Experimental obstructive hydronephrosis in newborn rats. III. Long-term effects on renal function

Could CA 19-9 be a useful biomarker in the diagnosis, prognosis, and prediction of adequate relief in lower urinary tract obstructions?

INTRODUCTION

posterior urethral valves represent an important cause of childhood chronic kidney disease. The identification of biomarkers that indicate early kidney damage and even adequate clearance could reduce how many patients head towards kidney failure.

OBJECTIVE

this study evaluated how this easy-analysis biomarker (CA 19-9) could help identifying potential renal damage and adequate clearance in obstructive uropathies.

METHODS

46 female Wistar rats were divided into 5 groups, with different patterns of partial urinary tract obstruction: group control; group OIV: infravesical obstruction; group OIVd: infravesical obstruction with reversion, obstruction relief 7 postoperative days later; group OUu: unilateral ureteral obstruction; group OUb: bilateral ureteral obstruction. The CA 19-9s performance was compared to another biomarker: Ngal. Determination of basal CA 19-9 and Ngal in urine and blood and serum creatinine levels was performed in the rats prior to surgery (T0) and after 14 days (T1). Group OIVd underwent intermediate (Ti) collection before clearance.

RESULTS

the urinary concentration of CA 19-9 increased in groups OIV, OIVd and OUb; elevation at T1 and Ti, reached statistical significance compared to the T0 value (p<0,05). Changes in urinary CA 19-9 were more expressive in infravesical obstruction groups (AUC 0.81). Obstruction relief in group OIVd promoted significant urinary CA 19-9 reduction (p<0,05) in the final evaluation.

CONCLUSIONS

CA 19-9 urinary concentration increased in partial urinary tract obstruction. Its best performance was in the bladder neck obstruction group, in which the elevation was detected early (6 days after infravesical obstruction) and the CA19-9 urinary concentration declined after clearance.

O antígeno carboidrato CA 19-9 poderia ser um biomarcador útil no diagnóstico, prognóstico e acompanhamento da obstrução baixa do trato urinário?

RESUMO Introdução: a válvula de uretra posterior representa uma importante causa de doença renal crônica na infância. A identificação de biomarcadores que monitorem danos renais precoces e o sucesso da desobstrução do trato urinário podem reduzir o número de pacientes que evoluem para insuficiência renal. Objetivo: avaliar o desempenho do biomarcador antígeno carboidrato CA 19-9 nas obstruções parciais do trato urinário. Método: 46 ratas Wistar foram divididas em 5 grupos: grupo controle; grupo OIV: obstrução infravesical; grupo OIVd: obstrução infravesical com alívio da obstrução após 7 dias; grupo OUu: obstrução ureteral unilateral; grupo OUb: obstrução ureteral bilateral. O desempenho do CA 19-9 foi comparado a outro biomarcador, a Ngal. A dosagem de CA 19-9 e Ngal na urina e no sangue, e os níveis de creatinina sérica foram avaliados nas ratas antes da cirurgia (T0) e após 14 dias (T1). O grupo OIVd foi submetido a uma coleta intermediária (Ti). Resultados: a concentração urinária de CA19-9 aumentou nos grupos OIV, OIVd e OUb; a elevação em T1 e Ti alcançou significância estatística em relação ao valor de T0 (p<0,05). As alterações no CA 19-9 urinário foram mais expressivas nos grupos de obstrução infravesical (AUC 0,81). O alívio da obstrução no grupo OIVd promoveu redução do CA 19-9 urinário (p<0,05). Conclusões: a concentração urinária de CA19-9 aumentou na obstrução parcial do trato urinário. Seu melhor desempenho foi no grupo de obstrução infravesical, no qual a elevação foi detectada precocemente (6 dias de pós-operatório) com queda após a retirada do fator obstrutivo.

Mast Cells and MCPT4 Chymase Promote Renal Impairment after Partial Ureteral Obstruction

Obstructive nephropathy constitutes a major cause of pediatric renal progressive disease. The mechanisms leading to disease progression are still poorly understood. Kidney fibrotic lesions are reproduced using a model of partial unilateral ureteral obstruction (pUUO) in newborn mice. Based on data showing significant mast cell (MC) infiltration in patients, we investigated the role of MC and murine MCPT4, a MC-released chymase, in pUUO using MC- (W^sh/sh), MCPT4-deficient (Mcpt4^−/−), and wild-type (WT) mice. Measurement of kidney length and volume by magnetic resonance imaging (MRI) as well as postmortem kidney weight revealed hypotrophy of operated right kidneys (RKs) and compensatory hypertrophy of left kidneys. Differences between kidneys were major for WT, minimal for W^sh/sh, and intermediate for Mcpt4^−/− mice. Fibrosis development was focal and increased only in WT-obstructed kidneys. No differences were noticed for local inflammatory responses, but serum CCL2 was significantly higher in WT versus Mcpt4^−/− and W^sh/sh mice. Alpha-smooth muscle actin (αSMA) expression, a marker of epithelial–mesenchymal transition (EMT), was high in WT, minimal for W^sh/sh, and intermediate for Mcpt4^−/− RK. Supernatants of activated MC induced αSMA in co-culture experiments with proximal tubular epithelial cells. Our results support a role of MC in EMT and parenchyma lesions after pUUO involving, at least partly, MCPT4 chymase. They confirm the importance of morphologic impairment evaluation by MRI in pUUO.

Congenital ureteropelvic junction obstruction: human disease and animal models

Ureteropelvic junction (UPJ) obstruction is the most frequently observed cause of obstructive nephropathy in children. Neonatal and foetal animal models have been developed that mimic closely what is observed in human disease. The purpose of this review is to discuss how obstructive nephropathy alters kidney histology and function and describe the molecular mechanisms involved in the progression of the lesions, including inflammation, proliferation/apoptosis, renin-angiotensin system activation and fibrosis, based on both human and animal data. Also we propose that during obstructive nephropathy, hydrodynamic modifications are early inducers of the tubular lesions, which are potentially at the origin of the pathology. Finally, an important observation in animal models is that relief of obstruction during kidney development has important effects on renal function later in adult life. A major short-coming is the absence of data on the impact of UPJ obstruction on long-term adult renal function to elucidate whether these animal data are also valid in humans.

