Nephrotic Syndrome Rats Research Articles

Proteinuria and plasma compositional changes contribute to defective lipoprotein catabolism in the nephrotic syndrome by separate mechanisms

Triglyceride (TG)-rich lipoproteins are primarily increased in the nephrotic syndrome (NS) as a result of decreased catabolism. Lipoprotein lipase (LpL) is the rate limiting enzyme for lipolysis of TG. The biologically active endothelial bound LpL pool is reduced in NS providing one mechanism for decreased clearance of very low density lipoprotein (VLDL). LpL, however, is also reduced in the Nagase Analbuminemic Rat (NAR) to the same extent as in NS, suggesting that other factors contribute to decreased VLDL clearance. Hyperlipidemia worsens with the onset of proteinuria and is reduced when proteinuria abates. We established that while VLDL from NS rats bind poorly to bovine aortic endothelial cells (BAEC) in the presence of saturating LpL while, VLDL from NAR bind more avidly than control. We then established that rat aortic endothelial cells (RAEC) incubated with serum from NAR or from NS rats bind significantly less exogenous LpL. Thus decreased clearance of VLDL in NS results from: 1) reduced endothelial bound LpL; an effect of serum from animals with reduced oncotic pressure (π) that makes cells unable to bind LpL; and 2) an alteration in VLDL binding to endothelial bound LpL. The former has no relationship to proteinuria while the latter occurs as a consequence of proteinuria. These effects combine to suppress VLDL clearance.

Glomerulosclerosis in adriamycin-induced nephrosis is accelerated by a lipid-rich diet.

The present study was performed to determine quantitatively the effect of hypercholesterolemia induced by a lipid-rich diet on glomerulosclerosis in an animal model of nephrotic syndrome (NS) induced by Adriamycin (ADR). Twenty NS Wistar rats administered ADR with a single intravenous dose of 5 mg/kg body weight were divided into standard and lipid-rich chow groups. Another 20 weight-matched non-NS rats that received a vehicle alone were grouped as controls. Quantitative analyses of renal histological changes were performed with determination of blood and urine biochemical parameters. It was found that serum cholesterol was markedly higher in rats with lipid-rich chow in both NS and non-NS rats. Urinary protein was significantly higher in rats on the lipid-rich diet in the NS group. The mesangial matrix and cell indices were significantly increased in rats with the lipid-rich diet and the most obvious changes were found in the NS group. Lipid deposits and foam cells were observed in mesangial areas, and some glomeruli had progressed to form focal and segmental glomerulosclerosis in the NS group. Findings indicated that diet-induced hyperlipidemia can lead to proliferation of mesangial cells and accumulation of mesangial matrices, and further aggravate glomerulosclerosis in Adriamycin-induced nephrosis.

Down-regulation of hepatic high-density lipoprotein receptor, SR-B1, in nephrotic syndrome

Nephrotic syndrome (NS) is a prototype of acquired hypercholesterolemia. Hepatic synthesis and removal of cholesterol play major roles in the regulation of plasma concentration of this sterol. Low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particles are the primary vehicles for cholesterol transport to the liver. We have recently demonstrated that NS results in acquired hepatic LDL receptor deficiency in rats. This study was undertaken to determine the effect of NS on hepatic expression of the newly discovered, long-sought HDL receptor. Hepatic HDL receptor and apolipoprotein A-I (apo A-I) expressions were studied in rats with puromycin-induced NS. The results were compared with those obtained in placebo-treated, normal controls. The NS group exhibited a marked reduction in hepatic tissue HDL receptor protein abundance when compared with the control group. In contrast, hepatic HDL receptor mRNA abundance in the NS group was similar to that of the control group. As expected, the NS group showed a marked increase in hepatic apo A-I mRNA abundance. The study explored the effect of experimental NS on hepatic HDL receptor expression, and the results revealed a marked down-regulation of HDL receptor in rats with NS. In contrast, hepatic expression of Apo A-I, the principal protein constituent of HDL, was markedly increased in NS rats. The HDL receptor deficiency shown here can potentially limit the efficiency of HDL as the primary vehicle for reverse cholesterol transport in NS.

Reflex influences on renal nerve activity characteristics in nephrosis and heart failure.

