Smooth muscle development in the obstructed fetal bladder

Fetal Lower Urinary Tract Obstruction: Current Diagnostic and Therapeutic Strategies and Future Directions

BACKGROUND

Fetal lower urinary tract obstruction (LUTO) is a rare congenital anomaly in which the bladder cannot empty properly. The clinical presentation is variable. On the severe end of the spectrum, the amniotic fluid index can be sufficiently low, resulting in fetal lung development that is incompatible with life outside the womb. The pressure in the urinary tract system can also result in severe damage to the kidney, resulting in renal failure in utero or in the first couple years of life. Therefore, much work has been done to determine which fetuses need intervention in utero to allow for survival outside of the womb and avoidance of end-stage renal disease. Multiple therapies have been developed to relieve the obstruction in utero with the mainstay being vesicoamniotic shunting and posterior urethral valve ablation.

SUMMARY

While much has been investigated to determine which fetuses would benefit from fetal intervention, the current indications are not without their flaws. This review describes the current indications and their shortcomings, as well as new experimental methods of determining need for intervention. Additionally, this review describes the milestone animal studies that established the challenges of current fetal interventions and the utility of an experimental valved shunt in sheep over the last 20 years.

KEY MESSAGES

Our understanding of LUTO and which fetuses benefit from in utero intervention has grown over the last 20 years. However, traditional markers have proven to be less predictive than previously thought, opening the door to exciting new advances. Vesicoamniotic shunting, while lifesaving, does not preserve bladder function and frequently dislodges. Animal studies over the last 20 years have established the utility of a valved shunt to maintain bladder function. Current advances are working to create such a shunt that can be percutaneously deployed and have greater adherence to the bladder wall to avoid dislodgement.

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.

Chronic Kidney Disease in Boys with Posterior Urethral Valves-Pathogenesis, Prognosis and Management

Posterior urethral valves (PUV) are the most common form of lower urinary tract obstructions (LUTO). The valves can be surgically corrected postnatally; however, the impairment of kidney and bladder development is irreversible and has lifelong implications. Chronic kidney disease (CKD) and bladder dysfunction are frequent problems. Approximately 20% of PUV patients will reach end-stage kidney disease (ESKD). The subvesical obstruction in PUV leads to muscular hypertrophy and fibrotic remodelling in the bladder, which both impair its function. Kidney development is disturbed and results in dysplasia, hypoplasia, inflammation and renal fibrosis, which are hallmarks of CKD. The prognoses of PUV patients are based on prenatal and postnatal parameters. Prenatal parameters include signs of renal hypodysplasia in the analysis of fetal urine. Postnatally, the most robust predictor of PUV is the nadir serum creatinine after valve ablation. A value that is below 0.4 mg/dl implies a very low risk for ESKD, whereas a value above 0.85 mg/dl indicates a high risk for ESKD. In addition, bladder dysfunction and renal dysplasia point towards an unbeneficial kidney outcome. Experimental urinary markers such as MCP-1 and TGF-β, as well as microalbuminuria, indicate progression to CKD. Until now, prenatal intervention may improve survival but yields no renal benefit. The management of PUV patients includes control of bladder dysfunction and CKD treatment to slow down progression by controlling hypertension, proteinuria and infections. In kidney transplantation, aggressive bladder management is essential to ensure optimal graft survival.

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.

Development of contractile properties in the fetal porcine urinary bladder

BackgroundIn early fetal life, the bladder is merely a conduit allowing urine to pass through freely into the amniotic cavity. As the striated external urethral sphincter evolves, the bladder acquires its reservoir and voiding functions. We characterized the myogenic and neurogenic contractions of the normal fetal porcine bladder from midterm until close to full-term gestation.MethodsContractile responses were measured in vitro using bladder strips from fetuses at 60 (N=23) and 100 days (N=21) of gestation. Spontaneous activity, and the responses to potassium chloride (KCl) solution, electrical field stimulation (EFS), and receptor activation were recorded. The smooth muscle content was evaluated histologically.ResultsHistological studies revealed that the fractional content of smooth muscle doubled between the two time points, and passive tension was adjusted to take that into account. Spontaneous activity was regular at 60 days, changing toward an irregular pattern at 100 days. Contractile force elicited by KCl and carbachol increased significantly with gestational age, while contractions to the purinergic agonist, α-β-methylene adenosine 5'-triphosphate did not. The responses to EFS were almost completely blocked by atropine.ConclusionSpontaneous myogenic contractions become irregular and contractile responses to muscarinic receptor stimulation increase during gestation, as the bladder reservoir and voiding functions develop.

