Increase In Protein Excretion Research Articles

Effects of dietary phosphorus and protein in dogs with chronic renal failure

Summary Four diets were formulated to contain: 16% protein and 0.4% phosphorus–diet 1; 16% protein and 1.4% phosphorus– diet 2; 32% protein and 0.4% phosphorus–diet 3; and 32% protein and 1.4% phosphorus–diet 4. Forty-eight dogs were fed diet 1 for 3 months after surgical reduction of renal mass, then were allotted to 4 groups of 12 dogs each, with equal mean values for glomerular filtration rate (gfr). Dog of groups 1–4 were fed diets 1–4, respectively, for 24 months. Data collected from the dogs during and at termination of the study were analyzed statistically for effects of dietary protein, phosphorus (P), time, and interactions between these factors. During the 24 months of study, 24 dogs developed uremia and were euthanatized for necropsy. Necropsy also was performed on the remaining 24 dogs after they were euthanatized at the end of the study. Dog survival was significantly enhanced by 0.4% P diets (vs 1.4% P diets), but survival was not significantly influenced by amount of dietary protein. The 0.4% P diets (vs 1.4% P diets) significantly increased the period that gfr remained stable before it decreased, but dietary protein did not have significant effect. Significant blood biochemical changes attributed to P, protein, and time were identified during the study. Terminally, plasma parathyroid hormone concentration was significantly increased from prediet values in all groups of dogs. Urine protein excretion was not significantly affected by dietary amount of either protein or P, when measured by either timed urine collection or urine protein-to-creatinine ratio. A tendency was seen for increased protein excretion with passage of time. Histologic and mineral analyses of kidneys removed at necropsy revealed some significant difference attributable to diet, but differences were more marked when diet was ignored, and the 24 surviving dogs were compared with the 24 that developed uremia. Overall, amount of dietary P was more important than amount of dietary protein for preventing adverse responses. However, because renal damage specifically attributable to either dietary component was not obvious, it is possible that the effects of P were manifested by extrarenal mechanisms.

Platelet-activating factor alters glomerular barrier size selectivity for macromolecules in rats

The effect of platelet-activating factor (PAF) on glomerular permeability to macromolecules was investigated in the isolated kidneys from normal male Sprague-Dawley rats perfused at constant pressure. Compared with basal values, infusion of PAF (10 nM final concentration) into the isolated kidneys induced a progressive and significant increase in protein excretion (6.7 +/- 2.7 vs. 40.7 +/- 10.4 micrograms/min, P less than 0.01), completely reversible 20 min after PAF infusion was discontinued (8.5 +/- 1.3 micrograms/min). In additional experiments, during PAF infusion the fractional clearance of small neutral dextrans (radius 24-48 A), defined as the ratio of the clearance of neutral dextrans to the clearance of creatinine, was comparable to preinfusion values, whereas fractional clearance of large dextrans (greater than 50 A) was significantly elevated (P less than 0.005) above preinfusion values. The specific PAF receptor antagonist L 652731 completely prevented the increased fractional clearance of large dextrans induced by PAF. Finally, lowering Ca2+ concentration in the perfusion medium from 2.5 to less than 0.1 mM markedly reduced proteinuria in isolated kidneys exposed to PAF (80.0 +/- 10.3, 42.8 +/- 3.1, and 22.0 +/- 7.6 micrograms/min, respectively, for 2.5, 1.25, and less than 0.1 mM). These results indicate that in isolated perfused kidneys 1) PAF-induced proteinuria is a functional phenomenon reversible on discontinuing PAF infusion, 2) PAF modifies glomerular size-selective properties by increasing transmural passage of large dextran molecules, and 3) PAF-induced change in glomerular permselective properties is dependent on Ca2+ concentration in the extracellular medium.

Salt blocks the renal benefits of ramipril in diabetic hypertensive rats.

