The effect of obstruction on the developing bladder

The importance of animal specificity in animal experimentation, part II: Physiological challenges and opportunities in relation to pediatric urology

When performing animal experimentation in Pediatric Urology studies, it is important to be aware of physiological differences between species and to understand when relevant disease models are available. Diseased animal models may be more relevant in many cases, rather than performing studies in healthy and normally developed animals. For example, they may be more appropriate for the study of congenital malformations, to investigate the secondary effects of prenatal urinary obstruction, to study the effect of prenatal exposure to endogenous or exogenous factors which may lead to disease, or in testing bioengineered structures. In this short educational article, we aim to describe some disease models that have been used to simulate human pathologies and how, if properly designed, these studies can lead to important new knowledge for human translation. In addition, we also highlight the importance of formulating a research question(s) before deciding on the animal experimental model and species to choose.

Bladder function in children with posterior urethral valves: impact of antenatal versus postnatal diagnosis

Purpose:

Posterior urethral valves (PUVs) are the most common cause of congenital bladder obstruction in boys. Our aim was to assess the impact of early diagnosis and fulguration of PUVs on bladder function and compare their functional and urodynamic outcome with children who underwent delayed intervention.

Materials and Methods:

We retrospectively evaluated 153 patients who underwent primary valve ablation from two tertiary hospitals between 2001 and 2018. Patients have been divided into 2 groups, group 1 included 69 patients who were detected antenatally and underwent early fulguration of PUVs while group 2 included 84 children presented postnatally and underwent delayed valve ablation. The recorded data throughout follow-up in renal function tests, urodynamics and changes in the upper urinary tracts were evaluated and compared.

Results:

Median age at time of valve ablation was 10 days in group 1 and 7 months in group 2. The median follow-up period was 6.5 and 7 years in group 1 and 2, respectively. Chronic kidney disease (CKD) developed in 15 (22%) boys in group 1 while in group 2 it was observed in 31 (37%), p=0.04. While Q-max, mean bladder capacity and post-void residual (PVR) volumes were comparable in both groups, percent PVR was significantly higher in group 2 (3.27 vs. 1.44, p=0.002). Detrusor overactivity was slightly different in both groups (p = 0.07).

Conclusions:

Compared to delayed intervention, primary ablation of PUVs during the early neonatal life possibly provides the optimum chance to have optimum renal function without impact on bladder function.

Antenatal biological models in the characterization and research of congenital lower urinary tract disorders

Congenital lower urinary tract disorders are a family of diseases affecting both urinary storage and voiding as well as upstream kidney function. Current treatments include surgical reconstruction but many children still fail to achieve urethral continence or progress to chronic kidney disease. New therapies can only be achieved through undertaking research studies to enhance our understanding of congenital lower urinary tract disorders. Animal models form a critical component of this research, a corner of the triangle composed of human in-vitro studies and clinical research. We describe the current animal models for two rare congenital bladder disorders, posterior urethral valves (PUV) and bladder exstrophy (BE). We highlight important areas for researchers to consider when deciding which animal model to use to address particular research questions and outline the strengths and weaknesses of current models available for PUV and BE. Finally, we present ideas for refining animal models for PUV and BE in the future to stimulate future researchers and help them formulate their thinking when working in this field.

Contractile function of detrusor smooth muscle from children with posterior urethral valves - The role of fibrosis

INTRODUCTION

Posterior urethral valves (PUV) is the most common cause of congenital bladder outflow obstruction with persistent lower urinary tract and renal morbidities. There is a spectrum of functional bladder disorders ranging from hypertonia to bladder underactivity, but the aetiology of these clinical conditions remains unclear.

AIMS AND OBJECTIVES

We tested the hypothesis that replacement of detrusor muscle with non-muscle cells and excessive deposition of connective tissue is an important factor in bladder dysfunction with PUV. We used isolated detrusor samples from children with PUV and undergoing primary or secondary procedures in comparison to age-matched data from children with functionally normal bladders. In vitro contractile properties, as well as passive stiffness, were measured and matched to histological assessment of muscle and connective tissue. We examined if a major pathway for fibrosis was altered in PUV tissue samples.

METHODS

Isometric contractions were measured in vitro in response to either stimulation of motor nerves to detrusor or exposure to cholinergic and purinergic receptor agonists. Passive mechanical stiffness was measured by rapid stretching of the tissue and recording changes to muscle tension. Histology measured the relative amounts of detrusor muscle and connective tissue. Multiplex quantitative immunofluorescence labelling using five epitope markers was designed to determine cellular pathways, in particular the Wnt-signalling pathway, responsible for any changes to excessive deposition of connective tissue.

RESULTS AND DISCUSSION

PUV tissue showed equally reduced contractile function to efferent nerve stimulation or exposure to contractile agonists. Passive muscle stiffness was increased in PUV tissue samples. The smooth muscle:connective tissue ratio was also diminished and mirrored the reduction of contractile function and the increase of passive stiffness. Immunofluorescence labelling showed in PUV samples increased expression of the matrix metalloproteinase, MMP-7; as well as cyclin-D1 expression suggesting cellular remodelling. However, elements of a fibrosis pathway associated with Wnt-signalling were either reduced (β-catenin) or unchanged (c-Myc). The accumulation of extracellular matrix, containing collagen, will contribute to the reduced contractile performance of the bladder wall. It will also increase tissue stiffness that in vivo would lead to reduced filling compliance.

CONCLUSIONS

Replacement of smooth muscle with fibrosis is a major contributory factor in contractile dysfunction in the hypertonic PUV bladder. This suggests that a potential strategy to restore normal contractile and filling properties is development of the effective use of antifibrotic agents.

