Compensatory adaptation of structure and function following progressive renal ablation

Signaling mechanisms in renal compensatory hypertrophy revealed by multi-omics

Loss of a kidney results in compensatory growth of the remaining kidney, a phenomenon of considerable clinical importance. However, the mechanisms involved are largely unknown. Here, we use a multi-omic approach in a unilateral nephrectomy model in male mice to identify signaling processes associated with renal compensatory hypertrophy, demonstrating that the lipid-activated transcription factor peroxisome proliferator-activated receptor alpha (PPARα) is an important determinant of proximal tubule cell size and is a likely mediator of compensatory proximal tubule hypertrophy.

Estimation of Glomerular Filtration Rate in Obese Patients: Utility of a New Equation

There is no consensus on the best equation to estimate glomerular filtration rate (eGFR) in obese patients (OP). Objective: to evaluate the performance of the current equations and the new Argentinian Equation ("AE") to estimate GFR in OP. Two validation samples were used: internal (IVS, using 10-fold cross-validation) and temporary (TVS). OP whose GFR was measured (mGFR) with clearance of iothalamate between 2007/2017 (IVS, n = 189) and 2018/2019 (TVS, n = 26) were included. To evaluate the performance of the equations we used: bias (difference between eGFR and mGFR), P30 (percentage of estimates within ±30% of mGFR), Pearson's correlation (r) and percentage of correct classification (%CC) according to the stages of CKD. The median age was 50 years. Sixty percent had grade I obesity (G1-Ob), 25.1% G2-Ob and 14.9% G3-Ob, with a wide range in mGFR (5.6-173.1 mL/min/1.73 m2). In the IVS, AE obtained a higher P30 (85.2%), r (0.86) and %CC (74.4%), with lower bias (-0.4 mL/min/1.73 m2). In the TVS, AE obtained a higher P30 (88.5%), r (0.89) and %CC (84.6%). The performance of all equations was reduced in G3-Ob, but AE was the only one that obtained a P30 > 80% in all degrees. AE obtained better overall performance to estimate GFR in OP and could be useful in this population. Conclusions from this study may not be generalizable to all populations of obese patients since they were derived from a study in a single center with a very specific ethnic mixed population.

Development and autoregulation of kidney function in children: a retrospective study using 99mTc-MAG3 renography

BACKGROUND

Both the development of kidney function in healthy children and autoregulation ability of kidney function in patients with asymmetric kidneys are important in clinical diagnosis and treatment of kidney-related diseases, but there are however only limited studies. This study aimed to investigate development of kidney function in normal children with healthy symmetric kidneys and autoregulation of the healthy kidney compensating the functional loss of a diseased one in children with asymmetric kidneys.

METHODS

Two hundred thirty-seven children (156 male, 81 female) from 0 to 20y (average 4.6y ± 5.1) undergoing ^99mTc-MAG3 renography were included, comprising 134 with healthy symmetrically functioning kidneys and 103 with asymmetric kidneys. Clearance was calculated from kidney uptakes at 1-2 min. A developmental model between MAG3 clearance (CL) and patient age in normal group was identified (CL = 84.39Age^0.395 ml/min, r = 0.957, p < 0.001). The clearance autoregulation rate in abnormal group with asymmetric kidneys was defined as the ratio of the measured MAG3 clearance and the normal value predicted from the renal developmental model of normal group.

RESULTS

No significant difference of MAG3 clearance (p = 0.723) was found between independent abnormal group and normal group. The autoregulation rate of kidney clearance in abnormal group was 94.2% on average, and no significant differences were found between two age groups (p = 0.49), male and female (p = 0.39), and left kidney and right kidney (p = 0.92) but two different grades of asymmetric kidneys (p = 0.02).

CONCLUSIONS

The healthy kidney of two asymmetric kidneys can automatically regulate total kidney function up to 94% of two symmetric kidneys in normal children.

Three-Dimensional Kidney-on-a-Chip Assessment of Contrast-Induced Kidney Injury: Osmolality and Viscosity

Increased viscosity of concentrated contrast media (CM) in the renal tubules can perturb renal hemodynamics and have a detrimental effect on tubular epithelial cells. However, the effects of viscosity on contrast-induced nephropathy (CIN) remain poorly understood. Conventional in vitro culture studies do not reflect the rheological properties of CM. Therefore, we investigated the effects of CM viscosity on renal tubules using a kidney-on-a-chip and two different types of CM. Renal proximal tubule epithelial cells (RPTEC) were cultured in a three-dimensional microfluidic culture platform under bidirectional fluid shear stress. We treated the RPTEC with two types of CM: low- (LOCM, iopromide) and iso-osmolar contrast media (IOCM, iodixanol). Renal tubular cell injury induced by LOCM and IOCM was examined under different iodine concentrations (50–250 mgI/mL) and shear-stress conditions. LOCM showed a significant dose-dependent cytotoxic effect, which was significantly higher than that of IOCM under static and low-to-moderate shear stress conditions. However, high shear-stress resulted in reduced cell viability in IOCM; no difference between IOCM and LOCM was found under high shear-stress conditions. The cytotoxic effects were pronounced at a mean shear stress of 1 dyn/cm2 or higher. The high viscosity of IOCM slowed the fluid flow rate and augmented fluid shear-stress. We suggest an alternative in vitro model of CIN using the three-dimensional kidney-on-a-chip. Our results indicate a vital role of viscosity-induced nephrotoxicity under high shear-stress conditions, contrary to the findings of conventional in vitro studies.

How Do Kidneys Adapt to a Deficit or Loss in Nephron Number?

A deficit or loss in the number of nephrons, the functional unit of the kidney, can induce compensatory growth and hyperfunction of remaining nephrons. An increase in single nephron glomerular filtration rate (SNGFR) aims to compensate but may be deleterious in the long term. The increase in SNGFR is determined by the dynamics of nephron loss, total remaining GFR, the body's excretory demand, and the functional capacity to sustain single nephron hyperfunction.

Renal tubular solute transport and oxygen consumption: insights from computational models

PURPOSE OF REVIEW

To maintain electrolyte homeostasis, the kidneys reabsorb more than 99% of the filtered Na under physiological conditions, resulting in less than 1% of the filtered Na excreted in urine. In contrast, due to distal tubular secretion, urinary K output may exceed filtered load. This review focuses on a relatively new methodology for investigating renal epithelial transport, computational modelling and highlights recent insights regarding renal Na and K transport and O2 consumption under pathophysiological conditions, with a focus on nephrectomy.

RECENT FINDINGS

Recent modelling studies investigated the extent to which the adaptive response to nephrectomy, which includes elevation in single-nephron glomerular filtration rate and tubular transport capacity, may achieve balance but increases O2 consumption per nephron. Simulation results pointed to potential mechanisms in a hemi-nephrectomized rat that may attenuate the natriuresis response under K load, or that may augment the natriuretic, diuretic and kaliuretic effects of sodium glucose cotransporter 2 inhibition.

SUMMARY

Computational models provide a systemic approach for investigating system perturbations, such as those induced by drug administration or genetic alterations. Thus, computational models can be a great asset in data interpretation concerning (but not limited to) renal tubular transport and metabolism.

EFFECTS OF RENAL DYSFUNCTION ON HEALING OF COLONIC ANASTOMOSIS: EXPERIMENTAL STUDY IN WISTAR RATS

BACKGROUND

Chronic kidney disease affects more than 500 million people worldwide. In this context, the uremic toxins present are related to worsening in tissue healing.

AIM

Evaluate on healing of colonic anastomosis in uremic rats, serum and anatomopathological indicators, which may be related to the change tissue repair process.

METHODS

Twenty Wistar rats, were randomly separated into two groups. In the sham group they were submitted to 5/6 nephrectomy simulation in left kidney, simulation right nephrectomy, median laparotomy, colotomy and colorraphy. In the uremia group, they were submitted to 5/6 nephrectomy of the left kidney, total nephrectomy of the right kidney and median laparotomy, colotomy and colorraphy. Were collected for serum urea, creatinine and CRP dosages and the colonic segments were studied for evaluation of granulation tissue, collagen maturation, microvascular and myofibroblasts density, and cell viability. Through histochemical processing, microvascular density was evaluated by anti-CD34 monoclonal antibody marking, cell viability by cell proliferation nuclear antigen screening and myofibroblasts density with monoclonal anti-α-actin antibody. Computerized histometry was used for evaluations of collagens type I and III by the coloration of picrosirius.

RESULTS

The group submitted to nephrectomy 5/6, compared to the sham group, show urea increase (p<0.0000) and higher C reactive protein (p=0.0142). Decrease of granulation tissue formation (border reepithelialization p=0,0196, angiofibroblast proliferation p=0.0379), mean collagen I (p=0,0009) and collagen III (p=0,016), microvascular density (p=0,0074), cell proliferation nuclear antigen (p<0,0000) and myofibroblasts (p<0,0001).

