Evidence for operation of the magnification phenomenon in patients with chronic renal insufficiency

It has been proposed that the functional adaptations of surviving nephrons in advancing chronic renal failure (CRF) are not random but characterized by an excretory response which varies inversely with the number of surviving nephrons ('magnification phenomenon'). Because validation of this hypothesis in man is incomplete, we undertook to characterize the excretory response to acute volume expansion in patients with CRF. In normals, water immersion to the neck (NI) results in a redistribution of blood volume with preferential central hypervolemia (CV) in the absence of plasma compositional change. NI was utilized, therefore, to assess the response to acute CV. 13 patients with CRF (GFR = 3-65 ml/min) were studied twice while ingesting a constant diet (60-150 mEq Na/day): during a seated control study (C) and during 4 h of NI. FENa was constant during C. In contrast, during NI, there was a prompt and marked increase in FENa which markedly exceeded that of 29 normal subjects undergoing an identical study. In the CRF group the extent of the augmentation of FENa during immersion varied inversely with GFR (r = -0.54; p less than 0.05). These results provide evidence that the 'magnification phenomenon' subtends renal sodium handling in patients with CRF.

Profiling of urinary medium-sized peptides in normal and uremic urine by high-performance liquid chromatography

This report describes the profiling of medium-sized peptides in both normal and uremic urine by ion-pair reversed-phase high-performance liquid chromatography using an acetonitrile--heptafluorobutyric acid solvent system as eluent. Several medium-sized peptide peaks could be detected in both normal and uremic urine at low picomole level by using post-column fluorescence derivatization with fluorescamine. Contrary to expectation, uremic urine contained slightly larger amounts of medium-sized peptides compared with normal urine.

Amine metabolite profile of normal and uremic urine using gas chromatography--mass spectrometry

A method for the simultaneous analysis of phenolic amines and aliphatic amines in human urine is described. The amine metabolites in urine were extracted using Dowex 50W-X8 cationic resin, derivatized and analyzed by a gas chromatographic--mass spectrometric--computer system. The amine metabolites profile of 5 ml of urine was obtained with good gas chromatographic separation. The gas chromatographic method described here separates urinary phenolic amines, di- and polyamines and methylguanidine in a single chromatographic separation. The urinary levels of methylguanidine, putrescine, cadaverine, spermidine, p-tyramine, dopamine, and 3-methoxytyramine were quantitated by using a mass spectrometric technique. In uremic patients, only the urinary excretion of methylguanidine was increased in comparison with normal subjects, although the urinary excretion of other amines was decreased in uremic patients.

[Medium molecular weight uremic toxins and endogenous polyamines. Behavior of polymorphonuclear leukocyte chemotaxis with respect to chromatographic peaks of dialysate and standard polyamines]

The aim of our study is to evaluate the eventual activity of the total dialysate of two uremic nephrectomized patients in recirculating dialysis and the chromatographic peak of the dialysate fractionated by Sephadex column G 15 on PMN chemotaxis. Only the total dialysate and the chromatographic peak B showed inhibition of chemotaxis. On the contrary the commercial polyamines in the same concentration range, and the other chromatographic peaks, containing polyamines too, did not revealed inhibition. Our data show, therefore, that the chemotaxis inhibition could be due to the middle-molecules present in the peak B, rather than the polyamines itself. Polyamines were determined by dansylation method, separated by thin layer chromatography and quantified by spectrofluorimeter. Chemotaxis was evaluated using the modified Boyden chamber.

Furosemide-induced increase in urinary and peritoneal excretion of uric acid during peritoneal dialysis in patients with chronic uremia

Intermittent peritoneal dialysis was performed in 17 patients with chronic uremia in order to observe the effect of furosemide added to the dialysate on urinary and peritoneal elimination of uric acid. Two kinds of dialysate were used: moderately hypertonic (osmolality, 431.2 mOsm/kg of water) and slightly hypertonic (osmolality, 368.9 Osm/kg of water). Significant increases in urine volume, urinary and peritoneal excretion of uric acid, and renal and peritoneal clearances were found. The increase in urinary excretion of uric acid exceeded that of urine volume. These findings were interpreted to be the result of furosemide action on renal function after being transferred through the peritoneum into the blood stream with the concomitant increase in the uric acid shift from the circulation into the peritoneal cavity. We concluded that the addition of furosemide is useful in increasing uric acid elimination in patients with chronic uremia.

