Renal renin-angiotensin system dysregulation caused by partial bladder outlet obstruction in fetal sheep

Arginine-dependent immune responses

A growing body of evidence indicates that, over the course of evolution of the immune system, arginine has been selected as a node for the regulation of immune responses. An appropriate supply of arginine has long been associated with the improvement of immune responses. In addition to being a building block for protein synthesis, arginine serves as a substrate for distinct metabolic pathways that profoundly affect immune cell biology; especially macrophage, dendritic cell and T cell immunobiology. Arginine availability, synthesis, and catabolism are highly interrelated aspects of immune responses and their fine-tuning can dictate divergent pro-inflammatory or anti-inflammatory immune outcomes. Here, we review the organismal pathways of arginine metabolism in humans and rodents, as essential modulators of the availability of this semi-essential amino acid for immune cells. We subsequently review well-established and novel findings on the functional impact of arginine biosynthetic and catabolic pathways on the main immune cell lineages. Finally, as arginine has emerged as a molecule impacting on a plethora of immune functions, we integrate key notions on how the disruption or perversion of arginine metabolism is implicated in pathologies ranging from infectious diseases to autoimmunity and cancer.

Study of serum and urinary markers of the renin-angiotensin-aldosterone system in myelomeningocele patients with renal injury detected by DMSA

Introduction:

The Renin-Angiotensin-Aldosterone System (RAAS) has been suggested as a possible marker of renal injury in chronic diseases. This study proposes to analyze the serum and urinary markers of the RAAS in myelomeningocele patients with renal function abnormalities detected on DMSA.

Material and Methods:

Seventeen patients followed in our institution that presented with renal injury on DMSA. We review nephrologic and urologic clinical aspects and evaluated ultrassonagraphy, voiding urethrocystography and urodynamics. Urinary and serum samples were collected to evaluate possible correlations of renal lesions with RAAS. Control group urine and serum samples were also sent for analysis.

Results:

Serum ACE 2 activity means in relation to urodynamic findings were the only values that had a statistically significant difference (p = 0.040). Patients with normal bladder pattern presented higher ACE 2 levels than the high risk group. Statistical analysis showed that the study group (SG) had a significantly higher mean serum ACE than the CG. The means of ACE 2 and urinary ACE of the SG and CG were not statistically different. The ROC curve for serum ACE values had a statistically significant area for case and non-case differentiation, with 100% sensitivity and 53% specificity for values above 60.2 mg/dL. No statistically significant areas were observed in relation to ACE 2 and urinary ACE values between SG and CG.

Conclusion:

The analysis of serum ACE, ACE 2 and urinary ACE were not significant in patients with myelomeningocele and neurogenic bladder with renal injury previously detected by renal DMSA.

Fetal cardiac findings and hemodynamic changes associated with severe lower urinary tract obstruction in utero

OBJECTIVES

To describe fetal echocardiographic findings associated with lower urinary tract obstruction (LUTO) and to compare anatomic and hemodynamic measurements between fetuses with LUTO and gestational age (GA)-matched controls, with an emphasis on quantitative indices of diastolic function and cardiac output.

METHODS

This was a retrospective cohort study of fetuses diagnosed with severe LUTO with giant bladder, which underwent at least one fetal echocardiogram at our center between January 2005 and June 2018. Fetuses with major congenital heart disease were excluded. Control fetuses did not have any structural or functional abnormalities and were GA-matched to the LUTO fetuses based on the time of the first fetal echocardiogram. Cardiac anatomy and hemodynamic measurements were compared between fetuses with LUTO and controls. In infants with LUTO, serial fetal and postnatal echocardiographic data were assessed, when available, and clinical outcomes were reviewed.

RESULTS

Twenty-six fetuses with LUTO and at least one fetal echocardiogram available were identified, one of which was excluded due to hypoplastic left heart syndrome, leaving 25 LUTO fetuses in the final cohort. The mean GA at the first fetal echocardiogram was 25.4 ± 5.1 weeks in the LUTO group and 25.3 ± 5.0 weeks in the control group. Common findings in fetuses with LUTO included cardiomegaly (40%), pericardial effusion (44%), right ventricular (RV) hypertrophy (64%) and left ventricular (LV) hypertrophy (48%). Compared with GA-matched controls, LUTO fetuses had lower ascending aorta Z-score (-0.10 ± 0.94 vs -0.93 ± 1.03; P = 0.02) and aortic isthmus Z-score (-0.14 ± 0.86 vs -1.62 ± 1.11; P < 0.001), shorter mitral valve inflow time indexed to cardiac cycle length (0.46 ± 0.04 vs 0.41 ± 0.06; P = 0.002), and worse (increased) LV myocardial performance index (0.39 ± 0.03 vs 0.44 ± 0.04; P < 0.001). In addition, the ratio of RV to LV cardiac index was higher in LUTO fetuses compared with controls (1.62 ± 0.13 vs 1.33 ± 0.11; P < 0.001). Of the 25 LUTO pregnancies, two were lost to follow-up, three underwent elective termination of pregnancy and three ended in intrauterine fetal demise. Four (16%) patients had mildly hypoplastic left-heart structures, comprising two with aortic arch hypoplasia and two with mitral and aortic stenosis.