CONCLUSION

The uremia induced by nephrectomy 5/6 model establishes negative impact in the colonic wound healing.

GDF11 induces kidney fibrosis, renal cell epithelial-to-mesenchymal transition, and kidney dysfunction and failure

BACKGROUND

GDF11 modulates embryonic patterning and kidney organogenesis. Herein, we sought to define GDF11 function in the adult kidney and in renal diseases.

METHODS

In vitro renal cell lines, genetic, and murine in vivo renal injury models were examined.

RESULTS

Among tissues tested, Gdf11 was highest in normal adult mouse kidney. Expression was increased acutely after 5/6 nephrectomy, ischemia-reperfusion injury, kanamycin toxicity, or unilateral ureteric obstruction. Systemic, high-dose GDF11 administration in adult mice led to renal failure, with accompanying kidney atrophy, interstitial fibrosis, epithelial-to-mesenchymal transition of renal tubular cells, and eventually death. These effects were associated with phosphorylation of SMAD2 and could be blocked by follistatin. In contrast, Gdf11 heterozygous mice showed reduced renal Gdf11 expression, renal fibrosis, and expression of fibrosis-associated genes both at baseline and after unilateral ureteric obstruction compared with wild-type littermates. The kidney-specific consequences of GDF11 dose modulation are direct effects on kidney cells. GDF11 induced proliferation and activation of NRK49f renal fibroblasts and also promoted epithelial-to-mesenchymal transition of IMCD-3 tubular epithelial cells in a SMAD3-dependent manner.

CONCLUSION

Taken together, these data suggest that GDF11 and its downstream signals are critical in vivo mediators of renal injury. These effects are through direct actions of GDF11 on renal tubular cells and fibroblasts. Thus, regulation of GDF11 presents a therapeutic target for diseases involving renal fibrosis and impaired tubular function.

Adaptive changes in GFR, tubular morphology, and transport in subtotal nephrectomized kidneys: modeling and analysis

Removal of renal mass stimulates anatomical and functional adaptations in the surviving nephrons, including elevations in single-nephron glomerular filtration rate (SNGFR) and tubular hypertrophy. A goal of this study is to assess the extent to which the concomitant increases in filtered load and tubular transport capacity preserve homeostasis of water and salt. To accomplish that goal, we developed computational models to simulate solute transport and metabolism along nephron populations in a uninephrectomized (UNX) rat and a 5/6-nephrectomized (5/6-NX) rat. Model simulations indicate that nephrectomy-induced SNGFR increase and tubular hypertrophy go a long way to normalize excretion, but alone are insufficient to fully maintain salt balance. We then identified increases in the protein density of Na⁺-K⁺-ATPase, Na⁺-K⁺-2Cl^- cotransporter, Na⁺-Cl^- cotransporter, and epithelial Na⁺ channel, such that the UNX and 5/6-NX models predict urine flow and urinary Na⁺ and K⁺ excretions that are similar to sham levels. The models predict that, in the UNX and 5/6-NX kidneys, fractional water and salt reabsorption is similar to sham along the initial nephron segments (i.e., from the proximal tubule to the distal convoluted tubule), with a need to further reduce Na⁺ reabsorption and increase K⁺ secretion primarily along the connecting tubules and collecting ducts to achieve balance. Additionally, the models predict that, given the substantially elevated filtered and thus transport load among each of the surviving nephrons, oxygen consumption per nephron segment in a UNX or 5/6-NX kidney increases substantially. But due to the reduced nephron population, whole animal renal oxygen consumption is lower. The efficiency of tubular Na⁺ transport in the UNX and 5/6-NX kidneys is predicted to be similar to sham.

Mechanical challenges to the glomerular filtration barrier: adaptations and pathway to sclerosis

Podocytes are lost as viable cells by detachment from the glomerular basement membrane (GBM), possibly due to factors such as pressure and filtrate flow. Distension of glomerular capillaries in response to increased pressure is limited by the elastic resistance of the GBM. The endothelium and podocytes adapt to changes in GBM area. The slit diaphragm (SD) seems to adjust by shuttling SD components between the SD and the adjacent foot processes (FPs), resulting in changes in SD area that parallel those in perfusion pressure.Filtrate flow tends to drag podocytes towards the urinary orifice by shear forces, which are highest within the filtration slits. The SD represents an atypical adherens junction, mechanically interconnecting the cytoskeleton of opposing FPs and tending to balance the shear forces.If under pathological conditions, increased filtrate flows locally overtax the attachment of FPs, the SDs are replaced by occluding junctions that seal the slits and the attachment of podocytes to the GBM is reinforced by FP effacement. Failure of these temporary adaptive mechanisms results in a steady process of podocyte detachment due to uncontrolled filtrate flows through bare areas of the GBM and, subsequently, the labyrinthine subpodocyte spaces, presenting as pseudocysts. In our view, shear stress due to filtrate flow-not capillary hydrostatic pressure-is the major challenge to the attachment of podocytes to the GBM.

Shear stress is normalized in glomerular capillaries following ⅚ nephrectomy

Loss of significant functional renal mass results in compensatory structural and hemodynamic adaptations in the nephron. While these changes have been characterized in several injury models, how they affect hemodynamic forces at the glomerular capillary wall has not been adequately characterized, despite their potential physiological significance. Therefore, we used intravital multiphoton microscopy to measure the velocity of red blood cells in individual glomerular capillaries of normal rats and rats subjected to ⅚ nephrectomy. Glomerular capillary blood flow rate and wall shear stress were then estimated using previously established experimental and mathematical models to account for changes in hematocrit and blood rheology in small vessels. We found little change in the hemodynamic parameters in glomerular capillaries immediately following injury. At 2 wk postnephrectomy, significant changes in individual capillary blood flow velocity and volume flow rate were present. Despite these changes, estimated capillary wall shear stress was unchanged. This was a result of an increase in capillary diameter and changes in capillary blood rheology in nephrectomized rats.

Nephron Deficiency and Predisposition to Renal Injury in a Novel One-Kidney Genetic Model

Some studies have reported up to 40% of patients born with a single kidney develop hypertension, proteinuria, and in some cases renal failure. The increased susceptibility to renal injury may be due, in part, to reduced nephron numbers. Notably, children who undergo nephrectomy or adults who serve as kidney donors exhibit little difference in renal function compared with persons who have two kidneys. However, the difference in risk between being born with a single kidney versus being born with two kidneys and then undergoing nephrectomy are unclear. Animal models used previously to investigate this question are not ideal because they require invasive methods to model congenital solitary kidney. In this study, we describe a new genetic animal model, the heterogeneous stock-derived model of unilateral renal agenesis (HSRA) rat, which demonstrates 50%-75% spontaneous incidence of a single kidney. The HSRA model is characterized by reduced nephron number (more than would be expected by loss of one kidney), early kidney/glomerular hypertrophy, and progressive renal injury, which culminates in reduced renal function. Long-term studies of temporal relationships among BP, renal hemodynamics, and renal function demonstrate that spontaneous single-kidney HSRA rats are more likely than uninephrectomized normal littermates to exhibit renal impairment because of the combination of reduced nephron numbers and prolonged exposure to renal compensatory mechanisms (i.e., hyperfiltration). Future studies with this novel animal model may provide additional insight into the genetic contributions to kidney development and agenesis and the factors influencing susceptibility to renal injury in individuals with congenital solitary kidney.

A potential role for mechanical forces in the detachment of podocytes and the progression of CKD

Loss of podocytes underlies progression of CKD. Detachment of podocytes from the glomerular basement membrane (GBM) rather than apoptosis or necrosis seems to be the major mechanism of podocyte loss. Such detachment of viable podocytes may be caused by increased mechanical distending and shear forces and/or impaired adhesion to the GBM. This review considers the mechanical challenges that may lead to podocyte loss by detachment from the GBM under physiologic and pathophysiologic conditions, including glomerular hypertension, hyperfiltration, hypertrophy, and outflow of filtrate from subpodocyte spaces. Furthermore, we detail the cellular mechanisms by which podocytes respond to these challenges, discuss the protective effects of angiotensin blockade, and note the questions that must be addressed to better understand the relationship between podocyte detachment and progression of CKD.