Long-term consequences of posterior urethral valves

Posterior urethral valves (PUV) are the most common congenital cause of bladder outlet obstruction in infancy, and it is the effect of this obstruction on the bladder and the kidneys that will decide a patient's prognosis. With the improvements in diagnosis and treatments, what was previously a poor prognosis for boys with PUV has improved, and more patients will encounter the long-term sequelae of PUV during puberty and adulthood. In these patients the long-term prognosis in terms of renal and bladder function and fertility, as well as the risk of malignancy in those whose bladders were augmented with gastrointestinal segments, is still a matter of great concern and all of these topics will be discussed in this article.

The bladder extracellular matrix. Part I: architecture, development and disease

From the earliest studies with epithelial cells implanted into detrusor muscle to later experiments on smooth muscle in defined collagen gels, cell niche and extracellular matrix (ECM) have been clearly shown to orchestrate cellular behavior and fate whether quiescent, migratory, or proliferative. Normal matrix can revert transformed cells to quiescence, and damaged matrix can trigger malignancy or dedifferentiation. ECM influence in disease, development, healing and regeneration has been demonstrated in many other fields of study, but a thorough examination of the roles of ECM in bladder cell activity has not yet been undertaken. Structural ECM proteins, in concert with adhesive proteins, provide crucial structural support to the bladder. Both structural and nonstructural components of the bladder have major effects on smooth muscle function, through effects on matrix rigidity and signaling through ECM receptors. While many ECM components and receptors identified in the bladder have specific known functions in the vascular smooth musculature, their function in the bladder is often less well defined. In cancer and obstructive disease, the ECM has a critical role in pathogenesis. The challenge in these settings will be to find therapies that prevent hyperproliferation and encourage proper differentiation, through an understanding of matrix effects on cell biology and susceptibility to therapeutics.

Prenatal resolution of megacystis possibly caused by spontaneous rupture of posterior urethral valves

We report herein a case of resolution of severe megacystis, possibly caused by spontaneous rupture of posterior urethral valves during follow-up on a prenatal ultrasound. A 32-year-old woman presented at gestational week 15 for evaluation of fetal bladder enlargement. Prenatal ultrasonography revealed megacystis and posterior urethral dilatation. The longitudinal diameter of the bladder was 25 mm. Megacystis spontaneously resolved at gestational week 16. No association with urinary ascites was observed, and amniotic fluid volume remained normal throughout gestation. A boy was delivered vaginally at week 37. Apgar scores were 8 at 1 minute and 9 at 5 minutes. The neonate voided smoothly. Ultrasonography revealed a thickened bladder wall and normal kidneys and upper urinary tracts. Voiding cystourethrography showed dilatation of the posterior urethra but confirmed normal bladder capacity with smooth voiding and no vesicoureteral reflux. On day 57, remnant valves were incised. Postoperatively, filling cystometry showed a compliant bladder with no involuntary phasic contraction. At 7 months follow-up, the infant was asymptomatic, and ultrasonography showed some improvement of bladder wall thickness. Resolution of megacystis in utero appears to have resulted from spontaneous rupture of the posterior urethral valves. To the best of our knowledge, no similar cases have been previously reported.

Effects of doxycycline on voiding behaviour of rats with bladder outlet obstruction

OBJECTIVE

To examine the voiding behaviour changes in rats with bladder outlet obstruction (BOO) while inhibiting matrix metalloproteinase (MMP) activity with doxycycline, as increased MMP activity may be involved in obstruction-induced bladder hypertrophy.

MATERIALS AND METHODS

Female Sprague-Dawley were divided into eight groups (three rats in each group): normal control (NC) +/- doxycycline, 3 weeks partial BOO (3WPBOO) +/- doxycycline, 6 weeks PBOO +/- doxycycline, and 3 weeks PBOO followed by 3 weeks de-obstruction (3WOD) +/- doxycycline. All rats received the same food and water and were on the same 12 h dark/light cycle housed in metabolic cages. Treatment groups were given doxycycline 15 mg/kg/day subcutaneously twice daily. The voiding variables measured were average voided volume (AV V) and voiding frequency (VF) in 24 h. After completion of the voiding behaviour studies, the rats were killed and their bladders were excised and weighed.

RESULTS

The AV Vs were significantly increased (P < 0.05) in all study groups compared with the NC group except for the 3WPBOO-doxycycline and 3WOD-doxycycline groups. The VF was significantly increased (P < 0.05) only in the 3WOD-doxycycline group. The bladder weights were significantly increased after PBOO in all the study groups (P < 0.05), except for the 3WOD group.

CONCLUSION

These data show that MMP inhibition may affect voiding behaviour during the response to BOO or its relief. This is the first clinical demonstration that interfering with a principal target of bladder muscle wall remodelling may have a direct effect on bladder function.

Vesicostomy vs primary ablation for posterior urethral valves: always a difference in outcome?

OBJECTIVE

A vesicostomy is believed to have a detrimental effect in boys with posterior urethral valves compared to primary valve ablation. We compared the outcomes of boys managed by initial vesicostomy with those undergoing primary fulguration.

MATERIALS AND METHODS

The outcomes of 54 boys (23 vesicostomy, 31 primary valve fulguration) over 1 year of age who had not undergone renal transplant were considered. Outcome parameters identified were ultrasound findings, continence status, glomerular filtration rate (GFR) and 1-year creatinine. Dryness was defined as completely dry both day and night with no need to wear pads. Results are presented with 95% confidence intervals.

RESULTS

Ultrasound examinations were normal in 9/19 (47.4%) of the vesicostomy group and 11/24 (45.8%) of the fulguration group. Graded ultrasound results were not significantly different (p=0.24). The vesicostomy patients were more often dry (79% vs 64%, p=0.43). The vesicostomy group had on average higher GFR (95.26 vs 85.79) and lower 1-year creatinine (49.58 vs 52.46) values. After accounting for age differences between groups, there was no significant difference in the GFR and 1-year creatinine values (p=0.16 and p=0.87, respectively).