Urinary indices for differentiation of prerenal azotemia and renal azotemia in horses

The urine urea nitrogen/plasma urea nitrogen ratio (Uun/Pun), urine creatinine/plasma creatinine ratio (Ucr/Pcr), urine osmolality/plasma osmolality ratio (Uosm/Posm), and fractional excretion of filtered sodium (FENa) were evaluated in 16 horses with acute azotemia to ascertain the significance of each index in the differentiation of prerenal azotemia from renal azotemia. Renal azotemia was diagnosed when renal biopsy or postmortem histologic examination demonstrated evidence of organic renal disease or when azotemia was found in the presence of isosthenuria. The diagnosis of prerenal azotemia was based on the absence of renal histologic lesions or stabilization of blood urea nitrogen and serum creatinine soon after therapy. In 10 horses with renal azotemia, Uun/Pun was 2.1-14.3, Ucr/Pcr was 2.6-37.0, Uosm/Posm was 0.8-1.7, and FENa was 0.08-10.0. In 6 horses with prerenal azotemia, Uun/Pun was 15.2-43.7, Ucr/Pcr was 51.2-241.5, Uosm/Posm was 1.7-3.4, and FENa was 0.02-0.50. The values for each of these indices differed significantly between the 2 groups of horses (P less than 0.05). It was concluded that these indices were of value in the early classification of renal failure in the horse and that this information could be utilized in planning of therapy of acute azotemia in the horse.

Potentiometric analysis for sodium and potassium in biological fluids

Results obtained with a potentiometric analyzer, NOVA 1, specific for sodium and potassium, were compared with those by flame photometry. Both instruments showed linearity within a physiological range of sodium and potassium concentrations and had similar precisions. Volume displacements from addition of albumin or Intralipid to aqueous samples yielded the predicted lower flame-photometric results because of the relative decrease in sample water. There may be a small interaction between sodium and albumin. Physiological measurements on plasma from uremic patients showed no change after dialysis that could be ascribed to a decrease in interaction of these ions with creatinine and urea. Potentiometric values for sodium and potassium did not differ significantly, whether measured in cerebrospinal fluid or in the corresponding plasma. Results for urine were the same potentiometrically and by flame photometry.

Analysis of the oxocarboxylic acid fraction in serum and urine as O-methyloximes by thermionic specific detection

After O-methyloximation of the carbonyl functions, the organic acids in serum and urine are extracted by anion-exchange chromatography, transformed into the methyl esters and pre-fractionated by thin-layer chromatography. In one of the four fractions and on the basis of the nitrogen in the O-methyloxime esters, the profiles of the oxocarboxylic acids are analyzed by gas chromatography with thermionic specific detection. The method has good specificity for the oxocarboxylic acids and is suitable for comparative studies. During diabetic or fasting ketoacidosis the serum concentrations of 3-oxobutyric acid and of the amino acid metabolites 2-oxobutyric, 2-oxoisovaleric and especially 2-oxo-3-methylvaleric and 2-oxoisocaproic acid are increased. In urine mainly 3-oxobutyric acid and only small amounts of the 2-oxocarboxylic acids are excreted.

High resolution gas chromatography mass spectrometry of the methyl esters of organic acids from uremic hemofiltrates

The organic acid fraction of hemofiltrates was investigated in the form of methylates by glass capillary gas chromatography-mass spectrometry. The pattern obtained is similar to that of urinary organic acid methylates from healthy individuals. A marked difference was noted for N-phenylacetyl-alpha-aminoglutarimide, present in hemofiltrate at levels 50-100 times higher than those in urine. Analysis of hemofiltrate samples taken at different times during a hemofiltration with post-dilution technique revealed that the hemofiltrate concentration of most compounds was drastically reduced the course of the hemofiltration treatment. Compared to the other compounds, the reduction in hemofiltrate concentration of N-phenylacetyl-alpha-aminoglutarimide was extremely rapid.

Measurement of urine electrolytes: clinical significance and methods

There are specific clinical settings in which each of the urine electrolytes may be diagnostically useful. The urine sodium alone is not efficient in differentiating prerenal azotemia from acute tubular necrosis, but if urine sodium is coupled with some measure of the renal concentrating ability, e.g., the urine:plasma creatinine ratio. discrimination between these two conditions is much improved. Usefulness of the urine sodium in other settings (evaluation of hyponatremia, prediction of acute rejection in renal transplant recipients, index of salt balance) is controversial. Urine potassium may be useful in the evaluation of hypokalemia of obscure etiology and, occasionally, in the form of the urinary Na/K ratio, as a guide to diuretic therapy. Urine chloride is assuming importance in the differential diagnosis of metabolic alkalosis, particularly when Bartter's syndrome is a consideration.

[Urinary guanidinosuccinic acid in uremic children]

Urinary guanidinosuccinic acid (GSA) was measured in pediatric age: six normal subjects, six chronically uremic patients and five with acute renal failure. Urinary GSA was increased in uremic patients as compared to that in normal subjects: our levels was less than in the growth-up people. These differences might be correlated with different protein metabolism in children.