Loss of a kidney during fetal life: long-term consequences and lessons learned

Epidemiological studies reveal that children born with a solitary functioning kidney (SFK) have a greater predisposition to develop renal insufficiency and hypertension in early adulthood. A congenital SFK is present in patients with unilateral renal agenesis or unilateral multicystic kidney dysplasia, leading to both structural and functional adaptations in the remaining kidney, which act to mitigate the reductions in glomerular filtration rate and sodium excretion that would otherwise ensue. To understand the mechanisms underlying the early development of renal insufficiency in children born with a SFK, we established a model of fetal uninephrectomy (uni-x) in sheep, a species that similar to humans complete nephrogenesis before birth. This model results in a 30% reduction in nephron number rather than 50%, due to compensatory nephrogenesis in the remaining kidney. Similar to children with a congenital SFK, uni-x sheep demonstrate a progressive increase in arterial pressure and a loss of renal function with aging. This review summarizes the compensatory changes in renal hemodynamics and tubular sodium handling that drive impairments in renal function and highlights the existence of sex differences in the functional adaptations following the loss of a kidney during fetal life.

Renal vascular structural properties and their alterations by removal of uraemic toxins in a rat model of chronic kidney disease

1. Renal vascular structural properties and their alterations by removal of uraemic toxins with AST-120, an oral adsorbent, were examined in subtotal nephrectomized rats. 2. Eight- or 9-week-old Sprague-Dawley rats received 3/4 nephrectomy (n = 18) and thereafter were fed 24.5% protein diet with (AST; n = 9) or without (AST-; n = 9) AST-120 (0.4 g/100 g bodyweight). Sham-operated rats (Sham; n = 9) received the diet without AST-120. At 21-22 weeks of age, flow-pressure (F-P) and pressure-glomerular filtration rate (P-GFR) relationships were determined for maximally vasodilated, perfused kidneys. 3. The gradient of F-P (minimal renal vascular resistance reflecting the overall luminal dimensions of pre- and post-glomerular vasculature) was lower in AST- than Sham rats. In contrast, the x-intercept (preglomerular : post-glomerular vascular resistance ratio) and gradient (glomerular filtration capacity) of P-GFR did not differ between the two groups. The vascular wall and lumen at the interlobular arteries were greater in AST- than Sham rats. 4. Although the vascular wall and lumen at the interlobular arteries were less in AST than in AST- rats, the gradient of F-P and the x-intercept of P-GFR did not differ between the two groups. In contrast, the glomerular filtration capacity was greater in AST than AST- rats. 5. In conclusion, the lumen of both pre- and post-glomerular resistance vessels increased and glomerular filtration capacity failed to increase in subtotal nephrectomized rats. Uraemic toxins could play an important role in the development of structural alterations in glomeruli rather than renal resistance vessels in chronic kidney disease.

The physical basis of renal fibrosis: effects of altered hydrodynamic forces on kidney homeostasis

Healthy kidneys are continuously exposed to an array of physical forces as they filter the blood: shear stress along the inner lumen of the tubules, distension of the tubular walls in response to changing fluid pressures, and bending moments along both the cilia and microvilli of individual epithelial cells that comprise the tubules. Dysregulation of kidney homeostasis via underlying medical conditions such as hypertension, diabetes, or glomerulonephritis fundamentally elevates the magnitudes of each principle force in the kidney and leads to fibrotic scarring and eventual loss of organ function. The purpose of this review is to summarize the progress made characterizing the response of kidney cells to pathological levels of mechanical stimuli. In particular, we examine important, mechanically responsive signaling cascades and explore fundamental changes in renal cell homeostasis after cyclic strain or fluid shear stress exposure. Elucidating the effects of these disease-related mechanical imbalances on endogenous signaling events in kidney cells presents a unique opportunity to better understand the fibrotic process.

Reduced glomerular filtration rate due to loss of nephron mass may be an independent risk factor for atherosclerosis

BACKGROUND

Whether living with reduced nephron mass (RNM) poses a risk to humans is the subject of ongoing controversy. The aim of this study was to discover whether or not RNMs are associated with greater atherosclerotic plaque burdens.

METHODS

Using the post-operative abdominal CT scans of 739 nephrectomized patients [NP; 315 women and 424 men; mean age 64.5 ± 15.0 years; observation period 4.9 ± 5.7 years (3675.9 patient-years)] and of an age- and a gender-matched control group, a retrospective observational and case-control study was conducted. The V600 calcium scoring method was used to determine the aortic calcium volume score (ACS) and thus the APB.

RESULTS

The ACS was 0.47 ± 0.77 mm(3) in the NPs compared with 0.41 ± 0.69 mm(3) in the control group (P <0.0001). The ACS and the glomerular filtration rate (GFR using the CKD-EPI formula) after nephrectomy correlated inversely (P = - 0.3652; P <0.0001), and the ACS and the time since nephrectomy correlated positively (P = 0.2919; P <0.0001). In linear regression models, age, time interval and GFR after nephrectomy proved to be independent factors of influence on ACS (P <0.05 each). Including the control group, age, GFR after nephrectomy and nephrectomy were independent factors of influence on the ACS. The factor GFR after nephrectomy explains ~ 10.7% in NPs, and 28% of the variance of the ACS in all patients.

CONCLUSIONS

The factors 'low GFR' and RNM are risk factors for greater atherosclerotic plaque burden. Patients with RNM should undergo regular control examinations to monitor arterial blood pressure and treat hypertension if it occurs.

Tubular cell-enriched subpopulation of primary renal cells improves survival and augments kidney function in rodent model of chronic kidney disease

Established chronic kidney disease (CKD) may be identified by severely impaired renal filtration that ultimately leads to the need for dialysis or kidney transplant. Dialysis addresses only some of the sequelae of CKD, and a significant gap persists between patients needing transplant and available organs, providing impetus for development of new CKD treatment modalities. Some postulate that CKD develops from a progressive imbalance between tissue damage and the kidney's intrinsic repair and regeneration processes. In this study we evaluated the effect of kidney cells, delivered orthotopically by intraparenchymal injection to rodents 4-7 wk after CKD was established by two-step 5/6 renal mass reduction (NX), on the regeneration of kidney function and architecture as assessed by physiological, tissue, and molecular markers. A proof of concept for the model, cell delivery, and systemic effect was demonstrated with a heterogeneous population of renal cells (UNFX) that contained cells from all major compartments of the kidney. Tubular cells are known contributors to kidney regeneration in situ following acute injury. Initially tested as a control, a tubular cell-enriched subpopulation of UNFX (B2) surprisingly outperformed UNFX. Two independent studies (3 and 6 mo in duration) with B2 confirmed that B2 significantly extended survival and improved renal filtration (serum creatinine and blood urea nitrogen). The specificity of B2 effects was verified by direct comparison to cell-free vehicle controls and an equivalent dose of non-B2 cells. Quantitative histological evaluation of kidneys at 6 mo after treatment confirmed that B2 treatment reduced severity of kidney tissue pathology. Treatment-associated reduction of transforming growth factor (TGF)-β1, plasminogen activator inhibitor (PAI)-1, and fibronectin (FN) provided evidence that B2 cells attenuated canonical pathways of profibrotic extracellular matrix production.

[Surgical model of chronic renal failure: study in rabbits]

OBJECTIVES

To establish a model of chronic renal failure in rabbits, with perspectives of its use for therapeutic and repairing actions.

METHODS

Nineteen males, adults rabbits (New Zealand) randomly distributed into three groups were used: Group 1 - Control (n =5); Group 2-Sham (n =7); and Group 3 - Experimental (n =7). They were anaesthetized by using intramuscular Cetamine, Diazepam and Fentanyl followed by Sevorane with vaporizer device. In Group 3, a bipolar left nephrectomy was carried out and after four weeks, it was also done a right nephrectomy. All the samples of the renal tissue were weighed. The Group 2 was only submitted to both abdominal laparotomies, without nephrectomy. Biochemical evaluations, with urea, creatinina, sodium and potassium measurement; abdominal ultrasound scan; scintigraphy and histological analysis were performed in all animals.

RESULTS

In group 3 there was a progressive increase of urea (p=0.0001), creatinine (p=0.0001), sodium (p = 0,0002) and potassium (p=0,0003). The comparison of these results with those one of the Groups 1 and 2, in all intervals, revealed blood rising with statistical significant level (p < 0,05). In Group 3, the ultrasound scan identified an increasing of the left kidney size, after 16 weeks and at the 4th week the scintigraphy confirmed the loss of 75% of the left renal mass. In the same group, the histological evaluation showed subcapsular and intersticial fibrosis and also tubular regeneration.

CONCLUSION

The experimental model of IRC is feasible, with animal's survival in middle term which allows the use of this interval like a therapeutic window for testing different approaches in order to repair the kidney damages.

Renal agenesis and unilateral nephrectomy: what are the risks of living with a single kidney?