CONCLUSION

In addition to presenting with cardiomegaly, pericardial effusion and ventricular hypertrophy, fetuses with LUTO demonstrate LV diastolic dysfunction and appear to redistribute cardiac output as compared to control fetuses, which may contribute to the development of left-heart hypoplasia. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Fetal cardiovascular effects of lower urinary tract obstruction with giant bladder

OBJECTIVE

Lower urinary tract obstruction (LUTO) with massive bladder distension impacts on a variety of developing organ systems with consequent morbidity and mortality. The impact of LUTO on the fetal cardiovascular system has not previously been investigated. We hypothesize that a giant, distended bladder within the pelvis may cause vascular compression with observable consequences.

METHODS

Fetal echocardiography was performed in 42 fetuses with LUTO and compared with 35 normal controls matched for gestational age. Parameters investigated included cardiothoracic ratio, presence or absence of ventricular hypertrophy and pericardial effusion. Doppler echocardiographic examination of mitral and tricuspid valve inflow and the ductus venosus was performed. To assess arterial vascular impedance, pulsatility indices (PIs) were calculated for segments of the descending aorta and right and left iliac arteries (RIA and LIA).

RESULTS

In the LUTO group an increased cardiothoracic ratio was seen in nine (21%), ventricular hypertrophy in 12 (29%) and small pericardial effusion in 15 (36%). Filling characteristics of the right ventricle in the LUTO group demonstrated greater dependency upon atrial contraction, and ductus venosus flow demonstrated higher downstream impedance to filling, than in controls, suggesting altered compliance. The LUTO group also had lower distal descending aorta PI (1.53 ± 0.38 vs. 1.76 ± 0.44, P = 0.04), lower RIA-PI (1.31 ± 0.29 vs. 1.76 ± 0.44, P < 0.001) and lower LIA-PI (1.41 ± 0.44 vs. 1.73 ± 0.31, P < 0.01) than controls, suggesting vascular compression and increased impedance to flow.

CONCLUSIONS

LUTO with giant urinary bladder compresses the iliac arteries, which may lead to increased afterload. Further study is warranted to examine the impact of fetal treatment such as bladder drainage on these cardiovascular parameters.

Renin-angiotensin system dysregulation in fetuses with hydronephrosis

OBJECTIVES

To evaluate if fetal hydronephrosis is associated with dysregulation of the renin-angiotensin system (RAS), and if it could represent an early predictor of future renal damage or arterial hypertension.

STUDY DESIGN

The study consisted of 26 pregnant women and their fetuses. Ultrasound scans were performed to evaluate the renal pelvis in fetuses. Four fetuses with hydronephrosis were included in the study, while the rest were found to have normal renal pelvis. Active and inactive renin was calculated by IRMA method in fetal and maternal blood, during the second trimester of pregnancy.

RESULTS

A comparison of plasma active and inactive renin levels was made between pregnant women and their fetuses, as well as between fetuses with and without hydronephrosis. Active and inactive renin levels obtained from fetuses with hydronephrosis were significantly higher compared to those obtained from fetuses with normal kidneys.

CONCLUSIONS

Dilatation of renal pelvis in the second trimester of pregnancy seems to up-regulate the renin and prorenin system in fetal blood. Both factors are indicative of possible future renal pathology.

Diuretic renography in hydronephrosis: renal tissue tracer transit predicts functional course and thereby need for surgery

PURPOSE

The recognition of those hydronephrotic kidneys which require therapy to preserve renal function remains difficult. We retrospectively compared the 'tissue tracer transit' (TTT) of (99m)Tc-mercaptoacetyltriglycine ((99m)Tc-MAG(3)) with 'response to furosemide stimulation' (RFS) and with 'single kidney function < 40%' (SKF < 40%) to predict functional course and thereby need for surgery.

METHODS

Fifty patients with suspected unilateral obstruction and normal contralateral kidney had 115 paired (baseline/follow-up) (99m)Tc-MAG(3) scintirenographies. Three predictions of the functional development were derived from each baseline examination: the first based on TTT (visually assessed), the second on RFS and the third on SKF < 40%. Each prediction also considered whether the patient had surgery. Possible predictions were 'better', 'worse' or 'stable' function. A comparison of SKF at baseline and follow-up verified the predictions.

