Sublethal X-irradiation during acute puromycin nephrosis prevents late renal injury: role of macrophages

Acute puromycin aminonucleoside (PA) nephrosis is associated with a surge in the glomerular macrophage number. Whole body X-irradiation (XI) was used to assess whether bone marrow depression, which depletes normal rat glomeruli of macrophages, is efficacious in ameliorating progressive glomerular disease. A solitary, sublethal dose of XI (600 rad) was administered 3 days after PA delivery to rats (PA/XI) that were followed for 18 wk. In contrast to a sham-irradiated nephrotic cohort (PA/Sham), the PA/XI rats had a complete prevention of the recurrent albuminuria and manifested a significant reduction in the percent of glomeruli exhibiting glomerulosclerosis (GS) lesions at 18 wk after PA. XI significantly reduced the glomerular and interstitial macrophage number as well as the circulating white blood and monocyte counts during peak albuminuria. This protection was independent of the magnitude of the acute albuminuria and elevations in the circulating lipid levels. These data show that whole body XI delivered during acute nephrosis is capable of preventing progressive glomerular disease in association with a reduction in the glomerular and interstitial macrophage number. Additionally, this study suggests that this immune effector cell is important in mediating the propagation of initial glomerular injury to GS.

Glomerular tumor necrosis factor and interleukin 1 during acute aminonucleoside nephrosis. An immunohistochemical study

Acute aminonucleoside nephrosis progresses to glomerulosclerosis. The mechanisms for this phenomenon are not entirely known. Our objectives were to identify macrophage (m phi)-derived peptide growth factors (i.e., tumor necrosis factor and interleukin 1), using immunohistochemical means, in glomeruli of rats with acute aminonucleoside nephrosis. Recently, a role for glomerular m phi s has been suggested as one of the possible mechanisms responsible for this transition from acute glomerular injury to glomerulosclerosis. Since peptide growth factors are elaborated by m phi s and produce alterations in mesangial cell proliferation and protein biosynthesis, we investigated whether these cytokines were present in glomeruli during aminonucleoside nephrosis, which has been typically regarded as a nonimmune toxic glomerulopathy. Fourteen days after puromycin aminonucleoside (PA) delivery, nephrotic control rats (PA/control) and nephrotic animals that had been maintained on an essential fatty acid-deficient (EFAD) diet (PA/EFAD) for 8 weeks before PA, manifested cytoplasmic tumor necrosis factor and interleukin 1 within cells located in the glomerular mesangium as detected by immunohistochemical means. Despite equivalent levels of albuminuria and fasting total cholesterol during peak nephrosis, the PA/EFAD rats had significant reductions in the number of tumor necrosis factor-positive glomerular cells (1.8 +/- 0.1 versus 8.5 +/- 0.4, p less than .001) and interleukin 1-positive glomerular cells (1.5 +/- 0.1 versus 7.2 +/- 0.5, p less than .001) in comparison with the PA/control group. These data correlated with a reduction in the number of ED-1-positive cells (i.e. glomerular m phi s) in glomeruli of PA/EFAD animals as compared with PA/control rats (2.2 +/- 0.3 versus 10.9 +/- 1.4, p less than .001), suggesting that m phi-derived peptide growth factors may be important determinants in initiating a pathobiologic sequence culminating in glomerulosclerosis in this model.

Irreversible tubulointerstitial damage associated with chronic aminonucleoside nephrosis. Amelioration by angiotensin I converting enzyme inhibition

Chronic aminonucleoside nephrosis is variably associated with tubulointerstitial damage, depending on the route and frequency of drug administration. Recently, different groups have shown this injurious tubulointerstitial process to be reversible, coinciding with the resolution of heavy proteinuria to normal values. The authors have previously shown that a single jugular intravenous administration of puromycin aminonucleoside (PA) to male Munich-Wistar rats produces a triphasic pattern of glomerular injury and proteinuria, which culminates in focal glomerulosclerosis 70 weeks after drug administration. The authors now report the later progression of the tubulointerstitial morphologic abnormalities associated with acute nephrosis (phase I), despite spontaneous resolution of glomerular injury during the intermediate period (phase II) in this model. Although treatment of rats with the angiotensin I converting enzyme inhibitor enalapril (50 mg/l drinking water) over the 70-week period did not affect the magnitude of proteinuria during the acute nephrotic phase, enalapril prevented the recurrence of proteinuria (phase III), as well as significantly reducing the severity of interstitial fibrosis, extent of tubular dilatation, and number of intratubular casts on semiquantitative scoring at the conclusion of the study. In addition, enalapril-treated rats had less low-molecular-weight protein excretion during the recurrent phase of proteinuria, suggesting a preservation of tubular functional capacity to reabsorb these proteins. In vitro cytotoxicity studies showed only the glomerular visceral epithelial cell to be sensitive to PA, in contrast with rat tubular epithelium and other cellular controls. Although the exact pathogenetic mechanism responsible for the development of the tubulointerstitial damage remains unknown, PA in vitro does not adversely affect rat tubular epithelium; there is however a clear correlation between the magnitude of recurrent proteinuria and the severity of tubulointerstitial morphologic abnormalities, as suggested by the beneficial effect of converting enzyme inhibition on both of these untoward processes.

