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

Megaesophagus Is a Major Pathological Condition in Rats With a Large Deletion in the Rbm20 Gene

A spontaneously arising, loss-of-function mutation in the RNA binding motif protein 20 (Rbm20) gene, which encodes a nuclear splicing protein, was previously identified as the underlying reason for expression of an abnormally large TITIN (TTN) protein in a rat model of cardiomyopathy. An outbreak of Pseudomonas aeruginosa led to submission of rats with dyspnea, sneezing, lethargy, nasal discharge, and/or unexpected death for diagnostic evaluation. Necropsy revealed underlying megaesophagus in Rbm20^–/– rats. Further phenotyping of this rat strain and determination of the size of esophageal TTN was undertaken. The Rbm20-defective rats developed megaesophagus at an early age (26 weeks) with high frequency (13/32, 41%). They also often exhibited secondary rhinitis (9/32, 28%), aspiration pneumonia (8/32, 25%), and otitis media/interna (6/32, 19%). In addition, these rats had a high prevalence of hydronephrosis (13/32, 41%). RBM20 is involved in splicing multiple RNA transcripts, one of which is the muscle-specific protein TTN. Rbm20 mutations are a significant cause of dilated cardiomyopathy in humans. In Rbm20-defective rats, TTN size was significantly increased in the skeletal muscle of the esophagus. Megaesophagus in this rat strain (maintained on a mixed genetic background) is hypothesized to result from altered TTN stretch signaling in esophageal skeletal muscle. This study describes a novel mechanism for the development of megaesophagus, which may be useful for understanding the pathogenesis of megaesophagus in humans and offers insights into potential myogenic causes of this condition. This is the first report of megaesophagus and other noncardiac pathogenic changes associated with mutation of Rbm20 in any species.

Localization of genetic loci controlling hydronephrosis in the Brown Norway rat and its association with hematuria

The aim of this study was to investigate the genetic basis of congenital hydronephrosis (HN), a poorly defined pathological entity, with a rat model. The Brown Norway (BN) strain spontaneously presents a high incidence of apparently asymptomatic HN, whereas the LOU strain does not. A backcross was established between these two strains [BN x (BN x LOU)] and a genomewide scan was performed with 193 microsatellite markers on 121 males and 118 females of this population, which had been phenotyped and scored for HN severity (defined as degree of renal pelvic dilation), followed by linkage analysis with Mapmaker/QTL software. Bilateral HN score was significantly linked to a locus on chromosome 6 (Z scores 4.4 and 4.8 for all rats and for females, respectively). Suggestive loci were identified on chromosomes 2 (for only right-sided HN) and 4. This is the first study in rats to identify genetic loci for HN. Three candidate genes present in these loci were sequenced and insertions detected in Id2 and Agtr1b genes in BN, which did not, however, lead to modified expression as measured by quantitative PCR. Production of a congenic line for part of the chromosome 6 locus confirmed its involvement in HN, but the phenotype was mild. Evidence of hematuria was observed in 9.6% of the backcross rats, mostly males and only in kidneys with HN, but not necessarily in the most severely affected. Hematuria also occurs in the BN colony used here, where it is due to papilloma-like lesions involving pelvic epithelial proliferation, but not in the LOU rat.

Quantitative genetic basis of arterial phenotypes in the Brown Norway rat

The Brown Norway (BN) rat presents several genetically determined arterial phenotypes of interest, i.e., ruptures of the internal elastic lamina (RIEL) in the abdominal aorta (AA), iliac (IAs), and renal arteries, aortic elastin deficit and higher frequency of persistent ductus arteriosus (PDA) than other strains. We investigated the genetic basis of these phenotypes. We established a backcross between BN and the LOU reference strain and performed a genome-wide scan on 104 males and 105 females with 193 microsatellite markers followed by linkage analysis. RIEL in AA and IAs showed highly significant linkage to a locus on chromosome 5 and suggestive linkage to a locus on chromosome 10, which is syntenic to one linked to a syndrome of thoracic aortic aneurysms with PDA in humans. In contrast, renal artery RIEL mapped to a chromosome 3 locus and thoracic aortic elastic content to two loci on chromosome 2. PDA was significantly linked to two different quantitative trait loci (QTL) on chromosomes 8 and 9. This is the first study in rats to identify genetic loci for PDA. We identified 21 candidate genes by functional relevance or integration of our mapping data with global expression analysis. Sequencing these genes identified 47 single nucleotide polymorphisms, but no functionally relevant amino acid changes. By expression analysis, myosin heavy chain 10, nonmuscle, in the chromosome 10 QTL, emerged as a candidate for RIEL in AA and IAs. Furthermore, production of a congenic line for the chromosome 5 QTL proved implication of this locus in RIEL formation.