RESULTS

The frequency of correct predictions for functional improvement following surgery was 8 of 10 kidneys with delayed TTT, 9 of 22 kidneys with obstructive RFS and 9 of 21 kidneys with SKF < 40%; for functional deterioration without surgery it was 2 of 3 kidneys with delayed TTT, 3 of 20 kidneys with obstructive RFS and 3 of 23 kidneys with SKF < 40%. Without surgery 67 of 70 kidneys with timely TTT maintained function. Without surgery 0 of 9 kidneys with timely TTT but obstructive RFS and only 1 of 16 kidneys with timely TTT but SKF < 40% lost function.

CONCLUSION

Delayed TTT appears to identify the need for therapy to preserve function of hydronephrotic kidneys, while timely TTT may exclude risk even in the presence of an obstructive RFS or SKF < 40%.

Perinatal 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure sensitizes offspring to angiotensin II-induced hypertension

In utero and lactational exposure of mice to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) leads to cardiac hypertrophy and hydronephrosis in adulthood. We tested the hypothesis that perinatal TCDD exposure increases the susceptibility to cardiovascular disease when offspring are exposed to a common cardiovascular disease risk factor, angiotensin II (Ang II). Pregnant C57BL/6N mice were exposed to corn oil (control) or 6.0 microg/kg TCDD on gestation day 14.5. Male offspring were then exposed to a subpressor (0.1 mg/kg/day) or pressor (0.7 mg/kg/day) dose of Ang II at 3.5 months and cardiac morphology and blood pressure analyzed, respectively. Perinatal TCDD exposure increased left ventricular cavity dilation during diastole, and wall thickness during diastole and systole. While Ang II stimulated an increase in wall thickness, the degree of increase was equivalent between control and TCDD offspring. In contrast, perinatal TCDD exposure did not alter basal blood pressure. However, Ang II increased systolic blood pressure more rapidly and to a greater degree in TCDD offspring. Further, Ang II stimulated renal myofibroblast differentiation and collagen deposition to a greater degree, and tended to increase procollagen I mRNA in TCDD offspring, compared to controls. These data suggest that perinatal TCDD exposure increases the susceptibility of offspring to renal fibrosis and hypertension in adulthood.

Diuretic renography in hydronephrosis: delayed tissue tracer transit accompanies both functional decline and tissue reorganization

The significance of delayed tissue tracer transit (TTT) of (99m)Tc-mercaptoacetyltriglycine ((99m)Tc-MAG3) has not been systematically evaluated in hydronephrosis. We sought to demonstrate that delayed TTT accompanies both functional decline and histomorphologic restructuring.

METHODS

Twenty 2- to 3-mo-old piglets with surgically induced partial unilateral ureteral stenosis were examined with magnetic resonance urography (MRU) to evaluate morphology and with (99m)Tc-MAG3 diuretic renography (DR) to determine single-kidney function (SKF), evaluate the response to furosemide stimulation (RFS), and assess TTT. All animals had DR and MRU before and after surgery and a third DR after surgery. Piglets were sacrificed after the final DR for renal histology. A total histologic score (THS) was generated.

RESULTS

Preoperative DR demonstrated nonobstructive RFS, timely TTT, and balanced SKF in all 20 kidneys. After ureteral ligature, MRU demonstrated pelvic dilatation in all piglets. The postoperative DRs revealed 12 kidneys with delayed TTT in one or both follow-ups. In these 12 kidneys, the SKF declined from 51% +/- 4% to 18% +/- 14%, and the THS was 9.0 +/- 4.0. Three kidneys always had timely TTT, balanced SKF, and a THS of 1.8 +/- 0.3. The contralateral, nonoperated kidneys had timely TTT and a THS of 1.2 +/- 0.9. Postoperative scintigrams showed that 3 of 8 kidneys (38%) with an obstructive RFS had timely TTT, which demonstrates that TTT and RFS are not equivalent.

CONCLUSION

In hydronephrosis, a delayed TTT of (99m)Tc-MAG3 accompanies both functional decline and histomorphologic restructuring in obstruction. According to the literature, a delayed TTT is determined by the filtration fraction of the kidneys and appears to identify an obstruction-mediated upregulated renin-angiotensin system.

Congenital urinary tract obstruction

Congenital urinary tract obstruction is a heterogenous condition with a varying natural history. Accurate diagnosis within the late-first and second trimesters allows for counselling of the parents and planning of multi-disciplinary care for the pregnancy and newborn. Antenatal investigations to predict postnatal renal function are of varying accuracy. However, some factors have been shown to be predictive of poor outcome in terms of renal function at birth and infancy. There is the possibility of in-utero intervention in these fetuses.