Cholestyramine resin ameliorates chronic aminonucleoside nephrosis

We chose to assess the role of cholesterol reduction in chronic aminonucleoside nephrosis by pharmacologically lowering serum cholesterol with cholestyramine. Two groups of rats were made nephrotic with a single intravenous dose of puromycin aminonucleoside (PA): one group (PA/resin) received 5% (w:w in diet) cholestyramine resin and the dietary control group (PA/cell) received 5% cellulose. Cholestyramine-treated rats demonstrated significant functional and histological protection. Recurrent proteinuria was significantly lower in PA/resin animals. Whole-kidney glomerular filtration rate in the PA/resin group was preserved at a level equivalent to normal age-matched control rats whereas the PA/cell group had a significantly lower value than did the normal animals. The extent of segmental glomerulosclerosis 24 wk after PA delivery was significantly lower in the PA/resin group. These results suggest a role for hyperlipidemia as one of the mechanisms involved in the pathogenesis of progressive glomerular disease.

Effects of dietary interventions on glomerular pathophysiology

Numerous dietary interventions have been utilized to modify the course of and further elucidate the pathophysiological processes involved in experimental progressive glomerulopathy. Alterations in dietary constituents can affect the glomerular capillary hemodynamic parameters, the permselectivity features of the filtration apparatus, as well as the morphology and function of resident glomerular cells and influxing bone marrow-derived monocytes. The three dietary modifications examined in this review are protein restriction, dietary cholesterol supplementation, and essential fatty acid deficiency. These maneuvers have been chosen from the myriad dietary interventions in the experimental and clinical literature and are not meant to be all inclusive. The implementation of these three dietary modifications, in experimental models of glomerular disease, amply demonstrate the concept of a stratified alteration in glomerular structure and function. Since perturbed glomerular pathobiology, involving the above-mentioned structures and cell types, is believed to contribute to progressive glomerulopathy, a review of these seemingly diverse, yet perhaps, interrelated responses to dietary modifications will only aid us in understanding this process.

Essential fatty acid deficiency during acute puromycin nephrosis ameliorates late renal injury

Puromycin aminonucleoside (PA) nephrosis is associated with a significant increase in the glomerular macrophage number during peak proteinuria. The significance of this observation remains uncertain. An essential fatty acid-deficient (EFAD) diet depletes normal rat glomeruli of resident macrophages and alters glomerular eicosanoid metabolism. In this study, we found that an EFAD diet, administered only for the duration of the acute nephrotic phase, significantly ameliorated the recurrent albuminuria, renal dysfunction, and morphological injury characteristic of the late, recurrent phase of chronic aminonucleoside nephrosis. Glomerular macrophage number, isolated glomerular thromboxane B2 production, and circulating leukocyte and monocyte counts were significantly reduced in nephrotic rats on the EFAD diet 2 wk after PA injection, which temporally corresponds to peak albuminuria. The exact mechanism(s) by which the EFAD diet conferred protection in the late phase of chronic aminonucleoside nephrosis and lowered glomerular macrophage number during the acute nephrotic phase remain to be elucidated.

Hyperlipidemia of nephrosis: pathophysiologic role in progressive glomerular disease

During the past few years, the increasing speculation that the hyperlipidemia of nephrosis may be one of several pathogenic mechanisms involved in the progression of initial glomerular injury to glomerulosclerosis has generated many clinical and experimental investigations. This discussion reviews pertinent studies that address two major issues. First, the underlying pathophysiologic mechanisms involved in the development of the hyperlipidemia of nephrosis are explored. Second, this article examines recent studies that investigate how this secondary hyperlipidemia may further aggravate initial glomerular injury and contribute to a progressive glomerulopathy, primarily mediated through alterations in monocyte/macrophage function.