To establish if the benefit of angiotensin converting enzyme inhibitor therapy in retarding progressive diabetic renal injury is due to a specific intrarenal effect of the systemic hypotensive effect, we studied the effect of long-term ramipril treatment on blood pressure, glomerular filtration rate, and urinary protein excretion in streptozotocin-diabetic spontaneously hypertensive rats. The hypotensive effect of ramipril was prevented by a high salt diet, which did not alter the degree of renal angiotensin converting enzyme inhibition. Three weeks after uninephrectomy and induction of diabetes, rats were allocated to three groups. Groups 1 and 2 were given 1% NaCl, whereas group 3 was given water as drinking solution. One week later, groups 2 and 3 received 0.4 mg/kg/day ramipril in their drinking solution, which was continued over a 2-month period. Ramipril produced a blood pressure fall only in water-drinking rats (group 3) despite a similar reduction in plasma and renal angiotensin converting enzyme activity in groups 2 and 3. Salt-loaded rats had a progressive increase in urinary protein excretion over the duration of study. Ramipril treatment prevented an increase in protein excretion only in animals given water and with a reduced systolic blood pressure. Glomerular filtration rate was similar in all three groups. Ramipril treatment improved animal survival independently of a reduction in blood pressure or an effect on proteinuria. Although it is possible that angiotensin converting enzyme inhibitors have specific intrarenal effects reducing progression of diabetic proteinuria, concomitant control of systemic blood pressure appears to be necessary to demonstrate a benefit.

The Effect of Protein Intake on the Lifelong Changes in Renal Function of Rats with a Solitary Kidney Damaged at Young Age

Changes in renal function were followed lifelong in male rats with only 1 kidney either intact or damaged by ureteral obstruction or ischemia. After surgery the rats were given a low (12%) or a high (36%) protein diet. After a period with a stable glomerular filtration rate, which was longer on the low protein diet, there was a linear decline in rats with an intact single kidney. The rate of decline was highest on the high protein diet, resulting in a shorter survival time. A decrease in urine osmolality and an increase in protein excretion preceded the decrease in filtration rate, while it was followed by an increase in blood pressure. The glomerular filtration rate of the rats with a single damaged kidney initially recovered to 75 to 80% of that of rats with an intact single kidney on the same diet. There was a linear decrease in the glomerular filtration rate, with the highest rate of decrease on the high protein diet. The mean survival time was less than that of rats with a single intact kidney. Proteinuria preceded the decrease in filtration rate, while hypertension was observed later. We conclude that in rats with a solitary kidney renal failure eventually develops. A low protein diet postpones and attenuates this development but it does not prevent it.

Dietary protein restriction and renal injury in the spontaneously hypertensive rat

We examined the influence of a low-protein diet on the course of the renal injury in spontaneously hypertensive rats (SHR) and SHR given antihypertensive drug therapy (SHRD). Antihypertensive drug treatment was hydralazine, reserpine, and chlorothiazide. Wistar-Kyoto (WKY) rats served as normotensive controls. SHR, SHRD, and WKY were each placed on a 24, 14, and 10% protein diet at 5 wk and followed to 80-90 wk of age. Untreated SHR showed a steady rise in protein excretion from 5 to 70 wk regardless of dietary protein content. Protein excretion in SHRD on a 24% protein diet was similar to untreated SHR. However, SHRD on a 14 or 10% diet had a more moderate increase in protein excretion. Glomerular, tubular, and vascular pathology in untreated SHR was not influenced by dietary protein intake. Despite successful antihypertensive therapy, kidney pathology in SHRD on a 24% diet was not significantly different from untreated SHR. In contrast, SHRD on 14 or 10% protein diets had less segmental glomerulosclerosis and vascular pathology than untreated SHR. The results indicate that dietary protein restriction does not influence the course of renal injury in untreated SHR. However, the combination of antihypertensive drug therapy with protein restriction in SHR delays and may arrest progression of glomerulosclerosis and proteinuria.