Captopril Reduces Interstitial Renal Fibrosis and Preserves More Normal Renal Tubules in Neonatal Dogs with Partial Urethral Obstruction: A Preliminary Study

PURPOSE

Chronic renal damage due to tubulointerstitial fibrosis is one of several complications of posterior urethral valves in a significant number of children. As activation of the renin-angiotensin system plays an important role in this injury, we conducted this study to investigate whether administration of captopril reduced renal fibrosis in an experimental model using partial urethral obstruction (PUO) in neonatal dogs.

MATERIAL AND METHODS

Experimental PUO was induced in all pups. These animals were then divided into two groups: in the first group (experimental), captopril 35 mg/kg/day, dissolved in drinking water, was administered for 6 weeks. The second group (positive control) did not receive any treatment. After 6 weeks all dogs underwent left nephrectomy. Volume fraction and absolute volume of the histological kidney parameters, i.e., normal glomerulus, normal tubule, vessels, degenerated glomerulus, degenerated tubule, fibrous tissue, were estimated using modern unbiased stereological methods.

RESULTS

The absolute volume of interstitial fibrosis was lower in the experimental group (PUO with captopril treatment) (approximately 73%; p < 0.008) in comparison with positive control animals (PUO with no treatment). The mean absolute volume of normal tubules in the experimental group was more than the positive control group (approximately 33%, p < 0.008). The mean absolute volume of normal and degenerated glomerulus, vessels and degenerated tubule did not show a significant difference between the two groups.

CONCLUSION

Administration of captopril decreases interstitial renal fibrosis and preserves renal tubules in neonatal dogs with PUO.

Clinical and molecular markers of chronic interstitial nephropathy in congenital unilateral ureteropelvic junction obstruction

PURPOSE

We evaluated clinical and biological variables, and their meaning as reliable markers of chronic interstitial nephropathy in a selected group of children with prenatally detected hydronephrosis who underwent pyeloplasty because of congenital unilateral ureteropelvic junction obstruction.

MATERIALS AND METHODS

We reviewed the clinical, prenatal and postnatal ultrasonographic, and scintigraphic records of children for whom intraoperative biopsy records were available. We performed histological analysis, and evaluated tubulointerstitial immunostaining for vimentin and alpha-smooth muscle actin, and the immunohistochemical and mRNA expression of the renin-angiotensin system peptides and transforming growth factor-beta1.

RESULTS

The children were divided in 2 groups according to the absence (group 1) or presence (group 2) of chronic interstitial nephropathy in the biopsy. Patients in group 2 were significantly younger at prenatal diagnosis (p = 0.031), and had decreased split renal function (p = 0.005) and worse drainage (p = 0.035) on preoperative diuretic renography. No differences were found in terms of degree of hydronephrosis, or its prenatal and postnatal variation. Group 2 biopsies exhibited greater immunostaining for alpha-smooth muscle actin and vimentin (p = 0.004 and p = 0.047, respectively), and transforming growth factor-beta1 mRNA levels (p = 0.06). Vimentin and alpha-smooth muscle actin positivity correlated with renin, angiotensin II receptors 1 and 2, and transforming growth factor-beta1 mRNA levels, and all correlated with preoperative split renal function and post-void washout.

CONCLUSIONS

In congenital unilateral ureteropelvic junction obstruction chronic interstitial nephropathy and poor postoperative recovery seem to be associated with an earlier diagnosis of hydronephrosis, functional loss greater than 10% and worse scintigraphic drainage. Moreover, there is a strong correlation between molecular fibrogenic markers and histologically and scintigraphically demonstrated renal damage.

Antenatal inflammation induced TGF-beta1 but suppressed CTGF in preterm lungs

Chorioamnionitis is frequently associated with preterm birth and increases the risk of adverse outcomes such as bronchopulmonary dysplasia (BPD). Transforming growth factor (TGF)-beta1 is a key regulator of lung development, airway remodeling, lung fibrosis, and regulation of inflammation, and all these processes contribute to the development of BPD. Connective tissue growth factor (CTGF) is a downstream mediator of some of the profibrotic effects of TGF-beta1, vascular remodeling, and angiogenesis. TGF-beta1-induced CTGF expression can be blocked by TNF-alpha. We asked whether chorioamnionitis-associated antenatal inflammation would regulate TGF-beta1, the TGF-beta1 signaling pathway, and CTGF in preterm lamb lungs. Fetal sheep were exposed to 4 mg of intra-amniotic endotoxin or saline for 5 h, 24 h, 72 h, or 7 days before preterm delivery at 125 days gestation (full term = 150 days). Intra-amniotic endotoxin increased lung TGF-beta1 mRNA and protein expression. Elevated TGF-beta1 levels were associated with TGF-beta1-induced phosphorylation of Smad2. CTGF was selectively expressed in lung endothelial cells in control lungs, and intra-amniotic endotoxin caused CTGF expression to decrease to 30% of control values and TNF-alpha protein to increase. The antenatal inflammation-induced TGF-beta1 expression and Smad signaling in the fetal lamb lung may contribute to impaired lung alveolarization and reduced lung inflammation. Decreased CTGF expression may inhibit vascular development or remodeling and limit lung fibrosis during remodeling. These effects may contribute to the impaired alveolar and pulmonary vascular development that is the hallmark of the new form of BPD.