Altered functional characteristics of rat macrophages during nephrosis. Synergistic effects of hypercholesterolemia

The effects of alimentary hypercholesterolemia and nephrotic hyperlipidemia, alone and in combination, on rat peritoneal macrophage phagocytosis, basal eicosanoid production, and glomerular macrophage number during peak PA nephrosis were evaluated in rats fed four different diets: 1) normal/standard chow; 2) PA/standard chow; 3) normal/cholesterol-supplemented diet; and 4) PA/cholesterol-supplemented diet. Both PA/standard chow and normal/cholesterol-supplemented rodent groups manifested significantly greater peritoneal macrophage phagocytosis and glomerular macrophage number when compared with normal/standard chow animals. However, the combination of the nephrotic state with superimposed alimentary hypercholesterolemia (PA/cholesterol-supplemented group) produced the greatest rise in these parameters, a rise that was significantly greater than was produced in the three other groups. Regarding basal eicosanoid production by macrophages, there was a numerical trend toward increased production of thromboxane B2 in the PA/standard chow animals and normal/cholesterol-supplemented rats when compared with normal/standard chow. Again, the combination of nephrosis and alimentary hypercholesterolemia in the PA/cholesterol-supplemented group was associated with a significantly greater amount of thromboxane B2 generated when compared with the other three groups. Regarding PGE2 production, there were no significant differences among the groups, despite marked differences in fasting serum lipid levels. This data suggest that there is a synergistic effect between alimentary hypercholesterolemia and the secondary hyperlipidemia of nephrosis in producing these macrophage functional alterations. Because fasting triglyceride values between the two nephrotic groups were indifferent, one can further speculate that it is the elevation of the serum cholesterol value that predominantly evokes these changes in macrophage function.

Mechanisms underlying transition from acute glomerular injury to late glomerular sclerosis in a rat model of nephrotic syndrome

Functional and morphologic measurements were performed in Munich-Wistar rats after a single central venous injection of puromycin aminonucleoside (PA) or saline vehicle (sham). During phase I, PA rats exhibited overt nephrotic syndrome and impaired glomerular filtration, primarily due to a reduction in the glomerular capillary ultrafiltration coefficient. The morphologic counterpart of the latter consisted of effacement of glomerular epithelial cell foot processes and decrease in the number of filtration slit diaphragms. Administration of the angiotensin I converting enzyme inhibitor (CEI) enalapril to PA rats did not ameliorate glomerular dysfunction. During phase II, PA rats exhibited spontaneous resolution of proteinuria, impaired function, and morphologic abnormalities. However, PA rats now demonstrated marked glomerular capillary hypertension and continued, albeit lesser, reductions in the ultrafiltration coefficient. Concurrent CEI administration modestly lowered systemic arterial pressure, and normalized the glomerular capillary hydraulic pressure and ultrafiltration coefficient. Additional rats were studied during phase III, 70 wk after injection. In PA rats, prior glomerular hypertension was associated with development of recurrent proteinuria and extensive glomerular sclerosis, whereas concurrent CEI administration limited these parameters to values comparable to those in sham rats. Glomerular hypertension thus may explain the development of glomerular sclerosis and renal failure long after an episode of acute glomerular injury.

Urinary parameters to assess renal function

Acute suppression of renal function has a multitude of etiologies. This review discusses the pathophysiologic basis, usefulness, and limitations of the commonly utilized urinary function parameters as well as some miscellaneous tests to properly diagnose specific disorders.