The long-term outlook for patients with unilateral renal agenesis or following unilateral nephrectomy in childhood is controversial. Animal studies suggest that the resultant compensatory increase in glomerular filtration might lead to progressive damage to the remaining renal tissue and may generate hypertension. Human studies addressing these concerns are limited in number and are difficult to interpret because they are small, retrospective, or cross sectional with significant variations in duration and completeness of follow-up. The published studies suggest that renal function remains stable for several decades in the majority of subjects. The clinical significance of mild-grade proteinuria and hypertension seen in some patients is unknown. Longitudinal studies are needed to understand the long-term effect and significance of the several pathophysiological changes observed in the solitary kidney.

Compensatory renal growth and mitochondrial function: the influence of warm ischemia and reperfusion

PURPOSE: To evaluate the influence of ischemia/reperfusion injury on renal compensatory growth (CGR) and mitochondrial function. METHODS: Forty five Wistar rats were divided in 3 groups: Control Group (GC) - 21 rats were submitted to a sham laparotomy and sacrificed at 1st (6 rats) and 7th (15 rats) postoperative days to evaluate the dry weight of both kidneys and their growth during 1 week (6 rats) and to quantify mitochondrial respiration (9 rats); Group 1 (G1) - 12 rats underwent right nephrectomy and were sacrificed 7 days later for analysis of renal mitochondrial function (6 rats) and dry weight (6 rats). Group 2 (G2) - renal warm ischemia for 60 minutes followed by right nephrectomy was performed in 12 rats; they were sacrificed 7 days later to evaluate renal mitochondrial function (6 rats) and dry weight (6 rats). RESULTS: Dry weight (mg) of left kidneys at 7th day: GC - 219±18, G1 - 281±23 and G2 - 338±39 (GCxG1 p<0.01; GCxG2 p<0.001; G1xG2 p<0.01). State 4 mitochondrial respiration rate and respiratory control ratio (RCR) were similar in all groups (p>0.05). State 3 respirations (mM/min/mg) in GC, G1 and G2 was respectively: 99±23, 132±22 and 82±44 (p<0.02; the only statistical difference noted was between groups G1xG2 - p<0.05). CONCLUSIONS: Following unilateral nephrectomy CRG is associated with an increase in state 3 of mitochondrial respiration. Renal ischemia/reperfusion injury enhances the CRG provoked by unilateral nephrectomy but such enhancement seems independent on mitochondrial respiration.

Sex and age differences of renal function in rats with reduced ANG II activity during the nephrogenic period

This study was designed to test the hypothesis that blockade of angiotensin II effects during renal development accelerates the aging-related changes in renal hemodynamics and proteinuria, and that these changes are sex dependent. It has also been examined whether the deterioration of urinary concentrating ability elicited by angiotensin II blockade is sex and/or aging dependent. Newborn Sprague-Dawley rats were treated with vehicle or an AT(1) angiotensin II receptor antagonist (ARA) during the first 14 postnatal days. Blood pressure, glomerular filtration rate, proteinuria, and urinary concentrating ability in response to dehydration were examined in conscious rats at 3 and 11 mo of age. ARA treatment elicited a similar increment in blood pressure in males and females that was greater (P < 0.05) at 11 than at 3 mo of age. Glomerular filtration rate only decreased (P < 0.05) in 11-mo-old male ARA-treated rats (0.59 +/- 0.07 vs. 0.80 +/- 0.07 ml.min(-1).g(-1) in control group). At 3 mo of age, proteinuria increased in male (107%) but not in female ARA-treated rats. However, at 11 mo of age, proteinuria increased in both sexes, but the increment was greater (P < 0.05) in male (244%) than in female (138%) ARA-treated rats. Renal ability to concentrate urine in response to prolonged water dehydration was only reduced in ARA-treated males. The reduction of urinary concentrating ability was accentuated by aging. Therefore, we conclude that blockade of angiotensin II effects during renal development elicits an important deterioration of cortical and medullary function that is sex and aging dependent.

Time course of the renal functional response to partial nephrectomy: measurements in conscious rats

Previous investigations into the functional responses of the surviving nephrons following reductions in renal mass have been performed largely in anaesthetized animals and have taken little account of how the compensatory changes develop with time. The present study has assessed a method for determining glomerular filtration rate (GFR) in unrestrained, uncatheterized, conscious rats (plasma disappearance of (99m)Tc-diethylenetriamene pentaacetic acid (DTPA)) and has used this method to document the time course of the changes in GFR over a 32 day period following uninephrectomy or 5/6 nephrectomy. Concurrent measurements of excretion rates and of the clearance of lithium (the latter being an index of end-proximal fluid delivery) provided information on changes in overall tubular function and segmental reabsorption. After uninephrectomy, the GFR of the remaining kidney (compared with that of a single kidney of sham-operated animals) increased maximally (by approximately 50%) within 8 days; after 5/6 nephrectomy, the increase in the GFR of the remnant kidney was maximal (at approximately 300%) within 16 days. Overall excretion rates of sodium and potassium were well maintained in partially nephrectomized animals throughout the period of study, while the excretion of water increased (by approximately 30% after uninephrectomy and by approximately 120% after 5/6 nephrectomy), partly as a result of the compensatory increases in GFR but mainly as a consequence of moderate (after uninephrectomy) or marked (after 5/6 nephrectomy) reductions in fractional reabsorption. During the early period after 5/6 nephrectomy, potassium excretion sometimes exceeded the filtered load, indicating net secretion. Lithium clearance data indicated that the changes in tubular function after 5/6 nephrectomy include a reduction in fractional reabsorption in the proximal tubule, whereas after uninephrectomy any such effect on the proximal tubule is minor and transient.

Jejunal dopamine and Na,K-ATPase activity in early chronic renal insufficiency

AIM

The uninephrectomised and three-quarter nephrectomised (3/4nx) rats present dopamine-sensitive enhanced natriuresis. This is accompanied in uninephrectomised rats by a reduced jejunal Na(+),K(+)-ATPase activity with recovered sensitivity to inhibition by dopamine. The present study examined the jejunal Na(+),K(+)-ATPase activity and the role of dopamine in 3/4nx animals.

METHODS

Fourteen days after surgery, the L-amino acid decarboxylase activity (AADC) activity, the enzyme responsible for the synthesis of dopamine, and the Na(+),K(+)-ATPase activity, were determined in jejunal epithelial cells from 3/4nx and Sham rats. In addition, the effect of dopamine (1 micromol/L) on jejunal Na(+),K(+)-ATPase activity was evaluated in both groups.

RESULTS

The 3/4nx rats presented a reduced AADC activity in jejunal epithelial cells (V(max) in nmol/mg prot/15 min, 142 +/- 6 vs 190 +/- 10, P < 0.05). In addition, the jejunal Na(+),K(+)-ATPase activity was increased in 3/4nx rats (Pi release in nmol/mg prot/min, 137 +/- 1 vs 122 +/- 2, P < 0.05). However, dopamine was unable to inhibit the Na(+),K(+)-ATPase activity in jejunal epithelial cells from both 3/4nx and Sham animals.

CONCLUSIONS

In contrast to uninephrectomy, the jejunal Na(+),K(+)-ATPase activity is increased in 3/4nx rats and is not sensitive to inhibition by dopamine.

Subclinical rejection impairs glomerular adaptation after renal transplantation

After transplantation, glomerular volumes increases and large glomerular volume at 4 months is associated with better renal function. The aim is to characterize glomerular adaptation after the fourth month in two serial protocol biopsies and its relationship with subclinical rejection and chronic allograft nephropathy (CAN). Mean glomerular volume (Vg) was estimated according to the Weibel and Gomez method in a 4-month and 1-year serial protocol biopsies in 61 stable grafts. Glomerular enlargement (deltaVg) was calculated as the Vg difference between both biopsies. Banff schema was used to evaluate renal biopsies. Vg increased from 4.4+/-2.4 to 5.7+/-2.6 x 10(6) microm3 (P<0.001). Mean deltaVg was 1.0 x 10(6) microm3. Patients with deltaVg<1 were considered as patients with impaired glomerular enlargement (n=29). Impaired glomerular enlargement was associated with increased acute index score in the 4-month (1.83+/-1.56 vs 1.06+/-1.48; P<0.05) and 1-year protocol biopsies (1.52+/-1.59 vs 0.62+/-1.07; P<0.05). Impaired glomerular enlargement was also associated with increased progression of chronic lesions between the 4-month and 1-year biopsy in the glomerular (0.17+/-0.38 vs 0.55+/-0.63; P<0.01), tubular (0.38+/-0.56 vs 0.83+/-0.85; P<0.01), and interstitial compartment (0.41+/-0.57 vs 0.90+/-0.86; P<0.01). The proportion of sclerotic glomeruli between both biopsies increased in patients with impaired glomerular enlargement (1.5+/-3.9 to 5.3+/-10.1, P<0.05) while it did not modify in patients with glomerular enlargement (2.1+/-7.3 vs 2.6+/-4.5; P=NS). During the first year, glomeruli enlarge but this adaptation mechanism is impaired in patients with subclinical rejection. Moreover, impaired glomerular enlargement is associated with progression of CAN.