Timing of morphologic and apoptotic changes in the sheep fetal kidney in response to bladder outflow obstruction

PURPOSE

Posterior urethral valves are the main cause of bladder outflow obstruction in human fetuses. Thirty per cent of boys with valves develop end-stage renal disease, despite intervention in the postnatal period. The timing and mechanisms of renal damage in bladder outflow obstruction are unknown. We investigated the timing of changes in morphology and apoptosis in the fetal sheep kidney in response to obstruction.

MATERIALS AND METHODS

Thirty-three fetal lambs at day 70 of gestation underwent surgical creation of bladder outflow obstruction. Twenty-nine fetal lambs had sham surgery. Fetal kidneys were collected 2, 5, 10, 20 and 30 days after surgery. Renal histology was examined. Real-time PCR was used to quantify the renal cortical expression of the pro-apoptotic gene Bax and anti-apoptotic gene Bcl-X. The TUNEL technique was used to assess regional renal apoptosis in response to obstruction.

RESULTS

Changes in renal morphology were evident as early as 2 days after surgery in fetuses with bladder outflow obstruction, and progressed over 20-30 days to cystic renal dysplasia. Bladder outflow obstruction increased the renal cortical expression of Bax relative to Bcl-X. Tubular apoptosis peaked after 2 days of obstruction. Blastemal apoptosis peaked after 5 days of obstruction.

CONCLUSIONS

Changes in pro- and anti-apoptotic gene expression in the fetal renal cortex, and alterations in the number of apoptotic cells and renal morphology are evident soon after the onset of bladder outflow obstruction. These findings suggest that damage to the developing fetal kidney begins to occur at the onset of obstruction. Attempts to preserve renal function by antenatal interventions may best be achieved by early treatment.

Complete unilateral ureteral obstruction in the fetal lamb. Part I: long-term outcomes of renal hemodynamics and anatomy

PURPOSE

We evaluated the long-term consequences of complete fetal UUO on renal hemodynamics and anatomy.

MATERIALS AND METHODS

A total of 26 fetal lambs underwent surgical UUO at 90 days of gestation and 14 twin matched animals served as controls. Synchronous bilateral ARBF was measured using mean transit time technology. Standard anatomical analysis, including evaluation of RPV, was performed in the kidneys. Measurements were done 10, 20 and 40 days following UUO in groups 1 to 3, respectively and in 1-month-old lambs in group 4.

RESULTS

All obstructed kidneys underwent typical hydronephrotic transformations with a progressive decrease in parenchymal volume compared to that of contralateral and control kidneys. ARBF in obstructed kidneys was significantly decreased compared to their contralateral counterparts in all groups (p <0.01). Comparing ARBF to RPV showed that the decrease in ARBF was proportional to the loss of parenchymal volume in fetal obstructed kidneys but it remained significant in lambs (p <0.05).

CONCLUSIONS

Complete UUO alters ARBF, while vascularization of the remaining renal parenchyma is maintained in fetuses. Profound impairment of the renal arterial supply observed in lambs may be due to physiological changes linked to birth.

Renal biopsy in congenital ureteropelvic junction obstruction: evidence for parenchymal maldevelopment