Focal and segmental glomerulosclerosis: analogies to atherosclerosis

In summary, both the developing atherosclerotic and FSGS lesions seem to share certain postulated pathophysiologic mechanisms, including endothelial cell injury, macrophage infiltration, hyperlipoproteinemia, and hypertension. As depicted in Figure 1, any initial glomerular injury results in flux of macromolecular substances into the glomerular mesangium. As an adjunct to increased glomerular barrier dysfunction, hyperlipoproteinemia is believed to secondarily develop from the dramatic losses of albumin, stimulating increased hepatic lipoprotein synthesis and the loss of lipoprotein lipase-activating substance into the urine which would effectively produce a reduction in circulating chylomicra and triglyceride catabolism. Certain elevated circulating lipoproteins could, theoretically, pass through the damaged glomerular filter into the mesangium, thereby enhancing the flux of macromolecules. Also associated with certain experimental glomerular disorders is the development of glomerular hypertension, as manifested by an elevated glomerular capillary hydrostatic pressure (PGC), which can further augment macromolecular flux into the mesangium. Overloading of the glomerular mesangium by the above mechanisms is believed to be an injurious stimulus for MC to both proliferate and produce excess mesangial matrix substance. Both of these events are thought to be pathologic harbingers of glomerulosclerosis. Glomerular hypertension is also capable of damaging endothelial cells within the glomerular microcirculation, and this purportedly can activate platelets and result in glomerular thrombosis. At present, it is unclear how glomerular thrombosis produces increased mesangial cell injury; however, this process is believed to cause both systemic and glomerular hypertension which may serve as intermediary mechanisms producing the untoward effects of mesangial cell proliferation and matrix overproduction.

Exacerbation of chronic aminonucleoside nephrosis by dietary cholesterol supplementation

Abnormalities in lipid metabolism resulting from nephrotic syndrome may play a role in the progression of initial glomerular injury to focal and segmental glomerulosclerosis (FSGS). In order to more specifically assess this, we fed male Sprague-Dawley rats, made nephrotic with a single intravenous injection of puromycin aminonucleoside (PA), either normal rodent chow (Group 1) or the same formulation supplemented with 4% cholesterol/1% cholic acid (Group 2). This 4% cholesterol/1% cholic acid-added diet was utilized because, in normal, non-nephrotic rats, this alimentary supplement produces, for the most part, only a significant rise in fasting serum cholesterol and not fasting serum triglycerides. FSGS developed 18 weeks after PA delivery, and both groups of rats were studied functionally and morphologically. Group 2 rats had significantly higher daily urine protein excretion, lower inulin clearance, and greater blood urea nitrogen concentrations than Group 1 animals. Histologically, Group 2 animals demonstrated a significantly greater percentage of glomeruli examined with segmental areas of glomerulosclerosis/hyalinosis, mesangial cell proliferation, and mesangial "foam" cells. At 2, 4, 12, and 18 weeks after PA delivery, the fasting serum cholesterol was always significantly greater in Group 2 rats, whereas in regards to fasting serum triglycerides it was only significantly elevated in Group 2 rats at 4 and 12 weeks after PA administration.

Ameliorative effects of dietary protein restriction in chronic aminonucleoside nephrosis

Because many investigators have demonstrated the efficacy of dietary protein restriction in various experimental models of glomerular injury that progress to focal and segmental glomerulosclerosis (FSGS), we used this dietary maneuver in chronic aminonucleoside nephrosis. This model of glomerular disease, which uses a single intravenous injection of the puromycin aminonucleoside (PAN), slowly progresses over 18 weeks with mesangial cell proliferation and FSGS as the pathologic hallmarks. We performed renal functional and histopathologic studies in 21 rats with chronic aminonucleoside nephrosis. Group 1 rats (n = 10) were fed a standard rodent diet containing 23.4% protein, whereas group 2 animals (n = 11) were maintained with a 6% protein diet replete with electrolytes, minerals, and vitamins. In those animals subjected to dietary protein restriction, proteinuria was significantly reduced at 14, 28, 84, and 126 days after PAN administration. In rats maintained with the 6% protein diet at 126 days after PAN delivery, there was also a significant reduction in the percent of glomeruli with segmental areas of glomerulosclerosis or hyalinosis and mesangial cell proliferation. We conclude that the renal functional and histologic consequences of chronic aminonucleoside nephrosis can be blunted by dietary protein restriction.

Focal and segmental glomerulosclerosis following a single intravenous dose of puromycin aminonucleoside

Focal and segmental glomerulosclerosis (FSGS) represents a final pathologic pattern of a number of human renal disorders. Among laboratory models, repeated intraperitoneal injections of the aminonucleoside of puromycin (PA) produces a histologic pattern not unlike the human process. A single intravenous dose of this drug usually results in glomerular morphologic changes in rats resembling those in human nephrotic syndrome with minimal changes. This report describes acute and chronic glomerular injury that begins as early as 8 days after a single central administration of PA and progresses to FSGS within an 18-week period. It seems likely that minimal change disease and FSGS are two pathologic processes in the same continuum of disease. In this model, the severity and persistence of the glomerular lesion may represent irreversible glomerular epithelial cell (GEC) injury secondary to the toxic effects of PA.