Renal Dopaminergic System Activity in the Rat Remnant Kidney

BACKGROUND

Renal dopamine exerts natriuretic and diuretic effects by activating D1-like receptors. Uninephrectomy results in increased renal dopaminergic activity and dopamine-sensitive enhanced natriuresis.

METHODS

The present study evaluated renal adaptations in sodium handling and the role of dopamine in rats submitted to (3/4) nephrectomy: right nephrectomy and excision of both poles of the left kidney ((3/4)nx rats).

RESULTS

Two weeks after surgery the absolute urinary levels of dopamine were markedly reduced in (3/4)nx rats whereas the urinary dopamine excretion per % of residual nephrons was significantly increased in the remnant kidney of (3/4)nx rats. The V(max) values for renal aromatic L-amino acid decarboxylase, the enzyme responsible for the synthesis of renal dopamine, were decreased in (3/4)nx rats. Renal catechol-O-methyltransferase activity, the enzyme responsible for the methylation of dopamine, was increased in (3/4)nx rats whereas the renal activities of monoamine oxidases A and B did not differ between (3/4)nx and Sham animals. Volume expansion (5% body weight) resulted in similar natriuretic responses in (3/4)nx and Sham rats. During D1 antagonist administration (Sch-23390, 30 microg x h(-1) x kg(-1)) the natriuretic response to volume expansion was reduced in (3/4)nx rats more pronouncedly than in Sham animals.

CONCLUSION

The decrease in absolute renal dopamine output in (3/4)nx rats is related with reduced renal synthesis and enhanced O-methylation of the amine. However, this is accompanied in (3/4)nx rats by increased renal dopamine excretion per residual nephrons and dopamine-sensitive enhanced natriuresis.

The physiological and pathophysiological roles of the GH/IGF-axis in the kidney: lessons from experimental rodent models

The growth hormone (GH)/insulin-like growth factor (IGF) system plays an important role in renal development, growth, function and pathophysiology. IGF-I has been associated with renal/glomerular hypertrophy and compensatory renal growth. Potential effects on glomerular size are of interest, since an increase in glomerular size may be permissive for the development of glomerulosclerosis. In an effort to abolish the decline of renal function and possibly to restore the renal structure, different approaches have been tested in experimental models of nephropathy, focusing mainly on early renal changes. The involvement of the GH/IGF system in renal pathophysiology has been studied in much detail in the rat. In view of the growing interest in murine physiology, occurring in large part by genetically modified animals, this review examines those aspects of GH, IGFs, their receptors and binding proteins that relate both to mouse kidney physiology and to a number of conditions characterized by pathophysiological renal changes. A deeper understanding of the role of the GH/IGF system in renal dysfunction may stimulate the development of novel therapeutic approaches aiming at preventing or retarding various kidney diseases.

Estimation of total glomerular number in stable renal transplants

Glomerular number (N(g)) is considered a major determinant of renal function and outcome. In the dog, it has been shown that Ng can be estimated with reasonable precision in vivo by means of a renal biopsy and magnetic resonance imaging (MRI). Thus, this method was applied to study anatomoclinical correlations in stable human renal transplants. Thirty-nine stable renal transplants were included. A protocol renal allograft biopsy was done at 4 mo. Biopsies were evaluated according to Banff criteria. Glomerular volume fraction (Vv(glom/cortex)) was measured by means of a point-counting method, and mean glomerular volume (V(g)) was estimated by means of Weibel and Gomez (V(g)-W&G) and maximal profile area (V(g)-MPA) methods. MRI was used to estimate renal cortical volume (V(cortex)). N(g) was calculated as (Vv(glom/cortex) x V(cortex))/V(g). GFR was estimated by the inulin clearance. Ten age-matched donor biopsies served as controls for V(g). Histologic diagnosis was as follows: normal (n = 20), borderline (n = 7), acute rejection (n = 1), and chronic allograft nephropathy (n = 11). Vv(glom/cortex) was 3.4 +/- 1.1%, V(cortex) was 167 +/- 46 cm(3), V(g)-W&G was 3.2 +/- 1.2 x 10(6) micro m(3), and V(g)-MPA was 3.3 +/- 1.0 x 10(6) micro m(3). V(g)-W&G in donor and recipient biopsies was not different (3.6 +/- 1.1 versus 3.2 +/- 1.2 x 10(6) micro m(3)). Total glomerular number estimated by means of V(g)-W&G (N(g)-W&G) was 0.73 +/- 0.33 x 10(6) and by V(g)-MPA (N(g)-MPA) was 0.74 +/- 0.31 x 10(6). A positive correlation between GFR and N(g)-W&G (r = 0.47, P = 0.002) was observed. Furthermore, the older the donor, the higher V(g)-W&G (r = 0.37, P = 0.01) and the lower N(g)-W&G (r = -0.40, P = 0.01). Total glomerular number can be estimated in stable renal allografts by means of a renal biopsy and MRI. Our data show that N(g) depends on donor age and positively correlates with GFR.

Glomerular enlargement assessed by paired donor and early protocol renal allograft biopsies

The aim of the study was to evaluate the evolution of glomerular volume 4 months after transplantation. Mean glomerular volume (Vg) was estimated according to the Weibel and Gomez method in a donor and a protocol biopsy done at 139 +/- 58 d in 41 stable grafts. Biopsies were also evaluated according to the Banff schema. Vg increased after transplantation from 4.1 +/- 1.4 to 5.1 +/- 2.4 x 10(6) micro3 (p=0.02). In patients with chronic allograft nephropathy in the protocol biopsy (n=14), the Vg enlargement was -0.3 +/-x 10(6) micro3 while in patients without chronic allograft nephropathy (n=27), glomerular enlargement was 1.6 +/- 2.1 x 10(6) micro3 (p=0.01). There was a negative association between glomerular volume in the donor biopsy and glomerular enlargement after transplantation (R=- 0.34, p=0.03). Multivariate regression analysis confirmed that Vg in the donor biopsy and chronic allograft nephropathy in the protocol biopsy were independent predictors of glomerular enlargement after transplantation (R=0.48, p=0.01). Moreover, Vg in the protocol biopsy correlated with creatinine clearance at the time of biopsy (R=0.38, p=0.01). Glomeruli enlarge after transplantation and glomerular volume after 4 months correlates with creatinine clearance, suggesting that glomerular enlargement is a necessary condition for renal adaptation to the recipient. Glomerular enlargement is impaired in patients with chronic allograft nephropathy.

Upregulation of NHE3 is associated with compensatory cell growth response in young uninephrectomized rats

It is well established that after removal of renal mass, the remaining tissue undergoes compensatory growth. Several laboratories have reported that the activity of the apical membrane Na+ - H+ exchanger (NHE3) is increased after a reduction in renal mass. These studies were designed to determine whether NHE3 expression is altered early after loss of renal mass and to investigate the possible role of NHE3 activation in the compensatory tissue growth response. Experiments were performed in young male Wistar rats submitted to left nephrectomy or sham operation. At either 4 or 24 h after the surgery, the right kidney from each animal was removed and weighed. Significant increases in the wet weight of the remaining kidney were only observed 24 h after uninephrectomy (UNX). Western blot analysis of brush-border membranes and Northern blot analysis of cortex RNA showed that NHE3 protein abundance and NHE3 mRNA were greatly enhanced 4 and 24 h after UNX in relation to the sham kidney. To identify which growth pattern was mostly responsible for the enlargement of the remained kidney in our experimental models, we measured 5-bromo-2-deoxyuridine incorporation (BrdU) and protein-to-DNA ratio (protein/DNA ratio). The number of BrdU-positive nuclei increased and protein/DNA ratio slightly decreased, indicating that a hyperplastic response was the main component involved in the early compensatory renal growth in our animals. BrdU incorporation and protein/DNA were also assessed in rats treated with S3226, a selective blocker of NHE3. Neither the number of BrdU-positive nuclei nor the protein/DNA ratio was significantly altered 4 and 24 h after UNX in rats treated with S3226. In conclusion, UNX induced an upregulation of NHE3, which was evidenced at both functional and expression levels. The compensatory growth response in young UNX rats could be blocked by inhibiting NHE3 activity, suggesting that NHE3 activation may result in a facilitator state for the cell growth response in the renal proximal tubule.

