Sodium balance in renal failure

Estimated 24-h urinary sodium excretion and risk of end-stage kidney disease

The association between sodium intake and long-term kidney disease endpoints is debated and yet to be proven. We aimed to investigate the associations of estimated 24-h urinary sodium excretion, reflecting daily sodium intake, with the incidence of end-stage kidney disease (ESKD). In this prospective cohort study including 444,375 UK Biobank participant, 865 (0.2%) ESKD events occurred after median follow-up of 12.7 years. For every 1 g increment in estimated 24-h urinary sodium excretion, multivariable-adjusted hazard ratio for incident ESKD was 1.09 (95% confidence interval 0.94-1.26). Nonlinear associations were not detected with restricted cubic splines. The null findings were confirmed by a series of sensitivity analyses, which attenuated potential bias from measurement errors of the exposure, regression dilution, reverse causality, and competing risks. In conclusion, there is insufficient evidence that estimated 24-h urinary sodium excretion is associated with the incidence of ESKD.

Nutrition and quality of life in chronic kidney disease patients: a practical approach for salt restriction

The clinical practice guidelines (CPGs) for nutrition in chronic kidney disease (CKD) were updated after 20 years from the previous guidelines by the Kidney Disease Outcomes Quality Initiative (KDOQI). During this period, the severity of CKD was defined by eGFR and albuminuria by the organization Kidney Disease: Improving Global Outcomes (KDIGO). Main risk factors for CKD such as hypertension, hyperlipidemia, obesity, metabolic syndrome, and diabetes mellitus are closely related to lifestyle. Nutritional management is important to prevent and retard the progression of CKD. Members of the International Society of Renal Nutrition and Metabolism (ISRNM) reviewed the KDOQI CPG draft. ISRNM is an international scientific society comprising members of multiple subspecialties. ISRNM proposed the medical term protein-energy wasting (PEW), which is a keyword in renal nutrition. The prevalence of PEW among dialysis patients is high. The success of dietary therapy depends on adherence to the diet. It has to be palatable, otherwise eating habits will not change. To prevent the development and progression of CKD and PEW, regular consultation with an expert dietitian is required, especially regarding salt and protein restriction. Our cluster-randomized trial showed that intervention by a dietician was effective at retarding the progression of stage 3 CKD. In this review, I focus on salt (sodium) restriction and introduce tips for salt restriction and Japanese kidney-friendly recipes. Due to the lack of randomized controlled trials, nutritional management of CKD inevitably relies on expert opinion. In this regard, well-designed observational studies are needed. Too strict salt restriction may decrease quality of life and result in PEW.

Validity of predictive equations for 24-h urinary sodium excretion at the population and individual levels among Chinese adults aged 18-69 years

Spot urine (SU) collection is a convenient method commonly used for sodium estimation, but its validity in predicting 24-h urinary sodium (24-hUNa) excretion has not been thoroughly evaluated among the general population. The aim of this study was to comprehensively assess the validity of eight existing methods in predicting 24-hUNa excretion by using SU samples among Chinese adults. We analyzed 1424 representative individuals aged 18 to 69 years. We compared the measured and estimated measurements of 24-hUNa at the population level by examining bias, the correlation, intraclass correlation coefficients (ICCs), receiver operating characteristic (ROC) curves and Bland–Altman plots and analyzed the relative and absolute differences and misclassification at the individual level. The bias for all methods was significant (all p < 0.001), among which the smallest bias was − 7.9 mmol for the Toft formula and the largest bias was − 53.8 mmol for the Mage formula. Correlation coefficients were all less than 0.380, all formulas exhibited an area under the ROC curve below 0.683, and the Bland–Altman plots indicated slightly high dispersion of the estimation biases at higher sodium levels regardless of the formula. The proportions of relative differences > 40% for the eight methods were all over one-third, the proportions of absolute differences > 51.3 mmol/24 h (3 g/day NaCl) were all over 40%, and the misclassification rates (7, 10, and 13 g/day NaCl as cutoff points) were all over 65%. Caution remains due to poor validity between estimated and actual measurements when using the eight formulas to obtain a plausible estimation for surveillance of the Chinese population sodium excretion, and the results do not support the application of SU to estimate sodium intake at the individual level due to its poor performance with respect to classification.