CONCLUSIONS

There was a tendency for the major outcomes to be more favourable in the vesicostomy group. Although trends were non-significant, confidence intervals were wide and potential differences of clinical importance could not be discounted.

Cyclic Pressure Stimulates DNA Synthesis through the PI3K/Akt Signaling Pathway in Rat Bladder Smooth Muscle Cells

Previous studies demonstrated that the bladder exhibited severe tissue remodeling following spinal cord injury. In such pathological bladders, uninhibited non-voiding contractions subject bladder cells to cyclic oscillations of intravesical pressure. We hypothesize that cyclic pressure is a potential trigger for tissue remodeling in overactive bladder. Using a custom-made setup, rat bladder smooth muscle cells (SMC) in vitro were exposed to cyclic hydrostatic pressure (40 cm H2O) at either 0.1 Hz or 0.02 Hz frequency for up to 24 h. When compared to static control and cells exposed to 0.02-Hz cyclic pressure, SMC exposed to 0.1-Hz cyclic pressure contained significantly (p < 0.05) higher amounts of DNA. We confirmed that the increase in DNA was due to increased cell proliferation, indicated by increased BrdU incorporation, but not due to decreased apoptosis rates in response to cyclic pressure. In addition, significant (p < 0.05) elevation of Akt phosphorylation in SMC following exposure to cyclic pressure and lack of pressure-induced SMC hyperplasia in the presence of PI3K inhibitors, wortmannin and LY294002, indicated the involvement of the PI3K/Akt pathway in the proliferative response of SMC to cyclic pressure. We concluded that chronic exposure to intravesical pressure oscillation may be a potential trigger for bladder tissue remodeling.

Ca 2+ Regulation in Detrusor Smooth Muscle From Ovine Fetal Bladder After In Utero Bladder Outflow Obstruction

PURPOSE

We characterized intracellular Ca(2+) regulation in fetal bladders following outflow obstruction by examining the Ca(2+) response to agonists in smooth muscle cells.

MATERIALS AND METHODS

Severe bladder outflow obstruction was induced in male fetal sheep by placing a urethral ring and urachal ligation midway through gestation at 75 days. Fetuses were examined 30 days after surgery. Intracellular Ca(2+) in single smooth muscle cells isolated from the bladder wall was measured with epifluorescence microscopy using fura-2(AM) during exposure to agonists, such as carbachol and adenosine triphosphate, and to other activators, such as caffeine and KCl.

RESULTS

Detrusor smooth muscle cells from obstructed bladders had resting intracellular Ca(2+) similar to that in sham operated controls. The maximal response to carbachol was decreased following obstruction (p <0.05). Construction of dose-response curves also demonstrated higher EC(50) (p <0.05). However, these changes were not mirrored by caffeine evoked Ca(2+) release, which was not significantly different between the obstruction group and sham operated controls. Kinetic analysis of carbachol transients further revealed an attenuated maximal rate of increase in obstructed bladders (p <0.01). The magnitude of intracellular Ca(2+) to purinergic neurotransmitter adenosine triphosphate was also found to be smaller in cells from obstructed bladders (p <0.05), although transmembrane influx by high K depolarization was not significantly affected.

CONCLUSIONS

Muscarinic and purinergic pathways were down-regulated in fetal detrusor muscle following outflow obstruction. These major functional receptors appeared to be more susceptible to obstruction than other Ca(2+) regulators. Their impairment may contribute to the compromised contractile function seen in in utero bladder outflow obstruction.

Structural and functional characterization of bladder smooth muscle in fetal rats with retinoic acid-induced myelomeningocele

Myelomeningocele (MMC) is the most common cause of neurogenic bladder dysfunction (NBD). We recently developed a novel retinoic acid (RA)-induced MMC model in fetal rats. The objective of this study was to use this model to assess functional and structural characteristics of the detrusor muscle in MMC-associated NBD. Time-dated pregnant Sprague-Dawley rats were gavage fed 60 mg/kg RA dissolved in olive oil or olive oil alone [embryonic day 10 ( E10)]. Bladder specimens from olive oil-exposed fetuses (OIL; n = 71), MMC ( n = 79), and RA-exposed-no MMC (RA, n = 62) were randomly assigned for functional and histopathological evaluation and protein analysis. Contractility responses to field and agonist-mediated stimulation (KCl and bethanecol) were analyzed. The expression patterns of α-smooth muscle actin, myosin, desmin, vimentin, and collagen III and I were analyzed by immunohistochemistry and Western blotting. Spatial and temporal distribution of nerve fibers within the detrusor muscle was monitored by neurotubulin-β-III throughout gestation. Neither OIL, MMC, nor RA detrusor responded to field stimulation. MMC bladder strips showed a significant decrease in contractility after KCl and bethanechol stimulation compared with OIL and RA bladders. Bladder detrusor morphology and expression patterns of smooth muscle markers were similar between groups. Detrusor muscles in OIL and RA fetuses were densely innervated, possessing abundant intramural ganglia and nerve trunks that branch to supply smooth muscle bundles. In MMC bladders, neurotubulin-β-III-positive nerve fibers were markedly decreased with advancing gestational age and were almost completely absent at term ( E22). We conclude that the biomechanical properties of fetal rat MMC bladders are analogous to that seen in humans with MMC-associated NBD. Decreased nerve density indicates loss of peripheral neural innervation throughout gestation. The early observation of decreased innervation and decreased contractility in the absence of morphologic abnormalities in muscle structure or extracellular matrix supports a pathophysiological hypothesis that denervation is the primary insult preceding the observed alterations in bladder muscle structure and function.