Intrarenal serotonin, dopamine, and phosphate handling in remnant kidneys

BACKGROUND

Serotonin (5-HT) and dopamine (DA) are intrarenal autocrine/paracrine substances that regulate phosphate reabsorption. The present studies explored intrarenal serotonin and DA metabolism and the implications for phosphate homeostasis in rats with remnant kidneys, a model for renal failure.

METHODS

The intrarenal productions of serotonin and DA were determined from measurements of renal interstitial fluid (microdialysate) and urine in rats with remnant or intact kidneys. In clearance studies, the effects of infusion of methiothepin, a serotonin receptor antagonist, or gludopa, a renal selective DA precursor, on phosphate and sodium excretion were determined in rats with a remnant or intact kidneys.

RESULTS

Renal interstitial serotonin (5-HT, 3.4 +/- 0.9 pg/min) was fourfold higher than DA (0.6 +/- 0.1 pg/min) in remnant kidneys. Conversely, urinary excretion of serotonin was fourfold less than DA in rats with a remnant kidney (5-HT 0.4 +/- 0.02 vs. DA 1.5 +/- 0.1 ng/min). Infusion of methiothepin or gludopa significantly increased the fractional excretion of phosphate (FE(Pi)) in rats with a remnant kidney from 54 +/- 3 to 67 +/- 7% (P < 0.05) and from 36 +/- 10% to 51 +/- 13% (P < 0.05), respectively.

CONCLUSION

We conclude that serotonin preferentially accumulates in the renal interstitium, whereas DA exits primarily via the tubular lumen. Phosphate excretion is increased by both the acute infusion of the serotonin receptor antagonist and the infusion of gludopa, suggesting that both serotonin and DA modulate phosphate excretion in rats with remnant kidneys.

Chronic oral L-DOPA increases dopamine and decreases serotonin excretions

Given the common pathways for uptake and synthesis for dopamine and serotonin, enhanced renal dopamine synthesis in response to increased substrate 3,4-dihydroxyphenylalanine (L-DOPA) is postulated to decrease renal serotonin synthesis. The present study compared the effects of chronic oral administration of L-DOPA on dopamine and serotonin excretion in vivo, with the effects of enhanced dopamine synthesis per nephron due to adaptation to reduced renal mass (RRM). Four groups of rats were studied: sham-operated rats and rats with RRM in the absence and presence of chronic oral L-DOPA. L-DOPA (2 mg. 100 g body wt(-1). day(-1)) for 6-14 days increased calculated dopamine synthesis per nephron in sham-operated rats from 2.0 +/- 0.3 (n = 7) to 13.6 +/- 1.8 pg. day(-1). nephron(-1) (n = 7, P < 0.05) and in rats with RRM from 6.1 +/- 1.3 (n = 7) to 39.3 +/- 5.2 pg. day(-1). nephron(-1) (n = 7, P < 0.05). Chronic oral L-DOPA concomitantly decreased serotonin synthesis per nephron in sham-operated rats (1.6 +/- 0.1 to 1.0 +/- 0.1 pg. day(-1). nephron(-1), n = 7, P < 0.05) and in rats with RRM (5.6 +/- 0.9 to 2.6 +/- 0.4 pg. day(-1). nephron(-1), n = 7, P < 0.05). Both serotonin and dopamine synthesis per nephron were increased in rats with RRM. In conclusion, chronic oral administration of L-DOPA enhances dopamine excretion and decreases serotonin excretion in normal rats and in rats with reduced renal mass. Both dopamine and serotonin excretions per nephron were elevated by renal mass reduction.

A rat model of progressive chronic renal failure produced by microembolism

We report a new model of chronic progressive renal failure in rats, produced by a single injection of microspheres (20 to 30 micrometer in diameter) into the left renal artery after right nephrectomy. Significant proteinuria appeared after 4 weeks, followed by hypoalbuminemia and hypercholesterolemia, in rats that received approximately 5 x 10(5) microspheres (0.8 mg). Renal function partially recovered by 4 weeks after nephrectomy and injection from postoperative dysfunction, but deteriorated again 12 weeks after operation. In the early stage, histologic examination showed tubules with cuff-like thickening of basement membranes scattered among apparently intact tubules. Many epithelial cells in the atrophic tubuli were immunoreactive for proliferating cell nuclear antigen (PCNA). Dilated tubules became apparent several weeks after development of tubular atrophy, most likely representing distal tubules. Dilated tubuli were mostly negative for the proliferation marker. These results showed similarity to findings in human chronic renal failure and strongly suggested that tubular atrophy and dilation in chronic tubulointerstitial lesions differ in pathogenesis. This new model of renal failure induced by microembolism should be useful for studying the interaction between normal and diseased tissue elements in histologically heterogenous lesions as well as the pathogenesis of interstitial fibrosis in disturbance of microcirculation.

Effect of experimentally induced renal failure on testicular testosterone synthesis in rats

Renal insufficiency is responsible for gonadal impairment, but the pathogenesis of testicular dysfunction remains unresolved. This study examines the possible role of the endocrine disturbance and angiotensin II-induced physiological abnormality for the pathogenesis of gonadal dysfunction of two different types of chronic renal failure. Chronic renal insufficiency was induced in rats given an adenine-excessive diet or in 5/6 nephrectomized animals. Circulating levels of blood urea nitrogen, creatinine, renin-angiotensin-aldosterone (R-A-A) system androstenedione, 17 alpha-hydroxy progesterone (17 alpha-OHP), testosterone, luteinizing hormone, and follicle-stimulating hormone were assayed. Systolic blood pressure, renal blood flow, and testicular blood flow were also determined. High serum levels of 17 alpha-OHP, androstenedione, and low testosterone were noted in the normotensive group. Enhanced R-A-A system decreased testicular blood flow and low testosterone were seen in the hypertensive group. The data provide evidence that gonadal dysfunction in adenine-induced renal failure appears to be caused by the suppression of 17 beta-hydroxysteroid oxydoreductase activity, and gonadal impairment in 5/6 nephrectomized uremia can be evoked by enhanced renin-angiotensin-aldosterone system and hypertension.

Amino acid handling in uremic rats: citrulline, a reliable marker of renal insufficiency and proximal tubular dysfunction

The kidney is involved in amino acid reabsorption and metabolism; consequently, in renal insufficiency, these important functions are disturbed, as has been reported in animals and patients. In a first experimental series, rats were subjected to degrees of nephrectomy (NX) varying between 10% and 90%. Three weeks later, amino acid levels were measured in plasma to correlate the levels with the degree of NX. The results indicate that in the range of 33% to 74% NX, the plasma concentration of only three to four amino acids was modified, whereas in rats with 84% NX, the concentration of 11 amino acids was disturbed, compared with sham-operated rats. Citrullinemia was enhanced in uremic rats and correlated with the degree of NX. More interestingly, citrullinemia was increased in the range of 10% to 33% NX without any changes in uremia and creatininemia, two well-known markers of uremic states. A second experimental series was designed to study the time course of changes in aminoacidemia to find a marker for the onset of renal failure. Rats were subjected to 36% NX for a period of 1 to 21 days. Uremia and creatininemia peaked 24 to 48 hours after NX, and creatinine clearance (Clcreat) concomitantly diminished. Unfortunately, these three markers of uremic states returned to control values during the next few days before increasing during the last 2 weeks. In contrast, citrullinemia increased twofold 48 hours after NX and plateaued over the next 20 days. We conclude that in rats, citrullinemia could be used (1) to detect acute and chronic renal failure, (2) as a specific marker of normal function of the proximal tubule, and (3) to estimate the degree of renal damage. From this study, renal insufficiency might be easily detected by measuring citrullinemia.

Guanidino compound metabolism in rats subjected to 20% to 90% nephrectomy

In mammalian kidney, the proximal convoluted tubule (PCT) is the main site of arginine (Arg) production. Arginine can be used in the biosynthesis of guanidino compounds (GC). Since uremic rats have a lower functional mass of PCT, GC synthesis might be modified, especially that of guanidinoacetic acid (GAA) which occurs in PCT. In order to study GC metabolism at different steps of uremia, rats were subjected to either 42% or 80% nephrectomy (NX); the experiment lasted for three weeks. Results show that: (1) in plasma, the pattern of GC levels in 42% NX rats was similar to that of controls except for a clear increase of beta-guanidinopropionic acid (beta-GPA), whereas in 80% NX rats, all GC levels sharply increased except that of creatine which decreased. (2) Urinary excretion of GC in control and 42% NX rats is quite similar except for GAA which strongly decreased, and for homoarginine (HArg) and argininic acid (ArgA) which increased. In rats with 80% NX, the principal modification in GC excretion was a four- to five-fold reduction in GAA output. (3) After induction of renal failure, Arg, creatine and guanidinosuccinic acid reabsorption remained unchanged, and that of HArg decreased. For guanidine and methylguanidine the negative renal balance remained unchanged, and that of gamma-guanidinobutyric acid, GAA and alpha-keto-delta-guanidinovaleric acid became smaller, suggesting a better reabsorption. In conclusion, uremia strongly modified GC metabolism involving mainly those synthesized from Arg; both GAA and creatine synthesis were strongly decreased probably because of the loss of renal tissue, mainly PCT.

