that IL6, while having no effect on blood pressure, impairs regulation of epoxygenase producing Cyp2c, which could contribute to the development of renal injury in angiotensin salt-sensitive hypertension.

Enhanced sodium sensitivity and disturbed circadian rhythm of blood pressure in essential hypertension

OBJECTIVE

To assess whether an association between sodium-sensitive hypertension and metabolic syndrome exists; and whether, in patients with metabolic syndrome, the nocturnal fall of blood pressure decreases and salt restriction affects the circadian blood pressure rhythm.

METHODS

Japanese patients with essential hypertension, who were treated without any antihypertensive agent, were maintained on a high-sodium diet and a low-sodium diet for 1 week each. On the last day of each diet, the 24-h blood pressures were measured. A diagnosis of metabolic syndrome was made according to the International Diabetes Foundation definition

RESULTS

Among the 56 patients with essential hypertension, 15 patients were complicated with metabolic syndrome while 41 patients were not. The nocturnal blood pressure fall was significant in patients without metabolic syndrome, while it was not so in patients with metabolic syndrome. Only in patients with metabolic syndrome was the nocturnal blood pressure fall enhanced by sodium restriction. The prevalence of sodium-sensitive hypertension in patients with metabolic syndrome was significantly higher than in those without metabolic syndrome (70.6 versus 36.0%, respectively; P = 0.017). A multiple logistic regression analysis revealed central obesity to be an independent risk factor for sodium-sensitive hypertension (odds ratio, 1.41; 95% confidence interval, 1.04-1.91).

CONCLUSIONS

In patients with essential hypertension, an inter-relationship exists among metabolic syndrome, enhanced sodium sensitivity of the blood pressure and non-dipping. The elevated risk of cardiovascular diseases in patients with metabolic syndrome may be related to sodium-sensitive hypertension and non-dipping.

Rat chromosome 19 transfer from SHR ameliorates hypertension, salt-sensitivity, cardiovascular and renal organ damage in salt-sensitive Dahl rats

OBJECTIVES

Unlike Dahl salt-sensitive (SS) rats, some strains of spontaneously hypertensive (SHR) rats develop only minor organ damage even when exposed to high-salt diet. In previous linkage studies, we identified quantitative trait loci on rat chromosome 19 (RNO19) linked to the SHR allele suggesting a protective effect against salt-induced hypertensive organ damage in SS.

METHODS

To test the relevance of this finding, we generated and characterized a consomic strain SS-19SHR in which RNO19 from SHR was introgressed into the susceptible background of SS. We compared the effects of low-salt (0.2% NaCl) and high-salt (4% NaCl) diet exposure for 8 weeks on the development of hypertension and target organ damage in male consomic and SS animals (n=14-20, each).

RESULTS

Systolic blood pressure, relative left ventricular weight and urinary protein excretion were significantly lower in SS-19SHR compared to SS under both low-salt and high-salt diet (P < 0.05, respectively). Left ventricular atrial natriuretic peptide mRNA expression showed a more pronounced 4.5-fold increase in SS compared to SS-19 (two-fold) after high-salt (P < 0.05). In comparison to low diet, high-salt exposure induced a significant increase in vascular aortic hypertrophy index, left ventricular interstitial fibrosis (+210%) and perivascular fibrosis (+195%) in SS but not in consomic SS-19SHR (P < 0.05, respectively).

CONCLUSIONS

These results demonstrate a strong protective effect of RNO19 from SHR on the development of hypertension, salt-sensitivity, cardiovascular and renal organ damage in SS. In particular, we demonstrate a genetic effect protecting against the development of cardiac fibrosis in salt-sensitive hypertension.

Benidipine Attenuates Glomerular Hypertension and Reduces Albuminuria in Patients with Metabolic Syndrome

Recent studies have shown that metabolic syndrome is associated with an increased risk for chronic kidney disease. We recently found that the prevalence of sodium-sensitive hypertension in patients with metabolic syndrome was significantly higher than that in patients with essential hypertension but without metabolic syndrome. We therefore assessed the effects of benidipine, a long-acting calcium channel blocker, on the sodium sensitivity of blood pressure and renal hemodymamics in 5 patients with metabolic syndrome. Glomerular hemodynamics were assessed using pressure-natriuresis curves, which were constructed by plotting the urinary excretion of sodium as a function of the mean arterial pressure, which was calculated as the mean of 48 values based on 24-h monitoring, during the intake of low (3 g NaCl daily) and relatively high (10 g NaCl daily) sodium diets. Under the relatively high sodium diet condition, benidipine significantly lowered systolic and diastolic blood pressure. The pressure-natriuresis curve was steeper after the administration of benidipine. Benidipine lowered glomerular capillary hydraulic pressure (P(GC)) levels (from 54.4+/-7.5 to 47.0+/-7.0 mmHg, p=0.0152) and reduced both the resistance of the afferent arterioles (from 10,338+/-2,618 to 9,026+/-2,627 dyn.s/cm5, p=0.047) and the resistance of the efferent arterioles (from 4,649+/-2,039 to 2,419+/-2,081 dyn.s/cm(5), p=0.003). The urinary albumin excretion rate also decreased after the administration of benidipine. These findings indicated that benidipine may be effective for reducing the risk of developing chronic kidney disease in patients with metabolic syndrome.