The renal histologic changes associated with congenital ureteropelvic junction obstruction (UPJO) and the relationship to clinical imaging have not been well studied. In order to better understand the histologic alterations of congenital UPJO and their relationship with clinical imaging and outcomes, we examined renal biopsies from 61 patients undergoing pyeloplasty for congenital UPJO. Glomeruli were analyzed for various injury patterns and the tubulointerstitium was examined for tubular atrophy/simplification and fibrosis. Two methods were used to evaluate tubular mass: glomerular density and morphometric measurement of tubular size and density. Control specimens were obtained from age-matched autopsy specimens without renal pathology. Glomerular changes were identified in 73% of all biopsies and were present in a range from 1.7 to 91% of glomeruli in each patient. Overt tubulointerstitial changes were present in 26% of all biopsies. Fibrosis was noted to occur with tubulointerstitial changes in a significantly greater fraction of children over the age of 1 year (P=0.026). Increased glomerular density was associated with severe hydronephrosis (P<0.02). Normal glomerular density was inversely correlated with age (P<0.001), but this relationship was more variable in UPJO (P<0.01). Among patients with intact differential function preoperatively (>45%), postoperative functional decline was predicted only by increased glomerular density. 20 biopsies without overt tubulointerstitial changes were analyzed morphometrically and showed a significant reduction in proximal tubular (PT) size, but unchanged density. Distal tubular (DT) size was unchanged in UPJO, but density was increased. The PT/DT ratio was therefore markedly decreased in UPJO (P<0.0001). Both PT and DT sizes were significantly larger in children with a diuretic renogram washout time less than 20 min than those with greater than 20 min, a common threshold for functionally significant obstruction (P<0.05). Capsular thickness was significantly increased in UPJO. In all, 36% of biopsies had a thickness >0.5 mm and this was associated with greater degrees of tubulointerstitial changes and glomerular alterations. Congenital UPJO produces a variety of renal parenchymal changes, which may in part reflect abnormal development. Some of these alternations are seen in clinical imaging and may help predict outcomes, but there is significant discordance between conventional imaging and histological findings.

Experimental models to study the physiology, pathophysiology, and pharmacology of the lower urinary tract

The lower urinary tract is subject to a number of functional disorders, the most common of which, in humans, is bladder overactivity. To understand its pathophysiological basis, several in vitro and in vivo methodologies have been developed. In vitro tension recording from multicellular strips is in widespread use, and alternative experimental arrangements to a conventional organ bath are described, the relative merits are discussed, and the different experimentally derived variables are evaluated. Other methodologies, such as skinned fibres and whole bladder preparations, are also described. Electromyography in the isolated bladder is now feasible, and its potential uses discussed. The use of isolated smooth muscle cells is presented, especially with respect to the measurement of intracellular ion concentrations and electrophysiological parameters. The development of methods to prepare other cell types from the lower urinary tract is also introduced. A large-scale culture of urothelial and smooth muscle cells is possible, and their use as experimental tools, as well as a substrate for the development of surgical implants, is presented. Finally, different in vivo models of the lower urinary tract are presented, with reference to their investigation of clinical problems. These include models of bladder outflow obstruction, bladder ischaemia, bladder denervation, and congenital abnormalities and their influence on foetal development of the lower urinary tract.

Prognostic significance of captopril renography for managing congenital unilateral hydronephrosis

PURPOSE

In this prospective study we evaluated the results of captopril enhanced diuretic renography in patients with congenital unilateral ureteropelvic junction type hydronephrosis. Captopril renography helps to distinguish patients who have renin-angiotensin system activation from those in whom it is not yet activated. Renin-angiotensin system activation heralds the beginning of compensatory vasoactive response in the kidney. Identifying grades of such activation may help in determine the end points of nonoperative management.

MATERIALS AND METHODS

We prospectively studied 25 patients with suspected unilateral ureteropelvic junction obstruction treated at our department. A prenatal diagnosis was made in 60% of cases. Patient age was 1 to 144 months (mean 40) and the male-to-female ratio was 4:1. Followup was 6 to 72 months (mean 30). Patient evaluation and analysis included sonography, standard diuretic and captopril renography, glomerular filtration rate, serum creatinine and blood pressure. The indications for surgery were symptoms, differential function below 35%, or a documented decrease of 10% or more during followup. Activation of the renin-angiotensin system was considered positive when split renal function decreased significantly by 5% or more in an obstructed system on a post-captopril study. The results of captopril renography were examined retrospectively in patients who required surgery according to preexisting criteria.

RESULTS

Society for Fetal Urology hydronephrosis grade was II to IV in 8, 10 and 7 renal units, respectively. The renin-angiotensin system was activated in 8 of the 25 cases (32%) of unilateral ureteropelvic junction obstruction. In 15 patients there was no change on pre-captopril and post-captopril studies and in 2 split renal function on the obstructed side marginally increased on the post-captopril study. Surgical correction was required in only 6 of the 8 patients with renin-angiotensin system activation. Of those who required surgery hydronephrosis was grades II to IV in 3, 1 and in 2 patients, respectively.

CONCLUSIONS

In the current study renin-angiotensin system activation correlated with the need for surgery in 75% of the cases of congenital unilateral ureteropelvic type hydronephrosis. Since captopril serves to identify patients who have renin-angiotensin system activation, it may also be possible to grade this activation. Our preliminary results show that there may be a role for captopril renography for identifying the risk group for surgical intervention.