Isotachophoretic separation of middle molecule peptides in uremic body fluids

By applying analytical isotachophoresis six solutes in the middle molecule range were isolated as a further separation of a middle molecule fraction isolated from uremic body fluids using an earlier described technique of combined high speed gel filtration--gradient elution chromatography. The solutes separated with isotachophoresis could be identified by determining the net mobilities and the corresponding UV levels. Identical net solute mobilities were found in different biological fluids from different uremic patients. By measuring the zone length it was possible to estimate the amounts of material present in uremic biological fluids. During these investigations the reproducibility was better than +/-2% for the six solutes measured.

Separation and quantification of the "middle molecules" in uremia

A modification of a two-stage chromatographic procedure (molecular sieve followed by ion-exchange) to separate potentially toxic uremic "middle molecules" from body fluids has been established. The procedure has an analysis time less than half that previously reported with improved resolution. Elution volumes have been found to be reproducible to within 2% and concentrations (as measured by peak height) to within 10%. Careful attention, however, must be paid to artifacts that may arise from sample preparation, drug therapy, and dialysis conditions. Up to ten identifiable subpeaks were observed in sera, urine, and red cell hemolysate samples following ion-exchange separation of a molecular sieve peak in the middle molecule range (300 to 2000 daltons). Red cell concentrations of five of these moieties were significantly higher than those in serum. Four peaks were not detected at all in red cells, and one peak was not detected in sera or urine samples. In addition, although serum concentrations are elevated in uremia, red cell levels in patients with uremia are comparable with those obtained in normal subjects. If any of these species are subsequently shown to be uremic toxins, then their two-compartment distribution within the body has important ramifications in the choice of an appropriate mathematic model to program optimal dialysis therapy.

A potent inhibitor of cell proliferation in "middle molecules" isolated from the urine of uremic patients

A potent inhibitor of cell proliferation was found in the urine of a patient with chronic renal failure. This substance included in "middle molecules" (MM) fraction, was obtained by chromatography. This factor was shown to inhibit noticeably the proliferation of various cells : lymphocytes stimulated by allogeneic cells, monolayer cell lines of normal or tumorous origin and leukemic cell lines derived from acute lymphoblastic leukemia. This effect was reversible and thus could not be related to a direct, rapid cytotoxic effect of MM. Such substances could play an important part in uremic symptoms, such as immunodeficiency, anemia, thrombopenia, gastrointestinal or skin manifestations.

Diamine oxidase activity in plasma and urine in uremia

Diamine oxidase activity was measured in plasma or urine in 12 normal men, 4 men with chronic liver or heart disease, 13 men with chronic renal failure, and 12 men undergoing maintenance hemodialysis. Also in five studies in 4 patients, plasma diamine oxidase activity and total amine levels were measured at hourly intervals during a hemodialysis treatment. Plasma diamine oxidase activity was normal in patients with liver or heart disease and was at least three times normal in chronically uremic patients and in patients undergoing maintenance hemodialysis. Plasma diamine oxidase activities before and after a hemodialysis therapy were similar and did not change during dialysis until the 4th hour when they fell transiently; plasma total amine levels, which were elevated initially, tended to rise during the 4th hour of dialysis. Urinary diamine oxidase activity was reduced in the chronically uremic patients as compared to normal subjects. These observations are consistent with three alterations in diamine oxidase in patients with renal failure: activity (a) is increased in plasma of chronically uremic patients and those undergoing maintenance hemodialysis, (b) does not increase normally in response to heparin administration during dialysis therapy, and (c) is reduced in urine of chronically uremic patients.

Enzymuria as a marker of renal injury and disease: studies of N-acetyl-beta-glucosaminidase in the general population and in patients with renal disease

Urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) was shown to be reproducible in random urine specimens when expressed as the ratio of NAG to milligrams of urinary creatinine. The enzyme/creatinine ratio in 815 healthy people was relatively constant throughout childhood and adult life except for the first two years after birth and in individuals 56 years or greater. High ratios in the young children may be explained by low urinary creatinine excretion probably related to small body mass and reduced glomerular filtration rate at this age. The ratio was increased in adult uremic patients and children and adults with a variety of neurologic and obstructive lesions of the voiding mechanism. The presence of bacteriuria did not appear to increase the ratio. Significant enzymuria (greater than 2 SD above the mean for age and sex) was detected in 38 of 81 children with well-characterized renal disease. Among patients with predominantly glomerular disorders there was a close relationship between activity of the disease and enzymuria. In patients with tubulointerstitial disease enzymuria was frequent even in the absence of proteinuria. One of the highest enzyme/creatinine ratios was observed in a child with cystinosis. These studies indicate that NAG enzymuria is a sensitive indicator of activity of renal disease and may prove to be a suitable screening test for significant renal disease or injury in childhood.

