Ureteral obstruction in the neonatal rat: Renal nerves modulate hemodynamic effects

In the neonate, chronic unilateral ureteral obstruction (UUO) reduces renal blood flow (RBF) of the ipsilateral kidney and increases RBF of the opposite kidney. To determine whether renal nerves mediate or modulate these responses complete left UUO in the neonatal rat was used as a model of severe obstructive uropathy, and was compared with sham-operated controls. At 24–28 days of age, animals underwent left or right mechanical renal denervation or left sham renal denervation. One week after denervation, animals were anesthetized and blood pressure and heart reate were measured. Cardiac output and RBF were determined by the radioactive microsphere technique. UUO increased blood pressure and heart rate, and decreased RBF in the obstructed kidney, regardless of denervation. While left UUO increased RBF to the intact opposite kidney in rats with left renal denervation, this was attenuated by right renal denervation. Thus, in the neonatal rat, UUO modulates systemic renal hemodynamics, possibly through activation of the renin-angiotensin system. While renal nerves do not mediate the vasoconstriction of the obstructed kidney, renal nerves modulate vascular tone of the kidney contralateral to UUO.     

Ureteral obstruction in the neonatal guinea pig: Interaction of sympathetic nerves and angiotensin

The contribution of sympathetic nerves to the hemodynamic effects of unilateral ureteral obstruction (UUO) was investigated in the neonatal guinea pig. The left ureter was partially constricted (or sham-operated) at birth, and sympathetic innervation was inhibited by guanethidine and compared with saline vehicle-treated animals. At 15–20 days of age, blood presure, cardiac output, total vascular resistance (TVR), renal blood flow, and renal vascular resistance (RVR) were determined before and after infusion of enalapril. UUO reduced cardiac output, increased TVR, and increased RVR of the ipsilateral kidney, whereas guanethidine treatment had no additional effects. Enalapril decreased RVR only in obstructed kidneys and not in intact opposite kidneys of animals with UUO. This was not affected by guanethidine administration. In contrast, enalapril decreased RVR only in guanethidine-treated (but not saline-treated) sham-operated guinea pigs. Therefore, UUO increases angiotensin-dependent vascular tone of the ipsilateral kidney independent of renal innervation. However, UUO decreases angiotensin-mediated vascular tone of the contralateral kidney, an effect unmasked by sympathectomy.     

Glomerulotubular disconnection in neonatal mice after relief of partial ureteral obstruction

Ureteropelvic junction obstruction is a common cause of congenital obstructive nephropathy. To study the pathogenesis of nephropathy, a variable-partial, complete or a sham unilateral ureteral obstruction (UUO) was produced in mice within 2 days of birth. The obstruction was released in some animals at 7 days and kidneys harvested at 7-42 days of age for histologic and morphometric study. Renal parenchymal growth was stunted by partial UUO with the impairment proportional to the duration and severity of obstruction. Proximal tubule apoptosis and glomerulotubular disconnection led to nephron loss. Relief of partial UUO arrested glomerulotubular disconnection, resolved tubule atrophy, and interstitial fibrosis with remodeling of the renal architecture. Relief of severe UUO did not result in recovery. Compensatory growth of the contralateral kidney depended on the severity of obstruction. Our studies indicate that relief of moderate UUO will minimize nephron loss. Application of this technique to mutant mice will help develop future therapies to enhance nephron recovery.     

Hair cell loss and regeneration after exposure to intense sound in neonatal chicks

Neonatal chicks (between 1 and 3 days of age) were exposed to an intense pure tone for 48 hours, then killed immediately after removal from the sound, or 14 days later. Nonexposed age-matched animals served as controls. The inner ear was removed and the auditory receptor organ (the basilar papilla) was prepared for evaluation by scanning electron microscopy. The site of injury on the papilla was described in terms of hair-cell loss and location. The ears with no recovery showed a discrete lesion area, within which there was complete disruption of the hair-cell field and a 35% loss in hair cells. After 14 days' recovery, no hair cell loss could be detected, though the lesion could still be recognized by the disorganization of hair cells in the previously injured area. These data demonstrate hair-cell restoration after severe acoustic injury from intense sound exposure in the neonatal ear.     