Animal models of fetal renal disease

Fetal models of urinary tract disease have been used for many years and have provided unique and important insights into the pathophysiology of these conditions. This review will summarize the principal model systems used and the current directions of investigation. These models (including rabbit, opossum, sheep and recently swine) have demonstrated that in utero obstruction of the urinary tract alters renal growth, differentiation and produces stereotypical patterns of tissue response, particularly fibrosis. New molecular understanding of these processes has identified specific mechanisms that may be key elements in the development of renal dysfunction due to obstruction. These factors include the renin-angiotensin system (RAS) and its interaction with TGF-beta in altering growth regulation and tissue fibrosis. These factors offer the prospect of clinical utility as markers of disease progression as well as pharmacologic therapy. Gene knockout systems have opened a new horizon of molecular models of congenital obstructive uropathy with insights into the role of the RAS in particular. It remains to be defined how closely these knockouts represent the human conditions they resemble. Continued application of fetal models of urinary obstruction, integrating large animal and knockout systems offers promise for improved diagnosis and treatment in these challenging conditions.

Partial ureteral obstruction dysregulates the renal renin-angiotensin system in the fetal sheep kidney

OBJECTIVES

To investigate whether partial ureteral obstruction (PUO) in the fetus induces dysregulation of the renin-angiotensin system (RAS) and of transforming growth factor-beta 1 (TGF-beta1) and tissue inhibitors of metalloproteinase (TIMP1) expression. Previous studies have indicated that renal and urinary tract development depend on an intact renal RAS. Fetal urinary obstruction is distinct from postnatal obstruction. It has been suggested in postnatal animal studies that dysregulation of the RAS, and subsequent increased expression of TGF-beta1 and TIMP1, leads to changes in extracellular matrix composition.

METHODS

Bilateral PUO was created in 4 fetal sheep. Seven animals (four obstructed and three controls) were killed at birth and their kidneys removed. Semiquantitative reverse transcriptase-polymerase chain reaction was used to quantify the levels of renin, angiotensinogen, angiotensin receptor type 1 (AT1 receptor), angiotensin receptor type 2 (AT2 receptor), TGF-beta1, and TIMP1. These messages were normalized to glyceraldehyde-3-phosphate dehydrogenase mRNA.

RESULTS

All obstructed animals had moderate to severe hydronephrosis with enlarged kidneys (mean weight 22.0 g versus 9.4 g for the control animals; P <0.05). The increase in the levels of renin, angiotensinogen, AT1 receptor, TGF-beta1, and TIMP1 mRNA was significant in the PUO group compared with the control group (P <0.05). AT2 receptor levels did not increase, but the AT1/AT2 mRNA ratio was significantly increased over normal (P <0.005). Also, a significant linear correlation was found between the increased renal weight and increased TGF-beta1 mRNA levels (P <0.005).

CONCLUSIONS

Our findings suggest that fetal PUO can cause upregulation of the renal RAS and increased expression of TGF-beta1 and TIMP1, which may alter the balance between the generation and degradation of the extracellular matrix. The coordinate increases in renin, angiotensinogen, and AT1 receptor mRNA levels in chronic fetal PUO may represent a maladaptive response that contributes to interstitial fibrosis and prolonged vasoconstriction. RAS components and growth factors, particularly TGF-beta1, may be considered relevant targets in the prevention and treatment of congenital obstructive nephropathy.

Impaired nephrogenesis in rats with congenital obstructive uropathy

PURPOSE

Alterations caused by renal obstruction in developing kidneys are of particular interest in basic research of congenital obstructive uropathy. In rats nephrogenesis mainly occurs 7 to 10 days postnatally. Therefore, surgically induced neonatal ureteral obstruction in rats has been suggested to be analogous to congenital obstruction in the fetus. An attempt less prone to surgical artifacts and assessing even earlier developmental stages is to monitor the development of obstructed kidneys in rats with congenital obstructive uropathy.

MATERIALS AND METHODS

Rats from an inbred strain with congenital renal obstruction in 70% of their littermates were observed. Morphologically, significant hydronephrosis was not detected before day 5 post partum and progressed with age. Unilateral obstructed kidneys were compared with contralateral kidneys and kidneys from healthy control animals at ages of 1, 5, 10, 18 and 32 days. A total of 72 renal units were investigated. The renal messenger RNA expression of renin and transforming growth factor-beta1 (TGF-beta1) was quantified by competitive quantitative reverse transcription polymerase chain reaction using a gene specific complementary RNA standard.

RESULTS

In controls the gene expression of renin decreased from day 1 to day 18 and remained stable. TGF-beta1 expression increased during the first 10 days and then decreased again. Renin expression of the obstructed kidneys was reduced (p <0.05) on day 1, increased to a maximum versus controls (p <0.01) on day 10 and decreased to an unchanged elevated level (p <0.01) on days 18 and 32. Renin expression of the contralateral kidneys showed no significant alterations to control kidneys. Messenger RNA expression of TGF-beta1 of obstructed kidneys stayed decreased during the first 10 days (p <0.05), then increased excessively on day 18 (p <0.01) and slightly decreased on day 32. TGF-beta1 expression of the contralateral kidneys was parallel to controls on a slightly elevated level, increased on day 18 and returned to control level on day 32.