Parathyroid hormone and calcitonin secretion in uraemic infants

In six infants aged between 4 and 8 months with chronic renal failure, we have studied blood levels of calcium (Ca), phosphorus (P), alkaline phosphatase, immunoreactive parathyroid hormone (PTH), and calcitonin (CT), as well as urinary excretion of Ca, P, hydroxyproline and cyclic AMP under basal conditions and during an infusion of 20 mg/kg of 10% Ca gluconate in normal saline over 4 h. Under basal conditions four infants had normal serum Ca and P values, alkaline phosphatase levels at the upper limit of normal, and very high PTH (range: 1450--2550 pg Eq/ml) and CT (range: 700--1900 pg/ml) levels. The urinary Ca excretion was low, whereas the urinary excretion of P, hydroxyproline and cyclic AMP was high. During Ca infusion, the total serum Ca and CT levels increased, PTH fell without however reaching the normal upper limit, and urinary P and cyclic AMP excretion decreased. In two infants with osteodystrophy and the highest levels of PTH (2900 and 3500 pg Eq/ml respectively) there was no suppression of PTH during Ca infusion.

[Effect of hematocrit variation on the urinary sodium excretion in normal and uremic dogs (author's transl)]

The effect of progressive increase in hematocrit on urinary sodium excretion was studied in normal and uremic dogs submitted to expansion of the extracellular fluid volume. In normal dogs concomitant with hematocrit increases it was observed a decrease in urinary sodium excretion. On the other hand in uremic dogs submitted to the same experimental conditions it was verified an increase in urinary sodium excretion.

beta2-Microglobulin in Balkan endemic nephropathy

The results of low molecular weight (LMW) proteinuria test in urines of patients and suspect subjects in an endemic area of Balkan endemic nephropathy (BEN) in Yugoslavia are reported. An accordance between the positive LMW test and the clinical diagnosis of BEN has been found in more than 70%. The authors claim that LMW immunodiffusion test is a very useful procedure for detecting BEN and a great aid in the epidemiological work in the endemic field. The results of determining beta2-microglobuline (beta2m) in serums and urines by radioimmunoassay technique as well as counting of clearances of endogenous creatinine in healthy persons, "endangered" subjects in endemic area, and BEN patients without azotemia, with azotemia and uremia are reported. The group of 17 patients suffering of BEN without azotemia having slightly or more markedly lowered creatinine clearances showed higher serum and much higher urinary concentration of beta2m which are not in proportion with creatinine clearance. The results are interpreted so far as a consequence of the predominant tubular lesion in BEN. In groups of patients with azotemia and uremia no differences in beta2m handling have been found. The report has a preliminary character and requires further study.

Isolation and identification of urinary beta-aspartyl dipeptides and their concentrations in human urine

beta-Aspartyl-methionine, -aspartic acid and -glutamic acid and gamma-glutamyl-threonine and -glycine were isolated and identified in human urine by ion-exchange chromatography, high-voltage paper electrophoresis, acid hydrolysis and determination of N-terminal amino acids of the isolated compounds, and comparison of their behaviors in paper electrophoresis and chromatography with those of the authentic compounds. The concentrations of acidic beta-aspartyl dipeptides in human urine were determined using an amino acid analyzer. Their concentrations were as follows: beta-aspartyl-glycine, male, 44.4 +/- 8.5, female, 61.4 +/- 18.9, child, 83.7 +/- 27.1; -alanine, male, 11.0 +/- 4.9, female, 20.7 +/- 12.0, child, 25.3 +/- 9.1; -glutamic acid, male, 10.0 +/- 3.7, female, 23.0 +/- 8.5, child, 20.4 +/- 7.5; -serine, male, 9.9 +/- 2.8, female, 13.6 +/- 3.8, child, 14.9 +/- 4.7; -aspartic acid, male, 4.3 +/- 1.0, female, 9.1 +/- 2.2, child, 18.4 +/- 6.5; -threonine, male 3.9 +/- 0.9, female, 5.8 +/- 1.1, child, 13.2 +/- 4.9 mumol/g creatinine (mean +/- S.D.). The order of the sum of their concentrations tended to be child greater than female greater than male. Patients receiving intravenous hyperalimentation also excreted acidic beta-aspartyl dipeptides into urine in amounts similar to those in females and in a pattern similar to that observed in healthy persons. This finding indicates that urinary beta-aspartyl dipeptides were probably of endogenous origin because oral nutrition was stringently excluded in these patients.

Urinary diagnostic indices in acute renal failure: a prospective study

A prospective analysis of the value of urinary diagnostic indices in ascertaining the cause of acute renal failure was undertaken. Our results show that in the setting of acute oliguria a diagnosis of potentially reversible prerenal azotemia is likely with urine osmolality greater than 500 mosm/kg H2O, urine sodium concentration less than 20 meq/litre, urine/plasma urea nitrogen ratio greater than 8, and urine/plasma creatinine ratio greater than 40. Conversely, a urine osmolality less than 350 mosm/kg, urine sodium concentration greater than 40 meq/liter, urine/plasma urea nitrogen ratio less than 3, and urine/plasma creatinine ratio less than 20 suggest acute tubular necrosis. A significant number of oliguric patients will not have urinary indices that fall within these guidelines. In this setting, urine sodium concentration divided by the urine-to-plasma creatinine ratio (the renal failure index) and the fractional excretion of filtered sodium provide a reliable means of differentiating reversible prerenal azotemia from acute tubular necrosis.

