Lovastatin enhances ecto-5'-nucleotidase activity and cell surface expression in endothelial cells: implication of rho-family GTPases

Extracellular adenosine production by the GPI-anchored Ecto-5'-Nucleotidase (Ecto-5'-Nu) plays an important role in the cardiovascular system, notably in defense against hypoxia. It has been previously suggested that HMG-CoA reductase inhibitors (HRIs) could potentiate the hypoxic stimulation of Ecto-5'Nu in myocardial ischemia. In order to elucidate the mechanism of Ecto-5'-Nu stimulation by HRIs, Ecto-5'-Nu activity and expression were determined in an aortic endothelial cell line (SVAREC) incubated with lovastatin. Lovastatin enhanced Ecto-5'-Nu activity in a dose-dependent manner. This increase was not supported by de novo synthesis of the enzyme because neither the mRNA content nor the total amount of the protein were modified by lovastatin. By contrast, lovastatin enhanced cell surface expression of Ecto-5'-Nu and decreased endocytosis of Ecto-5'-Nu, as evidenced by immunostaining. This effect appeared unrelated to modifications of cholesterol content or Ecto-5'-Nu association with detergent-resistant membranes. The effect of lovastatin was reversed by mevalonate, the substrate of HMG-CoA reductase, by its isoprenoid derivative, geranyl-geranyl pyrophosphate, and by cytotoxic necrotizing factor, an activator of Rho-GTPases. Stimulation of Ecto-5'-Nu by lovastatin enhanced the inhibition of platelet aggregation induced by endothelial cells. In conclusion, lovastatin enhances Ecto-5'-Nu activity and membrane expression in endothelial cells. This effect seems independent of lowering cholesterol content but could be supported by an inhibition of Ecto-5'-Nu endocytosis through a decrease of Rho-GTPases isoprenylation.

Two apical multidrug transporters, P-gp and MRP2, are differently altered in chronic renal failure

Tubular function is altered in chronic renal failure (CRF). Whether drug secretion by renal tubules is modified in CRF is questioned because of frequent accumulation of various toxins in CRF. This function mainly involves ATP-dependent drug transporters, particularly P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP) 2, both present in apical membrane of epithelial cells. The present study was aimed at determining the changes in P-gp and MRP2 expression induced by experimental CRF in kidney and liver. The relationship between MRP2 and glutathione metabolism changes was examined because MRP2 transports GSSG and glutathione conjugates. Rats underwent either 80% subtotal nephrectomy (Nx) or sham operation, and determinations were performed 3 and 6 wk later. CRF induced a 70--200% rise in protein and mRNA expression of MRP2 after 3 and 6 wk post-Nx in remnant kidney and after 6 wk in liver. However, P-gp expression was unchanged by CRF. Relative to whole kidney mass, total MRP2 levels decreased by only 27% in Nx rats whereas total P-gp levels were reduced by 60%. Renal GSSG and total glutathione levels were increased by 30% in Nx rats, but glutathione-S-transferase (GST) activity was normal; liver GSSG levels and GST activity were reduced in Nx rats. In conclusion, CRF resulted in specific overexpression of MRP2 in kidney and liver. This could be an adaptative response to some elevated circulating toxins. The later MRP2 induction and different glutathione changes in liver compared with kidney suggest different mechanisms for MRP2 induction and/or action in these two tissues.

Sulfate homeostasis, NaSi-1 cotransporter, and SAT-1 exchanger expression in chronic renal failure in rats

BACKGROUND

It is known that hypersulfatemia, like hyperphosphatemia, occurs in chronic renal failure (CRF). The aim of this study was to assess the effects of CRF on sulfate homeostasis and on sodium sulfate cotransport (NaSi-1) and sulfate/oxalate-bicarbonate exchanger (Sat-1) expression in the kidney. In addition, sulfate homeostasis was compared with phosphate homeostasis.

METHODS

Experimental studies were performed in adult male rats at three and six weeks after 80% subtotal nephrectomy (Nx) or sham-operation (S) (N = 9 per group). Transporter protein and mRNA expressions were measured by Western blot and RNase protection assay (RPA), respectively. Results were quantitated by densitometric scanning (Western) and electronic autoradiography (RPA), and were expressed in densitometric units (DUs; Western) and cpm (RPA).

RESULTS

Creatinine clearance was lower in Nx-3 compared with S-3 rats (0.23 vs. 0.51 mL/min/100 g body weight, P < 0.001) and was further impaired in Nx-6 rats (0.15 vs. 0.48, P < 0.001). Sulfatemia was significantly higher in Nx-3 rats (1.08 vs. 0.84 mmol/L, P < 0.05) and further increased in Nx-6 rats (1.42 vs. 0.90 mmol/L, P < 0.01). Fractional sulfate excretion (FESO4) was increased by twofold in Nx-3 and Nx-6 rats compared with corresponding S rats. Phosphatemia did not differ between Nx-3 rats and controls, but was increased in Nx-6 rats (P < 0.01). Total amounts of both NaSi-1 and Sat-1 proteins were significantly decreased in both Nx-3 and Nx-6 rats when compared with controls. However, NaSi-1 protein and mRNA densities did not significantly change in Nx-3 rats, but were significantly increased in Nx-6 rats when compared with controls (4.8 vs. 3.7 DU/microg protein, P < 0.05, and 7.1 vs. 2.8 cpm/microg RNA, P < 0.01, respectively, for protein and mRNA). In contrast to NaSi-1, Sat-1 protein density was significantly decreased both in Nx-3 (2.9 vs. 3.6 DU/microg protein, P < 0.05) and Nx-6 rats (2.4 vs. 3.4 DU/microg protein, P < 0.05), and Sat-1 mRNA density significantly decreased in Nx-6 rats (10.7 vs. 14.7 cpm/microg RNA, P < 0.05). Na-PO4 cotransporter (NaPi-2) protein total abundance and density were decreased at three and six weeks in Nx rats.