Urinary biomarkers in prenatally diagnosed unilateral hydronephrosis

The introduction of prenatal ultrasonography as a screening method entails an increasing number of infants diagnosed with prenatal hydronephrosis. Ureteropelvic junction obstruction accounts for 35% of prenatal hydronephrotic cases. Urinary tract obstruction that occurs during early kidney development affects renal morphogenesis, maturation and growth, and in the most severe cases this will ultimately cause renal insufficiency. A major challenge in the clinical management of these patients is to preserve renal function by selection of the 15%-20% who require early surgical intervention, leaving those for whom watchful waiting may be appropriate because of spontaneous resolution/stabilization without significant loss of renal function. Today, this requires medical surveillance, including repetitive invasive diuretic renograms relying on arbitrary threshold values, and therefore there is a need for non-arbitrary, non-invasive urinary biomarkers that may be used as predictors for renal structural changes and/or decreasing renal function, and thereby provide the surgeon with more clear indications for surgical intervention. In this review, we summarize the currently well-known facts about urinary biomarkers in ureteropelvic junction obstruction concerning renal function, and we also suggest potential novel urinary biomarkers.

Mechanisms of renal injury and progression of renal disease in congenital obstructive nephropathy

Congenital obstructive nephropathy accounts for the greatest fraction of chronic kidney disease in children. Genetic and nongenetic factors responsible for the lesions are largely unidentified, and attention has been focused on minimizing obstructive renal injury and optimizing long-term outcomes. The cellular and molecular events responsible for obstructive injury to the developing kidney have been elucidated from animal models. These have revealed nephron loss through cellular phenotypic transition and cell death, leading to the formation of atubular glomeruli and tubular atrophy. Altered renal expression of growth factors and cytokines, including angiotensin, transforming growth factor-beta, and adhesion molecules, modulate cell death by apoptosis or phenotypic transition of glomerular, tubular, and vascular cells. Mediators of cellular injury include hypoxia, ischemia, and reactive oxygen species, while fibroblasts undergo myofibroblast transformation with increased deposition of extracellular matrix. Progression of the lesions involves interstitial inflammation and interstitial fibrosis, both of which impair growth of the obstructed kidney and result in compensatory growth of the contralateral kidney. The long-term outcome depends on timing and severity of the obstruction and its relief, minimizing ongoing injury, and enhancing remodeling. Advances will depend on new biomarkers to evaluate the severity of obstruction, to determine therapy, and to follow the evolution of lesions.

Upper urinary tract dilatation: prenatal diagnosis, management and outcome

Upper urinary tract dilatation is one of the most common abnormalities detected on prenatal ultrasound scanning. It is commonly due to transient urine flow impairment (UFI) at the level of the pelvi-ureteric and vesico-ureteric junctions, which improves with time in most cases. It is usually in the neonatal period that the diagnosis is confirmed and during the first 18 months of life that the prognosis of the dilatation is defined.

Chronic partial ureteral obstruction and the developing kidney

Although congenital urinary tract obstruction is a common disorder, its pathophysiology remains poorly understood and clinical practice is controversial. Animal models have been used to elucidate the mechanisms responsible for obstructive nephropathy, and the models reveal that renal growth and function are impaired in proportion to the severity and duration of obstruction. Ureteral obstruction in the neonatal rat or mouse leads to activation of the renin-angiotensin system, renal infiltration by macrophages, and tubular apoptosis. Nephrons are lost by glomerular sclerosis and the formation of atubular glomeruli, and progressive injury leads to tubular atrophy and interstitial fibrosis. Recovery following release of obstruction depends on the timing, severity, and duration of obstruction. Growth factors and cytokines are produced by the hydronephrotic kidney, including MCP-1 and TGF-beta1, which are excreted in urine and can serve as biomarkers of renal injury. Because MRI can be used to monitor renal morphology, blood flow, and filtration rate, its use might supplant current imaging modalities (ultrasonography and diuretic renography), which have significant drawbacks. Combined use of MRI and new urinary biomarkers should improve our understanding of human congenital obstructive nephropathy and should lead to new approaches to evaluation and management of this challenging group of patients.

Antenatally detected hydronephrosis

The strategy of management of children with hydronephrosis has considerably changed as a result of the development of ultrasound techniques, allowing a prenatal detection. Hydronephrosis is defined as a dilation of the renal collecting system, and several entirely different clinical entities can be considered this general heading, whereas early detection may have a different impact depending on the entity considered. The present work aims to describe a certain number of these clinical entities, to discuss the strategic options of management that are proposed, and to evaluate the role of medical imaging, in particular the radionuclide approach. Congenital ureteropelvic junction anomaly, vesicoureteral reflux, posterior urethral valves, and duplex kidney will be successively considered. Multicystic dysplastic kidney disease, although not classified as hydronephrosis, will be mentioned because it may be mistaken for hydronephrosis.

Glomerular and tubular function during AT1 receptor blockade in pigs with neonatal induced partial ureteropelvic obstruction

Previously, we showed that neonatal induced chronic partial unilateral ureteral obstruction (PUUO) of the multipapillary pig kidney decreased glomerular filtration rate (GFR) of the obstructed kidney. We hypothesized that ANG II and nitric oxide (NO) are important for the changes in renal function and in the present study we examined the effects of chronic AT1 receptor blockade using CV-11974 (0.12 mg/h candesartan from age 23 to 30 days) on kidney function development after PUUO was induced in 2-day-old piglets. Moreover, the effect of superimposed acute NO inhibition using NG-nitro-l-arginine methyl ester (l-NAME; 15 mg/kg) was examined to identify if this has diagnostic potential. PUUO significantly increased GFR in the nonobstructed contralateral kidney independent of candesartan. In candesartan-treated piglets, the l-NAME-induced GFR reduction seen in normal and nonobstructed kidneys was absent in the partial obstructed kidneys. Urine output and fractional excretion of water were increased from the partial obstructed kidneys. Consistent with this immunohistochemical analyses showed a reduced aquaporin-2 labeling in the collecting duct principal cells. Moreover, renal sodium handling was compromised by PUUO evidenced by an increased fractional excretion of sodium which was enhanced by candesartan treatment. In conclusion, our findings suggest that the counterbalance between AT1 receptor-mediated vasoconstriction and NO-mediated vasodilatation which maintain GFR in normal young porcine kidneys is changed by neonatal induced chronic PUUO. This may have diagnostic potential in children with suspected congenital obstruction. Our results also demonstrate compromised tubular functions in response to chronic PUUO despite preservation of glomerular function.