Pressure-limited vesico-amniotic shunt tube for fetal obstructive uropathy

INTRODUCTION

In utero shunting (vesico-amniotic shunt) of obstructive uropathy in fetal lambs produces a shrunken, noncompliant bladder. We hypothesized that using a ventriculo-peritoneal shunt for the vesico-amniotic shunt may preserve the filling/emptying cycle and thus normal bladder development.

MATERIALS AND METHODS

We created obstructive uropathy in 60-day gestation fetal lambs, ligating the urethra and urachus. Vesico-amniotic shunting was performed 21 days later using the valve end of a ventriculo-peritoneal shunt (valve shunt) or silastic tubing (nonvalve shunt). They were delivered at term (145 days), and the bladder volume was measured and compared to normal term fetuses. The lambs were sacrificed, and the kidneys and bladder removed for histology.

RESULTS

Twenty-seven lambs were shunted. Of 14 valve shunts, 8 were effective. Of 13 nonvalve shunts, 11 were effective. The mean bladder volume was 57 +/- 41 mL with a valve shunt and 8.8 +/- 4.7 mL with a nonvalve shunt (P < .05) (normal term lambs, 65 +/- 18 mL, n = 5). Histology of the shunted bladders showed increased fibrosis in the submucosal and muscle layers. This was less obvious in lambs with a valve shunt.

CONCLUSION

A pressure controlled shunt for fetal obstructive uropathy improves bladder volume but does not prevent bladder wall fibrosis.

Early bladder wall changes after creation of obstructive uropathy in the fetal lamb

Vesico-amniotic shunting of obstructive uropathy in fetal lambs produced a thick-walled, poorly compliant bladder. We report the early histological changes in the obstructed bladder wall. We created an obstructive uropathy in fetal lambs at 60 days gestation by ligating the urethra and urachus. Vesicostomy or vesico-amniotic shunt tube insertion and biopsy of the bladder wall were performed 21 days later. The fetuses were delivered at term (145 days) and the kidneys and bladder sampled for histology. Colloidal iron (Col Fe), and alpha-smooth muscle actin (alpha-SMA) immunohistochemical stains were used for these samples. Seventeen fetuses were shunted with 15 biopsies taken at that time. Six (shunt failure or missed urachal ligation) were excluded. All biopsies taken at shunting had positive Col Fe and alpha-SMA. Term lambs had mild multicystic dysplastic kidney (MCDK) in five, severe MCDK in two, and hydronephrosis in four. All bladders had small volume and were severely fibrotic. Fetal shunt operations 3 weeks after the creation of obstructive uropathy provided partial preservation of renal histology but did not preserve normal bladder histology. We suggest that the high hyaluronic acid synthesis activity or hyperplasia of the myofibroblasts in the dilated fetal bladder wall at the time of shunting results in irreversible damage to the developing bladder muscle and fibrosis.

Experimental short-term fetal bladder outflow obstruction: I. Morphology and cell biology associated with urinary flow impairment

PURPOSE

In fetal sheep, combined urethral and urachal obstruction initiated at 75 days' gestation and maintained for 30 days led to dysmorphic bladders, similar to those found in humans with prune belly syndrome, and uniformly disrupted kidney development. We aimed to create a less severe model of fetal bladder outlet obstruction, more closely resembling infants with posterior urethral valves, and additionally to further our understanding on the role of the urachus. We hypothesized that milder morphological renal tract changes would occur after shorter term experimental obstruction.

MATERIALS AND METHODS

Male fetal lambs were assigned to urachal and urethral ligation, urachal ligation only or sham operations. Analyses were performed after 9 days.

RESULTS

Concurrent urachal and urethral obstruction resulted in increased bladder weight, and protein and DNA content. Detrusor smooth muscle was well maintained, as assessed by light and electron microscopy, although urothelia showed basal apoptosis. Bladder obstruction led to hydronephrosis but failed to produce significant perturbations in urine osmolality. The nephrogenic cortex was either well preserved or was replaced by glomerular cysts; the latter group tended to have heavier bladders. Urachal obstruction alone produced similar changes suggesting that the male sheep fetal urethra is a high-resistance conduit in mid-gestation.

CONCLUSIONS

Concurrent urachal and urethral obstruction, or urachal obstruction alone, initiated in mid-gestation and maintained for 9 days leads to bladder overgrowth but preserved renal tubular function. In future, it will be interesting to determine whether bladder decompression around this stage leads to reversal of bladder overgrowth and/or ameliorates severe renal tract damage described after longer term fetal bladder outflow obstruction.

Experimental short-term partial fetal bladder outflow obstruction: II. Compliance and contractility associated with urinary flow impairment

PURPOSE

Posterior urethral valves (PUV) is the commonest cause of congenital bladder outlet obstruction. Despite valve ablation in the neonatal period, up to 70% of patients develop renal failure by their teenage years, and progressive bladder dysfunction. This study forms part of a continuing project examining the relationship between severity and duration of obstruction and urinary tract dysfunction. Here is the assessed result of short-term (9-day) obstruction.

MATERIALS AND METHODS

Fourteen male fetal lambs at 75 days' gestation were assigned to one of three groups: urachal ligation, urachal ligation with partial urethral obstruction, sham-operated controls. Pregnancy proceeded for 9 days. At autopsy, filling cystometry was performed with the urinary tract in situ and the bladder harvested for nerve counts using PGP 9.5 immunohistochemistry, or in vitro measurement of contractile function.

RESULTS

Obstruction was associated with an increase in bladder:fetal weight ratio. Compliance was variable in the obstructed bladders, but the calculated wall stress per unit strain was either similar or less than controls. Nerve-mediated or agonist-induced contraction magnitude in tissue from obstructed bladders and nerve counts did not differ from controls.