Cardiac baroreflex regulation of efferent renal sympathetic nerve activity (ERSNA) is abnormal in nephrotic syndrome (NS). The purpose of the present study was to examine the responses of amplitude and frequency of synchronized ERSNA discharge in anesthetized NS rats subjected to reflex maneuvers that alter the activity of and the interaction between aortic and cardiac baroreceptors. Steady-state ERSNA was analyzed in three groups of anesthetized rats: control, NS, and congestive heart failure (CHF) (in the latter, the defect in cardiac baroreflex regulation of ERSNA is peripheral rather than central). In protocol A, analysis was performed during control, after bilateral aortic depressor nerve section, after bilateral cervical vagus nerve section, and during central vagus nerve stimulation (VAGSTIM). In protocol B, analysis was performed during control, after bilateral cervical vagus nerve section, after bilateral aortic depressor nerve section, and during central aortic depressor nerve stimulation. In protocol A, VAGSTIM decreased ERSNA and peak height (fewer active fibers), but not peak frequency, in control and CHF but not NS rats. In NS rats, this lack of effect of VAGSTIM was specific for ERSNA, because depressor and bradycardia responses to VAGSTIM were unaffected. In protocol B, central aortic depressor nerve stimulation decreased ERSNA and peak height, but not peak frequency, in control, CHF, and NS rats similarly. It is concluded that the defect in cardiac baroreflex function in NS is specific for ERSNA, is central rather than peripheral, and affects the number of active renal sympathetic nerve fibers rather than their firing frequency.

Characteristics of renal sympathetic nerve activity in sodium-retaining disorders.

Characteristics of renal sympathetic nerve activity in conscious rats with established congestive heart failure, cirrhosis, or nephrotic syndrome were analyzed using three methods: mean integrated voltage over time, power spectrum analysis, and sympathetic peak detection analysis. Compared with control rats, all three disease models had increased mean integrated voltage. On power spectrum analysis, all three disease models had increased relative power at the heart rate frequency, indicating that it was related to renal sympathetic nerve discharge coupled to the cardiac cycle. Congestive heart failure and nephrotic syndrome rats showed increased relative power in the low-frequency range, whereas cirrhotic and nephrotic syndrome rats showed decreased relative power in the high-frequency range. On sympathetic peak detection analysis, the frequency of sympathetic peaks was greater in the three disease models compared with the control rats. In cirrhotic rats, the distribution of sympathetic peak heights was shifted toward an increased number of peaks of lesser height. It is concluded that basal renal sympathetic nerve activity is chronically increased in these disease models. This is manifest as increased power coupled to the cardiac cycle, which may reflect the disease-specific defects in arterial and cardiac baroreflex control. In cirrhosis, there is possible selective activation of a subgroup of renal sympathetic nerve fibers.

Hemodynamics and baroreflex function in rats with nephrotic syndrome

The excess renal sodium retention leading to edema formation in the nephrotic syndrome (NS) is substantially dependent on increased efferent renal sympathetic nerve activity (RSNA). This study examined whether the hypoalbuminemia in NS is reflected as a decrease in cardiac output or cardiac function and whether the increased RSNA in NS is due to alterations in arterial and/or cardiopulmonary baroreflex function. NS was induced in rats with adriamycin (3.5 mg/kg i.v.), and they were studied 4 wk after injection. Mean arterial pressure (MAP) was similar in control (C) and NS rats. Cardiac indexes (CIs; cardiac output/body wt) were 29 +/- 1 and 26 +/- 1 ml.min-1.100 g-1 in C and NS rats, respectively. Total peripheral resistance indexes were significantly greater in NS than in C rats (4.7 +/- 0.2 vs. 4.1 +/- 0.1 mmHg.100 g.min.ml-1). Cardiac function during increases in cardiac filling pressure was not different between C and NS rats. The afferent limb of the arterial baroreflex was assessed by measuring aortic depressor nerve activity (ADNA) while the efferent limb was assessed by measuring RSNA in C and NS rats during increases in MAP. The central component of the arterial baroreflex was assessed from plots of RSNA (output) vs. ADNA (input). Comparisons between C and NS rats before and after vagotomy revealed no differences in the gains of any component of the arterial baroreflex. The cardiopulmonary baroreflex was assessed in a similar manner by measuring afferent vagus nerve activity (VGNA) and efferent RSNA during volume expansion before and after sinoaortic denervation (SAD). Before SAD, gains were similar in C and NS rats. After SAD, gains of the total (-1.59 +/- 0.44 vs. -3.64 +/- 0.65%/mmHg) and the central/efferent limb (-0.26 +/- 0.07 vs. -0.67 +/- 0.14 %/%) were significantly reduced (P < 0.05) in NS compared with C rats while the gain of the afferent limb of the reflex was similar in C and NS rats. These results indicate that NS rats with significant hypoalbuminemia maintain an arterial pressure similar to C rats by increasing total peripheral resistance, which serves to offset the tendency to a lower CI. Arterial baroreflex function in NS does not differ from that in C, but decreased cardiopulmonary baroreflex inhibition of RSNA in NS may contribute to the increased RSNA.