Sex differences in nephrotoxic and gastrointestinal effects of phenylbutazone

Male and female Wistar rats were used to study the sex differences in nephrotoxic, ulcerogenic and lethal effects of phenylbutazone (PBZ). In one series of experiments, male and female rats were given daily oral doses of 25, 125, 250, 400 and 500 mg PBZ/kg for 7 days to assess mortality, gross and microscopic lesions of the stomach, intestine and kidneys and to determine the PBZ effects on renal protein and glucose excretion. In another series of experiments, PBZ effects on renal gluconeogenesis and p-aminohippurate (PAH) accumulation in renal cortical slices were measured 12 h after administration of the same PBZ doses to male and female rats. Reduced glutathione (GSH) depletion and malondialdehyde (MDA) content in kidney cortex and liver were determined 2 h after a single administration of 250 mg PBZ/kg to male and female rats. To measure the effects of PBZ on blood urea nitrogen (BUN), male and female rats were given a single dose of PBZ (125 mg/kg) and were sacrificed at different time intervals, from 0 to 48 h. Gross and microscopic examination of the kidneys and gastrointestinal tract showed more pronounced renal and gastrointestinal lesions in surviving female than in male rats at the same doses. In PBZ treated male rats, BUN did not differ from control rats 48 h after PBZ administration. In female rats, BUN increased from 18 to 96 mg/100 ml 48 h after PBZ administration. After 7 days of PBZ treatment there was a greater increase of protein excretion in female than in male rats, but there were almost no sex differences in glucose excretion. Twelve hours after PBZ administration, renal PAH accumulation and gluconeogenesis were not different from controls in male rats but decreased in a dose-dependent fashion in females. A significant depletion of GSH and a significant increase in MDA content in liver and renal cortex occurred in female but not in male rats. In conclusion, the PBZ treatment was associated with nephrotoxic and gastrointestinal effects which could be detected earlier and were greater in female than in male rats.

Toxic properties of the mushroom Cortinarius orellanus (Fries). II. Impairment of renal function in rats.

Oral administration of the toxic mushroom Cortinarius orellanus (Fr.) to male Sprague Dawley rats caused serious impairment of renal function. The signs observed were similar to those produced in humans who ingest this fungus. Administration of 2.0 g dried Cortinarius orellanus per kg body weight led to acute renal dysfunction within 48 h. The pattern of impairment included reduced glomerular filtration rate, decreased renal absorption of water, sodium and potassium, and proteinuria and glucosuria. The nephrotoxic effect was further characterized by decreased activities of the brush border enzymes alkaline phosphatase and gamma-glutamyltranspeptidase in urine, despite a remarkable increase in protein excretion of predominantly tubular origin. These findings were substantiated by morphologic changes, which could be detected as early as 12 h after dosing. Morphologically discernible signs of renal tubular damage start with deformation of the proximal tubular brush border region. Within 48 h after toxin ingestion, prenecrotic and necrotic cells could be found in all nephron segments contained in the renal cortex. The most prominent changes were a vesiculation of the apical cell pole and a swelling of the smooth surfaced endoplasmic reticulum and of mitochondria. The latter was accompanied by a loss in matrix material and a massive fragmentation of mitochondrial cristae membranes. Detectable quantities of the toxic principle of the mushroom, orellanine, were excreted only within the first 24 h after dosing. No impairment of liver function was detected.

Cathepsin B and L in nephron segments of rats with puromycin aminonucleoside nephrosis

The intralysosomal proteinases, cathepsins B and L, were measured in microdissected segments of rat nephrons following a single injection of puromycin aminonucleoside (PAN). Z-Phenylalanyl-arginine-7-amido-4-methylcoumarin served as substrate. Enzyme activities, proteinuria, creatinine clearance and renal morphology were determined at specific time intervals following induction of PAN nephrosis. During the first three days following PAN injection, enzyme activities in S2 and S3 segments, protein excretion, creatinine clearance and appearance of the renal parenchyma resembled control animals. The enzyme activity in S1 segments was slightly decreased, but returned to control levels at day six after injection. Days four through eight post-PAN injection were characterized by a dramatic increase in protein excretion and an increase in cathepsin B and L activity in S2 and S3 segments of the proximal tubule. During days 9 through 15 enzyme activity decreased significantly in S2 segments despite continued proteinuria. Overt necrosis and cell injury were seen in the proximal tubule and probably account for the decrease in proteolytic activity. After day 15 following PAN injection, the level of proteinuria decreased, restoration of cathepsin activities occurred and a histopathologic picture of healing was present. The data suggest a positive relationship exists between stimulation of cathepsin B and L activity in S2 and S3 segments of the proximal tubule and increased protein filtration in PAN nephrosis. The increased enzyme activity reflects enhancement of the proteolytic capacity of the lysosomal system that is necessary for increased protein catabolism.