Imaging kidney in conscious rats with high-frequency ultrasound and detection of two cases of unilateral congenital hydronephrosis

A quick noninvasive screen of laboratory animal organ phenotype by high-resolution ultrasound is useful in biomedical research and new drug discovery. During new drug testing, imaging animal at the conscious state avoiding anaesthesia does not only speed up the screening process, but also avoids the potential compounding interaction of anaesthetic agents with the new drugs. The feasibility of imaging kidney in conscious rats with high-frequency ultrasound was explored in this study. Two operators were involved with the procedure, with one operator holding the rat and the other operator doing the imaging process. A VisualSonics ultrasound system was used, with a 30 MHz central frequency probe at the resolution of 115 x 55 microm. It was feasible to hold the conscious rats still, allowing ultrasound imaging of kidneys, without causing stress to the animals. In a group of 12 male Han Wistar rats (Charles River, UK), two cases of unilateral congenital hydronephrosis of the right kidney were identified. The right kidneys with hydronephrosis showed an echolucent dilated pelvis and overall parenchymal hypotrophy.

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.

Increased transforming growth factor-beta1 and tubulointerstitial fibrosis in rats with congenital hydronephrosis

OBJECTIVES

Most of our knowledge concerning renal obstruction has been derived from experimental animal models, and it is not yet well defined in spontaneous hydronephrosis. The aim of our study is to evaluate the roles of transforming growth factor-beta1 (TGF-beta1) and apoptosis in congenital hydronephrotic kidneys in comparison with experimental models.

METHODS

We made histological studies on kidneys from 6-week-old Wistar-Imamichi rats with congenital unilateral hydronephrosis as well as surgical models of complete or partial unilateral ureteral obstruction. The severity of hydronephrotic kidneys was evaluated on routine hematoxylin and eosin (H&E) stained sections, and the tubulointerstitial fibrosis analyzed morphometrically on Masson's trichrome stained sections. Renal tubular atrophy was assessed on periodic acid Schiff (PAS) stained sections, and tubular cell apoptosis assessed with TUNEL technique. The renal TGF-beta1 level was determined by a sandwich enzyme-linked immunosorbent assay (ELISA).

RESULTS

We observed a significant loss of kidney weight with profound compensatory growth of the contralateral kidney in rats with congenital hydronephrosis. Most of the hydronephrotic kidneys were markedly enlarged with dilatation of the collecting system, renal parenchymal thinning, tubular atrophy, interstitial infiltration and fibrosis. The renal TGF-beta1 level was markedly elevated in hydronephrotic kidneys as compared with normal controls (326.01 +/- 30.64 pg/mg protein vs 227.81 +/- 11.07 pg/mg protein, P < 0.01). The tubular apoptotic score in hydronephrotic kidneys was also significantly higher than normal controls (2.17 +/- 0.50/HPF [high power field]vs 0.14 +/- 0.04/HPF, P < 0.01). The increased TGF-beta1 and apoptotic status paralleled the histological changes of tubulointerstitial fibrosis and tubular atrophy. Similar findings were also obtained in experimental obstructive models.

CONCLUSION

In comparison with surgical models of partial and complete ureteral obstruction, our data provide solid morphological and molecular evidences of renal obstruction in rats with congenital hydronephrosis.

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.

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.

Urinary tract obstruction in children

PURPOSE

Perinatal identification of children with congenital urinary obstruction has challenged our understanding of the pathophysiology and clinical treatment of many children with hydronephrosis.