Total Body Sodium Balance in Chronic Kidney Disease

Excess sodium intake is a leading but modifiable risk factor for mortality, with implications on hypertension, inflammation, cardiovascular disease, and chronic kidney disease (CKD). This review will focus mainly on the limitations of current measurement methods of sodium balance particularly in patients with CKD who have complex sodium physiology. The suboptimal accuracy of sodium intake and excretion measurement is seemingly more marked with the evolving understanding of tissue (skin and muscle) sodium. Tissue sodium represents an extrarenal influence on sodium homeostasis with demonstrated clinical associations of hypertension and inflammation. Measurement of tissue sodium has been largely unexplored in patients with CKD. Development and adoption of more comprehensive and dynamic assessment of body sodium balance is needed to better understand sodium physiology in the human body and explore therapeutic strategies to improve the clinical outcomes in the CKD population.

High-Salt Diet Accelerated the Decline of Residual Renal Function in Patients With Peritoneal Dialysis

Objective: This study aims to investigate the relationship between dietary salt intake and residual renal function in peritoneal dialysis (PD) patients.

Methods: The daily salt intake of the patients was calculated based on a 3 day dietary record. Sixty-two patients were divided into three groups: 33 patients in the low salt intake group (salt intake <6.0 g/day), 17 in the medium salt intake group (salt intake 6.0 to <8.0 g/day), and 12 in the high salt intake group (salt intake ≥8.0 g/day). Regular follow-up was conducted every 3 months. Urine volume, peritoneal ultrafiltration volume, and other clinical indicators were recorded. Biochemical indexes were detected to evaluate the changes in residual renal function and peritoneal function during follow-up.

Results: A positive correlation between dietary sodium intake and sodium excretion was found. During 12-month follow-up, a decrease of residual renal function showed a significant difference among the three groups (p = 0.041) (15.3 ± 27.5 vs. 12.5 ± 11.5 vs. 32.9 ± 18.4 L/W/1.73 m² in the low-, medium-, and high salt intake groups, respectively). Consistently, a higher decline of residual renal function (adjusted β, 20.37; 95% CI, 2.83, 37.91) was found in participants with high salt intake (salt intake ≥8 g/day) compared with those in non-high salt intake.

Conclusion: Our study showed that the sodium excretion by peritoneal dialysis was positively correlated with dietary sodium intake in PD patients. The high salt intake diet (salt intake ≥8 g/day) may lead to a faster decline of residual renal function in PD patients.

Fluid assessment in dialysis patients by point-of-care magnetic relaxometry

Magnetic resonance imaging (MRI) is a powerful diagnostic tool, but its use is restricted to the scanner suite. Here, we demonstrate that a bedside nuclear magnetic resonance (NMR) sensor can assess fluid status changes in individuals at a fraction of the time and cost compared to MRI. Our study recruited patients with end-stage renal disease (ESRD) who were regularly receiving hemodialysis treatments with intradialytic fluid removal as a model of volume overload and healthy controls as a model of euvolemia. Quantitative T ₂ measurements of the lower leg of patients with ESRD immediately before and after dialysis were compared to those of euvolemic healthy controls using both a 0.28-T bedside single-voxel NMR sensor and a 1.5-T clinical MRI scanner. In the MRI data, we found that the first sign of fluid overload was an expanded muscle extracellular fluid (ECF) space, a finding undetectable at this stage using physical exam. A decrease in muscle ECF upon fluid removal was similarly detectable with both the bedside sensor and MRI. Bioimpedance measurements performed comparably to the bedside NMR sensor but were generally worse than MRI. These findings suggest that bedside NMR may be a useful method to identify fluid overload early in patients with ESRD and potentially other hypervolemic patient populations.