Urinary enzymes and protein patterns as indicators of injury to different regions of the kidney

Acute experimental models of renal damage to the proximal tubular, glomerular, and papillary regions of the rat were produced by administration of hexachloro-1:3-butadiene (HCBD), puromycin aminonucleoside (PAN), and 2-bromoethylamine (BEA), respectively. Several routine indicators of nephrotoxicity, the enzymes alkaline phosphatase and N-acetyl-β-glucosaminidase, and the molecular weight pattern of protein excretion were determined on urine samples. Tubular damage produced by HCBD or BEA was discriminated both quantitatively and qualitatively from glomerular damage produced by PAN. The latter was characterized by a pronounced increase in protein excretion, especially proteins with molecular weight >40,000 Da. In contrast, protein excretion in tubular damage was raised only slightly and characterized by excretion of proteins of a wide range of molecular weights. Proximal tubular damage caused by HCBD and papillary damage caused by BEA were distinguished both by conventional urinalysis (volume and specific gravity) and by measurement of the two urinary enzymes. Alkaline phosphatase and glucose were markedly and transiently elevated in proximal tubular damage and N-acetyl-β-glucosaminidase showed a sustained elevation in papillary damage. It is concluded that both selective urinary enzymes and the molecular weight pattern of urinary proteins can be used to provide diagnostic information about the possible site of renal damage.

Urinary Enzymes and Protein Patterns as Indicators of Injury to Different Regions of the Kidney

Urinary Enzymes and Protein Patterns as Indicators of Injury to Different Regions of the Kidney. STONARD, M. D., GORE, C. W., OLIVER, G. J. A., AND SMITH, I. K. (1987). Fundam. Appl. Toxicol. 9, 339–351. Acute experimental models of renal damage to the proximal tubular, glomerular, and papillary regions of the rat were produced by administration of hexachloro 1:3-butadiene (HCBD), puromycin aminonucleoside (PAN), and 2-bromoethylamine (BEA), respectively. Several routine indicators of nephrotoxicity, the enzymes alkaline phosphatase and N-acetyl-β-glucosaminidase, and the molecular weight pattern of protein excretion were determined on urine samples. Tubular damage produced by HCBD or BEA was discriminated both quantitatively and qualitatively from glomerular damage produced by PAN. The latter was characterized by a pronounced increase in protein excretion, especially proteins with molecular weight >40,000 Da. In contrast, protein excretion in tubular damage was raised only slightly and characterized by excretion of proteins of a wide range of molecular weights. Proximal tubular damage caused by HCBD and papillary damage caused by BEA were distinguished both by conventional urinalysis (volume and specific gravity) and by measurement of the two urinary enzymes. Alkaline phosphatase and glucose were markedly and transiently elevated in proximal tubular damage and N-acetyl-β-glucosaminidase showed a sustained elevation in papillary damage. It is concluded that both selective urinary enzymes and the molecular weight pattern of urinary proteins can be used to provide diagnostic information about the possible site of renal damage.

Effect of 3-hydroxybutyrate infusion on urinary protein excretion in healthy man.