Ureteral obstruction due to fecal impaction in patient with colonic loop urinary diversion

An interesting case report of ureteral obstruction due to fecal impaction in a meningomyelocele patient with colon loop diversion is presented. This case is an important reminder that neurologic deficits in patients with meningomyelocele are not limited to the genitourinary system. Conservative management of our patient's colonic hypotonicity obviated surgical intervention and has been successful in preventing recurrence of ureteral obstruction.     

Relation of distal nephron changes to proximal tubular damage in uranyl acetate-induced acute renal failure in rats

AIMS: To elucidate the pathophysiological roles of the changes of distal nephron in uranyl acetate (UA)-induced acute renal failure (ARF), we investigated the relation of changes of constituent molecules in distal nephron to proximal tubular damage and repair in UA-treated rats. METHODS: ARF was induced in rats by intravenous injection of UA, and all rats received bromodeoxyuridine (BrdU) intraperitoneally 1 h before sacrifice. RESULTS: Proximal tubular damage with necrosis appeared as early as day 2, mainly in the outer stripe of outer medulla and reached a peak level at day 5. Slight cellular damage was evident in the distal nephron as early as day 3, reaching a peak level around day 9. Immunoreactive BrdU- or vimentin-positive regenerating proximal tubules (PT) appeared at day 2 and regenerating PT relining was almost completed by day 7. Immunostaining for EGF, which was constitutively expressed in the thick ascending limb (TAL) and distal convoluted tubule (DCT), diminished significantly as early as day 2, when PT regeneration became evident, and remained below normal levels until day 21. In contrast, slight immunoreactivity for EGF was observed in regenerated PT accompanying brush-border formation mainly after day 9, suggesting newly expressed EGF might contribute to PT maturation. Lectin staining or immunostaining for representative constituent molecules of the thin descending limb, TAL, DCT and collecting duct demonstrated marked and transient reduction after day 5. CONCLUSIONS: EGF was not associated with regenerating PT, but may be involved in the maturation of PT. Transient reduction in expression of constituent molecules of the distal nephron following the reduction in EGF could reflect dedifferentiation or phenotypic simplification during regenerative repair of PT in UA-induced ARF in rats.     

The L1 cell adhesion molecule is a potential biomarker of human distal nephron injury in acute tubular necrosis

The L1 cell adhesion molecule (CD171) is a multidomain membrane glycoprotein of the immunoglobulin superfamily. We evaluated its expression in human acute kidney injury and assessed its use as a tissue and urinary marker of acute tubular injury. Using immunohistochemical studies with antibodies to the extracellular or cytoplasmic domains, we compared L1 expression in normal kidneys in 24 biopsies taken from patients with acute tubular necrosis. L1 was found at the basolateral and the lateral membrane in all epithelial cells of the collecting duct in the normal kidney except for intercalated cells. In acute tubular necrosis, L1 lost its polarized distribution being found in both the basolateral and apical domains of the collecting duct. Further, it was induced in thick ascending limb and distal tubule cells. Apically expressed L1 found only when the cytoplasmic domain antibody was used in biopsy specimens of patients with acute tubular necrosis. The levels of urinary L1, normalized for creatinine, were significantly higher in all 24 patients with acute tubular necrosis compared to five patients with prerenal azotemia or to six patients with other causes of acute kidney injury. Our study shows that a soluble form of human L1 can be detected in the urine of patients with acute tubular necrosis and that this may be a marker of distal nephron injury.     

Antibody to transforming growth factor-beta ameliorates tubular apoptosis in unilateral ureteral obstruction