CONCLUSIONS

Nine days of outflow obstruction at mid-gestation generated a bladder of increased weight but without evidence of contractile failure. An increase in bladder compliance as a function of bladder growth was observed even at this stage, and represents one of the initial responses to outflow tract obstruction.

Collagen prolyl 4-hydroxylase is up-regulated in an acute bladder outlet obstruction

OBJECTIVE

Compliance is primarily related to extracellular matrix deposition, and prolyl 4-hydroxylase (P4Hs) plays a critical role in the synthesis of the matrix. To study the alteration of P4Hs, under the influence of variable hydrostatic pressure, a novel pressure device was used to expose human bladder smooth muscle cells (HBSMC) and fibroblasts (HBF) to pressures in the physiologic range. We then studied acute obstructed porcine bladder tissues to see if changes can also be seen after in-vitro obstruction.

MATERIALS AND METHODS

HBSMC and HBF were exposed to pressures at 0, 20 and 40 cmH(2)O for up to 72 h. In-vivo studies were carried out next, using six normal (control) and five obstructed porcine bladders. Pigs were exposed to a consistent hydrostatic pressure of < or =20 cm for 24 h after ligation of the urethra. We used 2-DE to compare protein profiling of HBSMC under normal and increased pressures. Other analyses were used to detect molecular alteration and altered expression of mRNA for P4Hs.

RESULTS

We identified 437 proteins from 476 spots (91.8%) obtained from HBSMC that were differentially expressed under normal and increased pressures. Under increased pressure, 48 unique proteins were significantly increased or decreased, and a prominent protein regulating extracellular matrix synthesis highly correlated with P4Hs. The exposure of both HBSMC and HBF to a sustained hydrostatic pressure resulted in the increased expression of P4Hs in a time- and pressure-dependent manner. In vivo, P4Hs expression was also significantly increased in the obstructed group.

CONCLUSIONS

P4Hs is up-regulated, in the human bladder, time and pressure dependently. The alteration of P4Hs over a short period may significantly influence the synthesis of extracellular matrix in vivo and lead to decreased compliance. Our results also support the concept that bladder outlet obstruction, with resultant pressures of 40 cmH(2)O or less, results in molecular changes consistent with decreased compliance.

Management of the valve–bladder syndrome and congenital bladder obstruction: the role of nocturnal bladder drainage

Valve-bladder syndrome often develops after the resolution of posterior urethral valves, but is also found after the resolution of congenital bladder obstruction. The features of this syndrome include the persistent dilation of the upper urinary tracts, a thick-walled, noncompliant urinary bladder, urinary incontinence, and polyuria secondary to nephrogenic diabetes insipidus. Nocturnal bladder management, which involves timed emptying of the bladder or continuous drainage, has been recommended in conjunction with diurnal timed voiding therapy as an adjunct to the treatment of valve-bladder syndrome. This treatment is derived from the hypothesis that valve-bladder syndrome is caused by congenital obstruction, and that the resultant changes in detrusor muscle are associated with a persistent bladder dysfunction characterized by chronic overdistention of the urinary bladder. Such overdistention is exacerbated by polyuria, and can be a cause of secondary hydronephrosis. Bladder dysfunction and overdistention is usually treated during waking time, but occasionally this is not effective on its own, and nocturnal therapy is used as well. To date, there are a few sets of data that suggest overnight bladder drainage can bring about profound improvements in the degree of upper-tract hydronephrosis, renal function, or bladder function. Nocturnal bladder drainage seems, in these initial reports, to be a simple and safe therapeutic maneuver. This review discusses the etiology of valve-bladder syndrome and examines each of the studies which have investigated nocturnal bladder drainage in its treatment.

Ca2+ regulation in detrusor smooth muscle from developing fetal sheep bladders

Sheep fetus is a useful model to study in utero bladder outflow obstruction but little is known about cell physiology of fetal bladders. To remedy this defect we have characterised intracellular Ca(2+) regulation in fetal sheep myocytes of different developmental ages. Fetal detrusor myocytes had a similar resting [Ca(2+)](i) to adult cells and exhibited transient [Ca(2+)](i) increases in response to carbachol, ATP, high-K, caffeine and low-Na. The carbachol transients were abolished by atropine and caffeine; the ATP response was blocked by alpha,beta-methylene ATP; high-K-evoked [Ca(2+)](i) rises were antagonised by verapamil. The maximal responses to carbachol, high-K, caffeine and low-Na in fetal cells were similar to those of adult counterparts, whilst the ATP response was smaller (p < 0.05). These variables were largely similar between the three gestational groups with the exception of ATP-induced response between early fetal and adult bladders (p < 0.05). Dose-response curves to carbachol demonstrated an increase of potency between mid-gestation and early adulthood (p < 0.05). These data show that muscarinic receptors coupled to intracellular Ca(2+) release, P2X receptor-linked Ca(2+) entry, depolarisation-induced Ca(2+) rise via L-type Ca(2+) channels, Na(+)/Ca(2+) exchange and functional intracellular Ca(2+) stores are all operational in fetal bladder myocytes. Whilst most of Ca(2+) regulators are substantially developed and occur at an early fetal age, a further functional maturation for cholinergic sensitivity and purinergic efficacy continues throughout to adulthood.

Contractile properties of the developing fetal sheep bladder

AIM

To characterise the developmental changes to the normal bladder by examining the in vitro contractile properties of the fetal sheep detrusor smooth muscle bladder at different gestational ages.

METHODS

Three groups of normally developing fetal sheep bladders were investigated: (1) 65-70 days gestation (2nd trimester); (2) 105-110 days (3rd trimester); (3) 135-140 days (term). Isometric contractions in isolated detrusor strips were measured during either electrical field stimulation (EFS) or exposure to agonists: carbachol, alpha-beta methylene-ATP (ABMA) and KCl.