Pediatric applications of renal nuclear medicine

This review should be regarded as an opinion based on personal experience, clinical and experimental studies, and many discussions with colleagues. It covers the main radionuclide procedures for nephro-urological diseases in children. Glomerular filtration rate can be accurately determined using simplified 2- or 1-blood sample plasma clearance methods. Minor controversies related to the technical aspects of these methods concern principally some correction factors, the quality control, and the normal values in children. However, the main problem is the reluctance of the clinician to apply these methods, despite the accuracy and precision that are higher than with the traditional chemical methods. Interesting indications are early detection of renal impairment, hyperfiltration status, and monitoring of nephrotoxic drugs. Cortical scintigraphy is accepted as a highly sensitive technique for the detection of regional lesions. It accurately reflects the histological changes, and the interobserver reproducibility in reporting is high. Potential technical pitfalls should be recognized, such as the normal variants and the difficulty in differentiating acute lesions from permanent ones or acquired lesions from congenital ones. Although dimercaptosuccinic acid scintigraphy seems to play a minor role in the traditional approach to urinary tract infection, recent studies suggest that this examination might influence the treatment of the acute phase, the indication for chemoprophylaxis and micturating cystography, and the duration of follow-up. New technical developments have been applied recently to the renogram: tracers more appropriate to the young child, early injection of furosemide, late postmicturition and gravity-assisted images and, finally, more objective parameters of renal drainage. Pitfalls mainly are related to the interpretation of drainage on images and curves. Dilated uropathies represent the main indication of the renogram, but the impact of this technique on the management of the child is, in a great number of cases, still a matter of intense controversy. Direct and indirect radionuclide cystography are interesting alternatives to the radiograph technique and should be integrated into the process of diagnosis and follow-up of vesicoureteral reflux.

Variable chronic partial ureteral obstruction in the neonatal rat: a new model of ureteropelvic junction obstruction

BACKGROUND

Congenital ureteropelvic junction (UPJ) obstruction is a common developmental anomaly. To elucidate the mechanisms underlying the renal consequences of congenital UPJ obstruction, we have developed a new model of variable partial unilateral ureteral obstruction (UUO) in the neonatal rat.

METHODS

Rat pups were subjected to sham-operation, complete UUO, or variable partial UUO within the first day of life. After 14 or 28 days, the relative number of glomeruli, cell proliferation, tubular apoptosis, tubular atrophy, and interstitial fibrosis were quantitated in histologic sections. Glomerular filtration rate (GFR) was determined after 28 days of partial or complete UUO.

RESULTS

Following 70% to 75% reduction in ureteral diameter, renal growth from 14 to 28 days was reduced by 60%, and the number of glomeruli decreased by 50%. Renal pelvic diameter increased in proportion to the severity of obstruction following 14 days of partial UUO, and by 28 days, was maximally dilated regardless of the luminal diameter. Renal proliferation was increased, while tubular apoptosis, tubular atrophy, and interstitial fibrosis were less severe 14 days following partial UUO than in complete UUO. GFR was reduced by 80%, and proteinuria developed following 28 days of partial UUO.

CONCLUSION

Renal function is impaired by chronic ipsilateral partial UUO, which reduces the number of nephrons, and leads to progressive renal pelvic dilatation. Tubular atrophy and interstitial fibrosis develop prior to significant renal pelvic dilatation. Correlation of clinically measurable parameters with renal morphometry or imaging studies in this model may lead to new approaches to the management of congenital UPJ obstruction.

Neonatal ureteral obstruction alters expression of renal sodium transporters and aquaporin water channels

BACKGROUND

Congenital urinary tract obstruction is a common cause of renal insufficiency in the neonate and during infancy. Recently, we demonstrated that ureteral obstruction in adult rats is associated with reduction in the abundance of renal aquaporins (AQPs) and renal sodium transporters, which paralleled an impaired urinary concentrating capacity.

METHODS

In the present study, renal handling of sodium and water, together with the expression of renal aquaporins and major renal sodium transporters, was examined in rats with neonatally induced partial unilateral ureteral obstruction (PUUO) within the first 48 hours of life to clarify the molecular mechanisms involved in the tubular functional defects in response to congenital obstruction. Rats were then followed for 12 or 24 weeks.

RESULTS

Neonatal PUUO caused a progressive reduction in single kidney glomerular filtration rate (SKGFR) on the obstructed side to 43% of controls at 12 weeks (115 +/- 28 vs. 267 +/- 36 microL/min/100g bw, P < 0.05), and 31% of controls at 24 weeks (106 +/- 24 vs. 343 +/- 41 microL/min/100g bw, P < 0.05). Na-K-ATPase abundance was decreased in the obstructed kidney compared with the nonobstructed kidney at 24 weeks (79 +/- 6%, P < 0.05), and the abundance of bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1) located to the medullary thick ascending limb (mTAL) of the obstructed kidney was significantly reduced both at 12 weeks (42 +/- 10%, P < 0.05) and 24 weeks (50 +/- 10%, P < 0.05). Immunohistochemistry confirmed down-regulation of BSC-1 both at 12 and 24 weeks after onset of obstruction. Consistent with this, sodium excretion from the obstructed kidney was increased at 12 weeks (0.13 +/- 0.03 vs. 0.04 +/- 0.01 micromol/min/100g bw, P < 0.05), and persisted 24 weeks after onset of PUUO (0.15 +/- 0.02 vs. 0.06 +/- 0.01 micromol/min/100g bw, P < 0.05). AQP2 abundance in the collecting duct was also reduced both at 12 weeks (68 +/- 5%, P < 0.05) and at 24 weeks (69 +/- 13%, P < 0.05). Consistent with this, solute-free water reabsorption was decreased in the obstructed kidney at 12 weeks (0.61 +/- 0.42 vs. 1.97 +/- 0.63 microL/min/100g bw, P < 0.05) and remained decreased after 24 weeks of PUUO (0.42 +/- 0.04 vs. 1.56 +/- 0.39 microL/min/100g bw, P < 0.05).