BACKGROUND: Unilateral ureteral obstruction (UUO) is characterized by progressive renal atrophy, renal interstitial fibrosis, an increase in renal transforming growth factor-beta (TGF-beta), and renal tubular apoptosis. The present study was undertaken to determine the effect of a monoclonal antibody to TGF-beta (1D11) in UUO. METHODS: Mechanical stretch was applied to tubular epithelial cells (NRK-52E) by a computer-assisted system. Three doses of 1D11 (either 0.5, 2, or 4 mg/rat) were administered to rats one day prior to UUO and every two days thereafter, and kidneys were harvested at day 13. Fibrosis was assessed by measuring tissue hydroxyproline and mRNA for collagen and fibronectin. Apoptosis was assessed with the terminal deoxy transferase uridine triphosphate nick end-labeling assay. TGF-beta levels were determined by bioassay. Western blot and immunostaining were used to identify proliferating cell nuclear antigen (PCNA), p53, bcl-2, and inducible nitric oxide synthase (iNOS). RESULTS: Stretch significantly induced apoptosis in NRK-52E cells, which was accompanied by an increased release of TGF-beta; 1D11 (10 microg/mL) totally inhibited stretch-induced apoptosis. Control obstructed kidney contained 20-fold higher TGF-beta as compared with its unobstructed kidney; 1D11 neutralized tissue TGF-beta of the obstructed kidney. Control obstructed kidney exhibited significantly more fibrosis and tubular apoptosis than its unobstructed counterpart, which was blunted by 1D11. In contrast, 1D11 significantly increased tubular proliferation. p53 immunostaining was localized to renal tubular nuclei of control obstructed kidney and was diminished by 1D11. In contrast, bcl-2 was up-regulated in the 1D11-treated obstructed kidney. Total NOS activity and iNOS activity of the obstructed kidney were increased by 1D11 treatment. CONCLUSION: The present study strongly suggests that an antibody to TGF-beta is a promising agent to prevent renal tubular fibrosis and apoptosis in UUO.     

Renal proximal tubular cells acquire resistance to cell death stimuli in mice with hereditary tyrosinemia type 1

BACKGROUND: Hereditary tyrosinemia type 1 (HT1), which is associated with severe liver and kidney damage, is caused by deficiency of fumarylacetoacetate hydrolase (FAH), the last enzyme of the tyrosine breakdown cascade. HT1-associated liver and kidney failure can be prevented by blocking an enzyme upstream of FAH in the tyrosine breakdown pathway with 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC). FAH knockout mice develop the HT1 phenotype when NTBC treatment is discontinued. METHODS: The occurrence of cell death was investigated in kidneys of Fah(-/-) mice on and off NTBC either unchallenged or injected with 800 mg/kg of homogentisic acid (HGA), an intermediate of tyrosine breakdown. RESULTS: No cell death could be detected in kidneys of Fah(-/-) mice on NTBC. A slight increase of cleaved caspase-3 was the only apoptosis-related feature that could be detected in kidneys of Fah(-/-) mice off NTBC. Challenge of Fah(-/-) mice on NTBC with HGA led to massive death of renal proximal tubular cells, with positive terminal deoxynucleotidyl transferase-mediated deoxyuridine diphosphate (dUDP) nick-end labeling (TUNEL) and DNA fragmentation assays, but hardly any cleavage of caspase-9 and caspase-3. Fah(-/-) mice off NTBC acquired resistance to HGA-induced renal cell death and the kidneys exhibited relatively few features of apoptosis upon challenge with HGA, with a small increase in expression of cleaved caspase-9 and caspase-3. CONCLUSION: Kidneys of adult Fah(-/-) mice, withdrawn from NTBC for 15 days, reveal limited characteristics of apoptosis, and have acquired resistance to a caspase-9- and caspase-3-independent form of cell death provoked by HGA.     

Bcl-2-modifying factor induces renal proximal tubular cell apoptosis in diabetic mice

This study investigated the mechanisms underlying tubular apoptosis in diabetes by identifying proapoptotic genes that are differentially upregulated by reactive oxygen species in renal proximal tubular cells (RPTCs) in models of diabetes. Total RNAs isolated from renal proximal tubules (RPTs) of 20-week-old heterozygous db/m+, db/db, and db/db catalase (CAT)-transgenic (Tg) mice were used for DNA chip microarray analysis. Real-time quantitative PCR assays, immunohistochemistry, and mice rendered diabetic with streptozotocin were used to validate the proapoptotic gene expression in RPTs. Cultured rat RPTCs were used to confirm the apoptotic activity and regulation of proapoptotic gene expression. Additionally, studies in kidney tissues from patients with and without diabetes were used to confirm enhanced proapoptotic gene expression in RPTs. Bcl-2-modifying factor (Bmf) was differentially upregulated (P<0.01) in RPTs of db/db mice compared with db/m+ and db/db CAT-Tg mice and in RPTs of streptozotocin-induced diabetic mice in which insulin reversed this finding. In vitro, Bmf cDNA overexpression in rat RPTCs coimmunoprecipated with Bcl-2, enhanced caspase-3 activity, and promoted apoptosis. High glucose (25 mmol/L) induced Bmf mRNA expression in RPTCs, whereas rotenone, catalase, diphenylene iodinium, and apocynin decreased it. Knockdown of Bmf with small interfering RNA reduced high glucose-induced apoptosis in RPTCs. More important, enhanced Bmf expression was detected in RPTs of kidneys from patients with diabetes. These data demonstrate differential upregulation of Bmf in diabetic RPTs and suggest a potential role for Bmf in regulating RPTC apoptosis and tubular atrophy in diabetes.     