Primary hyperoxaluria (glycolic acid variant): a clinical and genetical investigation of eight cases

The clinical features of eight cases of primary hyperoxaluria have been summarized. The possibility of different phenotypes is discussed. A reduction, but no normalization, of the oxalate formation during pyridoxine therapy was found. A renal transplantation performed in one of the patients failed because of the formation of nephrocalcinosis.

Effect of arginine or creatinine administration on the urinary excretion of methylguanidine

The metabolic pathway of methylguanidine (MG) is mainly speculated from the change in urinary excretion of MG in the arginine (Arg)-injected normal rat, the creatinine (Cr)-injected normal rat, and the Arg-injected uremic rat. 15N-Arg was ingested to 2 uremic patients. Arg administration resulted in marked increase in urinary MG excretion both in the uremic rat and patient, but not in the normal rat. In the first phase of the 15N-Arg ingestion experiment, a rapid rise of 15N atom percent excess of urinary MG was observed in the uremic patient. In the second phase of this study, after 24 h of 15N-Arg ingestion, the 15N atom percent excess of urinary Cr and that of MG closely paralleled. These findings imply that there might be two metabolic origins of MG: one is a formation of MG from Arg itself or an Arg metabolite other than Cr, the other a pathway producing MG via Cr. The former is compatible with the hypothesis by Cohen.

Myo-inositol clearance in renal failure and in patients with normal kidney function

In order to determine the mechanism of elevated serum inositol in renal failure, the clearance values of inositol and of creatinine were measured in patients with normal kidney function and in those whose renal function was impaired due to varying causes. Mean serum inositol level in controls was 5.6 microgram/ml, and in patients with renal failure 28.6 microgram/ml. In control patients, inositol clearance was 2.8 ml/min, and tubular reabsorption of inositol was found to be over 97 percent. The inositol clearance of patients in renal failure varied from 0.62 to 17 ml/min. The ratio inositol clearance/creatinine clearance was elevated in uremic patients. Total amounts of inositol excreted in the urine of uremic patients were consistently higher than those excreted by control patients. The elevated serum inositol levels seen in renal failure were therefore not primarily caused by inability of the diseased kidney to excrete inositol.

Studies on digitalis. XI. Digitoxin metabolism in patients with impaired renal function

The metabolic pattern of cardioactive and conjugated digitoxin metabolites was studied in 10 uremic patients on maintenance treatment with digitoxin 24 hr after the last dose (mean dose, 0.060 mg/day). Urine was collected over 24 hr. The mean serum digitoxin level was 9.4 ng/ml, and urine level was 6.8 ng/ml. The metabolic pattern of cardioactive metabolites was studied in 5 patients on hemodialysis. Their mean serum digitoxin level was 6.3 ng/ml and urine level was 7.3 ng/ml, on a digitoxin dose of 0.072 mg/day. Unchanged digitoxin was the main cardioactive substance present in both serum and urine of uremic patients. Uremic patients had significantly less unchanged digitoxin and had more hydroxylated (DG-3) and hydroxylated and hydrolyzed (DG-2, DG-1, and DG-0) metabolites than control patients. The extent of conjugation was the same in the two groups. Our data suggest that uremic patients produce more digitoxose than control patients and that digitoxin elimination is more rapid in uremic patients. The altered pattern of digitoxin metabolites is most consistent with uremia-induced changes in hydroxylation and hydrolysis. The hemodialysis group had a pattern of digitoxin and cardioactive metabolites similar to control patients, indicating that patients on hemodialysis differ from other uremic patients with respect to digitoxin metabolism.

alpha1-Microglobulin, a new low molecular weight plasma protein

A new low molecular weight protein was purified from the urine of uraemic patients. The protein was found to be glycoprotein with a molecular weight of 31 500, determined by SDS-polyacrylamide gel electrophoresis, and a carbohydrate content of 19%. It was electrophoretically heterogenous and migrated in the slow alpha1-region. The mean serum level in 20 apparently healthy individuals was 32+/-10 mg/1. The serum level was normal in 5 patients with severe reduction of plasma protein synthesis caused by cirrhosis of the liver but elevated in patients with a decreased glomerular filtration rate. The mean urinary excretion in 5 healthy individuals was 1.3 mg/24 h. Increased excretion was seen in 10 patients with varying degrees of uraemia.