CONCLUSION

Major sodium transporters and aquaporins in the obstructed kidney are down-regulated in response to neonatally induced PUUO, which indicates that these transporters may play a crucial role for the persistent reduction in renal handling of sodium and water in response to PUUO.

Partial unilateral ureteral obstruction in rats

This review comprises an overview of the current knowledge on experimental partial unilateral ureteral obstruction (PUUO) and a summary of our latest original experimental PUUO studies in rats. Neonatal PUUO is the type of obstruction that is most often encountered in pediatric clinical practice. However, the pathogenesis of PUUO is still incompletely understood. Most of our knowledge on PUUO has been derived from experimental studies in a variety of animal models. Although progress has been made, the natural history of congenital hydronephrosis is still incompletely described. The effects on kidney functions of long-term urinary tract obstruction, especially PUUO, have been less intensively studied. Recently, we created models with mild and severe PUUO in young rats by embedding the upper one fourth or the upper two thirds of the left ureter into the psoas muscle, respectively. Thereafter, the technique was used to create mild and severe PUUO in newborn rats and magnetic resonance imaging studies showed that both mild and severe obstruction caused a time-dependent decrease in renal blood flow. Compensatory increase in total kidney volume and renal vein blood flow in contralateral non-obstructed kidneys was not detectable when functional deterioration in the partially obstructed kidneys was present. Finally, we investigated the dynamic changes in renal relative signal intensity (RSI) of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) using magnetic resonance imaging in rats with partial, complete unilateral ureteral obstruction and sham-operated controls. The results showed that changes in Gd-DTPA RSI are compatible with the known physiological and anatomical changes in kidneys in response to ureteral obstruction and useful for distinguishing an obstructed from a non-obstructed collecting system and also for differentiating a partially obstructed from a completely obstructed collecting system.

The protective effects of captopril and nitric oxide on solitary kidney after chronic partial ureteric obstruction

OBJECTIVE

To determine whether vasodilator agents (captopril and nitric oxide) change the morphological and functional effects of chronic partial ureteric obstruction in solitary kidney tissue in unilaterally nephrectomized rats.

MATERIALS AND METHODS

Each of 50 prepubertal Wistar albino rats underwent right nephrectomy and were then assigned to one of five groups. Rats in group 1 underwent a sham operation (control) and in the other groups the ureter of the remaining kidney was partially obstructed by surgery. In group 2, no drug treatments were given; in groups 3, 4 and 5 captopril, L-arginine methyl ester (L-Arg) or NG- nitro-L-arginine-methyl ester, respectively, were given for 3 weeks. In all rats, diuretic scintigraphy was used to measure kidney perfusion, glomerular filtration rate (GFR) and concentration. Blood urea nitrogen (BUN), serum creatinine levels, kidney parenchymal weight and pelvic volume were measured and the kidneys evaluated histopathologically.

RESULTS

Renal perfusion was significantly greater in both group 3 and 4 than in group 2. The GFR was 18% greater in group 3 and 22.3% greater in group 4 than in group 2. The GFR was decreased by 67% in group 5 compared with the control group. The mean parenchymal weight, mean pelvic volume, BUN and serum creatinine in the four groups with a partially obstructed ureter were significantly different from the control group. There also were significant differences between group 2 and groups 3--5, and between group 2 and group 3. Histological damage was severe in all four groups with partial ureteric obstruction, but in the drug-treated groups, medullary fibrosis was less frequent.

CONCLUSION

After 3 weeks of treatment, captopril and L-Arg both improved kidney perfusion, GFR, BUN and serum creatinine levels, but were less effective in preventing parenchymal atrophy and changes in pelvic volume.

Unilateral ureteral obstruction in neonatal rats leads to renal insufficiency in adulthood

BACKGROUND

Although unilateral ureteropelvic junction obstruction is the most common cause of congenital obstructive nephropathy in infants and children, management remains controversial, and follow-up after pyeloplasty is generally limited to the pediatric ages. We have developed a model of temporary unilateral ureteral obstruction (UUO) in the neonatal rat: One month following the relief of five-day UUO, the glomerular filtration rate (GFR) of the postobstructed kidney was normal despite a 40% reduction in the number of glomeruli and residual vascular, glomerular, tubular, and interstitial injury.

METHODS

To determine whether hyperfiltration and residual injury of remaining nephrons leads to progression of renal insufficiency in later life, 31 rats were sham operated or subjected to left UUO at one day of age, with relief of UUO five days later, and were studied at one year of age. GFR was measured by inulin clearance, and the number of glomeruli, tubular atrophy, glomerular sclerosis, and interstitial fibrosis were measured by histomorphometry in sham, obstructed (UUO), and intact opposite kidneys. Intrarenal macrophages and alpha-smooth muscle actin were identified by immunohistochemistry.

RESULTS

Despite relief of UUO, ultimate growth of the postobstructed kidney was impaired. The number of glomeruli was reduced by 40%, and GFR was decreased by 80%. However, despite significant compensatory growth of the opposite kidney, there was no compensatory increase in GFR, and proteinuria was increased. Moreover, glomerular sclerosis, tubular atrophy, macrophage infiltration, and interstitial fibrosis were significantly increased not only in the postobstructed kidney, but also in the opposite kidney.

CONCLUSIONS

Although GFR is initially maintained following relief of five-day UUO in the neonatal rat, there is eventual profound loss of function of the postobstructed and opposite kidneys because of progressive tubulointerstitial and glomerular damage. These findings suggest that despite normal postoperative GFR in infancy, children undergoing pyeloplasty for ureteropelvic junction obstruction should be followed into adulthood. Elucidation of the cellular response to temporary UUO may lead to improved methods to assess renal growth, injury, and functional reserve in patients with congenital obstructive nephropathy.