MATERIALS AND METHODS

A critical review of recent reports relating to congenital urinary obstruction in children was performed in an attempt to integrate clinical and experimental information.

RESULTS

Several themes emerged from the many reports relating to congenital urinary obstruction that have not been previously emphasized. Congenital obstruction begins and evolves in a developing fetal kidney, indicating the importance of the effect of obstruction on renal growth and development, which is distinct from the postnatal renal response to obstruction. Variation in the ability of the developing kidney to compensate for obstruction may be an important factor in explaining variability in clinical and experimental reports. Clinical data show an unpredictable outcome of congenital hydronephrosis. Nonoperative management of hydronephrosis is supported by empirical evidence yet raises many questions regarding the certainty of outcome and the risks involved. It imposes on the practitioner a significant clinical obligation. The ability to differentiate between clinically significant and insignificant obstruction is the current challenge to be fulfilled by integrated clinical and experimental investigation.

CONCLUSIONS

The unique features of congenital urinary obstruction separate it from better understood acquired postnatal obstruction. Understanding the effects of obstruction on the developing kidney prenatally and postnatally is critical. A definition is proposed for congenital urinary obstruction in children, that is a condition of impaired urinary drainage which, if uncorrected, will limit the ultimate functional potential of a developing kidney.

Urinary tract obstruction in children

PURPOSE

Perinatal identification of children with congenital urinary obstruction has challenged our understanding of the pathophysiology and clinical treatment of many children with hydronephrosis.

MATERIALS AND METHODS

A critical review of recent reports relating to congenital urinary obstruction in children was performed in an attempt to integrate clinical and experimental information.

RESULTS

Several themes emerged from the many reports relating to congenital urinary obstruction that have not been previously emphasized. Congenital obstruction begins and evolves in a developing fetal kidney, indicating the importance of the effect of obstruction on renal growth and development, which is distinct from the postnatal renal response to obstruction. Variation in the ability of the developing kidney to compensate for obstruction may be an important factor in explaining variability in clinical and experimental reports. Clinical data show an unpredictable outcome of congenital hydronephrosis. Nonoperative management of hydronephrosis is supported by empirical evidence yet raises many questions regarding the certainty of outcome and the risks involved. It imposes on the practitioner a significant clinical obligation. The ability to differentiate between clinically significant and insignificant obstruction is the current challenge to be fulfilled by integrated clinical and experimental investigation.

CONCLUSIONS

The unique features of congenital urinary obstruction separate it from better understood acquired postnatal obstruction. Understanding the effects of obstruction on the developing kidney prenatally and postnatally is critical. A definition is proposed for congenital urinary obstruction in children, that is a condition of impaired urinary drainage which, if uncorrected, will limit the ultimate functional potential of a developing kidney.

Alterations in glomerular dynamics in congenital, unilateral hydronephrosis

We have previously shown that rats with congenital, unilateral hydronephrosis exhibit a reduction in GFR that returns to normal when either the renin angiotensin system or thromboxane A2 (TxA2) is blocked. The current study defines the single nephron defect in congenital, unilateral hydronephrosis and evaluates the roles of angiotensin II (Ang II) and TxA2 in this renal derangement. Renal micropuncture experiments were performed on the right kidney of rats from an inbred colony with unilateral right-sided hydronephrosis (HYDRO), or non-affected litter mates (CONTROL). In addition, four separate groups of hydronephrotic animals were treated with either the TxA2 receptor antagonist SQ-29548 (SQ), one of two Ang II receptor antagonists [saralasin (SAR) or DuP-753 (DUP)]; or combined treatment with DuP-753 and SQ-29,548 (S&D). SNGFR was significantly reduced (P < 0.05) in HYDRO compared to CONTROL (17.6 +/- 2.0 vs. 35.9 +/- 3.7 nl/min, respectively). Treatment with SQ-29,548 normalized SNGFR (29.0 +/- 3.0 nl/min), while saralasin and DuP-753 resulted in only a partial recovery of function (25.6 +/- 1.6 and 27.8 +/- 1.4 nl/min, respectively). Combined SQ-29,548 and DuP-753 treatment resulted in full recovery of SNGFR to 32.9 +/- 4.4 nl/min. The glomerular ultrafiltration coefficient (Kf) was reduced (P < 0.05) approximately 45% in HYDRO compared to CONTROL (1.64 +/- .08 vs. 2.84 +/- .22 nl/min/mm Hg, respectively). Kf returned to control levels in SAR, DUP and SQ, and increased above control in S&D (5.58 +/- 1.6 nl/min/mm Hg). There were no differences (P > 0.05) in hydrostatic or oncotic pressures across the glomerular capillary between any of the groups studied. The observation that Kf increases above CONTROL with combined blockade of TxA2 and Ang II suggests that these regulatory hormones decrease Kf via independent mechanisms. These data indicate that the reduction in SNGFR in congenital, unilateral hydronephrosis is a result of a marked fall in Kf that is mediated by both Ang II and TxA2.