A role for oxygen free radicals in aminonucleoside nephrosis

The cellular processes responsible for the proteinuria induced by the aminonucleoside of puromycin (PA) remain inadequately defined. Hypoxanthine is both a metabolic breakdown product of PA as well as a substrate for xanthine oxidase, which catalyzes its enzymatic conversion to xanthine and uric acid, yielding the superoxide anion in the process. We examined whether oxygen free radical production contributes to the development of proteinuria in this model. Seven groups of male Sprague-Dawley rats were studied. Proteinuria was quantitated and histology examined 7 days after rats were treated with PA intravenously over 5 min. PA-treated animals received either saline, dimethyl sulfoxide, superoxide dismutase, or catalase over 30 min prior to and 30 min following PA administration. Another group received allopurinol over 4 hr prior to PA. The superoxide dismutase and allopurinol treatment groups had a significant suppression of urinary protein excretion compared to the PA control group. There were also less severe glomerular morphologic changes in the superoxide dismutase group vs. the PA controls, which demonstrated a pathologic pattern that included epithelial cell blebbing, segmental mesangial cell proliferation and matrix expansion, loss of glomerular capillary lumina, and occasional adhesions between the glomerular tuft and Bowman's capsule. The allopurinol group exhibited normal glomerular morphology on light microscopy, with the exception of occasional epithelial cell blebs. All groups showed spreading of the epithelial cell cytoplasm along the glomerular basement membrane with loss of foot processes, focal areas of lifting of the epithelial cell from the glomerular basement membrane, cytoplasmic vacuolization, and protein reabsorption droplets; however, allopurinol-treated animals demonstrated these changes to a lesser extent.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonanticoagulant protective effect of heparin in chronic aminonucleoside nephrosis

Aminonucleoside nephrosis progresses over an 18-week period to focal and segmental glomerulosclerosis (FSGS). Whole heparin has been shown to blunt the extent of renal injury in another model of FSGS, renal ablation; however, the precise mechanism of protection has remained uncertain. Since heparin has a variety of physiologic actions unrelated to anticoagulation, we administered three different heparin compounds, each with a distinct profile of biological properties, to groups of rats given a single intravenous dose of puromycin aminonucleoside (PA). In the absence of a prolongation of the activated partial thromboplastin time (aPTT), both whole heparin (WH) and a 7,000- to 11,000-dalton-molecular-weight nonanticoagulant heparin (NAH) ameliorated the functional and histologic abnormalities of chronic aminonucleoside nephrosis as evidenced by significant reductions in 24-hour urine protein excretion while preserving the glomerular filtration rate and blunting the rise in serum creatinine as compared to untreated PA control animals at the conclusion of the study. In addition, the NAH and WH groups exhibited significantly fewer glomeruli with either segmental mesangial proliferative areas or glomerulosclerosis/hyalinosis lesions 18 weeks after PA administration. A fragment of heparin (HF) was ineffective. We conclude that heparin may exert its beneficial effect in chronic aminonucleoside nephrosis through a biologic action, other than anticoagulation, perhaps by inhibition of mesangial cell proliferation.

Acute hemolysis and renal failure with rifampicin-dependent antibodies after discontinuous administration

Acute hemolysis as a reaction to rifampicin is extremely rare; case reports number less than 15. We recently evaluated a 65-year-old Cambodian refugee who self-regulated the use of rifampicin and isoniazid for pulmonary tuberculosis. Fifteen minutes after a single discontinuous oral dose, he developed flank pain, chills, rigors, vomiting, diarrhea, fever, and brown turbid urine. Laboratory tests at presentation showed acute intravascular hemolysis. Nonoliguric renal failure ensured, and he was transferred to our institution 2 days later. The patient was group A, Rh (D) positive, P1 negative with a cold autoantibody and cold anti-P1 alloantibody. The direct antiglobulin test was negative at the time of transfer. To evaluate the hemolysis, studies were done to test for rifampicin- or isoniazid-dependent antibodies. Rifampicin-dependent antibodies were detected in the antiglobulin phase with broad spectrum anti-human globulin, monospecific anti-gamma chain, and anti-complement antisera. Agglutination titers did not change after dithiothreitol reduction of the patient's serum. We conclude that this patient developed rifampicin-dependent IgG antibodies with complement-fixing capability. The presence of rifampicin-dependent antibodies should be suspected in a patient with hemolysis and/or renal failure taking rifampicin.