Contralateral compensatory kidney growth in rats with partial unilateral ureteral obstruction monitored by magnetic resonance imaging

PURPOSE

We studied dynamic changes in total volume and renal vein blood flow in the kidneys contralateral to partial ureteral obstruction induced in newborn rats.

MATERIALS AND METHODS

Using magnetic resonance imaging we investigated changes in total kidney volume and renal vein blood flow in 20 rats with mild and 18 with severe partial ureteral obstruction that was induced on the left side 2 days after birth. A total of 15 sham operated control rats were also studied. Total kidney volume and renal vein blood flow were monitored sequentially every 2 to 6 weeks for a total of 24 weeks. Renal parenchymal volume measured in vivo by magnetic resonance imaging was compared with that measured in vitro at week 24.

RESULTS

Total volume and renal vein blood flow increased significantly in contralateral nonobstructed kidneys from week 14 and thereafter in rats with severe partial unilateral ureteral obstruction. At week 24 volume had increased by 22% and blood flow had increased by 25%. Volume and flow did not increase significantly in contralateral nonobstructed kidneys in rats with mild partial unilateral ureteral obstruction (p = 0.09). Before changes occurred in volume and blood flow in the contralateral nonobstructed kidneys, renal vein blood flow had decreased significantly from week 8 and thereafter in severely obstructed kidneys. In rats with mild partial unilateral ureteral obstruction renal vein blood flow decreased significantly in obstructed kidneys from week 18 and thereafter. Good correlation was noted between MRI in vivo and in vitro kidney volume measurements (r = 0.972, p <0.001).

CONCLUSIONS

A significant increase in total volume and renal vein blood flow in contralateral nonobstructed kidneys did not develop immediately after the onset of detectable functional deterioration in partially obstructed kidneys. Therefore, caution should be used when incorporating compensatory growth into surgical decision making.

Recovery following relief of unilateral ureteral obstruction in the neonatal rat

BACKGROUND

Obstructive nephropathy is a primary cause of renal insufficiency in infants and children. This study was designed to distinguish the reversible and irreversible cellular consequences of temporary unilateral ureteral obstruction (UUO) on the developing kidney.

METHODS

Rats were subjected to UUO or sham operation in the first 48 hours of life, and the obstruction was removed five days later (or was left in place). Kidneys were removed for study 14 or 28 days later. In additional groups, kidneys were removed at the end of five days of obstruction. Immunoreactive distribution of renin was determined in arterioles, and the distribution of epidermal growth factor, transforming growth factor-beta1, clusterin, vimentin, and alpha-smooth muscle actin was determined in tubules and/or interstitium. The number of glomeruli, glomerular maturation, tubular atrophy, and interstitial collagen deposition was determined by morphometry. Renal cellular proliferation and apoptosis were measured by proliferating cell nuclear antigen and the TdT uridine-nick-end-label technique, respectively. The glomerular filtration rate was measured by inulin clearance.

RESULTS

Renal microvascular renin maintained a fetal distribution with persistent UUO; this was partially reversed by the relief of obstruction. Although glomerular maturation was also delayed and glomerular volume was reduced by UUO, the relief of obstruction prevented the reduction in glomerular volume. Although relief of obstruction did not reverse a 40% reduction in the number of nephrons, the glomerular filtration rate of the postobstructed kidney was normal. The relief of obstruction did not improve tubular cell proliferation and only partially reduced apoptosis induced by UUO. This was associated with a persistent reduction in the tubular epidermal growth factor. In addition, the relief of obstruction reduced but did not normalize tubular expression of transforming growth factor-beta1, clusterin, and vimentin, all of which are evidence of persistent tubular injury. The relief of obstruction significantly reduced interstitial fibrosis and expression of alpha-smooth muscle actin by interstitial fibroblasts, but not to normal levels.

CONCLUSIONS

The relief of obstruction in the neonatal rat attenuates, but does not reverse, renal vascular, glomerular, tubular, and interstitial injury resulting from five days of UUO. Hyperfiltration by remaining nephrons and residual tubulointerstitial injury in the postobstructed kidney are likely to lead to deterioration of renal function later in life.

Neonatal management. Role for early intervention

Although performing pyeloplasty on an infant with a relatively healthy kidney prior to the onset of renal damage is not as well-accepted as "aggressive observation," the authors argue that early intervention is the more "conservative" or safe method of treatment for infants with ureteropelvic junction (UPJ) obstruction. Using experimental and clinical data, the authors demonstrate that prolonged partial UPJ obstruction in the developing kidney causes significant renal morbidity with time.

Renal tubular apoptosis after partial ureteral obstruction

Partial ureteral obstruction in the weanling rat leads to hydronephrosis of the ipsilateral kidney and renal cell deletion through the process of programmed cell death known as apoptosis. The apoptotic response following partial ureteral obstruction in weanling Sprague-Dawley rats was studied using the traditional markers of apoptosis, including deoxyribonucleic acid (DNA) laddering pattern on agarose gel electrophoresis, in situ gap labeling of fragmented DNA for quantitative apoptotic body determination, polyadenylated messenger ribonucleic acid (mRNA) expression of sulfated glycoprotein-2, and polyadenylated mRNA expression of epidermal growth factor and transforming growth factor-beta. Partial ureteral obstruction resulted in a progressive increase in the intensity of DNA fragmentation associated with apoptosis during the initial 3 weeks. Quantitative apoptotic body counting revealed a 3-fold increase by week 3 of partial obstruction. This increase represented a level of apoptosis, which is 65% of that observed in complete ureteral obstruction. By week 2 of partial obstruction there was a 13-fold increase in the expression of sulfated glycoprotein-2 mRNA, as well as changes in the growth factor environment characterized by a decline in the constitutive expression of epidermal growth factor mRNA and an increase in the expression of transforming growth factor-beta mRNA. These altered levels represent changes in expression comparable to those observed during the apoptotic response following complete ureteral obstruction, although the time course is delayed by 2 to 3 weeks.