CONCLUSIONS

These results demonstrate that both NaSi-1 and Sat-1 total protein abundances are decreased in CRF, which may contribute to the increase in fractional sulfate excretion. Strikingly, NaSi-1 density was not decreased in CRF three weeks after Nx, and furthermore, increased six weeks after Nx, in contrast to NaPi-2 density, which was decreased at both times. The significance of this difference remains to be determined, but may explain why hypersulfatemia occurs earlier than hyperphosphatemia in CRF.

Influence of renal failure on intestinal clearance of ciprofloxacin in rats

Following intravenous doses, ciprofloxacin pharmacokinetics in control and nephrectomized rats were studied. There were no differences between control and nephrectomized rats for area under the concentration-time curve in plasma or biliary clearance. The intestinal clearance of ciprofloxacin was increased in nephrectomized rats. Intestinal elimination seems to compensate partially for the decrease in urinary excretion of ciprofloxacin in nephrectomized rats.

Influence of renal failure on ciprofloxacin pharmacokinetics in rats

Ciprofloxacin pharmacokinetics have been shown to be modified in patients with renal failure (e.g., the intestinal secretion of ciprofloxacin is increased). This study investigated the influence of renal failure on the pharmacokinetics of ciprofloxacin following oral and parenteral administration to rats of a dose of 50 mg/kg of body weight. After parenteral administration, only renal clearance (CLR) was reduced in nephrectomized rats (5.3+/-1.4 versus 17.8+/-4.7 ml/min/kg, P < 0.01, nephrectomized versus control rats). However, nonrenal clearance was increased in nephrectomized rats (32+/-4 versus 15+/-5 ml/min/kg, P < 0.01, nephrectomized versus control rats), suggesting compensatory mechanisms for reduced renal function. After oral administration, apparent total clearance and CLR were reduced (P < 0.01) in nephrectomized rats (117+/-25 and 6.8+/-4.4 ml/min/kg, respectively) compared with the values for control rats (185+/-9 and 22.6+/-5.3 ml/min/kg, respectively) and the area under the concentration-time curve was higher (P < 0.01) for nephrectomized rats (436.3+/-90.5 mg. min/liter) than for control rats (271.3+/-14.3 mg.min/liter). Terminal elimination half lives in the two groups remained constant after oral and parenteral administration. These results suggest an increased bioavailability of ciprofloxacin in nephrectomized rats, which was confirmed by a nonlinear mixed-effect model.

Subtotal nephrectomy alters tubular function: effect of phosphorus restriction

Few studies have examined tubular function after subtotal nephrectomy (Nx) and conservative treatments. The effects of 70% and 80% Nx (associated with dietary phosphate restriction in the latter case) on the apical brush border membrane (BBM) enzymes 5'-nucleotidase, gamma glutamyl-transferase and alkaline-phosphatase, and one BBM Na-phosphate cotransporter (NaPi-2) were studied in rats after a six week period. Changes in activity and mRNA abundance of the BBM enzymes and in NaPi-2 protein and mRNA abundance were compared with changes in the distal markers of Na,K-ATPase activity and epidermal growth factor (EGF) production. The activity, but not the mRNA of BBM enzymes, was moderately reduced by the 70% Nx. Both the mRNA and activity of gamma glutamyl-transferase and alkaline-phosphatase were decreased in the 80% Nx, and the NaPi-2 mRNA, protein and Na,K-ATPase activities were also reduced. These effects (except for 5'nucleotidase and Na,K-ATPase) were partly reversed by phosphate restriction. Overproduction of EGF occurred after the 70% Nx, was blunted in the 80% Nx, and then partially restored by phosphate restriction. Aggravation of tubular alteration was associated with enhanced renal hyperplasia (increased DNA mass), reduced GFR and hyperphosphatemia, and high PTH levels, but reduced cAMP excretion. Improvement following phosphate restriction was associated with reduced hyperplasia and lowering of phosphatemia and PTH levels. These data demonstrate that Nx selectively affected BBM function through transcriptional changes that were partially reversed by phosphate restriction. Regulatory factors involved in these changes may include intracellular phosphate content and growth factors, but not the PTH effects that are impaired in chronic renal failure.

Accelerated glycogenolysis in uremia and under sucrose feeding: role of phosphorylase alpha regulators

To understand the mechanism of hepatic glycogen depletion found in uremia and under sucrose feeding, we examined net hepatic glycogenolysis-associated active enzymes and metabolites during fasting. Liver was taken 2, 7, and 18 h after food removal in uremic and pair-fed control rats fed either a sucrose or cornstarch diet for 21 days. Other uremic and control rats fasted for 18 h were refed a sucrose meal to measure glycogen increment. Glycogen storage in uremia was normal, suggesting effective glycogen synthesis. During a short fast, sucrose feeding and uremia enhanced net glycogenolysis through different but additive mechanisms. Under sucrose feeding, there were high phosphorylase alpha levels associated with hepatic insulin resistance. In uremia, phosphorylase alpha levels were low, but the enzyme was probably activated in vivo by a fall of inhibitors (ATP, alpha-glycerophosphate, fructose-1,6-diphosphate, and glucose) and a rise of Pi, as verified in vitro. Enhanced gluconeogenesis was also suggested, but excessive hepatic glucose production was unlikely in uremia. During fasting, hypoglycemia occurred in uremia due to reduced glycogenolysis, inefficient hepatic gluconeogenesis, and impaired renal gluconeogenesis. This may be relevant to poor fasting tolerance in uremia, which could be aggravated under excessive sucrose intake.