RESULTS

There was a significant increase of absolute force elicited by EFS with fetal age. Contractures elicited by carbachol, ABMA and KCl increased between Groups 1 and 2, but not thereafter. The proportional increase of contractions elicited by carbachol and ABMA was also greater between Groups 1 and 2, than for EFS and KCl.

CONCLUSIONS

Fetal development between 65 and 140 days in the sheep is associated with increased contractile activation. The data are consistent with an increase of muscle development in the earlier stages (65-110 days). In the later stage (110-140 days) muscle development is complete but functional innervation of the tissue continues.

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.

Characterization of Neuropathic Bladder Smooth Muscle Cells in Culture

PURPOSE

Clinically bladder cells used in tissue engineering techniques will come from neuropathic bladders and not normal bladders. We determined if neuropathic bladder smooth muscle (SM) cells (SMCs) retain functional differences when cultured in vitro.

MATERIALS AND METHODS

Primary cultures of SMCs were established from patients with a neuropathic bladder (5) and a normal bladder (5). Expression of alpha-SM actin and SM myosin heavy chain was determined using immunocytochemical staining and Western blot analysis. Baseline cell proliferation and the mitogenic response to angiotensin II was assessed by cell counting and cell viability assays. Cell contractility was determined for normal and neuropathic SMCs using an in vitro collagen lattice assay. Cell adherence was measured assessed using partial and complete trypsinization assays.

RESULTS

Normal and neuropathic SMCs showed similar morphology in culture, and similar patterns of alpha-SM actin and SM myosin expression. Following 10 days of plating under optimal growth conditions the number of neuropathic SMCs was 170% more than normal SMCs. In response to angiotensin II neuropathic SMCs reached 54% of maximal growth capacity as opposed to 30% for normal SMCs (p <0.01). Neuropathic SMCs contracted significantly less in 10% serum and calcium ionophore (p <0.05), as determined by in vitro contractility assays. Neuropathic SMCs had 19% and 30% less adherent cells than normal SMCs (p <0.01) following isotonic solution washes and trypsinization, respectively.

CONCLUSIONS

These results demonstrate that cultured neuropathic bladder SMCs possess and maintain different characteristics than normal SMCs in vitro. The potential clinical implications of using these cells in conjunction with tissue engineering techniques for the promotion of bladder regeneration requires further investigation.

Decrease in Maximal Force Generation in the Neonatal Mouse Bladder Corresponds to Shift in Myosin Heavy Chain Isoform Composition

PURPOSE

A change in calcium handling has been proposed as the cause of decreased maximal force generation by neonatal bladders with growth. Recent studies suggest that increased myosin heavy chain isoform SM1 increases force generation. We studied force generation in neonatal mouse bladders to determine if decreases in SM1 corresponded with decreased force.

MATERIALS AND METHODS

C57Bl/6 mice were studied from birth to 12 weeks of life (adulthood). The bladder strip contractile response to KCl and bethanechol was followed by the inhibition of rho-kinase activity by Y-27632. The mRNA levels for SM1/SM2 were determined using reverse transcriptase-polymerase chain reaction and protein levels were determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Muscle fraction per cross-sectional area was determined by trichrome staining.

RESULTS

Newborn bladders generated significantly more tension in response to KCl (43.3 vs 17.4 mN/mm2, p = 0.02) and bethanechol (40.6 vs 11.9 mN/mm2, p = 0.05) than adult bladders. Inhibition of rho-kinase resulted in similar decreases in tension in all bladders. SM1 mRNA decreased slightly from 60% at birth to 50% at 12 weeks. SM1 protein decreased from 72.5% at birth to 50% by 3 weeks and it remained stable at 12 weeks. Total myosin per gm protein remained stable. Muscle fraction decreased from 63.8% at birth to 58.6% at 12 weeks (p = 0.4).

CONCLUSIONS

We noted a decrease in SM1 that corresponded to a decrease in bladder force generation. The concept that SM1 contributes to the optimal assembly of myosin filaments suggests that changes in myosin isoforms may have a role in the decrease in voiding pressures seen in normal children.

A preliminary study of natural-fill radiotelemetered ovine fetal cystometry

OBJECTIVE

To determine whether fetal cystometric studies by radiotelemetry are feasible in the fetal lamb, and potentially suitable for chronically monitoring fetal bladder pressures in an experimental fetal model of bladder outlet obstruction (BOO), as in utero BOO (e.g. caused by posterior urethral valves) results in significant postnatal bladder dysfunction but the pathophysiological progression of fetal bladder maldevelopment remains poorly understood.

MATERIALS AND METHODS

The procedure required fetal sheep surgery and anaesthesia. Radiotelemetry implants comprised catheters that transmitted pressure fluctuations to an implant body; data were then transmitted using radio frequency to a receiver that passed this information to a computer. Four fetuses were used with different methods of catheter placement to optimize the technique.

RESULTS

Recordings were possible in three of the four sheep; during observation there were: (i) quiet periods with no abdominal or bladder pressure rises; (ii) synchronous activity in the bladder and abdomen; and (iii) discriminate activity, associated with intravesical activity only. Four patterns of discriminate bladder activity were observed, defined as void, immature void, staccato activity and 'unstable' type activity.

CONCLUSIONS

Radiotelemetry cystometry for long-term monitoring is feasible in the experimental fetus without causing death or morbidity, or inhibiting growth. The method can discriminate reproducible patterns of detrusor activity. Recorded 'voiding' types were consistent between experiments and as reported in other fetal animal studies.