Relationship of urinary furosemide excretion rate to natriuretic effect in experimental azotemia

The relationship of natriuretic effect and furosemide excretion was studied in normal and azotemic dogs. Graded azotemia was produced in dogs by bilateral uretero-venous shunts of varying duration. The shunts were subsequently opened and urine and blood samples were taken to measure inulin, furosemide and sodium concentrations. Renal blood flow was measured by an electromagnetic flow probe. Two groups of dogs, control and experimental, were studied. The experimental group received a loading dose followed by a constant infusion of furosemide. This dose produced a natriuresis in nonazotemic normal dogs. The magnitude of this natriuresis correlated with furosemide excretion rate (P less than .005) and not with the plasma concentration of the drug. Furosemide clearance and extraction were inversely correlated with blood urea nitrogen. In the furosemide-treated group the augmentation of sodium excretion was not impaired except at blood urea nitrogen concentrations of greater than 200 mg/dl (two dogs). Thus the reduced clearance of furosemide may account in part for the high dose necessary. Further studies appear to be in order to clarify the relationship of the natriuretic response to furosemide to the rate of urinary excretion and plasma concentration of the drug.

Effect of urine metabolites from healthy and uremic subjects on gluconeogenesis in slices of rat kidney cortex and liver

A high molecular weight fraction was obtained by extended dialysis of urine of healthy and uremic subjects. After addition to the incubation medium, this fraction inhibited gluconeogenesis by rat kidney cortex slices. From the six subfractions extracted by gel chromatography (Sephadex G 100) fraction IV caused a decrease of glucose formation. The activity of PEP-carboxykinase but not of pyruvate carboxylase was reduced, indicating a decreased formation of phosphoenol pyruvate. The total high molecular weight fraction stimulated glucose release by liver slices from fed but not from starved rats. In the absence of amino acids, urea formation was not stimulated. The activity of pyruvate carboxylase was reduced in both groups, PEP-carboxykinase activity was, however, only reduced in the starved group. The addition of uremic serum caused increased glucose release. Inhibition of PEP-carboxykinase activity by quinolinic acid (15 mM) resulted in inhibition of glucose formation by 35% in the uremic group and 54% in the control group in livers of 24 hr starved rats. Thus in uremia there may be incorporation of serine carbon skeletons into glucose via hydroxypyruvate, not via pyruvate. Chromatography on calibrated columns indicated that about 40% of the urinary fractions had molecular weights in the upper range of the "middle molecules" category. The positive correlation between toxicity and the total amount of high molecular weight substances excreted do not confirm the hypothesis of augmented retention of "toxins" in uremic patients. It must be appreciated that these results refer only to the undialyzable fraction of urine which contains only 0.5% by weight of the total urine solids.

Enhanced end-organ responsiveness of the uremic kidney to the natriuretic factor

In chronic renal disease, the addition of a fixed quantity of Na to the extracellular fluid (ECF) will evoke a natriuretic response per nephron which is inversely proportional to the glomerular filtration rate (GFR). One factor that could contribute to this "magnification" phenomenon is an increased sensitivity of residual nephrons to physiologic natriuretic forces. The present studies were designed to examine this possibility. Natriuretic urine fractions from uremic patients, infused into one renal artery of normal rats, produced a small but significant unilateral natriuresis. Infusion of the same fractions in identical amount into remnant kidneys of stage II nonuremic rats (i.e., rats with a contralateral normal kidney in situ) produced a natriuresis in the remnant kidney only which was equivalent to that observed in the normal kidneys. The i.v. infusion of natriuretic fractions into stage II rats produced comparable increments in the fractional excretion of sodium (FENa) bilaterally. However, when the natriuretic fractions were infused into remnant kidneys of stage III rats (no contralateral kidney), deltaFENa was significantly greater than in the foregoing groups. Because stage III rats have increased control values for FENa, baseline FENa was increased to an equivalent level in normal rats by unilateral renal denervation. Natriuretic factor was administered into the ipsilateral renal artery. Although the natriuretic response was increased, it was significantly less than in the stage III remnant kidneys. The data support the view that the uremic state per se is associated with an enhanced responsiveness of the residual nephrons to the natriuretic factor found in the urine (and blood) of uremic patients.

Hypertension and renal disease in systemic lupus erythematosus

A retrospective analysis of 235 patients at the National Institutes of Health who met at least five criteria for systemic lupus erythematosus (SLE) indicated that 45% were hypertensive. Approximately two thirds of these hypertensive patients had creatinine clearances of more than 60 ml/min and nonnephrotic range proteinuria. Only 16% of normotensive patients had creatinine clearances of less than 60 ml/m9n. A subgroup of 36 patients with SLE and with biopsy-proved diffuse renal disease were studied. For these patients, the presence of hypertension could not be correlated with the degree of proteinuria or hematuria, with the level of serum complement, or with the presence of casts, focal necrosis, crescent formation, or interstitial inflammation. Hypertensive patients had a median age of 24.5 years; the majority had creatinine clearances of more than 60 ml/min. In SLE, hypertension is not necessarily associated with advanced renal disease, and high blood pressure may occur relatively early in the course of the disease.