CONCLUSIONS

Within the postpartum period of nephrogenesis gene expression of renin and TGF-beta1 was decreased in obstructed kidneys compared to controls. As the renin angiotensin system and TGF-beta1 have important functions in normal kidney development, these results suggest impaired nephrogenesis of congenital obstructed kidneys even before the onset of morphological signs of hydronephrosis. These features differ from surgical induced unilateral ureteral obstruction at birth and promise new insights into the pathophysiology of congenital obstructive uropathy.

Impaired nephrogenesis in rats with congenital obstructive uropathy

PURPOSE

Alterations caused by renal obstruction in developing kidneys are of particular interest in basic research of congenital obstructive uropathy. In rats nephrogenesis mainly occurs 7 to 10 days postnatally. Therefore, surgically induced neonatal ureteral obstruction in rats has been suggested to be analogous to congenital obstruction in the fetus. An attempt less prone to surgical artifacts and assessing even earlier developmental stages is to monitor the development of obstructed kidneys in rats with congenital obstructive uropathy.

MATERIALS AND METHODS

Rats from an inbred strain with congenital renal obstruction in 70% of their littermates were observed. Morphologically, significant hydronephrosis was not detected before day 5 post partum and progressed with age. Unilateral obstructed kidneys were compared with contralateral kidneys and kidneys from healthy control animals at ages of 1, 5, 10, 18 and 32 days. A total of 72 renal units were investigated. The renal messenger RNA expression of renin and transforming growth factor-beta1 (TGF-beta1) was quantified by competitive quantitative reverse transcription polymerase chain reaction using a gene specific complementary RNA standard.

RESULTS

In controls the gene expression of renin decreased from day 1 to day 18 and remained stable. TGF-beta1 expression increased during the first 10 days and then decreased again. Renin expression of the obstructed kidneys was reduced (p <0.05) on day 1, increased to a maximum versus controls (p <0.01) on day 10 and decreased to an unchanged elevated level (p <0.01) on days 18 and 32. Renin expression of the contralateral kidneys showed no significant alterations to control kidneys. Messenger RNA expression of TGF-beta1 of obstructed kidneys stayed decreased during the first 10 days (p <0.05), then increased excessively on day 18 (p <0.01) and slightly decreased on day 32. TGF-beta1 expression of the contralateral kidneys was parallel to controls on a slightly elevated level, increased on day 18 and returned to control level on day 32.

CONCLUSIONS

Within the postpartum period of nephrogenesis gene expression of renin and TGF-beta1 was decreased in obstructed kidneys compared to controls. As the renin angiotensin system and TGF-beta1 have important functions in normal kidney development, these results suggest impaired nephrogenesis of congenital obstructed kidneys even before the onset of morphological signs of hydronephrosis. These features differ from surgical induced unilateral ureteral obstruction at birth and promise new insights into the pathophysiology of congenital obstructive uropathy.

Fetal rhesus monkey model of obstructive renal dysplasia

BACKGROUND

Disorders of kidney development represent a major cause of renal failure and end-stage renal disease in the pediatric population. To understand further the prenatal pathogenesis of obstructive renal dysplasia, a fetal monkey model was developed using ultrasound-guided techniques.

METHODS

Ureteropelvic obstruction (N = 13) was induced during the early or late second trimester by the injection of purified guluronic alginate spheres. All fetuses were monitored sonographically, and then fetal tissues were removed at varying time points during the second and third trimesters.

RESULTS

There was no evidence of oligohydramnios during the course of gestation, and the obstructed kidneys were typically progressively smaller than the contralateral (nonobstructed) kidneys when monitored sonographically over time. Obstructed kidneys displayed most features of renal dysplasia, including numerous cortical cysts of various sizes derived predominantly from collecting ducts and glomeruli. Mesenchymal changes included expansion of both the cortical and medullary interstitium, as well as mesenchymal-myocyte transformation, expressed as pericystic and peritubular fibromuscular collar formation. An important feature of this model was the disruption of normal glomerular development and architecture, associated with significant podocyte apoptosis, evident as early as the prevascularized S-shaped nephron. As in other models, collecting duct cell apoptosis was apparent, particularly in areas of cyst formation and cellular atrophy.

CONCLUSIONS

These results demonstrate the importance of this nonhuman primate model for exploring the pathophysiology of congenital obstructive uropathy and highlight the potential role of podocyte injury in determining long-term renal function associated with this condition.