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.     

Ureteral obstruction secondary to a patent umbilical artery in a 79-year-old man: a case report

Aberrant blood vessels are a rare cause of ureteral obstruction, with 9 cases having been reported, mostly in children. A 79-year-old man presented with left flank pain. At operation a patent left umbilical artery was partially obstructing the distal left ureter. Partial ureterectomy and ureteroureterostomy provided relief of symptoms. Aberrant blood vessels should be considered in the differential diagnosis of extrinsic distal ureteral obstruction.     

Renal hemodynamic and tubular responses to salt in women using oral contraceptives

BACKGROUND: The use of oral contraceptives is associated with an increased risk of developing hypertension but the mechanisms of this hypertensive effect are not completely defined. The purpose of the present study was to assess prospectively the systemic and renal hemodynamic and tubular responses to salt in women taking oral contraceptives. METHODS: Twenty seven young healthy normotensive women taking oral contraceptives containing monophasic combination of 30 microg ethynilestradiol and 150 microg desogestrel for>6 months were enrolled. All women were assigned at random to receive a low (40 mmol/day) or a high (250 mmol/day) sodium diet for 1 week on two consecutive menstrual cycles during the active oral contraceptive phase. At the end of each diet period, 24-hour ambulatory blood pressure, renal hemodynamics, sodium handling, and hormonal profile were measured. RESULTS: The blood pressure response to salt on oral contraceptives was characterized by a salt-resistant pattern with a normal circadian rhythm. Salt loading results in an increase in glomerular filtration rate (GFR) (P < 0.05 vs. low salt), with no change in the renal plasma flow, thus leading to an increase in the filtration fraction (P < 0.05). At the tubular level, women on oral contraceptives responded to a low salt intake with a marked increased in proximal sodium conservation (P < 0.01 vs. high salt) and with an almost complete reabsorption of sodium reaching the distal tubule. After sodium loading, both the proximal and the distal reabsorption of sodium decreased significantly (P < 0.01). CONCLUSION: The use of oral contraceptives is not associated with an increased blood pressure response to salt in young normotensive women. However, oral contraceptives affect the renal hemodynamic response to salt, a high salt intake leading to an increase in GFR and filtration fraction. This effect is possibly mediated by the estrogen-induced activation of the renin-angiotensin system. Oral contraceptives also appear to increase the tubular responsiveness to changes in sodium intake. Taken together, these data point out evidence that synthetic sex steroids have a significant impact on renal function in women. The renal effects of oral contraceptives should be taken into account when managing young women with renal diseases.     

Paraplegic mice are leading to new advances in spinal cord injury research

STUDY DESIGN: Experimental laboratory investigations with paraplegic mouse models. OBJECTIVES: To review the most recent advances in the field of spinal cord injury research; immune system response, regeneration, and functional recovery.Settings:Laval University and Laval University Medical Center, Quebec, Canada. METHODS: Assessment of regenerative processes and locomotor function recovery induced by a variety of treatments and approaches in wild-type and genetically engineered mice with complete or incomplete lesions of the spinal cord. RESULTS: Recent studies have reported a number of significant observations providing additional insight into the role and mechanism of regeneration, immune system response, and functional recovery after spinal cord injury (SCI) using incomplete paraplegic mice with Nogo-A, NgR, EphA4, GFAP/vimentime, LIF, or Fas gene knock-out. A novel antibody called CXCL10 was also recently found to increase tissue sparing and angiogenesis after SCI. In an attempt to explore the possibilities of reactivating spared neurons below the injury level, researchers have found that pharmacological activation of specific subtypes of serotonin receptors (eg, 5-HT1A/2A/7) can sustain the production of basic locomotor-like movements in complete paraplegic mice. CONCLUSION: The growing availability of genetically engineered and mutant mouse strains along with molecular biology tools has led scientists to increasingly use murine models in SCI research. These new tools and models may assist scientists in understanding further the complex pathological consequences of SCI.