Diabetic ketoacidosis is often associated with a temporary increase in protein excretion, but the mechanisms are not completely known. The aim of the present study was to examine the effect of acute experimental moderate ketosis on kidney function and specifically on protein handling using an infusion of 3-hydroxybutyrate in healthy subjects. Seven young healthy males were infused with sodium 3-hydroxybutyrate, the peak blood level attained being 1.96 +/- 0.53 mmol/l (SD). The pH in blood and urine rose significantly from 7.40 +/- 0.03 to 7.45 +/- 0.05 (2p less than 0.01) and from 7.29 +/- 0.79 to 8.51 +/- 0.82 (2p less than 0.01), respectively. Urinary beta-2-microglobulin excretion rose significantly from 0.038 microgram/min x/ divided by 1.9 to 0.082 microgram/min x/ divided by 1.4 (geometric mean x/ divided by tolerance factor) (2p less than 0.01) but urinary albumin excretion was unchanged. No changes were seen in blood pressure, glomerular filtration rate and renal plasma flow. A marked reduction in urine flow from 15 to 5 ml/min was noted, but could not be attributed to changes in plasma arginine-vasopressin, which was reduced before and during infusion due to considerable oral water loading. It is concluded that moderate elevation in blood ketone body levels does not induce albuminuria. It is suggested that the temporary proteinuria present in diabetic ketoacidosis may be related to acidosis per se.

Prednisone-induced fluctuations of proteinuria in patients with a nephrotic syndrome.

We studied the effect of prednisone on urinary protein excretion in 19 patients with a nephrotic syndrome, who were treated with prednisone (125-150 mg) on alternate days. We found a typical, fluctuating pattern of proteinuria resulting from an increased protein excretion rate on prednisone days and a decreased protein excretion rate on nonprednisone days. The urinary protein excretion on prednisone days was 9.9 +/- 3.3 g/24 h, as compared to 5.7 +/- 3.8 g/24 h on nonprednisone days (mean +/- SD). In the whole group of patients the percentual change in proteinuria was significantly correlated with the endogenous creatinine clearance. However, systematic differences between creatinine excretion rates on prednisone and nonprednisone days were not found in individual patients. In 6 patients, renal hemodynamics were studied more precisely, using a single injection technique. Only a slight and nonsignificant decrease in glomerular filtration rate was found on nonprednisone days (delta = -9.6 +/- 16.3%; mean +/- SD). Filtration fraction remained unchanged. It is therefore suggested that the effects of prednisone on proteinuria are not simply mediated by overall changes in renal hemodynamics.

Glomerular permselectivity in the isolated perfused rat kidney

Glomerular permselectivity characteristics were studied in the Sprague-Dawley rat in vivo and in the isolated rat kidney perfused with an erythrocyte-free Krebs-Henseleit buffered 5% albumin solution (IPK). IPK permselectivity in vitro, assessed by fractional clearances of neutral dextran (FCND) and dextran sulfate (FCDS) with molecular radii 18-43 A, was essentially similar to that of the Sprague-Dawley rat in vivo. The negative charge barrier of the IPK glomerular filter was intact [e.g., FCND of 36 A = 0.10 +/- 0.01 (SE) vs. FCDS of 36 A = 0.01 +/- 0.00 (P less than 0.01)]. Dextrans of an intermediate size (26-34 A) had lower fractional clearances in the IPK than in vivo [e.g., FCND of 30 A in IPK = 0.23 +/- .04 vs. FCND of 30 A in vivo 0.40 +/- 0.01 (P less than 0.01)]. This decreased clearance of dextrans of an intermediate molecular size is predicted by pore theory, since the IPK has an increased afferent glomerular plasma flow rate. As glomerular permselectivity characteristics in the IPK simulate in vivo characteristics, such preparations are suitable in vitro models in which to study factors that modulate permselectivity. The demonstration that the glomerular filter in the IPK has a normal negative charge barrier indicates that the increased protein excretion in IPK systems cannot be attributed to abnormalities of this component of the filtration barrier.

Gentamicin-induced hypercalciuria in the rat.