Fractional excretion of sodium. Exceptions to its diagnostic value

Determining the cause of acutely deteriorating renal function is a common problem in clinical nephrology. The fractional excretion of filtered sodium (FENa) has been demonstrated to be a reliably discriminating test between prerenal azotemia and acute tubular necrosis. However, with increasing clinical use of the FENa, numerous reports of low FENa (less than 1%) have appeared. The clinical settings of these reports include oliguric and nonoliguric acute tubular necrosis, urinary tract obstruction, acute glomerulonephritis, hepatorenal syndrome, renal allograft rejection, sepsis, and drug-related alterations in renal hemodynamics. One particular urinary index cannot be expected to reliably discriminate between prerenal azotemia and acute renal failure in all cases. The utility of the FENa test in the differential diagnosis of acute renal failure must be interpreted in conjunction with the patient's clinical course and the use of additional urinary and serum tests.

Nifedipine-induced renal dysfunction. Alterations in renal hemodynamics

Nifedipine caused acute, reversible deterioration in renal function in four patients with chronic renal insufficiency. The absence of hypotension, clinical course, benign urinary sediments, and normal results of renal ultrasound examinations excluded acute tubular necrosis, pyelonephritis, interstitial nephritis, obstructive uropathy, and acute glomerulonephritis. It is postulated that this slow calcium channel blocker produced deleterious intrarenal hemodynamic alterations in the setting of moderate to severe renal functional impairment. Nifedipine may alter renal function by blocking calcium entry into renal vascular smooth muscle, thereby reducing the efficacy of vasoconstrictor hormones in regulation of renal blood flow and glomerular filtration rate. An alternative explanation is that nifedipine may inhibit the compensatory synthesis of vasodilatory prostaglandin E2 analogous to the clinical observation of acute deterioration in renal function by nonsteroidal anti-inflammatory drugs in patients with pre-existing renal insufficiency. These observations suggest that clinicians should monitor renal function closely and exercise caution when administering nifedipine to patients with underlying renal insufficiency.

IgG-mediated intravascular hemolysis and nonoliguric acute renal failure complicating discontinuous rifampicin administration

Acute renal failure following intermittent or discontinuous rifampicin therapy is a relatively infrequent clinical observation. Many pathogenetic mechanisms for the renal failure have been proposed, including intravascular hemolysis with hemoglobinuria and its consequent nephrotoxicity. We report the case of a patient who used rifampicin in a discontinuous fashion and developed hemolysis with nonoliguric acute renal failure. Most reported cases of antirifampicin antibodies are of the IgM class; thus, the development of an IgG antirifampicin antibody is of interest, especially because of its strong in vivo hemolytic properties. In addition, this patient developed a nonoliguric uremic course that did not require dialysis, both of which are distinctly unusual for this clinical setting.

Nonoliguric acute renal failure

Nonoliguric acute renal failure is being recognized more commonly as a frequent initial observation for azotemia. Use of automated biochemical monitoring, aminoglycoside antibiotic utilization, and administration of potent diuretics and mannitol in settings of oliguria all contribute to its increased incidence. There appears to be less morbidity and mortality in patients with nonoliguric acute renal failure, and diagnostic urinary indexes suggest less of an insult to renal function. This article reviews the available literature and explores the reasons for the increased frequency of recognition of nonoliguric acute renal failure. Another aim is to compare nonoliguric acute renal failure with the oliguric from because there are important differences to be recognized by the clinician.

Nonoliguric acute renal failure associated with a low fractional excretion of sodium

Measurement of the fractional excretion of sodium has been recommended as a useful clinical tool in evaluating acute renal failure. Six patients with nonoliguric acute renal failure had a fractional excretion of sodium less than or equal to 1.0%; these patients had severe liver dysfunction, which suggested a sodium-avid state. A review of the literature showed that in patients with other sodium-avid states (congestive heart failure, nephrotic syndrome, and burns) the fractional excretion of sodium was frequently less than or equal to 1.0%. The fractional excretion of sodium is thus a less useful diagnostic test in patients whose clinical state makes them sodium avid.