Changes in Total Sodium Intake Do Not Lead to Proportionate Changes in Total Sodium Removal in CAPD Patients

Background

Dietary salt and fluid restriction is important in controlling fluid balance in patients on continuous ambulatory peritoneal dialysis (CAPD). However, it is often difficult to monitor patients’ dietary total sodium intake (TSI). Usually, total sodium removal (TSR), the sum of urinary sodium removal (USR) and dialysate sodium removal (DSR), is suggested to represent TSI. In the present study, we investigated the reliability of using TSR as a surrogate to TSI in CAPD patients.

Methods

40 clinically stable CAPD patients were closely followed for 3 months. Their TSI, USR, DSR, and fluid status were measured twice: at baseline and at the end of this study respectively. Fluid status was evaluated by bioimpedance analysis. Patients with increased sodium intake (group ISI) or decreased sodium intake (group DSI) (both >0.5 g/day or >21.74 mmol/day elemental sodium) were included in this study.

Results

There were 15 patients in group ISI and 9 patients in group DSI. During the follow-up, although TSI increased in group ISI and decreased in group DSI ( p < 0.05), there were no significant changes in USR, DSR, or TSR in either group. No relationship was found between TSI and TSR. Changes in weight, blood pressure, urine volume, ultra-filtration, and small solute removal (Kt/V and creatinine clearance) were not statistically significant between the two groups. Fluid status deteriorated in group ISI and improved in group DSI ( p < 0.05).

Conclusions

Our study suggests that changes in total sodium intake do not lead to proportionate changes in total sodium removal in CAPD patients. Therefore, TSR (the sum of USR and DSR) should be used cautiously to monitor TSI in this patient population.

Association of 24-Hour Blood Pressure With Urinary Sodium Excretion in Healthy Adults

BACKGROUND

While the positive relationship between urinary sodium excretion and blood pressure (BP) is well established for middle-aged to elderly individuals using office BP, data are limited for younger individuals and ambulatory BP measurements.

METHODS

Our analysis included 2,899 individuals aged 18 to 90 years from 2 population-based studies (GAPP, Swiss Kidney Project on Genes in Hypertension [SKIPOGH]). Participants with prevalent cardiovascular disease, diabetes, or on BP-lowering treatment were excluded. In SKIPOGH, 24-hour urinary sodium excretion was used as a measure of sodium intake, while in GAPP it was calculated from fasting morning urinary samples using the Kawasaki formula. Multivariable linear regression models were used to assess the relationships of 24-hour urinary salt excretion with office and ambulatory BP measurements.

RESULTS

Mean age, ambulatory BP, sodium excretion, and estimated glomerular filtration rate in GAPP and SKIPOGH were 35 and 44 years, 123/78 and 118/77 mm Hg, 4.2 and 3.3 g/d, and 110 and 99 ml/min/1.73 m2, respectively. A weak linear association was observed between 24-hour ambulatory systolic BP and urinary sodium excretion (β (95% confidence interval [CI]) per 1 g increase in sodium excretion (0.33 % (0.09; 0.57); P = 0.008). No significant relationships were observed for 24-hour ambulatory diastolic BP (β (95% CI) (0.13 % (-0.15; 0.40) P = 0.37). When repeating the analyses in different age groups, all BP indices appeared to have stronger relationships in the older age groups (>40 years).

CONCLUSIONS

In these large cohorts of healthy adults, urinary sodium excretion was only weakly associated with systolic 24-hour ambulatory BP.