Neurotransmission and viscoelasticity in the ovine fetal bladder after in utero bladder outflow obstruction

Fetal bladder outflow obstruction, predominantly caused by posterior urethral valves, results in significant urinary tract pathology; these lesions are the commonest cause of end-stage renal failure in children, and up to 50% continue to suffer from persistent postnatal bladder dysfunction. To investigate the physiological development of the fetal bladder and the response to urinary flow impairment, we performed partial urethral obstruction and complete urachal ligation in the midgestation fetal sheep for 30 days. By electrical and pharmacological stimulation of bladder strips, we found that muscarinic, purinergic, and nitrergic mechanisms exist in the developing fetal bladder at this gestation. After bladder outflow obstruction, the fetal bladder became hypocontractile, producing less force after nerve-mediated and muscarinic stimulation with suggested denervation, and also exhibited greater atropine resistance. Furthermore, fetal bladder urothelium exerted a negative inotropic effect, partly nitric oxide mediated, that was not present after obstruction. Increased compliance, reduced elasticity, and viscoelasticity were observed in the obstructed fetal bladder, but the proportion of work performed by the elastic component (a physical parameter of extracellular matrix) remained the same. In addition to denervation, hypocontractility may result from a reduction in the elastic modulus that may prevent any extramuscular components from sustaining force produced by detrusor smooth muscle.

Urinary outflow obstruction increases apoptosis and deregulates Bcl-2 and Bax expression in the fetal ovine bladder

During organogenesis, net growth of tissues is determined by a balance between proliferation, hypertrophy, and apoptotic death. Human fetal bladder outflow obstruction is a major cause of end-stage renal failure in children and is associated with complex pathology in the kidney and lower urinary tract. Experimental manipulation of the fetal sheep urinary tract has proved informative in understanding the pathobiology of congenital obstructive uropathy. In this study we used an ovine model of fetal bladder outflow obstruction to examine effects on apoptotic cell death in the developing urinary bladder. While 30 days of obstruction in utero between 75 and 105 days gestation resulted in overall growth of the fetal bladder as assessed by weight, protein, and DNA measurements, we found that apoptosis, as assessed by in situ end-labeling, was up-regulated in fetal bladder detrusor muscle and lamina propria cells and that this was accompanied by a down-regulation of the anti-death protein Bcl-2 and an up-regulation of the pro-death protein Bax. Moreover, activated caspase-3, an effector of apoptotic death, was increased in obstructed bladders. This is the first study to define altered death in an experimental fetal model of bladder dysmorphogenesis. We speculate that enhanced apoptosis in detrusor smooth muscle cells is part of a remodeling response during compensatory hyperplasia and hypertrophy. Conversely, in the lamina propria, an imbalance between death and proliferation leads to a relative depletion of cells.

Alterations in the molecular determinants of bladder compliance at hydrostatic pressures less than 40 cm. H2O

PURPOSE

Bladder outlet obstruction with intravesical pressures exceeding 40 cm. H2O often results in irreversible renal damage. Bladder outlet obstruction also results in alterations in bladder physiology, including wall thickening, reduced compliance and decreased capacity. If unchecked these changes may lead to the subsequent need for bladder augmentation. From a biomechanical standpoint, compliance is primarily related to extracellular matrix deposition, which in turn is dependent on the balanced activity of proteolytic enzymes (that is matrix metalloproteinases [MMPs]) and their endogenous inhibitors (that is tissue inhibitors of metalloproteinases [TIMPs]). To date, the threshold pressure above which alterations in these key determinants of bladder compliance occur has not been determined. Therefore, using a novel device of our own design, we applied hydrostatic pressures in the physiological range to human bladder smooth muscle cells to determine the effect on MMPs, TIMP-1 and transcription of the major structural collagens (types I and III).

MATERIALS AND METHODS

Human bladder smooth muscle cells (staining positive for alpha-smooth muscle actin) were plated at a density of 100,000 cells per 10 cm.2 and cultured for 2 days in Dulbecco's modified Eagle's medium (DMEM) with 10% fetal bovine serum. Cells were subsequently exposed to pressures of 0.3, 20 and 40 cm. H2O for 1, 3, 7 and 24 hours in serum-free DMEM. A computer interface maintained pressure levels for the duration of the experiments and collected pressure data. MMP-1 and 3, and TIMP-1 immunoassay and zymography for MMP-2 and 9 were performed. Polymerase chain reaction for human collagen types I and III was performed following reverse transcription of total purified mRNA. All experiments were repeated 3 times and statistical analysis was performed using a 2-tailed Student t test.

RESULTS

Exposure of bladder smooth muscle cells to a sustained hydrostatic pressure of 20 cm. H2O for 7 hours in serum-free DMEM resulted in a time dependent decrease in MMP-1, 2 and 9 activity (15%, 37% and 25%) compared to controls maintained at atmospheric pressure (p <0.01). TIMP-1 levels increased an average of 10% after exposure to 20 cm. H2O. These changes became statistically significant when the cells were exposed to 40 cm. H2O pressure for 3, 7 and 24 hours (+14%, +21% and +50%, respectively). No statistically significant differences in MMP-3 and collagen type I or III mRNA levels were observed.

CONCLUSIONS

Our results reveal that MMP-1, 2 and 9 are significantly down-regulated in a time and pressure dependent fashion following exposure of bladder smooth muscle cells to 20 cm. H2O for as little as 7 hours. TIMP-1 levels increased under similar conditions. These alterations in MMPs and TIMP-1 favor accumulation of extracellular matrix, structural components associated with bladder wall thickness and decreased compliance. These results are consistent with previous data from animal models of complete outlet obstruction. Our results support the concept that pressures 40 cm. H2O or less contribute to molecular changes consistent with decreased compliance associated with bladder dysfunction.