A study was made of the effects of gentamicin (40 mg/kg/day for 7 days) on the excretion of sodium, potassium, calcium and magnesium in the urine of rats. Volume of urine, protein excretion and the urinary activities of the enzymes alanine aminopeptidase, lactate dehydrogenase and N-acetyl-beta-glucosaminidase were also monitored. There were no significant changes in the excretion of sodium or potassium and the excretion of magnesium was too variable to permit a meaningful interpretation of changes in its excretion. Significant changes occurred in the excretion of calcium and protein and in the 24 hr urine osmolarity. The earliest of these changes, on day 4, was an increase in calcium excretion (P less than 0.01) which progressed until the drug was stopped and persisted throughout the 5 follow-up days. The increase in protein excretion was significant (P less than 0.01) by day 5 and the decrease in osmolarity (P less than 0.01) by day 6. These changes were preceded, on day 1, by a significant (P less than 0.001) rise in the activities in urine of all three enzymes. This early enzymuria suggests that considerable perturbation of cell integrity occurred before the increase in calcium excretion. Further studies are required to elucidate what role, if any, the loss of calcium plays in the genesis of tubular cell injury.

Evaluation of the Coomassie Brilliant Blue G-250 method for urinary protein.

The Coomassie Brilliant Blue G-250 method for protein in urine has been evaluated for analytical accuracy and clinical applicability. Extremely simple to perform, the test exhibits good precision and sensitivity. The color developed per gram of protein is protein-type dependent, so no single protein standard is completely satisfactory. Color intensity is linearly related to concentration up to 1500 mg/L when used with a manual bichromatic method. Accuracy was clinically acceptable for patients with a variety of protein-losing diseases, and for patients having received renal transplants; however, the method underestimates urinary light-chain proteins. In athletes and premature neonates, we observed increased protein excretion during periods of stress. The upper reference limit for protein excretion in healthy adults is about 120 mg/24 h.

Proteinuria: Diagnostic Principles and Procedures

Proteinuria has been thought of as the first sign of serious renal disease. However, in some patients proteinuria may last for years without other evidence of kidney damage, and in other patients it may only be an insignificant and transient laboratory finding. The nature and severity of renal involvement in a particular patient are often suggested by the clinical picture, and the pattern and amount of proteinuria. The physician should use this information in evaluating the severity of the patient's disease. An approach for such evaluations is offered by briefly reviewing the causes and prognosis of the various types of proteinuria and by suggesting steps to take in treating patients with increased protein excretion.

Urinary protein patterns and preeclampsia.

A retrospective study of urinary protein patterns, as determined by SDS-PAA-disc-electrophoresis was performed in 107 patients in third trimester of pregnancy because of preeclampsia. The aim was to determine whether the protein patterns allow a differentiation between nephropathies associated with genuine toxaemia of pregnancy and those in which toxaemia was superimposed on preexisting renal glomerular or tubular disease. The magnitude and type of proteinuria was related to the mean arterial pressure (MAP). 47% of all patients showed a mixed protein pattern independent of the MAP-severity. This form of proteinuria is probably associated with a genuine toxaemia of pregnancy. It was not possible to determine if pure glomerulopathies whose frequency rose with MAP, had already been present before pregnancy. In a third of the 22 patients followed-up post-partum pathological protein patterns or increased protein excretion was detected. This implies that 35% of the nephropathies were present before pregnancy. However, differentiation between preexisting and toxaemia associated nephropathy was not always possible. SDS-PAA-analysis of urinary protein should be carried out in earlier stages of pregnancy in cases of increasing MAP and proteinuria.

Proteinuria in patients with cirrhosis: relationship between renal and hepatic function.

1. In 37 patients with cirrhosis of the liver of different severity (11 in class A, 18 in class B, and 8 in class C, according to Child's criteria modified by Hobbs), inulin and p-aminohippurate clearances, total fractional protein excretion and the fractional clearances of alpha 1-acid glycoprotein, albumin, transferrin, alpha 2-macroglobulin and beta 2-microglobulin (in 20 patients) were determined. 2. Insulin clearance was lower than 70 ml/min in 19 patients had p-aminohippurate clearance was lower than 300 ml/min in 20 patients. Total fractional protein excretion was above normal in 19 patients; alpha 1-acid glycoprotein fractional clearance was above normal in 11, albumin fractional clearance in 10, transferrin fractional clearance in five, alpha 2-macroglobulin fractional clearance in three, and beta 2-microglobulin fractional clearance in 10. 3. The increases in protein excretion were independent of any impairment of renal tubular function. An inverse relationship between protein excretion and the clearances of inulin and p-aminohippurate was found. No difference in protein excretion was found between the three groups of patients with different degrees of liver damage. 4. The results suggest that in cirrhosis an increase in glomerular permeability is frequent, though generally slight; it is correlated with an impairment of kidney function and is independent of the severity of the liver damage.