Acidosis prevents growth hormone-induced growth in experimental uremia

The effects of 2 weeks of a daily injection (2 IU/day) of recombinant human growth hormone (GH) were studied in young (60-g) growing rats in two experiments. Experiment 1 was performed in uremic animals (mean plasma creatinine 65-71 mumol/l) who were either acidotic (mean bicarbonate 11.5 mmol/l) or had acidosis corrected (mean bicarbonate 26 mmol/l) by addition of sodium bicarbonate to the diet. Experiment 2 used rats with normal renal function (plasma creatinine 25 mumol/l) who were either non-acidotic but restricted to the dietary intake of uremic rats or rendered acidotic by ammonium chloride. GH induced an increase in body weight and length in non-acidotic uremic (+33% and +41%) and in non-acidotic food-restricted (+13% and +42%) rats, associated with an increased rate of protein synthesis and little change in plasma insulin-like growth factor 1 (IGF 1). In both acidotic rat groups, GH altered none of the parameters studied. Thus: (1) the presence of severe metabolic acidosis blunts the response to GH in uremic and non-uremic rats and (2) the increment of growth rate does not depend on a rise in plasma IGF 1.

Deleterious effects of inhibition of the renin-angiotensin system in neonatal rats

The angiotensin I converting enzyme inhibitor (ACEI) perindopril (2 mg/kg body weight), the peripheral vasodilator dihydralazine (DHL) (25 mg/kg body weight) or distilled water was given daily from birth to day 14 to neonatal rats. Blood pressure, plasma creatinine, plasma renin activity (PRA), substrate (PRS) and concentration (PRC) and renin content of kidney tissue sections were evaluated on days 14 and 28. By day 14, a high mortality in the ACEI group was observed. ACEI, but not DHL, led to a significant fall (P < 0.01) in blood pressure, 57 +/- 11 versus 89 +/- 25 in the DHL group and 103 +/- 24 mmHg in controls, and to a dramatic increase in plasma creatinine. PRA and PRS were undetectable in ACEI-treated rats; in contrast, PRC and renal staining with anti-renin antibody were significantly increased in ACEI rats. On day 28, the blood pressure was normal in all groups and plasma creatinine returned to the normal range in ACEI rats. PRA, PRS and PRC were not significantly different in the ACEI group and controls. These results suggest that the renin-angiotensin system (RAS) plays a major postnatal role in the neonatal rat. Inhibition of the RAS during the first 2 weeks of life leads to high mortality, severe hypotension, reversible renal failure and a defect in circulating angiotensinogen.

Subtotal but not unilateral nephrectomy induces hyperplasia and protooncogene expression

It is generally accepted that renal compensatory growth after unilateral nephrectomy (Uni) is due to prominent hypertrophy with no involvement of protooncogenes. Neither the balance between hypertrophy and hyperplasia nor the expression of the early-growth-related genes has been studied after subtotal nephrectomy (Nx). The occurrence of cystic tubular dilatations after Nx may suggest an excessive cell proliferation in this model. We measured DNA, RNA, and protein content, number of nuclei per tubular section, as well as c-fos, c-jun, c-myc, c-H-ras, c-sis, and c-erb-B2 protooncogene expression in kidneys taken at time of surgery and 2, 7, and 14 days after sham operation (control rats), Uni, or Nx. After Uni, hyperplasia was greater than expected (+79% for DNA at day 14) and was associated with moderate hypertrophy (+11% for protein/DNA ratio). After Nx, compensatory growth was due only to hyperplasia (+117% for DNA at day 14), with unchanged protein/DNA ratio (vs. Uni, P < 0.02). The greater hyperplasia after Nx was confirmed by nuclei counting. The protooncogene mRNA expression was constantly absent in control and Uni rats, whereas that of c-fos and c-jun genes was detected in Nx rats at day 14 with a 2- to 12-fold increment. The c-fos and c-jun protein levels were also increased at that time in Nx rats. This suggests the following: 1) the cellular events following Uni and Nx are not the same, and 2) the late protooncogene expression in Nx exclusively could favor a particular type of cell proliferation possibly more related with cystic formation than with actual compensatory growth.

In vivo unaltered muscle protein synthesis in experimental chronic metabolic acidosis

Chronic metabolic acidosis (CMA) is a major cause of growth defect, implying disturbances of protein metabolism. Previously, in vivo studies performed in the fasting state showed enhanced whole body protein turnover, whereas in vitro studies showed unchanged muscle protein synthesis. The present study is the first to determine the effects of CMA on muscle protein synthesis and degradation in vivo. Two studies were performed in 60 g male rats fed a 30% casein diet. In study I, one group was sham-operated (C rats), and two groups underwent subtotal nephrectomy. One of them developed acidosis (UA rats) which was corrected in the other by NaHCO3 in the diet (UNA rats). Study II compared sham-operated rats rendered acidotic by NH4Cl in the drinking water (CA rats) and normal pair-fed (CNA) rats. Fractional protein synthesis rate (FSR) was determined in gastrocnemius muscle after injection of 3H-phenylalanine. Fractional protein degradation rate (FDR) was calculated as FSR minus fractional rate of muscle growth (FGR). In study I, UA rats had lower growth and N balance (163 +/- 12 vs. 216 +/- 11 mg N/day; P < 0.001) than UNA rats, despite identical food intake (11 g/day). This was associated with identical FSR (10.4 +/- 0.5 vs. 10.9 +/- 0.5%/day), but enhanced protein degradation (6.30 +/- 0.99 vs. 5.10 +/- 0.71%/day; P < 0.05). Plasma insulin, C peptide, PTH and corticosterone did not differ in UA and UNA rats, whereas plasma IGF-I was markedly reduced (147 +/- 21 vs. 283 +/- 27 ng/ml; P < 0.01) in UA rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Glomerular response to acute protein load is not blunted by high-protein diet or nephron reduction

Inulin clearance (CIn) was measured in the presence of varying degrees of renal excision (NX, 0-85% of renal mass by weight), in anesthetized rats fed on high-protein (HP, 30%), median-protein (MP, 10%), or low-protein (LP, 7%) diets, before and during amino acid (AA) infusion or before and after an intragastric protein load. CIn was higher in rats fed HP than in rats fed LP in controls (3.4 vs. 2.1 ml/min) and in rats with NX up to 70% after feeding for 3 wk (1.4 vs. 0.7 ml/min) or 4 days (1.5 vs. 1.1 ml/min). The difference decreased from 0% to 70% NX, and disappeared when NX exceeded 70%. Acute AA infusion and intragastric loads always increased CIn with wide individual variations. The increase was greater in rats fed HP than in rats fed MP and LP (+1.4 vs. 0.8 and 1.1 ml/min for 0% NX), diminished with greater NX (0.7 vs. 0.2 and 0.4 ml/min for 70% NX), and was very small for NX above 70%. However, when expressed as the percent of baseline values, the mean CIn increment after acute stimulation remained constant (30-45%), regardless of renal ablation and of diet. Thus preexisting hyperfiltration resulting from diet or from renal ablation does not suppress the glomerular response to an acute protein load, and acute loads afford no advantages over baseline glomerular filtration rate (GFR) measurements. By contrast, chronic protein feeding increases GFR only when nephron loss is not too severe.