Sodium Homeostasis in Chronic Kidney Disease

The pathologic consequences of sodium retention in the CKD population can lead to hypertension, edema, and progressive disease. Sodium excess is responsible for increases in oxidative stress, which alters kidney vasculature. As progression of CKD occurs, hyperfiltration by remaining nephrons compensates for an overall decrease in the filtered load of sodium. In the later stages of CKD, compensatory mechanisms are overcome and volume overload ensues. Nephrotic syndrome as it relates to sodium handling involves a different pathophysiology despite a common phenotype. Extrarenal sodium buffering is also examined as it has significant implications in the setting of advanced CKD.

Effect of Food Intake on the Pharmacodynamics of Tenapanor: A Phase 1 Study

Tenapanor (RDX5791/AZD1722) is a minimally systemic small-molecule inhibitor of the sodium/hydrogen exchanger NHE3. Tenapanor acts in the gut to reduce absorption of sodium and phosphate. This phase 1 open-label, 3-way crossover study (NCT02226783) evaluated the effect of food on the pharmacodynamics of tenapanor. Eighteen volunteers completed a randomized sequence of three 4-day treatments with tenapanor hydrochloride 15 mg twice daily: before food, after food, and while fasting. Participants received a diet standardized for sodium content. Stool sodium was significantly higher with tenapanor administration before versus after food (difference, +8.8 mmol/day, P = .006) or while fasting (+11.8 mmol/day, P = .0004). Differences in urinary sodium were not significant. Stool phosphorus was not significantly different with tenapanor before versus after food and significantly higher before food versus while fasting (+4.9 mmol/day, P = .006). Urinary phosphorus was significantly lower when tenapanor was administered before (-3.9 mmol/day, P = .0005) or after food (-3.7 mmol/day, P = .0009) versus while fasting. No serious adverse events were reported. These data suggest the effect of tenapanor on sodium absorption is most pronounced when administered before meals, whereas the effect on phosphate is similar whether administered before or after meals. This may support different timings of tenapanor administration with respect to food for sodium- and phosphate-related indications.

Determination of extracellular fluid volume in healthy and azotemic cats

BACKGROUND

Methods for determining extracellular fluid volume (ECFV) are important clinically for cats. Bromide dilution has been studied in cats to estimate ECFV. Markers of GFR also distribute in ECFV and can be used for its measurement.

HYPOTHESIS/OBJECTIVES

The primary objective was to develop a method of determining ECFV from iohexol clearance in cats and evaluate agreement with that determined using bromide dilution. Additional objectives were to compare ECFV between azotemic and nonazotemic cats and evaluate appropriate methods of standardizing ECFV.

ANIMALS

Client-owned cats with varying renal function.

METHODS

Validation of ECFV determined from slope-intercept iohexol clearance was performed in 18 healthy nonazotemic cats. ECFV was then determined using the validated method and bromide dilution and agreement assessed. Appropriateness of standardization to body weight (BW) and body surface area (BSA) was evaluated.

RESULTS

Extracellular fluid volume determined from slope-intercept iohexol clearance and bromide dilution was 0.84 ± 0.32 L and 0.85 ± 0.19 L (mean ± SD), respectively. There were wide limits of agreement between the methods (-0.58 to 0.54 L) and therefore, agreement was considered to be poor. ECFV did not differ significantly between azotemic and nonazotemic cats (P = .177). BSA was found to be the best method for standardizing ECFV measurement in cats.

CONCLUSIONS AND CLINICAL IMPORTANCE

This study developed a method for determining ECFV from slope-intercept iohexol clearance which provides simultaneous assessment of renal function and an estimate of ECFV. ECFV does not differ between azotemic and nonazotemic cats, which suggests fluid volume loss or overload is not an important clinical feature in cats with mild chronic kidney disease.