Effects of in utero bladder outflow obstruction on fetal sheep detrusor contractility, compliance and innervation

PURPOSE

Congenital bladder outflow obstruction caused by posterior urethral valves is a common cause of end stage renal failure in boys. We hypothesized that fetal bladder outflow obstruction perturbs detrusor contractility and innervation and bladder storage volume-pressure relationships.

MATERIALS AND METHODS

Severe bladder outflow obstruction was induced in male fetal sheep by placing a urethral ring and urachal ligation midway through gestation at 75 days. Fetuses were examined 30 days after surgery, when urinary tract dilatation, enlarged bladders and histologically abnormal kidneys were documented. Isolated strips of bladder detrusor from sham operated and obstructed fetuses were subjected to electrical field stimulation, carbachol, KCl and alpha-beta methylene-adenosine triphosphate. Whole bladder storage characteristics were determined by filling cystometry and bladder innervation was investigated by immunohistochemistry and Western blot.

RESULTS

Tension-frequency contractility studies showed that obstructed fetal bladder strips were significantly hypocontractile versus sham operated controls in response to electrical field stimulation and the specific agonists carbachol, KCl and alpha-beta methylene-adenosine triphosphate. Hypocontractility was greater with nerve mediated stimulation than with carbachol, suggesting relative denervation. Reduced innervation was confirmed by S100 and protein gene product 9.5 immunohistochemistry and by measuring a significant reduction in protein gene product 9.5 protein expression using Western blot. Filling cystometry showed that obstructed fetal bladders appeared more compliant (Delta V/Delta P, where Delta V is the change in volume and Delta P is the change in pressure) with larger capacity, more flaccidity and yet retained stress relaxation.

CONCLUSIONS

In response to severe experimental fetal bladder outflow obstruction the bladder becomes large and hypocontractile, and has aberrant innervation.

Bladder dysfunction as a prognostic factor in patients with posterior urethral valves

OBJECTIVE

To investigate the extent to which different types of bladder dysfunction can affect long-term renal function in boys with posterior urethral valves (PUV).

PATIENTS AND METHODS

Renal and bladder function were retrospectively assessed in 59 boys with PUV (mean age 10 years, range 5-17). All patients included in the study had at least 4 years of follow-up and their bladder behaviour had been evaluated in at least two urodynamic studies. At the time of the study, of the 59 PUV boys, 37 had normal renal function and 22 had end-stage renal disease (ESRD).

RESULTS

Of the 59 boys with PUV evaluated by urodynamic studies, 25 had normally behaving bladders (42%) and 34 had some type of bladder dysfunction (58%). Of the 22 in ESRD, 15 had abnormally behaving bladders (68%) and only seven had bladders with normal behaviour (32%). Of the 37 boys with normal renal function, 19 had dysfunctional bladders (51%) and 18 had normal bladders (49%). Instability was found in 17 of 19 boys with bladder dysfunction and normal renal function. On the contrary among 22 boys with ESRD, poor compliance was the most frequent urodynamic pattern (eight, 53%) while instability was only found in five. Overall, eight of nine boys with poorly compliant bladders, two of three with myogenic failure and a five of 22 with instability were in ESRD, and this situation occurred at an earlier age in patients with poorly compliant bladders.

CONCLUSION

Bladder dysfunction should be considered as a prognostic factor in renal failure. Those with poor bladder compliance and myogenic failure have the worst outcome, while bladder instability was associated with the lowest incidence of renal failure.

The valve bladder: etiology and outcome

The infravesical obstruction created by posterior urethral valves produces a series of structural, biochemical, and functional changes in these boys' bladders that begins during fetal life. Any change can be irreversible and result in the alterations in bladder function that can be found in some of these patients. Bladder instability, poor compliance, and myogenic failure are the three most common urodynamic patterns and are also responsible for some of these patients' poor long-term prognosis. Treatment of bladder dysfunction in these patients is basically directed toward improving their kidney function prognosis and also to avoid the urinary incontinence presented secondarily by some valve bladders.

The valve bladder syndrome: pathophysiology and treatment with nocturnal bladder emptying

PURPOSE

We determine the etiology and treat the specific pathophysiology of the valve bladder syndrome.

MATERIALS AND METHODS

Defined as persisting or progressive severe hydroureteronephrosis without residual or recurrent obstruction, the valve bladder syndrome developed in 18 boys who underwent successful ablation of the posterior urethral valve. Serial radiographic, renal function, renographic, urodynamic and perfusion studies were performed for a mean time of 11 years.

RESULTS

The cause of the valve bladder syndrome proved to be sustained bladder over distention due to a combination of polyuria with 24-hour urine volume greater than 2 l. in 10 boys, impaired bladder sensation in 18 and residual urine volume in 14. Treatment of over distention during the daytime alone was unsuccessful. Nocturnal bladder emptying was performed with an indwelling nighttime catheter, intermittent nocturnal catheterization and/or frequent nocturnal double voiding. Hydronephrosis markedly improved once nocturnal bladder emptying was started and was comparable to the results after urinary diversion.

CONCLUSIONS

The valve bladder syndrome is not due to a permanent prenatal alteration in bladder anatomy and function. Instead, it appears to result from sustained postnatal bladder over distention due to a combination of polyuria, impaired bladder sensation and residual urine volume, which represent sequelae of prenatal valve injury. These factors synergize to prevent bladder normalization after valve ablation and progressively reduce functional bladder capacity to maintain bladder over distention. Bladder decompensation, upper tract dilation, and renal injury develop and characterize the valve bladder syndrome. Because current therapy, including intermittent catheterization, leaves the bladder full throughout the night, it remains markedly over distended. Nocturnal bladder emptying is the specific antidote for this pathophysiological situation, and results in prompt and impressive improvement or elimination of hydronephrosis in these and similar groups of patients. This response to nocturnal bladder emptying suggests that the bladder is not the primary cause for the valve bladder syndrome.