Chronic hydronephrosis: renographic drainage patterns and renal morphology in an animal model

OBJECTIVE

To develop an animal model of chronic progressive hydronephrosis; to establish patterns of diuretic renography during development of the condition; and to relate renographic abnormality to morphological change in the renal parenchyma.

MATERIALS AND METHODS

The cellophane sclerosis technique was used to produce a hydronephrosis in the left kidney of six rabbits. Post-operatively MAG3 diuretic renography was performed at weekly intervals. When a steady renographic trend was noted the rabbits were killed and the kidneys examined histologically.

RESULTS

Four rabbits had persistent type II renographic curves on the left for 12 weeks. The measured split renal function fell steadily to < 20% in this time. Morphologically there was hydronephrosis with marked structural changes in the parenchyma seen on histological examination. Two rabbits had stable type IIIa renographic drainage patterns on the left with preserved renal function. Morphologically there was hydronephrosis but histologically the kidneys were normal. There were no renographic or structural changes in a control rabbit after a sham laparotomy.

CONCLUSIONS

The cellophane sclerosis technique can be used to create a reproducible chronic progressive hydronephrosis. In this animal model hydronephrosis and a persistent type II curve are associated with renographic evidence of deteriorating renal function and disruption of renal architecture histologically. Hydronephrosis and a type IIIa curve are associated with preservation of normal renal function and histological structure.

Collagen studies in newborn rat kidneys with incomplete ureteric obstruction

Collagen studies in newborn rats with incomplete ureteric obstruction were performed to describe and quantify changes in collagen deposition resulting from urinary tract obstruction at an early developmental age. Incomplete ureteric obstruction was created in three-day-old rats by placing the left ureter in a tunnel formed by the psoas muscle, and sham-operated controls underwent a laparotomy. The rats were sacrificed at 10, 17, 24 or 31 days. Collagen types I, III, IV, and V were localized by indirect immunofluorescence microscopy, the total collagen content of the kidney was quantitated using hydroxyproline analysis, and collagen types I and III were quantitated using cyanogen bromide (CNBr) peptide analysis. Increased immunofluorescent staining for all of the collagens was found in the diffusely widened medullary interstitium of the obstructed kidney, and more focally in the cortical interstitium. Collagen types I, III and V, but not collagen type IV, were also found in bands in the interstitium at the junction of the cortex with the medulla. Increased staining for collagen type IV was found in thickened and tortuous tubular basement membranes (TBM) of the obstructed kidneys. The total collagen content of the obstructed kidney was significantly increased compared to the amounts in both the contralateral kidneys and in the kidneys from sham-operated controls at 24 and 31 days of age (P < 0.01 in each case, Wilcoxon matched pairs rank sum test and Mann Whitney U-test, respectively). The amount of collagen in the kidneys correlated with the degree of hydronephrosis (Spearman correlation test, r = 0.78, P < 0.02). CNBr peptide analysis demonstrated that over 50% of the collagen in the normal neonatal rat kidney was collagen type I and approximately 25% was collagen type III. In the obstructed kidneys most of the collagen was also collagen type I and collagen type III, although the proportion of total collagen comprised by these collagen types was decreased compared with the controls. The amount of collagen type III in the contralateral kidneys was reduced compared to that in the controls. Thus, the neonatal renal response to obstruction resulted in increased amounts of a range of collagens in the interstitium and TBM, and the extent of this response was partially related to the degree of hydronephrosis.

Long-term partial ureteral obstruction and its effects on kidney function

Previously it has been shown that partial ureteral obstruction present in young rats for 12 weeks results in small morphological changes in the kidney as well as slightly decreased kidney function. In the present study the aim was to examine whether rats obstructed for one year had more advanced changes in morphology and kidney function. The first group of animals examined after three weeks of obstruction showed only modest changes in kidney function with a reduced potassium concentration in the urine but no reduction in the glomerular filtration rate. After one year there was a reduction in urine flow as well as in the excretion of both potassium and sodium. Urine osmolality was also reduced. Glomerular filtration rate measured in this group of animals was reduced in the obstructed kidney by about 60% compared to the contralateral one. There were only small changes in the morphology with no loss in parenchymal weight or compensatory hypertrophy, but there was a significant deformation of the papilla and an increase in inflammatory cells in the parenchyma. In conclusion hydronephrosis during a shorter period is not harmful to kidney function but if sustained for an extended time period kidney function will deteriorate.

Urinary PGE2 in rats with chronic partial unilateral ureteral obstruction

Urinary prostaglandin E2 (PGE2) was measured in Munich-Wistar rats with surgically created chronic partial unilateral ureteral obstruction (UUO). Mean values of bladder urine PGE2 were higher in sham than in UUO (24.5 +/- 14.4 vs 12.9 +/- 8.2 ng/mg creatinine, respectively, P less than 0.05). Following diuresis, both ureters were cannulated and urine was collected. PGE2 excretion was increased in sham (66.5 +/- 34.4 and 70.1 +/- 44.5 ng/mg creatinine, left and right, respectively). But in UUO, the obstructed kidney excreted less PGE2 than the contralateral kidney (32.1 +/- 6.0 vs 62.3 +/- 40.4 ng/mg creatinine, obstructed vs contralateral, respectively, P = 0.08). PGE2 synthesis was then determined in separated renal medullary and cortical slices. Renal medullary slices from kidneys with severe obstruction synthesized less PGE2 than the contralateral unobstructed side (3.30 +/- 1.22 vs 10.52 +/- 3.23 ng/mg wet wt-30 min, respectively, P less than 0.05) and failed to respond to arachidonic acid stimulation with any significant increase in PGE2 synthesis (3.30 +/- 1.22 vs 4.47 +/- 1.04 ng/mg wet wt-30 min, baseline vs stimulated). In contrast, contralateral unobstructed kidney slices responded with a significant increase in PGE2 synthesis (10.52 +/- 3.23 vs 21.10 +/- 2.50 ng/mg wet wt-30 min, baseline vs stimulated, P less than 0.05). We conclude that chronic partial UUO in the Munich-Wistar rats resulted in significantly less PGE2 elaboration.