Uremia-induced disturbances in hepatic carbohydrate metabolism: enhancement by sucrose feeding

A high-sucrose (S) diet accentuates anorexia and stunts growth in uremic (U) rats, and an oral S load induces a greater hyperfructosemia in U rats than in control (C) rats. Four studies were performed to determine the roles of S feeding and an acute S load on liver carbohydrate (CHO) metabolism in U and C rats (eight to 10 rats per group). We also examined the plasma responses to either water or a S load. Levels of the main metabolites of glycolysis, gluconeogenesis, and glycogenesis were measured under basal conditions (7 hours' postmeal) in U and C rats fed either a cornstarch diet (study I) or S diet (study II) and at 30 and 60 minutes after an intragastric S load (studies III and IV) in s-fed U and C rats. The weight gain, food intake, and plasma creatinine and urea levels of the rats in the four studies were comparable. Weight gain and liver weight (g/100 g body weight) were lower in U than in C rats. In the plasma, baseline levels of lactate were decreased by uremia and S feeding and those of glucose (G) were increased by S feeding. The increases in plasma G and fructose (F) levels after a S load were greater in U rats than in C rats, whereas those of plasma lactate were comparable. In the liver under basal conditions, uremia markedly decreased levels of glycogen, F-1,6-diphosphate (F-1,6-diP), F-2,6-diP, 3-glycero-phosphate (3-glycero-P), dihydroxyacetone phosphate (DHAP), pyruvate, lactate, and adenosine triphosphate (ATP), and the phosphorylation state (ATP/adenosine diphosphate [ADP] x inorganic phosphorus [PI]), increased phosphoenolpyruvate (PEP), ADP, and Pi levels, but did not affect the cytosolic redox state (pyruvate/lactate). In addition to uremia, S feeding further decreased levels of glycogen, F-2,6-diP, 3-glycero-P, and ATP. After S loading, liver F levels increased more in U than in C rats, but glycogen and 3-glycero-P levels increased less in U than in C rats. Liver lactate and pyruvate levels increased more in U than in C rats, and the pyruvate/lactate and DHAP/3-glycero-P ratios were higher in U than in C rats after a S load. The ATP level and the phosphorylation state in U rats increased 30 minutes later in U than in C rats. Our findings indicate that uremia causes a depletion in liver glycogen, which is enhanced by S feeding and could be partially attributed to decreased glycogen synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

[Growth and protein metabolism in chronic metabolic acidosis from experimental renal insufficiency]

Two studies of uremia-induced chronic metabolic acidosis (CMA) were carried out to determine: 1) the level of acidosis beyond which growth failure occurs; 2) the protein metabolism anomalies which are associated with growth failure. Rats rendered uremic by subtotal nephrectomy were fed a diet containing sufficient protein amounts (30% casein) to induce CMA. CMA was left uncorrected in half the rats (group A) and was corrected by administration of bicarbonate in the other half (group B). 1) Fifty-two group A rats were compared with 52 group B rats matched for renal function. Results showed that a) CMA failed to reduce food intake; b) weight gain decreased only when CMA was profound (pH < 7.20) whereas reductions in length gain occurred at less severe levels of acidosis (pH < 7.25) suggesting that bone may be more susceptible to CMA than muscle mass. 2) Protein fractional synthesis rate was evaluated in skeletal muscle after a flooding dose of 3H-phenylalanine in group A rats (pH 7.22 +/- 0.01, HCO3-: 15.2 +/- 0.8 mmol/l) and group B rats matched for renal function. Values were identical in both groups (10.4 +/- 0.5 vs 10.8 +/- 0.5%/day). However, fractional muscle protein accretion rate was decreased in group A rats. These data demonstrate that CMA-associated growth failure in uremia is due to increased breakdown of protein with no change in protein production.

Nutritional effects of feeding a ketoanalogue mixture in growing and adult uremic rats

Insufficient protein diets supplemented with ketoanalogue/essential amino acid (KA/EAA) mixtures are proposed to maintain nutrition and to retard renal deterioration. We compared in growing and in adult uremic rats diets containing limited or usual amounts of protein (12%, 20% for growing rats, and 10% and 16% for adult rats) with diets containing 50% or 60% less casein plus a KA/EAA mixture providing KA at an equimolar amount of removed EAA or at higher amounts. The latter supplement caused stunting, the former caused no anorexia, a slight growth deficit when added to the lowest basal casein diets, and almost normal growth when added to higher casein diets. Growth was normal with EAA supplements. The plasma EAA changes were unrelated to intake and to growth. Thus, KA utilization is maximal, provided that basal protein is sufficient and KA are not in excess.