Mechanism of enhanced Na-K-ATPase activity in cortical collecting duct from rats with nephrotic syndrome.

The maximal hydrolytic activity of Na-K-ATPase is specifically increased in the cortical collecting duct (CCD) of rats with puromycin-induced nephrotic syndrome (NS). This stimulation is independent of aldosterone and of endogenous ouabain-like substance. To investigate the mechanism responsible for this change, we compared the maximal Na-K-ATPase hydrolytic activity, the ouabain sensitive 86Rb influx, the specific [3H]ouabain binding, and the sensitivity of Na-K-ATPase to ouabain in the CCD of control rats and of rats given an intraperitoneal injection of puromycin 7 d before study. Both Na-K-ATPase activity and ouabain-sensitive 86Rb influx increased two-fold in rats with NS (ATPase activity: 34.1 +/- 2.1 vs. 18.0 +/- 0.7 pmol.mm-1 x min-1 +/- SE, n = 6, P < 0.001; Rb influx: 14.4 +/- 0.7 vs. 7.4 +/- 0.4 peq.min-1 +/- SE, n = 6, P < 0.001) whereas specific [3H]ouabain binding decreased in rats with NS (6.9 +/- 0.7 vs. 9.0 +/- 0.6 fmol.mm-1 +/- SE, n = 6, P < 0.005). Therefore, the maximal turnover rate of Na-K-ATPase increased over twofold in rats with NS (5,053 +/- 361 vs. 2,043 +/- 124 cycles.min-1 +/- SE, n = 6, P < 0.001). Analysis of the curves of inhibition of Na-K-ATPase by ouabain showed the presence of two Na-K-ATPase populations in both control and NS rats: a highly sensitive population (apparent Ki: 1.4 x 10(-6) M and 0.9 x 10(-6) M) and a less sensitive moiety (apparent Ki: 2.6 x 10(-4) M and 1.1 x 10(-4) M). The enhancement of Na-K-ATPase activity observed in the CCD of rats with NS was entirely due to the stimulation of the population of Na-K-ATPase with low ouabain sensitivity. These results suggest that a dysregulation of this subclass of Na-K-ATPase might be the primary cause of sodium retention in this model of nephrotic syndrome.

Tubular resistance to furosemide contributes to the attenuated diuretic response in nephrotic rats.

A blunted response to loop diuretics frequently occurs in nephrotic syndrome (NS). Observations that nephrotic humans have reduced sodium excretion at normal rates of diuretic excretion have suggested that tubular resistance to the drug may contribute to diuretic resistance. To determine if tubular resistance to furosemide exists in NS, late proximal and early distal tubular micropuncture was performed in rats with puromycin aminonucleoside-induced NS and in control rats after an i.v. bolus dose of furosemide of 1 mg/kg body wt. Absolute and fractional urinary sodium excretions were less (P less than 0.05) in NS rats than in control rats after furosemide. Inulin clearance and total urinary furosemide excretion, however, were not different between groups. Thus, similar to reports in humans, the urinary sodium-to-furosemide excretion ratio was less (P less than 0.05) in NS than in control rats. Single-nephron GFR and chloride delivery to late proximal sites were not different between groups after furosemide. In contrast, absolute and fractional chloride deliveries to early distal sites were less (P less than 0.05) in NS rats after furosemide. Calculated loop chloride reabsorption after furosemide was greater (P less than 0.05) in NS than in control rats when expressed either as percentage of filtered load (39.4 +/- 3.1 versus 28.2 +/- 2.0%) or delivered load (67.9 +/- 4.7 versus 48.3 +/- 3.0%). Loop fluid reabsorption was not different between groups. Thus, loop chloride reabsorption is inhibited to a lesser extent by i.v. furosemide in NS than in normal rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Anticoagulant and antithrombotic effects of low-molecular-weight heparin

Low molecular weight heparin (Mr 8 kDa) was prepared from conventional heparin (Mr 18 kDa) by the chromatography on DEAE-sephadex with the recovery of 56%. Low molecular weight heparin had less affinity to antithrombin III than unfractionated heparin and had less anticoagulant and anti-IIa activities. The anti-Xa activity of low molecular weight heparin exceed by 17% the activity of conventional heparin. In the experiments on rats it was determined that the biological half-life of low molecular weight heparin exceed two-fold that of the unfractionated heparin. In the modified model of the arteriovenous shunt thrombosis in normal and nephrotic syndrome rats it was shown that the low molecular weight heparin was the most efficient antithrombotic remedy in normal and decreased level of antithrombin III in the organism.