The effect of a shift in sodium intake on renal hemodynamics is determined by body mass index in healthy young men

A body mass index (BMI)>or=25 kg/m2 increases the risk for long-term renal damage, possibly by renal hemodynamic factors. As epidemiological studies suggest interaction of BMI and sodium intake, we studied the combined effects of sodium intake and BMI on renal hemodynamics. Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were measured in 95 healthy men (median age 23 years (95% confidence interval: 22-24), BMI: 23.0+/-2.5 kg/m2) on low (50 mmol Na+, LS) and high (200 mmol Na+, HS) sodium intake. Mean GFR and ERPF significantly increased by the change to HS (both P<0.001). During HS but not LS, GFR and filtration fraction (FF) positively correlated with BMI (R=0.32 and R=0.28, respectively, both P<0.01). Consequently, BMI correlated with the sodium-induced changes in GFR (R=0.30; P<0.01) and FF (R=0,23; P<0.05). The effects of HS on GFR and FF were significantly different for BMI>or=25 versus <25 kg/m2, namely 7.8+/-12.3 versus 16.1+/-13.1 ml/min (P<0.05) and -0.1+/-2.2 and 1.1+/-2.3% (P<0.05). FF was significantly higher in BMI>or=25 versus <25 kg/m2, (22.6+/-2.9 versus 24.6+/-2.4%, P<0.05) only during HS. ERPF was not related to BMI. Urinary albumin excretion was increased by HS from 6.0 (5.4-6.7) to 7.6 (6.9-8.9). Results were essentially similar after excluding the only two subjects with BMI>30 kg/m2. BMI is a determinant of the renal hemodynamic response to HS in healthy men, and of GFR and FF during HS, but not during LS. Consequently, HS elicited a hyperfiltration pattern in subjects with a BMI>or=25 kg/m2 that was absent during LS. Future studies should elucidate whether LS or diuretics can ameliorate the long-term renal risks of weight excess.

Evidence relating dietary sodium to cardiovascular disease

The expectation that dietary sodium intake might influence cardiovascular disease occurrence has been based upon its impact on blood pressure (BP). Solid experimental data confirms the ability of large (75-100 mmols/24 hours) changes in dietary sodium to reduce pressure by, on average, mid-low single digits. However, there is substantial inter-individual variation in BP response. In addition, sodium restriction generates other, sometimes undesirable effects, including increased insulin resistance, activation of the renin-angiotensin system, and increased sympathetic nerve activity. The health effects of salt restriction are, therefore, the sum of these recognized, and probably other unrecognized, intermediate effects. Ideally, salt restriction would be tested in a randomized clinical trial. In its absence, there are 9 observational studies linking baseline sodium intake, estimated by either 24 hour urine or dietary intake, to morbidity and mortality. The results have been inconsistent. The only study in hypertensive patients, there was an inverse relation of sodium to cardiovascular outcome. In a Japanese study, stroke incidence was increased among males with the highest salt intake. Two studies found a direct relation of sodium intake to cardiovascular mortality in an obese minority of the group studied. Taken together, these results suggest, not surprisingly given the genetic, behavioral, and environmental variety of humankind, that heterogeneity best describes the relation of sodium intake to cardiovascular morbidity and mortality. In short, the available data provides no support for any universal recommendation of a particular level of dietary sodium.

Proximal tubular function and salt sensitivity

Blood pressure response to changes in dietary salt intake is highly variable among individuals. This heterogeneity results from the combined effects of genetic and environmental determinants. In recent years, considerable progress has been made in our understanding of the pathogenic mechanisms leading to the development of salt-sensitive hypertension. Much information has come from the investigation of rare monogenic forms of salt-sensitive hypertension, which has focused attention on alterations of renal sodium handling occurring essentially in the distal nephron. In this paper, we review the experimental, clinical, genetic, and epidemiologic evidence suggesting that proximal tubular function is also an important determinant of the blood pressure response to salt, which deserves greater attention.

Effect of aerobic exercise training on blood pressure sensitivity to dietary sodium in older hypertensives

Although aerobic exercise training has been shown to lower blood pressure (BP) in older adults, its effect on BP sensitivity to dietary sodium (Na(+)) is unknown. Therefore, the present study was undertaken to examine the effect of aerobic exercise training on BP sensitivity to dietary Na(+) in older hypertensive individuals. Blood pressure was measured after 8 days of low (20 mEq) and high (200 mEq) Na(+) diets in 31 older (63+/-7 years, mean+/-standard deviation), hypertensive (152+/-11/88+/-5 mm Hg) individuals at baseline and following 6 months of aerobic exercise training (at 75% VO(2)max, 3 times/week, 40 min/session). Subjects were grouped on the basis of the difference in mean arterial BP (MAP) between diets (Na(+) sensitive: >or=5 mm Hg increase in MAP on high Na(+), n=20; Na(+) resistant: <5 mm Hg increase in MAP on the high Na(+) diet, n=11). Following 6 months of aerobic exercise training, there was a significant increase in maximal aerobic capacity (VO(2)max: 18.3+/-3.8 vs 20.7+/-4.2 ml/kg/min, P<0.017). Aerobic exercise training had a significant (P=0.02) effect on Na(+) sensitivity status, with the proportion of Na(+)-resistant individuals increasing from 35% at baseline to 61% following the 6-month aerobic exercise training programme. This study demonstrates the importance of physical activity on BP sensitivity to dietary Na(+).