On the influence of the natriuretic factor from patients with chronic uremia on the bioelectric properties and sodium transport of the isolated mammalian collecting tubule

A gel filtration fraction of urine from patients with chronic renal disease (natriuretic factor) has been shown previously to cause natriuresis in rats and to inhibit sodium transport in the isolated toad bladder. The effect of this fraction on transtubular potential difference and sodium transport was examined on the isolated perfused cortical collecting tubule of the rabbit. A rapid inhibition of potential difference from -22.5 mV to -12 mV (P less than 0.001) was observed when the fraction was applied to the peritubular surface. This effect was accompanied by a decrease in net sodium flux from 6.29 to 3.21 pmol/cm per s (P less than 0.001). Unidirectional fluxes using isotopic sodium revealed that the inhibition of net sodium transport was due to a decrease in flux from the lumen to the peritubular surface, i.e., an inhibition of active sodium transport. There was no change in sodium flux in the reverse direction. These changes were all rapidly reversed by removal of the fraction from the peritubular surface. The addition of the fraction to the lumen had no effect on potential difference or net sodium flux. Control studies using the same fraction from the urine of normal subjects had no effect on any of the parameters studies. Where both a uremic and a normal fraction were sequentially applied to the peritubular surface of the same tubule, inhibition of potential difference was obtained only with the former. In the light of evidence implicating the collecting duct fraction from normal animals, the data are consistent with the view that the natriuretic factor may be biologically important in the regulation of sodium balance via it's regulatory role in active sodium transport in the collecting tubule.

Inhibition of bovine renal adenylate cyclase by urinary products

The secondary hyperparathyroidism in uremic patients is due to the modification plasma electrolyte concentrations accompanied by a renal resistance to PTH action. We postulate that the retention of a uremic toxin could be at least partly responsible for this resistance. We have tested this hypothesis "in vitro" by measuring the action of Middle Molecules on the adenylate cyclase activity stimulated by NaF, PTH and isoproterenol.

The roles of renal catabolism and uremia in modifying the clearance of fibrinogen and its degradative fragments D and E

Elevated levels of fibrinogen/fibrin degradation products (FDP) occur in uremia, and have been thought to be in part related to intravascular coagulation in the kidney. More recent data indicated that delayed catabolism of fibrinogen fragment D occurred in anephric animals. To further evaluate FDP catabolism in the kidney, turnover studies of purified dog 131I-Fg-D and 125I-Fg-E were performed on dogs before and after acute subtotal nephrectomies, and later during chronic uremia. 131I-fibrinogen clearances were also perfomed. Slowed catabolism of Fg-D and Fg-E was observed in both the acute and chronic uremic stages. Altered urinary excretion was not a factor as only minimal amounts of Fg-D and Fg-E were excreted in the urine of the control animals. In the 131I-fibrinogen studies, there were significant changes in plasma volume, fibrinogen t 1/2, and intravascular/extravascular distribution, but not in fractional catabolic rate. To differentiate fully, the effects of uremia from those of loss of catabolic renal tissue, the Fg-D and Fg-E turnover studies were repeated on other animals with intact kidneys whose ureters were diverted into the peritoneum and compared to subsequent studies after total nephrectomy. The control and ureter-severed studies had the same clearance pattern, whereas decreased catabolism occurred in the nephrectomized dogs. The results demonstrate uremia per se does not have a major effect upon the catabolism of fibrinogen, Fg-D, and Fg-E. Loss of renal tissue does impair the clearance of Fg-D and Fg-E, indicating these proteins are normally catabolized in part by the kidneys. Thus elevated plasma FRA in uremic patients may reflect decreased Fg-D and Fg-E catabolism rather than increased FDP production from primary or secondary fibrinolysis.

Parathyroid hormone and vertebral osteosclerosis in uremic patients

Six out of 30 patients with chronic renal failure showed osteosclerosis in the lateral radiograph of the lumbar spine. When two groups with a similar degree of renal impairment were compared, the patients with osteosclerosis were younger and had a significantly higher level of circulating PTH (p less than 0.05) and total hydroxyproline excretion (p less than 0.02), than patients without overt osteosclerosis. The metacarpal cortical thickness was significantly reduced in patients with vertebral osteosclerosis. The results suggest that in patients with chronic uremia endogenous hypersecretion of PTH is one of the most significant factors responsible for the development of osteosclerosis. The mineral released from other skeletal sites could be utilized in the mineralization of the newly formed trabecular bone without any external calcium gain.