Supplemented low-protein diets protect the rat kidney without causing undernutrition

Low-protein diets supplemented with keto-analogues and essential amino acid (KA-EAA) mixtures or with EAA have been widely used to retard renal deterioration without affecting nutrition. These assumptions have recently been challenged in clinical studies and rest on little or no experimental data. The effects of EAA and KA-EAA supplementations have not been compared. We compared three groups of rats with subtotal nephrectomy that were fed (1) a 16% casein reference (R) diet, (2) a 6% casein plus EAA (A) diet, or (3) a 6% casein plus KA-EAA (K) diet with KA as amino acid salts. The three diets had the same energy and mineral contents, and they induced comparable growth. The two supplements had the same nitrogen content. The only difference found until month 3 was higher proteinuria and plasma urea levels in group R rats. Renal biopsies performed at month 3 showed more severe glomerular sclerosis and tubular changes in R rats than in A and K rats. From months 3 through 7, R rats developed higher plasma creatinine levels than did A and K rats (final median values: 167, 106, and 83 mumol/L; p < 0.04), had more proteinuria (232, 56, and 84 mg/day), and showed greater mortality rates. At the time the rats were killed, 2 R, 6 A, and 5 K rats had survived while receiving the diets. Examination of the remnant kidneys, regardless of time of death, showed that renal lesions were significantly worse in R than in A and K rats, with sclerosis affecting more than 50% of the glomeruli in 7 of 13 R, 4 of 14 A, and 4 of 15 K rats, and less than 25% glomeruli in 2 of 13 R, 10 of 14 A, and 10 of 15 K rats (A and K vs R: p < 0.03). In conclusion, restriction of nonessential amino acids compensated by EAA or by KA-EAA mixtures retards renal damage without affecting growth, but no real benefit of KA or EAA has been observed.

Renal effect of anti-hypertensive drugs depends on sodium diet in the excision remnant kidney model

Angiotensin converting enzyme inhibitors (ACEI) are believed to protect remnant kidney, but all previous studies used the ligation model which causes severe hypertension, and very few have compared drugs in rats having similar control of blood pressure (BP). We compared rats with uremia obtained by 70% excision of total renal mass, a model which causes mild, late hypertension. Study I compared the effects of enalapril (E), cicletanine (C) and placebo (P) in uremic (U) rats fed a 0.50% (normal-high) Na diet. Study II compared the effects of E, C, P, and guanfacine (G) in U rats fed a diet restricted to 0.25% Na (normal-low). In study I, UP rats developed progressive hypertension (140, 146, 160 and 166 mm Hg at 3, 6, 9 and 12 weeks), proteinuria (240 mg/day at 9 and 12 weeks) which were not affected by E or C. The occurrence of end-stage renal disease (ESRD) led to the sacrifice of all rats after three months. All three groups had similar severe renal lesions (over 25% sclerosed glomeruli in 5 of 10 UP, 9 of 14 UE, 7 of 14 UC rats, with huge cystic tubular dilatations). In study II, rats could be sacrificed later (6 months) and had evidence of less severe renal disease. All the drugs tested prevented hypertension throughout the study (P less than 0.001), with lowest values in UE rats. E and G, but not C, reduced proteinuria. Renal damage was reduced with E and G, but not with C, despite similar BP in C and G rats. Thus, in contrast with what was obtained in the ligation model, ACEI affected neither the BP nor the renal lesions of rats made uremic by renal excision and fed a 0.50% Na diet. Moderate Na restriction improved the consequences of nephron loss and restored the anti-hypertensive effect of drugs. However, these drugs had a different effect on renal preservation: it was dramatic with E, good with G, and undetectable with C.

Zinc bone loss in chronic renal failure and chronic metabolic acidosis

The effects of chronic metabolic acidosis (CMA) on zinc (Zn) bone content and urinary excretion were examined in the presence of normal or reduced renal function together with some aspects of calcium (Ca) metabolism. Four groups of rats were compared. All were fed a 30% protein and 9 mg Zn/100 g diet. Two were uremic (U): The first developed acidosis (UA), which was suppressed in the other (UNA) by NaHCO3 supplement. Two other groups had normal renal function: One was normal (CNA), and the other had NH4Cl in the drinking water and acidosis (CA). Femur total Zn and Ca content was markedly reduced by CMA and was not affected by uremia. Zn urinary excretion was increased by CMA and unaltered by uremia. Ca urinary excretion was markedly reduced in uremic rats, but was enhanced in both acidotic conditions. Urinary Ca and Zn showed a strong correlation in uremic and in control rats. Plasma parathormone and 1,25(OH)2D3 were unchanged by CMA. These data are in agreement with a direct primary effect of CMA on bone in releasing buffers. CMA induces bone resorption and a parallel decrease of mineral bone components, such as Ca and Zn, with little or no role of PTH, 1,25(OH)2D3 and of uremia itself.

Contribution of experimental studies on the nutritional management of children with chronic renal failure

A few of the many reports of experimental chronic renal failure have been summarized. Anorexia and food selection have been studied in experimental uremia and the findings are comparable with those observed in uraemic children. The optimal dietary protein content for growth is close to the minimal requirement for "optimal" growth. Protein excess leads to growth retardation and renal deterioration in uraemic rats, at least with the commonly used dry diets. The increased water requirement may be more critical for growth than the blood urea level or acidosis, although this requires further investigation. Reduction of the dietary protein by 50% and supplementation with essential amino acids (EAA) results in growth similar to that of the 100% protein diet. There is no growth improvement despite low blood urea levels, but the renal parenchymal is preserved. Supplementation with nitrogen-free analogues is more frequently associated with defective growth; the optimal mixture remains to be defined, and to date, when nutrition is identical, nitrogen-free analogues offer no benefit for renal preservation compared with EAA. Sucrose-rich diets have adverse effects on uraemia. These effects are associated with fructose intolerance and with reduced energy storage in the liver. The precise metabolic alteration remains to be defined.

Growth, free plasma and muscle amino-acids in uraemic rats fed various low-protein diets

The nutritional effects of low-protein diets are difficult to assess in humans. Normal and uraemic growing rats were therefore fed: a moderately low-protein (12%) reference diet (diet R), two 5% casein diets, one supplemented with essential amino acids (AA) (diet A) and the other with their keto acids (diet K), and a 7% casein diet isonitrogenous with diet K (diet L). Appetite and growth of both uraemic and control rats were identical on diets R and A and were reduced on diets K and L. Stunting was prominent in rats fed diet L and more severe than in those on diet K. Diet K induced marked anorexia in controls. This effect was smaller in uraemic rats, which were all anorectic, regardless of the diet. Plasma essential AA were similar in rats on diets R and A but low in control rats fed diets L and K. In particular, diet K did not improve the branched-chain AA levels although it produced better growth than diet L. Plasma and muscle threonine were surprisingly elevated in rats on the semi-synthetic diets A and K, despite identical or lower consumptions. Regardless of the diet, uraemia resulted in unchanged or increased plasma essential AA, despite reduced appetite and stunting. Uraemia caused a marked rise in some non-essential AA. Muscle essential AA, except for threonine, were essentially unaltered and did not correlate with growth or uraemia.