Renal response to atrial peptides is reduced in experimental nephrosis.

The aim of this study was to evaluate the renal response to atrial extracts (AE) and synthetic atrial natriuretic factor (ANF) in control rats and in rats with experimental nephrotic syndrome (NS). NS was obtained by a single intravenous injection of adriamycin (7.5 mg/kg). Bolus injection of AE from normal or NS rats resulted in marked increase of diuresis and natriuresis in bioassay control rats (AE from normal rats, urine flow rate, 14.87 +/- 2.94 to 186.18 +/- 55.86 microliters/min; Na excretion, 0.68 +/- 0.26 to 21.80 +/- 5.45 mu eq/min; AE from NS, urine flow rate, 13.49 +/- 4.30 to 167.14 +/- 51.44 microliters/min; Na excretion, 0.98 +/- 0.57 to 20.71 +/- 9.76 mu eq/min). In contrast, blunted diuretic (from 11.26 +/- 3.05 to 65.20 +/- 27.30 microliters/min) and natriuretic (from 0.58 +/- 0.15 to 4.52 +/- 1.59 mu eq/min) effect was observed when AE were injected in rats with NS. Injection of the vehicle in which AE were dissolved or ventricular extracts did not increase urinary flow rate or Na excretion in both control and NS animals. Bolus injection of synthetic ANF (Arg-101-Tyr-126) induced marked diuretic and natriuretic response in control but not in NS rats. Similar results were obtained when AE were infused by constant infusion in control or in NS bioassay rats. AE given by constant infusion induced comparable increase in glomerular filtration rate (GFR) over basal values both in control and NS animals (controls, 39%; NS rats, 40%).(ABSTRACT TRUNCATED AT 250 WORDS)

Renal sodium retention during volume expansion in experimental nephrotic syndrome

We have studied sodium retention during volume expansion in rats with autologous immune complex nephropathy (AICN), a model of nephrotic syndrome (NS) in which GFR after volume expansion was not different from that in adjuvant-injected controls (C). AICN rats developed heavy proteinuria (298 +/- 27 vs. less than 10 mg/day), hypoalbuminemia (2.14 +/- 0.15 vs. 3.08 +/- 0.12 g/100 ml) and hypercholesterolemia (181 +/- 22 vs. 58 +/- 4 mg/100 ml). After saline, there were no significant differences in blood pressure (119 +/- 2 vs. 114 +/- 2 mm Hg), renal plasma flow (4.9 +/- 0.41 vs. 4.1 +/- 0.28 ml/min), inulin clearance (1.37 +/- 0.06 vs. 1.55 +/- 0.10 ml/min), or SNGFR (47 +/- 2 vs. 53 +/- 4 nl/min). Sodium excretion, however, was significantly lower in NS rats (4.7 +/- 1.1 vs. 9.2 +/- 1.2 muEq/min). Proximal sodium reabsorption was decreased in NS rats (35 +/- 2 vs. 41 +/- 2%, 2.5 +/- 0.2 vs. 3.3 +/- 0.2 nEq/min). Sodium delivery into the loop, however, was equal in NS and C, since the slightly lower filtered load in NS rats offset the depression in proximal reabsorption. Sodium reabsorption by the loop and by the distal convoluted tubules were equal in NS and C. Thus, sodium delivered into the cortical collecting ducts was the same in both groups (0.33 +/- 0.17 vs. 0.34 +/- 0.07 nEq/min; 4.5 +/- 0.6% of filtered sodium vs. 4.4 +/- 0.3%). The percent of filtered sodium excreted in the urine, however, was significantly lower in the NS rats, 2.18 +/- 0.48% vs. 4.0 +/- 0.58%. We conclude that antinatriuresis in this model of NS is determined beyond the superficial late distal convoluted tubule. The inability to excrete the sodium load during volume expansion is due to either enhanced reabsorption by the collecting duct or to abnormal function in deep nephrons.