Determination of endogenous middle molecules in normal and uremic body fluids

Methods have been developed which allow the separation and quantitation of middle molecules in biological fluids. The methods involve a newly developed high speed gel filtration technique (HSGF) combined with gradient ion exchange chromatography (GEC). The solutes were detected at 254 an 206 nm. The molecular weight range of the fractions isolated by HSGF was assessed with standards of known molecular weight. By the HSGF method normal and uremic plasma and urine were separted into 10 to 11 peaks based upon differences in molecular size. One of these peaks, no.7, which was present in uremic plasma but not detected in non-uremic plasma contained middle molecules (mol wt 1000-2000). Amino-acid analysis before and after acid hydrolysis showed this peak to contain a mixture of peptides. Using the GEC method peak 7 was further separated into 7-8 new peaks (7a,b,c, etc.). Plasma from six normal subjects and six non-uremic patients with various diseases yielded only two peaks, 7f and g, whereas urine from normal subjects, and plasma and urine from uremic patients contained all or most of these peaks. Amino-acid analysis of peak 7c, which was frequently found prominent in severly uremic patients indicates that it consists of a small peptide chain containing 8-10 amino acids.

Abnormal hydroxyproline polypeptides in the urine of patients with chronic uremia

An abnormal peak of hydroxyproline polypeptides has been observed when the polypeptide fraction from the urines of patients with advanced chronic uremia was subjected to gel chromatography. This abnormality was apparently related to the degree of uremia and to the presence of uremic osteodystrophy. The abnormal peak was not observed in patients with high turnover bone disease without renal insufficiency and in patients with nephrotic syndrome and normal glomerular filtration rate.

Determination of hydroxyproline polypeptides in urine and blood serum by gel filtration

Hydroxyproline-containing polypeptides were isolated from urine by filtration on polyacrylamide gel Bio-Gel P-2. This fraction was quantitatively and qualitatively similar to the nondialysable hydroxyproline in urines of normal adult subjects, patients with chronic uremia, and with primary or secondary hyperparathyroidism. Hydroxyproline polypeptides isolated from urines of patients with extensive Paget's disease or from normal growing subjects contained a group of smaller polypeptides slightly retarded on Bio-Gel P-2 which were not retained by the dialysis membrane Spectrapor-TM. In these two groups of subjects the values of hydroxyproline polypeptides were 35-45 percent higher than those of dialysable hydroxyproline. Increased excretion of hydroxyproline polypeptides was found in chronic uremia, primary and secondary hyperparathyroidism, Paget's bone disease and in normal growing subjects. With the notable exception of chronic uremia the excretion of hydroxyproline polypeptides paralleled that of total and oligopeptidic hydroxyproline. In some cases of chronic uremia the polypeptidic hydroxyproline represented the predominant fraction. On long columns of Bio-Gel P-6 hydroxyproline polypeptides separated into several peaks. The chromatographic pattern was rather characteristic for chronic uremia, secondary hyperparathyroidism, Paget's bone disease and physiological growth. Ahydroxyproline fraction of similar chromatographic properties was isolated from blood serum after deproteinisation with heat or ethanol at pH 4.8. High serum levels of this hydroxyproline fraction were observed in pathological conditions with increased urinary excretion of polypeptidic and nondialysable hydroxyproline.

Uricosuric agents in uremic sera. Identification of indoxyl sulfata and hippuric acid

Serum and urine from chronically uremic patients and normal individuals were subjected to gel filtration of Sephadex-G10. The effects of the eluted fractions on the uptake of urate and para-aminohippurate by isolated cortical tubules of rabbit kidney were investigated. According to the origin of the samples, one to three major groups of fractions inhibiting both urate and para-aminohippurate transport were disclosed. The first eluted group occurred for all the samples under study. The second one was demonstrated in both sera and urines from uremic patients but only in urines from normal individuals. The third one was exclusively detected in uremic sera and urines. Among all the compounds identified, only hippuric acid, eluted in the fractions of the second group, was capable of inhibiting the uptake of urate and para-aminohippurate in vitro. The concentration for which this inhbiitory effect of hippuric acid occurred was in the range of that existing in uremic sera. Indoxyl sulfate, which accumulates to very high concentrations in uremic serum, could not be disclosed in the above-mentioned fractions. This is explained by the strong adsorption of this indole derivative to Sephadex gel. Potassium indoxyl sulfate, when tested in vitro at the concentration existing in uremic serum, substantially inhibited the uptake of both urate and para-aminohippurate. In normal subjects, ingestion of hippuric acid or potassium indoxyl sulfate significantly increased fractional urinary excretion of uric acid. On the basis of these results, it is suggested that progressive retention of hippuric acid, indoxyl sulfate, and other yet unidentified inhibitors may explain the gradual increase in urinary fractional excretion of urate observed in uremia. The present results may be viewed as an example of a mechanism in which retention of normally excreted end products is responsible for adaptation of tubular transport in uremic subjects.