Optimal dietary substitution of racemic ketoanalogues for isoleucine in growing normal and uremic rats

Dietary ketoanalogues (KAs) were shown to replace their essential amino acids with a 50% efficiency for valine and leucine. We determined the optimal concentration of the racemic KA of isoleucine (KMVA) in uremic and control rats: nutrition responses were compared between a diet containing optimal isoleucine concentration and diets containing various KMVA concentrations. Isomolar replacement of isoleucine produced anorexia, stunting, and poor nitrogen balance. Doubling KMVA partially improved these indices. Tripling KMVA lessened urea production and improved growth up to that obtained with the isoleucine diet in uremic but not in control rats (20% lower). A further KMVA increase produced no further benefit. Among plasma branched-chain amino acids, only alloisoleucine was affected; it increased with increasing KMVA concentration, being maximum after tripling KMVA. Racemic KMVA could replace isoleucine with a 35% efficiency but supported no growth acceleration in uremic rats and no maximal growth in control rats. Plasma alloisoleucine rose without adverse nutrition effects.

[Kidney functional reserve. An experimental study]

The renal functional reserve (RFR), the increase in glomerular filtration rate (GFR) induced by a protein load, seems to be diminished or even lost in renal failure. Our experimental study was undertaken to determine whether the RFR is lost beyond a given level of nephron reduction, using different protein loads. In the first two studies, RFRs were evaluated during an oral protein load consisting in a high-protein diet (30% casein) compared to a low-protein diet (7% casein). Each diet was given to SD rats (200 g) either for three weeks immediately after nephrectomy (Nx) or for four days one month after Nx. Nx was subtotal and consisted in removal of 65 to 85% of the mass of the renal parenchyma. The GFR evaluated by inulin clearance measurements increased considerably after a prolonged (+188%) or short-lived (+35%) oral protein load if less than 70% of the renal mass had been removed. Beyond this threshold of nephron amputation, the high-protein diet had no effect on the GFR, despite an increase in the residual renal mass (+200% in moderate and severe Nxs). In a third study, the GFR was measured one month after Nx and the effects of an infusion of amino acids (vamine) or of a placebo were compared, each rat serving as his own control. Extent of Nx was 0%, 50%, 65-70%, and 80%. Regardless of the extent of nephron reduction, the GFR increased under vamine, but interindividual variations in each group were marked (+5 to +70%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adverse effects of sucrose-rich diets on uraemic rats

The nature of carbohydrate may affect the tolerance and progression of uraemia. The effects of three diets differing only in their carbohydrate source: namely corn starch (C), glucose (G) or sucrose (S) were examined. Study 1 examined the effects of the three carbohydrate diets on unilaterally nephrectomised control rats and severely uraemic rats. The three carbohydrates produced similar nutritional effects in uninephrectomised rats, whereas sucrose rapidly induced anorexia, stunting and slightly accelerated renal damage in uraemia. Study 2 examined the long-term effects of the three carbohydrates in moderate uraemia under conditions of high and identical carbohydrate intakes. Hyperphagic Zucker uraemic rats (F rats) received a daily allotment of each diet plus pure carbohydrate. Lean uraemic rats (L rats) received the same dietary allotment without the carbohydrate supplement. The F rats fed sucrose showed greater morbidity and mortality but little renal deterioration. Their plasma triglycerides increased dramatically. The L rats fed sucrose had the greatest urinary protein, the least creatinine clearance and the most severe renal damage. Thus, sucrose-rich but not glucose-rich diets have two adverse effects in uraemia: a deterioration in nutritional status, perhaps related to abnormal fructose utilisation, and a long-term effect on the kidney, resulting in accelerated renal deterioration.

Role of the urinary concentrating process in the renal effects of high protein intake

High protein diet is known to increase glomerular filtration rate (GFR) and induce kidney hypertrophy. The mechanisms underlying these changes are not understood. Since the mammalian kidney comprises different nephron segments located in well-delineated zones, it is conceivable that the hypertrophy does not affect all kidney zones and all nephron segments uniformly. The present experiments were designed to study the chronic effects of high or low isocaloric protein diets (HP = 32% or LP = 10% casein, respectively) on kidney function and morphology in Sprague-Dawley rats. HP diet induced significant increases in kidney mass, GFR, free water clearance, and maximum urine concentrating ability. Kidney hypertrophy was characterized by: 1. a preferential increase in thickness of the inner stripe of the outer medulla (IS) (+54%, P less than 0.001, while total kidney height, from cortex to papillary tip, increased only by 18%); 2. a marked hypertrophy of the thick ascending limbs (TAL) in the inner stripe (+40% epithelium volume/unit tubular length, P less than 0.05) but not in the outer stripe nor in the cortex; 3. an increase in heterogeneity of glomeruli between superficial (S) and deep (D) nephrons (D/S = 1.47 in HP vs. 1.17 in LP, P less than 0.05). In contrast, normal kidney growth with age and kidney hypertrophy induced by uninephrectomy were not accompanied by preferential enlargement of IS structures. The morphologic changes induced by high protein intake parallel those we previously reported in rats fed a normal diet (25% protein) but in which the operation of the urine concentrating mechanism was chronically stimulated by ADH infusion or by reduction in water intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficiency of substitution of 2-ketoisocaproic acid and 2-ketoisovaleric acid in the diet of normal and uremic growing rats

Effects of various intakes of the ketoanalogues of leucine (KICA) and valine (KIVA) on growth, nitrogen, and urea excretion were examined and compared to those of an optimal intake (A) of the corresponding amino acids. Diet KICA and KIVA contents varied from 1 to 4 times A. In controls, growth was significantly reduced with equimolar substitution, corrected with twice A, and unchanged at higher levels. Doubling KICA corrected growth except with substantial anorexia. In uremic rats fed KIVA, growth was corrected at twice A. Low-KICA diets reduced plasma-leucine level; higher KICA diets normalized plasma leucine and revealed branched-chain amino acid (BCAA) antagonism. Changes in 2-ketoacids were unrelated to those of BCAA. In uremia, KICA decreased plasma and urinary urea without changing nitrogen retention. Ketoacid substitution for amino acids was 50% efficient in normal rats and not altered by uremia. BCKAs, specifically KICA, could modify urea metabolism.