Renal handling of drugs and amino acids after impairment of kidney or liver function--influences of maturity and protective treatment

Renal tubular cells are involved both in secretion and in reabsorption processes within the kidney. Normally, most xenobiotics are secreted into the urine at the basolateral membrane of the tubular cell, whereas amino acids are reabsorbed quantitatively at the luminal side. Under different pathological or experimental circumstances, these transport steps may be changed, e.g., they may be reduced by renal impairment (reduction of kidney mass, renal ischemia, administration of nephrotoxins) or they may be enhanced after stimulation of transport carriers. Furthermore, a distinct interrelationship exists between excretory functions of the kidney and the liver. That means liver injury can influence renal transport systems also (hepato-renal syndrome). In this review, the following aspects were included: based upon general information concerning different transport pathways for xenobiotics and amino acids within kidney cells and upon a brief characterization of methods for testing impairment of kidney function, the maturation of renal transport and its stimulation are described. Similarities and differences between the postnatal development of kidney function and the increase of renal transport capacity after suitable stimulatory treatment by, for example, various hormones or xenobiotics are reviewed. Especially, renal transport in acute renal failure is described for individuals of different ages. Depending upon the maturity of kidney function, age differences in susceptibility to kidney injury occur: if energy-requiring processes are involved in the transport of the respective substance, then adults, in general, are more susceptible to renal failure than young individuals, because in immature organisms, anaerobic energy production predominates within the kidney. On the other hand, adult animals can better compensate for the loss of renal tissue (partial nephrectomy). With respect to stimulation of renal transport capacity after repeated pretreatment with suitable substances, age differences also exist: most stimulatory schedules are more effective in young, developing individuals than in mature animals. Therefore, the consequences of the stimulation of renal transport can be different in animals of different ages and are discussed in detail. Furthermore, the extent of stimulation is different for the transporters located at the basolateral and at the luminal membranes: obviously the tubular secretion at the contraluminal membrane can be stimulated more effectively than reabsorption processes at the luminal side.

Radiotelemetric BP monitoring, antihypertensives and glomeruloprotection in remnant kidney model

The mechanisms by which antihypertensives exert a glomeruloprotective effect in the remnant kidney model remain controversial. Based on periodic tail-cuff BP measurements, the variable glomeruloprotective efficacy of antihypertensive agents has been ascribed to mechanisms other than or in addition to their ability to lower BP. To more precisely define the relationship between BP control and glomeruloprotection, systolic BP was continuously monitored radiotelemetrically at 10-minute intervals for approximately 65 days in rats after approximately 5/6 renal ablation. Rats with remnant kidneys received either no therapy or one of three antihypertensive regimens in their drinking water after the first week: enalapril, a triple therapy regimen (reserpine, hydralazine, hydrochlorothiazide); or a high dose triple therapy regimen. Although all antihypertensive regimens significantly lowered BP, considerable interanimal variability was observed. Additionally, marked lability of BP was present in both untreated and treated rats. Glomerular injury in individual animals (N = 34) was very strongly correlated with their overall averaged systolic BP during the final eight weeks (r = 0.91) and with the frequency of systolic BP readings > 150 mm Hg (r = 0.89). These data do not provide evidence of a therapeutic advantage for any of the regimens independent of their antihypertensive effects but indicate that the glomeruloprotective efficacy of these antihypertensive regimens is directly proportional to their antihypertensive efficiency.

Infundibulopelvic stenosis: a long-term followup

We followed 21 patients with congenital infundibulopelvic stenosis, a rare obstructive disorder of the intrarenal collecting system, for a median of 11 years (range 2 to 28 years). Of these patients 19 (90%) had evidence of bilateral renal disease. In particular, 10 patients had bilateral infundibular pelvic stenosis, 6 a contralateral cystic dysplastic kidney and 3 a congenitally absent kidney. Extended observations of the patients with this disorder revealed that end stage renal disease or renal insufficiency developed in 8 patients (37%), all with bilateral renal anomalies. Renal biopsies in patients with end stage renal failure revealed widespread areas of renal dysplasia proximal to the stenotic infundibulum with focal or global glomerulosclerosis of the glomeruli, which was not involved in the dysplastic process. These pathological findings are consistent with the presence of a renal hyperfiltration injury. Our data suggest that the prognosis of infundibulopelvic stenosis is dependent upon the extent of total renal mass involved with the disease process and the duration of followup.

Intrathrombic urokinase reverses neonatal renal artery thrombosis

A term infant with aortic and renal artery thrombosis is described, in whom the right kidney experienced complete ischemia for 5 days. A continuous intrathrombic urokinase infusion induced complete clot lysis and reperfusion of the right kidney. Follow-up studies of renal function and renal growth have been normal. This is the first report to describe complete pharmacological salvage of a neonatal kidney after prolonged warm ischemia. This case underscores both the ability of the neonatal kidney to recover from prolonged ischemia and the need to effect thrombolysis before irreversible renal injury occurs. The intrathrombic use of fibrinolytic agents in similarly affected infants warrants consideration and further study.

Catecholamines and phosphate excretion by the remnant kidney

The remnant kidney (RK) exhibits an enhanced fractional excretion of phosphate (FEPi) even in the absence of parathyroid hormone (PTH). Thus, factors other than PTH contribute to this adaptive phosphaturia. Dopamine (DA) infusion is phosphaturic, whereas stimulation of adrenoreceptors is antiphosphaturic. Therefore, the hypothesis that alterations in catecholamines by the RK may be associated with the phosphaturia exhibited by this model was tested. Male Sprague-Dawley rats were subjected to right nephrectomy and surgical ablation of the left renal poles. Four weeks later rats with a RK (N = 10) and control rats with intact kidneys (N = 9) were anesthetized and thyroparathyroidectomized (TPTX). Two hours after TPTX, urine samples were collected for measurements of urinary free DA excretion. Subsequently, 3% inulin in saline was infused for one hour and a 30 minute clearance was taken. The kidneys were then removed and frozen for determination of tissue norepinephrine (NE) and DA concentrations. Glomerular filtration rate was significantly lower in rats with a RK than in controls (0.57 +/- 0.07 vs. 0.83 +/- 0.08 ml/min/g kidney wt), whereas fractional excretion of phosphate (FEPi) was significantly higher (29.4 +/- 4.7 vs. 8.3 +/- 3.4%). Tissue NE concentration was significantly lower in the RK than in the control intact kidney (85.10 +/- 4.95 vs. 129.60 +/- 7.20 ng/g), whereas urinary DA excretion per nephron was significantly higher in the RK (0.12 +/- 0.02 vs. 0.04 +/- 0.006 pg/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Number and dimensions of rat glomerular capillaries in normal development and after nephrectomy

Glomerular capillary growth was studied in kidneys in five- to 540-day-old perfusion-fixed normal or sham-operated rats (C) as well as in unilaterally nephrectomized three-day-old (NN) and 120-day-old (NA) rats. The number and volume of mature glomeruli were estimated using the fractionator. The glomerular number was unaffected by neonatal or adult nephrectomy, but the number of mature glomeruli in all rats aged five days (19.1 +/- 2.0 x 10(3); +/- SD) was significantly smaller than for all the older animals (26.5 +/- 3.1 x 10(3)). The mean glomerular volume increased 59% and 20% for the NN and NA rats, respectively, versus the C rats. A capillary unit has been defined according to the number of loops in the glomerular capillary network by the use of topology. Glomerular capillary number, estimated using a physical disector, increased 53% for NN rats and 26% for NA rats. The glomerular capillary length was estimated on isotropic, uniform random sections, and increased 47% for NN rats and 12% for NA rats. The glomerular capillary surface area increased 54% for NN rats and 14% for NA rats. The diameter of the glomerular capillaries increased 8% for the mature NN versus the C rats. The rather unexpected findings are discussed and related to interesting relationships, including the law of Poiseuille and LaPlace. In conclusion, the growth of glomerular capillaries after neonatal and adult nephrectomy is performed by branching that is making new glomerular capillaries, instead of simply lengthening the existing capillaries.