Estimating 24-hour urine sodium level with spot urine sodium and creatinine

The 24-hr urine sodium excretion level was estimated based on the spot urine sodium, and the efficacy of the formula was validated to determine the status of low salt intake <100 mEq Na/day. The 24-hr urine samples were collected from 400 patients. The 24-hr urine creatinine level was estimated with the use of three formulas: a newly derived Korean equation (E24UCR_K), and Tanaka (E24UCR_T) and Cockcroft-Gault (E24UCR_CG) equations. The correlation coefficients between the estimated and measured 24-hr urine creatinine for these three equations were 0.863, 0.846, and 0.896, respectively (All P<0.001). After estimating the 24-hr urine sodium levels, the correlation coefficients between the estimated and measured 24-hr urine sodium levels were 0.466, 0.490, and 0.516, respectively (All P<0.001). The sensitivity of three formulas to estimate the measured 24-hr urine sodium≥100 mEq/day using the estimated amount≥100 mEq/day was 84.3%, 87.6%, and 84.8%, respectively. In conclusion, the three equations used to estimate the 24-hr urine sodium content were useful to determine the status of low salt intake.

Influence of weather conditions, drugs and comorbidities on serum Na and Cl in 13000 hospital admissions: evidence for a subpopulation susceptible for SIADH

OBJECTIVES

Considerable variation in serum sodium (Na) and chloride (Cl) is found in patients at hospital admission. Our goal was to quantify the respective impact of drugs, comorbidities, demographic factors and weather conditions on serum Na and Cl.

DESIGN AND METHODS

For 13277 consecutive patients without terminal kidney disease admitted to the Department of Internal Medicine of the Kantonsspital St. Gallen drug history on admission, age, sex, body weight, ICD-10 diagnoses, and laboratory data were extracted from electronic medical records. Weather parameters prior to hospital admission were also integrated in a multivariate regression analysis.

RESULTS

Both serum Na and Cl showed an asymmetric left-tailed distribution. Median (interquartile range) Na was 138 (136/140) and Cl 104 (101/106). The distribution of sodium in patients with one or more risk factors for SIADH was best explained by the presence of two populations: one population with a similar distribution as the unexposed patients and a smaller population (about 25%) shifted to lower sodium levels. Lower weight, lower blood pressure, kidney dysfunction, fever, and diabetes were associated with both lower Na and Cl. Higher ambient temperature and higher air humidity preceding admission were associated with both higher Na and Cl values.

CONCLUSIONS

Na and Cl at hospital admission are highly influenced by ambient weather conditions, comorbidities and medication. The bimodal distribution of Na and Cl in persons exposed to risk factors for SIADH suggests that SIADH may only affect a genetically distinct vulnerable subpopulation.

Primary molecular disorders and secondary biological adaptations in bartter syndrome

Bartter syndrome is a hereditary disorder that has been characterized by the association of hypokalemia, alkalosis, and the hypertrophy of the juxtaglomerular complex with secondary hyperaldosteronism and normal blood pressure. By contrast, the genetic causes of Bartter syndrome primarily affect molecular structures directly involved in the sodium reabsorption at the level of the Henle loop. The ensuing urinary sodium wasting and chronic sodium depletion are responsible for the contraction of the extracellular volume, the activation of the renin-aldosterone axis, the secretion of prostaglandins, and the biological adaptations of downstream tubular segments, meaning the distal convoluted tubule and the collecting duct. These secondary biological adaptations lead to hypokalemia and alkalosis, illustrating a close integration of the solutes regulation in the tubular structures.

Time-dependent associations between total sodium removal and mortality in patients on peritoneal dialysis

PURPOSE

To determine if the time-dependent association between total sodium removal and mortality in patients on continuous ambulatory peritoneal dialysis (CAPD) is confounded by markers of diet and nutrition.

METHODS

The study enrolled 305 incident patients who started CAPD between July 2002 and February 2007. All patients were followed until death or censoring in February 2008. Demographics, blood pressure, and markers of volume and inflammation were collected at baseline. Biochemistry, fluid and solute removal, and diet and nutrition parameters were collected quarterly and thus calculated as time-averaged values.