Experimental evaluation of furosemide renography in unobstructed and partially obstructed upper urinary tracts in pigs

To evaluate the reliability and the constancy of the furosemide renography an experimental evaluation of the test has been performed. A standardized unilateral partial proximal ureteral obstruction was applied to 11 pigs. Preoperatively and again weekly in the three weeks following obstruction a furosemide renogram (FR) was done. The furosemide renography was a very constant parameter in the unobstructed kidney (85%) and in the partly obstructed kidney (85%). A type I FR pattern (O'Reilly classification) was an exact indicator of an unobstructed pelvis. After partial ureteral obstruction, an immediate change in the FR pattern was seen either into type II or type IIIa renography. In this experimental study furosemide renography was found to be a reliable tool in the differentiation between the unobstructed normal renal pelves and the partly obstructed dilated renal pelves.

Experimental ureteral obstruction in the fetal opossum. I. Renal functional assessment

The North American opossum Didelphis virginiana was used as a model for fetal urinary obstruction. In this animal the fetus develops on a teat in a pouch and, therefore, it is accessible to surgical intervention. Unilateral ureteral obstruction was created at a mid trimester developmental equivalent in 8 pups, late ureteral obstruction was created in a similar fashion in 6 pups at a full-term equivalent and unobstruction of 9 pups was accomplished with a ureteroneocystostomy at a full-term equivalent. After early intervention 6 pups were found to have only partial ureteral obstruction as measured by mild dilatation and probe patency of the ureter. The control group consisted of 11 unoperated animals. The animals were maintained until adulthood when they were harvested after obtaining creatinine clearances from both kidneys. All dilated urinary systems were cultured for bacteria and they were sterile.

Long-term follow-up of renal function in rats with unilateral hydronephrosis

In order to obtain more information on the long-term changes in renal function of hydronephrotic kidneys, we have measured the glomerular filtration rate (GFR) in rats with a congenital or an experimental unilateral hydronephrotic kidney (HK). In Brown Norway rats, with congenital hydronephrosis, the presence of an HK affected neither the total GFR nor the contribution of that kidney to the total GFR, during a follow-up of 70 weeks. In Wistar rats with experimental unilateral hydronephrosis two groups could be distinguished on the basis of the contribution of the HK to the total GFR. In the first, the contribution of the HK to the total GFR was not different from that of controls. This contribution as well as the total GFR remained similar to that of controls during the follow-up. In the second group, the contribution of the HK to the total GFR was reduced to 25%. In these rats the total GFR was slightly less than that of controls. The contribution of the HK to the total GFR remained unchanged for the next 56 weeks. It is concluded that the long lasting presence of unilateral hydronephrosis in rats does not necessarily result in a progressive loss of renal function with time.

Experimental obstructive hydronephrosis in newborn rats. XI. A one-year follow-up study of renal function and morphology

Partial obstruction of the left ureter was created in two-day-old rats and its effects on kidney function were studied with 99mTc-DMSA and 99mTc-DTPA after one, two, three and six weeks, and after one year. Kidneys from animals sacrificed at the age of six weeks or one year were also examined histologically. The obstructed renal pelvis was enlarged by about 35 times and there was a delayed excretion of 99mTc-DTPA during forced diuresis, indicating significant, chronic obstruction. The renal DMSA-uptake ratio (left kidney/(left and right kidney] was reduced to about 40% from the first week of obstruction. The parenchymal weight ratio (expressed as above) was reduced to about 45% after both six weeks and one year. The glomerular filtration rate, examined during forced diuresis and calculated on the basis of uptake capacity, was lowered to 42% after six weeks but was not significantly reduced after one year of obstruction. The incidence figures for medullary hemorrhage or accumulation of iron pigment, and chronic inflammatory changes in the cortex were somewhat higher after one year of obstruction than after 6 weeks, but the lesions were patchy in both groups. We conclude that partial unilateral ureteric obstruction, created in the neonatal period, leads to a slight but permanent functional disturbance and parenchymal weight reduction without prominent structural parenchymal damage.

Prospective management of neonates with pelviureteric junction stenosis. Therapeutic strategy based on 99m Tc-DPTA studies

A prospective therapeutic strategy based on separate glomerular filtration rate (SGFR) was evaluated in 14 prenatally detected asymptomatic neonates, suspected of having pelviureteric junction obstruction. The patients with low SGFR were referred for pyeloplasty with the hope to improve the renal function. A marked improvement occurred in only one patient, although the drainage function (furosemide test) did improve in all cases. A conservative attitude was adopted for those children with normal SGFR. In 6 of them, a progressive increase of SGFR was noted, related to the normal maturation of the function, followed by a stabilization in the normal range. In 1 patient, a sudden decrease of SGFR was observed around 1 year and the patient was shifted into the surgical group. In this patient, an initial partial response of the kidney to a furosemide injection changed into a persistent non-response, whereas in the other non-operated patients, partial or good response was always recorded, although the responses were essentially variable on successive tests. On the basis of these data, the protocol was slightly modified, the patients with persistent non-response to furosemide after 6 months of life being shifted to the surgical group.

Developmental determinants of recovery after relief of partial ureteral obstruction

Although obstructive nephropathy is a major cause of renal insufficiency at all ages, the functional consequences of relief of obstruction on the developing kidney are poorly understood. To evaluate recovery from chronic partial ureteral obstruction (CPUO) in the neonatal period, the left ureter of guinea pigs was constricted within the first 48 hours of life, and the obstruction was relieved 10 days later. At three and eight weeks of age, intraureteral pressure, number of perfused glomeruli (NPG), renal blood flow (RBF), and glomerular filtration rate (GFR) were measured. These animals were compared with sham-operated and unrelieved groups. Two additional groups underwent CPUO at five weeks of age, with persistent obstruction or relief in 10 days, and were also studied at eight weeks. In all animals, intraureteral pressure increased during ipsilateral ureteral obstruction and normalized following its release. Recovery of RBF and GFR after relief of ipsilateral CPUO in the newborns was only partial at eight weeks, with no renal growth or increase in NPG from three to eight weeks of age. In contrast, recovery of RBF in the adult was complete 10 days after relief of obstruction, with significant increase in GFR, and no decrease in renal mass or NPG. We conclude that if delayed, relief of CPUO in the neonate may not restore renal growth and functional maturation which have been impaired by CPUO.