Role of amount and nature of carbohydrates in the course of experimental renal failure

The renal effects of carbohydrates (CHO) were studied in two experiments. 1) The effects of CHO-energy restriction was evaluated by comparing uremic growing rats (initial weight: 80 g) fed "ad lib" (L rats) or CHO-restricted (starch and glucose) but receiving identical amounts of all other nutrients (R rats). R rats showed reduced growth, slower increase in plasma creatinine, lower mortality rate, and less histological renal damage than L rats. 2) Two types of CHO restriction, low glucose (R1 rats) or low starch (R2 rats) were compared to "ad lib" feeding (L1 rats) in adult rats (initial weight: 130 g). Growth was identically reduced in R1 and R2 rats. Mean plasma creatinine levels at week four was lower in R1 than in L1 rats. The overall rate mortality was higher for L1 and R2 than in R1 rats (79%, 81%, 53%) but included deaths from other causes than renal failure. Actuarial survival excluding these deaths was 27%, 83% and 10% in L1, R1 and R2 rats, respectively. Diffuse renal lesions were found in 25 of 30 L1, 5 of 15 R1, and 12 of 15 R2 rats (R1 vs. R1 and R2, P less than 0.01). The results show that CHO restriction may preserve the renal parenchyma, and suggest that restriction of "simple" rather than "complex" CHO restriction may be beneficial, a finding which could be of clinical importance if confirmed by further investigations.

Adverse effect of proteins on remnant kidney: dissociation from that of other nutrients

Several experiments have shown that deterioration of renal parenchyma after reduction of functional mass is affected by the protein content of the diet. The respective role of proteins and that of other nutrients that vary with proteins were never clearly separated. Three groups of 9 uremic rats received diets differing exclusively in protein (casein) content, which was 8% (group 1), 16% (group 2), and 32% (group 3). Energy and minerals were maintained identical. Food intake was similar in groups 1 and 2 and was lower in group 3. Mortality rate remained closely related to protein intake. Of group 3 rats, 78% died within 10 weeks and 100% within 15 weeks. Of group 2 rats, 56% were dead at week 15, and 100% at week 30. Mortality occurred significantly later in group-1 rats fed the lowest protein diet. Histology of remnant kidneys showed severe glomerular and tubular damage, with no or little calcium deposits despite normal phosphorus diet and frequent hyperphosphatemia. These data suggest that protein intake, independent of any other nutrient, influences survival by accelerating the renal damage in rats with reduced kidney mass.

Changes in 25-hydroxyvitamin D3 alpha- and 24-hydroxylase activities of kidney cells isolated from rats with either unilateral kidney damage or acute renal insufficiency

25-Hydroxyvitamin D3 1 alpha- and 24-hydroxylase, NADPH-cytochrome c reductase, heme oxygenase, and ATPase activities were studied in viable kidney cells isolated from rats submitted to unilateral kidney damage (cortical electrocoagulation) and during the development of acute renal failure subsequent to excision of the contralateral undamaged kidney. Measurements of blood pH, plasma total and ionized calcium, phosphorus, creatinine, kidney histology, and phosphorus nuclear magnetic resonance spectroscopy determinations of phosphorus-containing compounds in kidney tissue were also performed. Seventy-two hours after unilateral kidney damage, no significant changes were observed in blood pH or in the plasma parameters studied. During this period, a significant increase in the activity of the 25-hydroxyvitamin D3 hydroxylases could be demonstrated in the cells of the contralateral undamaged kidney. A similar pattern of compensatory rise in the activity of the other enzymes studied was not detected. However, in the damaged kidney viable cells, the hydroxylase activities remained unchanged relative to those in sham-operated controls, despite a 5-fold increase in the inorganic phosphate content and a marked decrease in the organophosphorus and ATP content of this tissue. During the development of acute renal failure, a significant decrease in the activity of the hydroxylases occurred only when the rise in plasma creatinine concentration suggested severe renal insufficiency.

Adverse effect of indomethacin in experimental chronic nephrosis

The effects of long-term indomethacin therapy were studied in rats with chronic nephrosis induced by puromycin of aminonucleoside (PAN). Fifteen PAN rats received indomethacin (2 mg/kg/d) administered by daily gavages, and fifteen received glucose. A control group received indomethacin but no PAN. Three to five animals per group were sacrificed monthly. Proteinuria was similar in both PAN rat groups. Renal function and histology were normal in the control rats. In the PAN animals, renal failure developed earlier in the treated rats than in the others. Histological examination revealed in all PAN rats early tubulo-interstitial lesions and progressive glomerular damage. The pattern of the lesions was identical in both PAN rats, but the glomerular changes developed earlier, were more diffuse and more severe in the indomethacin treated rats. Thus, indomethacin resulted in an accelerated destruction of the glomeruli in experimental nephrosis. Such a deleterious effect remains unexplained, and its relevance to human disease is not demonstrated.