RESULTS

Mean age of the study patients was 59.4 years, 42.3% were men, and 40.3% had diabetes. During the 31.4-month follow-up, 74 patients died. The time-averaged daily total sodium removal (TSR) in the overall cohort was 2.67 g (range: 2.02 g-3.47 g). Participants with a high time-averaged TSR tended to experience higher fluid, sodium, urea, and creatinine removal, mainly as a result of better residual renal function (RRF). They also had a higher nutrient intake and a higher lean body mass. Time-dependent TSR was an independent predictor of death, including when adjusted for age, Charlson index, time-dependent hemoglobin, RRF, and peritoneal transport rate (hazard ratio: 0.84; 95% confidence interval: 0.70 to 1.00; p=0.05), but the predictive effect disappeared in multivariate models after further individual adjustment for time-dependent total energy intake, total protein intake, serum albumin, and lean body mass. By contrast, the predictive effect did not disappear if the only adjustment was for time-dependent RRF.

CONCLUSIONS

The time-dependent association between TSR and mortality in patients on peritoneal dialysis can be largely explained by diet and nutrition parameters.

Chronic kidney disease: a large-scale population-based study of the effects of introducing the CKD-EPI formula for eGFR reporting

Objective To evaluate the effects of introducing the Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) formula for estimated glomerular filtration rate (eGFR) reporting in the adult population in routine clinical practice with clinician-directed testing. Design Retrospective study of all creatinine measurements and calculation of eGFRs using Modification of Diet in Renal Disease (MDRD) and CKD-EPI formulae. Setting General population, Oxfordshire, UK. Participants An unselected population of around 660 000. Interventions Reporting of eGFRs using MDRD or CKD-EPI formulae. Primary and secondary outcome measures Evaluation of the effects of the CKD-EPI formula on the prevalence of different stages of chronic kidney disease (CKD). Results The CKD-EPI formula reduced the prevalence of CKD (stages 2-5) by 16.4% in patients tested in primary care. At the important stage 2-stage 3 cut-off, there was a relative reduction of 7.5% in the prevalence of CKD stages 3-5 from 15.7% to 14.5%. The CKD-EPI formula reduced the prevalence of CKD stages 3-5 in those aged <70 but increased it at ages >70. Above 70 years, the prevalence of stages 3-5 was similar with both equations for women (around 41.2%) but rose in men from 33.3% to 35.5%. CKD stages 4-5 rose by 15% due exclusively to increases in the over 70s, which could increase specialist referral rates. The CKD classification of 18.3% of all individuals who had a creatinine measurement was altered by a change from the MDRD to the CKD-EPI formula. In the UK population, the classification of up to 3 million patients could be altered, the prevalence of CKD could be reduced by up to 1.9 million and the prevalence of CKD stages 3-5 could fall by around 200 000. Conclusions Introduction of the CKD-EPI formula for eGFR reporting will reduce the prevalence of CKD in a primary care setting with current testing practice but will raise the prevalence in the over 70s age group. This has implications for clinical practice, healthcare policy and current prevalence-based funding arrangements.

Low dietary sodium intake increases the death risk in peritoneal dialysis

BACKGROUND AND OBJECTIVES

To explore the correlation between dietary sodium intake and cardiovascular and overall mortality, and then determine whether this correlation can be explained by protein and energy intake paralleled with sodium intake in dialysis patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This single-center retrospective cohort study enrolled 305 incident patients who started peritoneal dialysis in our unit from July 2002 to February 2007. All patients were followed until death or until being censored in February 2008. Demographic data were collected at baseline. Biochemical, dietary, and nutrition data were examined at baseline and thereafter at regular intervals to calculate the average values throughout the study.

RESULTS

Participants with the highest average sodium intake were more likely to be younger, male, and overweight. Patients in the high tertile of average sodium intake had higher albumin, prealbumin, and lean body mass levels, and more nutrient intakes paralleling with sodium intake. Low average sodium intake independently predicted the increased risk for overall and cardiovascular death after adjusting for recognized confounders. Further adjustment for dietary protein, energy, and other nutrient intakes individually had minimal impact on the association between average sodium intake and overall death, with hazard ratios varying between 0.35 and 0.44, and cardiovascular death, with hazard ratios varying between 0.06 and 0.11.