Pressure and flow measurements in the partially obstructed ureter of the rat

Hydronephrosis in man or experimental animals can be caused by an increased ureteral flow resistance. This condition can in the long run prove harmful to renal function. We compared two ways of measuring ureteral flow resistance in animals with and without a ureteral hindrance, the hindrance being induced by embedding the ureter in the psoas muscle. One needle connected via catheters to a pressure recording system and another connected to a pump system were introduced through the parenchyma into the renal pelvis. Experiments were carried out with two procedures: 1) infusion of 0.5 ml x min-1 of saline into the renal pelvis was performed while recording the pressure response; 2) a servocontrolled pump system was used which regulated the flow introduced into the renal pelvis to keep a preset pressure at a constant level. In the first group of experiments we did not establish a steady-state pressure despite 20-30 min of infusion. The result from the second series of experiments indicated that steady-state flow measurements could be achieved at the different pressure levels between zero and 30 mmHg. A good linear relationship between pressure and flow was found, even though a considerable hysteresis was observed. Furthermore, a reduced flow resistance down to a certain level at increased pressure was also recorded. As expected, the resistance to flow was significantly lower in the control than in the hydronephrotic animals. In order to investigate the diagnostic ability of the linear relationship between pressure and flow, prediction regions for one future animal were calculated. It seemed possible that determination of the whole pressure-flow relationship in the pressure range between zero and 30 mmHg will prove useful to determine the flow hindrance in hydronephrotic animals.

Long-term follow-up of separate glomerular filtration rate in partially obstructed kidneys. Experimental study

An often encountered assumption is that non-relieved renal obstruction will lead soon or late to progressive deterioration of the renal function. The effect of non-relieved partial ureteral obstruction on the separate glomerular filtration rate (SGFR) was studied throughout the whole life of a series of rats, who were submitted at the age of 3 months to partial obstruction of the left ureter. An initial and variable postoperative SGFR decrease was gradually observed, but after this period, SGFR remained stable until the natural death of the animal.

Partial ureteric obstruction in the pubescent rat. I. Long-term effects on renal function

A partial obstruction of the left ureter was created in six-week-old rats. The effects on renal function were studied after three, nine and 15 weeks, first in normal hydration, and then after extracellular volume expansion. Moderate hydronephrosis without parenchymal weight reduction developed within three weeks. The hydronephrotic kidney i) excreted during normal hydration less urine and sodium than the intact one, because of increased reabsorption, ii) was capable of reacting fully on volume expansion and iii) had, after volume expansion, a higher renal blood flow and GFR but also a higher reabsorption of water, sodium, potassium and osmoles, resulting in excretions similar to those on the intact side. The differences noted were small (less than 20%) except for sodium excretion. The hydronephrotic kidney seemed to tolerate an increase in ureteral resistance better than the intact one would do. There were no significant differences between the three, nine and 15-week groups, with regard to the effects on the hydronephrotic kidney. Thus, except for a tendency to sodium retention, the effects of partial ureteric obstruction in young rats seem to be relatively harmless and do not increase with time.

Tubuloglomerular feedback in animals with unilateral, partial ureteral occlusion

Previous experiments have shown that the sensitivity of the tubuloglomerular feedback system (TGF) is reduced by volume expansion in normal rats. This reduction in sensitivity is probably mediated by changes in the renal interstitial pressure. The present study was designed to investigate the TGF control system during volume expansion in rats with chronic, partial ureteral occlusion--hydronephrosis. Hydronephrosis was induced on the left or right side according to the method described by Ulm and Miller, in weanling Sprague-Dawley rats three weeks old. Three to six weeks later the rats were prepared for whole kidney and micropuncture experiments. Sham-operated animals were used as controls. Net interstitial pressure (that is, interstitial hydrostatic pressure minus interstitial oncotic pressure) was higher in the hydronephrotic, volume expanded animals than in the volume expanded controls. From findings in earlier investigations this increase in interstitial pressure would have been expected to reduce TGF sensitivity but this sensitivity was increased in the hydronephrotic kidneys, as indicated by a reduction in the turning point, the tubular flow rate at which 50% of the maximal stop-flow pressure response was observed (14.4 nl/min, sham-operated control 33.4 nl/min). Strong activity of the TGF mechanism was also indicated by a large proximal-distal difference in the single-nephron glomerular filtration rate (11.9 nl/min versus 3.3 nl/min in sham-operated controls) in the hydronephrotic kidney during volume expansion. Thus, in hydronephrotic kidneys in the latter condition the TGF mechanism was highly sensitive and activated to reduce the glomerular filtration rate. This mechanism may protect the diseased kidney from high intrapelvic pressures which otherwise could damage the kidney during saline volume expansion.

Experimental partial ureteric obstruction in newborn rats. VII. Are the long term effects on renal morphology avoided by release of the obstruction?

Partial obstruction of the left ureter was created in newborn rats. The obstruction was either permanent or was released after two or seven days. The effects were studied at the age of six weeks. The permanently obstructed kidneys characteristically exhibited considerable enlargement (X 18) of pelvic volume and prominent deformation of the papilla, frequently associated with moderate widening of collecting ducts and convoluted tubuli, and focal inflammatory and degenerative lesions. The weight difference between the hydronephrotic and the contralateral, intact kidney was significantly higher than in a sham operated group, although the combined kidney weight was unchanged, indicating a reduction on the obstructed side and a compensatory contralateral hypertrophy. In the group released after seven days, the pelvic volume had returned to normal; nevertheless the parenchymal weight pattern and the histological lesions were similar to those found in animals obstructed for six weeks. In the group released after two days, the pelvic volume had normalized, and the histological changes were less prominent than in animals obstructed for seven days or six weeks. Yet there was a significant difference in parenchymal weight between the hydronephrotic and the contralateral kidney, almost entirely caused by hypertrophy on the nonobstructed side. Thus, the ureteric obstruction must be released very early to avoid parenchymal weight reduction and curb the tissue lesions. On the other hand, the resulting parenchymal damage is moderate and does not seem to progress with time.