[Nutritional factors in the development of experimental renal failure]

Several experimental studies have shown that the development of glomerular sclerosis during aging in rats is related to nutritional factors: it is impeded by overall food restriction, as well as by reduction of the protein, carbohydrate or sodium intake. It is enhanced by high protein or high sodium diets. In remnant kidneys, lesions develop that are similar to those in aging kidneys and that seem to be influenced by the same factors. Through several experiments, we have shown that the rapidity of the deterioration of renal function after subtotal nephrectomy is closely related to the protein intake and that the length of survival can be reduced by a high protein diet or increased by a low protein diet. The influence of protein intake remains clearly apparent when the intake of all other nutrients, particularly minerals, and of calories is strictly controlled. Low protein diets supplemented with essential amino acids resulting in increased appetite are of little benefit for survival, suggesting that the calorie intake or growth-related factors may be of significance. Prolonged survival observed with phosphorus (P) deficient diets compared to low or normal P diets is mainly due to decreased appetite. The optimal supply of protein, energy, sodium and other nutrients should be determined according, not only to nutritional status, but also to effects on the renal parenchyma.

Importance of proteins in the deterioration of the remnant kidneys, independently of other nutrients

Several experiments have shown that deterioration of renal parenchyma after reduction of functional mass is affected by the protein content of the diet. The respective role of proteins and that of other nutrients particularly phosphorus which varies with proteins was never clearly separated. Three groups of 9 uremic rats U I, U II, U III, received three diets differing exclusively in their protein content, which was supplied by casein and was respectively 8%, 16% and 32%. Other nutrients were maintained identical, including energy and minerals. Food intake was similar in U I and U II rats and was lower in U III rats. Mortality rate remained closely related to protein intake. Of U III rats, 78% died within 10 weeks and 100% within 15 weeks. Of U II rats, 56% were dead at week 15, and 100% at week 30. Mortality occurred significantly later in U I rats fed the lowest protein diet. Histology of remnant kidneys showed severe glomerular and tubular damage, with no or little calcium deposits despite normal phosphorus diet and frequent hyperphosphoremia. In conclusion, protein intake influences survival by accelerating the renal damage in rats with reduced kidney mass independently of any other nutrient.

Beneficial effect of low phosphorus diet in uraemic rats: a reappraisal

1. Diets deficient in phosphorus have been shown to preserve the renal function of uraemic rats, but the role of concomitant alterations in the intake of other nutrients caused by such diets was not elucidated.

2. Five groups of uraemic rats were compared. Three (A, B, C) received (ad libitum) diets deficient (0·03%), low (0·2%) or normal (0·5%) in P. Two groups (D, E) received restricted amounts of 0·2% and 0·5% P diets by pair-feeding with group A rats.

3. Phosphorus deficient diet resulted in marked anorexia, growth arrest, low P and high calcium plasma levels and severe rickets, but renal function became stabilized. Groups B and C had both higher total food intake and weight gain but a significantly higher mortality rate. After 36 weeks, mortality was 90% in these groups, and was 19%, 28% and 44% in groups A, D and E rats respectively, despite a higher P consumption in group E than in group B rats.

4. Normal P diet was associated with severe renal calcium deposits and high calcium heart content, which were related to the degree of hyperparathyroidism evaluated by bone histology.

5. Preservation of renal function was mainly mediated by reduction in some other components of the diet and not by P restriction itself. Normal P diet with restricted dietary allotments had little adverse effect on survival, and its influence on renal histology is not easy to explain.

6. Restriction in P sufficient to cause moderate hypophosphataemia, disappearance of phosphaturia and to prevent hyperparathyroidism without causing anorexia and other severe side effects, had little or no beneficial effect on renal deterioration.

Skin calcium binding protein is localized in the cytoplasm of the basal layer of the epidermis

Using a serum raised in rabbits against a calcium binding protein extracted from rat skin, the cutaneous localization of this protein was studied by indirect immunofluorescence. The skin calcium binding immunoreactivity was found in the epidermis but not in the dermis; it was localized in the cytoplasm of the basal cell layer of both skin and malpighian mucosa. There was not species specificity; this allowed the tracing of the protein in human epidermis as well where it was also expressed only in the basal cells. This is the first demonstration of the unique localization of a specific protein within the cytoplasm of the basal cell layer of the epidermis. This localization may help to elucidate the physiological role of this protein.

Lack of effect on ovariectomy on the metabolism of vitamin D and intestinal calcium-binding protein in female rats

The metabolism of 25-hydroxycholecalciferol (25-(OH)D3), plasma concentration of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) and the amount of calcium-binding protein (CaBP) in duodenal mucosa were determined in ovariectomized rats and were compared with data observed in normal age-matched cyclic rats. Sephadex LH-20 and high-pressure liquid chromatography were used for the study of the metabolism of 25-(OH)D3. The concentration of 1,25-(OH)2D3 in plasma and prolactin in serum were measured by radioimmunoassay. Calcium-binding protein in duodenal mucosa was determined immunologically using electroimmunodiffusion. The results showed that the lack of ovarian hormones and low prolactin levels observed in ovariectomized rats did not promote a significant change in the metabolism of 25-(OH)D3, in the levels of 1,25-(OH)2D3 in the circulation or in the amount of CaBP in duodenal mucosa. It is possible that the regulation of 25-(OH)D3 by sex hormones is restricted to the state of calcium stress such as during egg-laying in birds or pregnancy and lactation in mammals.

Intestinal calcium-binding protein 3 months after massive small bowel resection in the piglet

Changes in intestinal calcium-binding protein and calcium binding activity were studied at resection and 3 months after 90% small bowel resection in piglets and one adult pig. A calcium-binding protein (MW congruent to 11.000) with calcium-dependent eletrophoretic mobility was partially purified from mucosal extract of proximal jejunum, mid-gut, and ileum. The concentration of calcium-binding protein and the calcium-binding activity of the intact animals were found highest in the proximal jejunal segment, lowest in the ileal segment. After resection in the four surviving animals out of nine, a significant increase in calcium-binding activity was observed in the proximal jejunum and in the distal ileal segment. The change in calcium-binding activity was much more marked in the ileum than the jejunum. These data demonstrate that pig intestinal mucosa possesses an adaptive capacity to increase the synthesis of calcium-binding protein after massive small bowel resection.