Sequential renography and renal function in Brown-Norway rats with congenital hydronephrosis

Animal models may be helpful to gain insight into the long-term functional outcome of the hydronephrotic kidney. Inbred Brown-Norway rats frequently have kidneys with a delayed urine outflow. In 26 male rats 99mtechnetium-diethylenetriaminepentaacetic acid (Tc-DTPA) furosemide renography was performed to assess the presence and degree of obstruction, and the contribution of each kidney to the total glomerular filtration rate. The total glomerular filtration rate was measured as the plasma clearance of 51chromium-ethylenediaminetetraacetic acid. The measurements were first done at the age of 3 months, and repeated at ages 6, 10 and 15 months. From the renography curve we derived an obstruction score ranging from 0 (minimum) to 10 (maximum) based on the time to peak, the 99mTc-DTPA accumulation at 15 minutes and the furosemide response. Kidneys were classified as normal, obstructed or equivocal. At the first renography 21 kidneys were normal, 8 were equivocal and 23 were obstructed. The total obstruction score of the next 3 renographies indicated that 29 units were normal, 14 were equivocal and 9 were obstructed. Two groups of rats with unilateral hydronephrosis (hydronephrotic kidney-1 and hydronephrotic kidney-2) were selected based on the total obstruction score of all 4 renographies. These groups were compared with rats with 2 normal kidneys. The hydronephrotic kidney-1 rats had an obstruction score indicating equivocal obstruction, while the obstruction score of the hydronephrotic kidney-2 rats indicated obstruction. During the 15 months of followup the presence of a unilateral hydronephrotic kidney with an obstruction score indicating obstruction did not affect the contribution of the hydronephrotic kidney to the total glomerular filtration rate, or the total glomerular filtration rate. We conclude that the obstruction score of a hydronephrotic kidney in rats may change considerably with time. In cases in which renography suggested the permanent presence of ureteral obstruction the glomerular filtration rate remained stable. Thus, renal functional criteria did not indicate obstruction. In Brown-Norway rats a hydronephrotic kidney is able to maintain a normal glomerular filtration rate during at least 50% of the normal lfie span.

The effect of protein intake on the lifelong changes in renal function of rats with a solitary kidney damaged at young age

Changes in renal function were followed lifelong in male rats with only 1 kidney either intact or damaged by ureteral obstruction or ischemia. After surgery the rats were given a low (12%) or a high (36%) protein diet. After a period with a stable glomerular filtration rate, which was longer on the low protein diet, there was a linear decline in rats with an intact single kidney. The rate of decline was highest on the high protein diet, resulting in a shorter survival time. A decrease in urine osmolality and an increase in protein excretion preceded the decrease in filtration rate, while it was followed by an increase in blood pressure. The glomerular filtration rate of the rats with a single damaged kidney initially recovered to 75 to 80% of that of rats with an intact single kidney on the same diet. There was a linear decrease in the glomerular filtration rate, with the highest rate of decrease on the high protein diet. The mean survival time was less than that of rats with a single intact kidney. Proteinuria preceded the decrease in filtration rate, while hypertension was observed later. We conclude that in rats with a solitary kidney renal failure eventually develops. A low protein diet postpones and attenuates this development but it does not prevent it.