CONCLUSIONS

This study revealed that low dietary sodium intake independently predicts the high overall and cardiovascular mortality in dialysis patients. This correlation could not be entirely explained by deficient protein and energy intake.

Treatment of hypertension in patients with diabetes: lessons from recent trials

Hypertension plays a critical role in causing a high rate of cardiovascular events in patients with diabetes mellitus. Large trials show that lowering blood pressure in the patient with diabetes who has hypertension has profoundly favorable effects. This review discusses recent trials to answer the question of how low patients' blood pressure should go and which agents should be used to achieve this goal. The National Institutes of Health's guidelines, published in the Sixth Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure, call for a blood pressure goal of <130/85 mmHg in patients with diabetes. Based on data from the recent trials, an even lower blood pressure of <130/80 mmHg in patients with diabetes and hypertension appears to be appropriate. Observational studies show that the lowest cardiovascular event rate is observed in patients with diabetes whose systolic blood pressure is <120 mmHg. Thus, goal blood pressure in patients with diabetes who have hypertension may need to be revised lower, to <120/80 mmHg. In patients with overt proteinuria of 1 g/d or more, mean arterial pressure of <92 mmHg is recommended. Available evidence justifies the use of angiotensin-converting enzyme (ACE) inhibitors as first-line agents and angiotensin receptor blockers in those patients who are intolerant to ACE inhibitors. Because the blood pressure goal is lower in patients with diabetes who are hypertensive, these patients require the use of multiple agents. Diuretics or long-acting calcium channel blockers are logical second choices because of their synergistic blood pressure reduction effect observed with ACE inhibitors. Alpha-blockers should be used with caution, however. In patients with renal disease, loop diuretics may be required to reduce sodium and volume overload and to improve blood pressure control.

Antihypertensive therapy and progression of chronic renal disease

This paper reviews findings on the relationship between blood pressure control and the progression of renal disease. Experimental studies demonstrate a correlation between systemic blood pressure and histologic glomerular injury and the delay in progression of renal disease with antihypertensive therapy, particularly with angiotensin-converting enzyme inhibitors. Recent clinical findings are reviewed, including epidemiologic data linking hypertension to subsequent renal disease, and clinical studies showing a beneficial effect on progression of renal disease with lower than usual blood pressure targets.

Indices of activity of the nitric oxide system in hemodialysis patients

Arginine deficiency and/or increased levels of circulating nitric oxide (NO) synthesis (NOS) inhibitors can cause reduced NOS, which may contribute to hypertension in patients with end-stage renal disease (ESRD). To test these hypotheses, NO oxidation products (NO(2) + NO(3) = NO(x)) and cyclic guanosine monophosphate (cGMP), the vasodilatory second messenger of NO, were measured in the blood, urine, and dialysate effluent of hemodialysis (HD) patients and compared with the blood and urine of healthy subjects. The subjects ate a controlled low-nitrate diet (approximately 330 micromol/d) for 48 hours before and during blood, dialysis effluent, and 24-hour urine collection. NO(x) output was significantly reduced in HD patients versus controls (552 +/- 51 v 824 +/- 96 micromol/24 h; P < 0.001), whereas cGMP output was not low versus controls. Plasma arginine level was normal and plasma levels of citrulline and the endogenous NOS inhibitor, asymmetric dimethylarginine (ADMA), were markedly elevated in patients with ESRD versus controls. Systolic blood pressure was greater in HD patients compared with controls despite concurrent antihypertensive therapy in most patients with ESRD. These studies suggest NO production is low in patients with ESRD undergoing HD, possibly because of the increased ratio of plasma ADMA to arginine.