Membranous glomerulonephropathy with tubular dysfunction and linear tubular basement membrane IgG deposition

patient's condition progressed to end-stage renal disease. The decline in GFR was coincident with the development of poorly responsive and eventually severe and nonresponsive proteinuria. Glomerular damage and proteinuria may be causally related or independently related to another primary factor. We suggest that the proteinuric state might have been a causative factor in the progression of the mesangial sclerosis and glomerular capillary damage; there is experimental and clinical evidence to support such a causal relationship. Heavy proteinuria induced in rats by the injection of protein is associated with the development of focal glomerulosclerosis. 8' 9 These histologic changes are partially, and the functional changes completely, reversed when injections are discontinued? Fivesixths nephrectomy in the rat, with the accompanying increase in single nephron glomerular filtration and solute excretion, produces focal segmental glomerulosclerosis. 1~ The equivalent of these changes in the remnant kidney is seen in children with oligomeganephronia, a form of severe hypoplasia leading to renal insufficiency, and in children left with a marked decrease in GFR following relief of obstructive uropathy. All of these observations suggest that a large increase in the excretion of protein or other solute per nephron (functional overload) can lead to progressive glomerular sclerosis as was observed in our patient. If the degree of proteinuria is important in determining progressive glomerular damage, efforts to decrease the rate of protein excretion, including cytotoxic drugs, should be considered in patients with the most severe and persistent proteinuria. Unfortunately, no clear benefit has been shown for such therapy in patients with histologic patterns other than minimal lesion disease. Further, overly vigorous use of albumin infusions, together with diuretics, can produce increased protein excretion and lead potentially to epithelial Cell damage and mesangial sclerosis. The patient with the nephrotic syndrome described here developed end-stage renal disease after 18 years of steroidresponsive relapses, over which time there were 40 relapses, each responding to prednisone with disappearance of proteinuria. When resistance to steroid therapy developed, the renal histology was focal segmental glomerulosclerosis. We suggest that repeated episodes of heavy proteinuria were a factor in the development of the renal pathologic changes. REFERENCES

Glomerular charge and urinary protein excretion: Effects of systemic and intrarenal polycation infusion in the rat

To study the role of the fixed anionic sites of the glomerular capillary wall in protein filtration, the negative charges were neutralized in vivo. With systemic infusion of the polycation protamine sulfate, glomerular staining for polyanion was reduced and protein excretion increased by 154%. To avoid systemic side effects in subsequent studies, small doses of a polycation were infused directly into one renal artery. The contralateral kidney was infused with the vehicle solution. Albumin excretion from the experimental kidneys in the first 1-hr collection after infusing 0.5 mg protamine sulfate was 24.3 +/- 6.3 micrograms/min/kidney (N = 13; P less than 0.01). Albuminuria declined during the subsequent 3 hr with a second infusion inducing a second proteinuric response. The degree and longevity of the albuminuric response was correlated directly to the dose of protamine sulfate. The polycations hexadimethrine and poly-l-lysine also induced proteinuria. The increased protein excretion consisted of albumin; the excretion of nonalbumin protein was identical in the experimental and control kidneys. Hemodynamic factors did not explain the increase in proteinuria. Morphologically, the polycation-treated kidneys showed scanty foot process fusion and a decrease in free negative sites in the lamina rarae of the glomerular basement membrane. The results strongly support an important role for glomerular charge in preventing filtration of circulating plasma albumin.