Effect of uremia on aldosterone metabolism in the isolated perfused rat liver

The effect of uremia on hepatic metabolism of aldosterone was studied in the isolated perfused liver of female Wistar rats. Uremia was induced by five-sixths partial nephrectomy 4 weeks before experiments. Isolated livers of normal and uremic rats were perfused at a constant flow rate with a hemoglobin-free medium, to which 4-14C-D-aldosterone was added at 3 nmol/L. Aldosterone was analyzed by radioimmunoassay (RIA) and 4-14C-D-aldosterone radiometabolites in perfusate and bile were assayed by high-performance liquid chromatography (HPLC). Uremic rats had a 10% lower body weight (P < .01) and increased plasma urea, creatinine, and parathyroid hormone (PTH) levels (258%, 200%, and 208%, respectively; P < .01-.001). Blood pressure and plasma K+, Na+, and aldosterone levels were similar. Plasma renin activity was suppressed by 68% in uremic rats (P < .001). Liver wet weight and hepatic function were similar in livers of both groups of rats. Hepatic elimination of aldosterone was compatible with a first-order kinetics. Hepatic clearance of aldosterone per liver and per gram liver was similar; however, when expressed per 100 g rat body weight, a 21% higher value was observed in uremic rats (11.6 +/- 1.8 mL/min) compared with normal rats (9.6 +/- 1.5 mL/min, P < .01). Polar aldosterone radiometabolites accumulated in the perfusate to approximately 40% of the initial 14C added at 15 minutes, and were eliminated in bile at a similar rate in both groups. No qualitative difference was found in the pattern of radiometabolites of aldosterone in perfusate and bile.(ABSTRACT TRUNCATED AT 250 WORDS)

Reversible compensatory hypertrophy in rat kidneys: morphometric characterization

Functional renal compensatory hypertrophy (RCH) in the uninephrectomized rat is completely reversible by transplantation in Brown Norway (BN) rats, while anatomic RCH is not. To determine the nephron element(s) responsible for persistent anatomic RCH, we performed morphometric analysis on perfusion fixed rat kidneys following renal function studies. In this model the function of renal transplants is not different from contralateral and unmanipulated control kidneys, and there is no histological evidence of rejection. Rats uninephrectomized for three or six weeks had larger glomeruli than controls, and after transplantation of a previously hypertrophied kidney into a rat with a normal or a solitary hypertrophied kidney, glomerular size returned to control levels. Increased glomerular capillary volume (CVCP) in kidneys with RCH was due to increased capillary length (LCP; 13.1 +/- 1.0 mm cf. 10.3 +/- 0.9, P < 0.01) without increase in capillary radius (RCP; 3.26 +/- 0.33 microM cf. 3.28 +/- 0.24). In contrast, return of CVCP to control levels in kidneys undergoing regression was associated with persistently elevated LCP (13.0 +2- 2.9 mm; native previously hypertrophied kidney; 12.2 +/- 0.9; transplanted previously hypertrophied kidney vs. 10.3 +/- 0.9, P < 0.01) and decreased RCP (2.79 +/- 0.10 microM and 2.73 +/- 0.09, cf 3.28 +/- 0.24, P < 0.01). RCH was associated with proportional increases in glomerular, tubular, and vascular-interstitial volumes while only elevated tubular volume persisted during regression. Altered glomerular capillary dimensions and increased tubular volumes acquired during renal RCH induced by unilateral nephrectomy persisted during complete functional regression.(ABSTRACT TRUNCATED AT 250 WORDS)

Remnant kidney pathology after five-sixth nephrectomy in rat. I. A biochemical and morphological study

In Wistar male rats, hypertension was induced by 5/6 nephrectomy (5/6N). Body weight, blood pressure measurements, morphological and biochemical changes were followed (at four weekly intervals) for 12 weeks after 5/6N. Renal function was assessed by daily total urinary protein (TUP), plasma creatinine concentration [(Cr)p] and creatinine clearance rate. Plasma renin concentration (PRC), aldosterone concentration and erythrocyte content of sodium [Na]E and potassium [K]E were also investigated. Significant increases in systolic blood pressure (SBP), TUP, [(Cr)p] and [Na]E occurred after 4, 8, and 12 weeks of 5/6N. Progressive glomerulosclerosis (GSC), tubular atrophy and interstitial fibrosis were observed. Positive correlations were found between GSC and SBP and TUP. Positive correlations were also found between SBP and [Na]E and [(Cr)P]. PRC was not increased and showed no correlation with SBP. It is concluded that 5/6N produced hypertension associated with a series of morphological and biochemical alterations in kidney structure and function. In this model, mechanisms other than the renin-angiotensin system may be involved.

Evidence for activation of tubuloglomerular feedback following nephrectomy in human subjects

The intrarenal regulation of glomerular filtration rate (GFR) following a reduction in renal mass was evaluated in six normal subjects, studied before and 4 to 6 weeks after undergoing unilateral nephrectomy, performed for the purpose of living-related transplantation. The role of the tubuloglomerular feedback (TGF) system in regulating the final GFR on both occasions was assessed by determining the increase in GFR over baseline levels following blockade of TGF by a single dose of bumetanide, care being taken to replace sodium and water losses. Before donor nephrectomy, baseline GFR was 115 +/- 7 mL/min, which increased by 9.5% +/- 2.5% to 126 +/- 9 mL/min following the removal of TGF. Four to six weeks following donor nephrectomy, the baseline GFR was 83 +/- 8 mL/min, confirming significant hyperfiltration in the remaining kidney. After administration of bumetanide, the GFR increased by 15.6% +/- 3.1% to 96 +/- 9 mL/min. This greater fractional increase (P < 0.025) indicates an increase in tonic TGF activity in the uninephrectomized state compared with that demonstrated before nephrectomy. The results suggest that the hyperfiltration response following unilateral nephrectomy is limited by an appropriately activated TGF system. This phenomenon may be of importance in the maintenance of Na and water homeostasis, as well as limiting the pathological consequences that may result from, or be exacerbated by, an excessively high filtration rate in the remaining nephrons. Thus, dietary or therapeutic maneuvers that impair the TGF response may be best avoided following a reduction in renal mass.

Differential effects of calorie restriction on glomeruli and tubules of the remnant kidney

We have previously shown that 40% calorie restriction (CR) prevents renal injury 21 weeks after 5/6 nephrectomy (Nx) in rats, regardless of whether protein intake was concurrently restricted or not. Growth retardation appeared to be a necessary prerequisite for the protective effects of CR. To further study these mechanisms, we performed 5/6 Nx in male F344 rats and pair-fed them with a control diet (ad lib group) or a high protein diet restricted by 40% so that protein intake was similar, but calorie consumption was reduced (CR group). Four weeks after 5/6 Nx, when glomerulosclerosis had not yet developed, we compared various parameters as follows in both dietary groups and sham operated rats: urinary protein excretion (uPr), GFR (14C inulin clearance), mean nephron GFR (MNGFR; GFR divided by total number of glomeruli), glomerular volume (VG), tubulointerstitial index (TII), a measure of tubular damage kidney weight (kidney wt), kidney IGF-I content by RIA, and IGF-I immunohistochemistry. CR ameliorated the increase of MNGFR, but not glomerular hypertrophy. TII, kidney wt and kidney IGF-I content were increased in the ad lib Nx group; these changes were alleviated by CR. Two weeks after 5/6 Nx, immunohistochemistry for IGF-I showed increased staining in superficial distal nephrons in the ad lib group, and this was also suppressed by CR. The occurrence of tubulointerstitial pathology prior to glomerulosclerosis, and the beneficial effects of CR on all parameters except Vg indicate a dissociation of mechanisms which result in tubular versus glomerular hypertrophy and damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Prognosis of children with solitary kidney after unilateral nephrectomy

The clinical course of 138 children who underwent unilateral nephrectomy and had a normal contralateral kidney at the time of nephrectomy was reviewed. The diagnosis leading to nephrectomy included obstructive uropathy in 46% of the cases, reflux or pyelonephritis in 30%, Wilms tumor in 15%, hypertension in 4%, dysplastic kidney in 2% and trauma in 2%. Mean age at nephrectomy was 7.3 years and median followup was 24.7 years. Of the 138 patients 121 (88%) are well and 17 died, including 14 secondary to metastatic Wilms tumor and 1 of renal failure. Survival of nonWilms tumor patients was similar to that of an age-matched control group. In 30 patients 24-hour creatinine clearance and 24-hour urinary protein excretion were measured. Proteinuria (greater than 150 mg./24 hours) was found in 8 of the 30 patients (27%) (p less than 0.001), renal insufficiency developed in 9 (30%) (p less than 0.0001) and hypertension occurred in 10% (p greater than 0.10). Children with an acquired solitary kidney are at increased risk for proteinuria and renal insufficiency.