Can bladder fibrosis in congenital urinary tract obstruction be reversed?

A variety of conditions exists in adults and children in which functional or anatomical urinary tract obstructions cause bladder fibrosis, which reduces the bladder's ability to store and empty urine. Current surgical procedures include removal of the obstructions to facilitate bladder emptying or prompt prenatal or postnatal spinal closure to prevent further neurogenic damage. Bladder fibrosis may occur, and it can get worse if a flow hindrance persists or deteriorates. Anti-fibrotic therapeutic strategies that target a variety of factors have been developed in animal models, but currently there are no anti-fibrotic therapies available for clinical use. This review examines the pathogenesis of bladder fibrosis that is caused by congenital obstructions of the lower urinary tract, and it focuses on the principal signalling factors and potential treatment modalities.

Electron microscopic changes of detrusor in benign enlargement of prostate and its clinical correlation

AIMS

To study the ultra structural changes in bladder musculature in cases of BPE and their clinical relevance.

MATERIAL AND METHODS

In this descriptive longitudinal, controlled, observational study patients were enrolled into three groups, group 1, group 2A and group 2B. Control group (group-1) consisted of age matched normal male patients, who underwent surveillance or diagnostic cystoscopy for microscopic hematuria or irritative symptoms. Case group (group-2) comprised of patients with BPE, undergoing TURP. Case group (group-2) was further classified into: Category 2A (patients not on catheter) and cat-egory 2B (patients on catheter). All relevant clinical parameters like IPSS, prostate size, Qmax, PVR were recorded. Cystoscopy and bladder biopsy were performed in all patients. Various ultrastructural parameters like myocytes, fascicular pattern, interstitial tissue, nerve hypertrophy and cell junction pattern were analyzed under electron microscope and they were clinically correlated using appropriate statistical tests.

RESULTS

Control group had significant difference as compared to case group in terms of baseline parameters like IPSS, flow rate and prostate size, both preoperatively and postoperatively, except for PVR, which was seen only preoperatively. There was statistically significant difference in ultrastructural patterns between case and control group in all five electron microscopic patterns. However, no significant difference was found between the subcategories of case groups.

CONCLUSIONS

BPE is responsible for ultra structural changes in detrusor muscle and these changes remain persistent even after TURP. Nerve hypertrophy, which was not thoroughly discussed in previous studies, is also one of the salient feature of this study.

Morphology of the fetal bladder during the second trimester: comparing genders

OBJECTIVES

The aim of the present study was to determine, by histological and stereological analysis, whether there are between-gender structural differences in the bladder in the second gestational trimester in human fetuses.

MATERIAL AND METHODS

Forty bladders, which were obtained from 40 human fetuses (20 males and 20 females) ranging in age from 13 to 23 weeks post-conception (WPC), were studied. The fetuses were macroscopically well preserved, without anomalies of the urinary and genital systems; the cases with syndromes were abandoned. The bladders were dissected and embedded in paraffin, from which 5-μm thick sections were obtained and stained with: Masson's trichrome, to quantify connective and smooth muscle tissue; Weigert's resorcin fuchsin, to observe elastic fibers; picrosirius red with polarization, to observe collagen; and anti-beta III tubulin antibody, to observe the bladder nerves. The images were captured with an Olympus BX51 microscope and Olympus DP70 camera. The stereological analysis was performed with the Image Pro and Image J programs, using a grid to determine volumetric densities (Vv). Means were statistically compared using simple linear regression and the paired t-test (P<0.05).

RESULTS

The fetuses weighed between 60 and 490 g, and had crown-rump lengths between 9.5 and 20.4 cm. No elastic system fibers were observed in any bladders. Quantitative analysis indicated no differences in the Vv of the smooth muscle cells in the male bladders (26.19-50.16%; mean=35.66%) compared to the female ones (30.60-45.63%; mean=38.73%) (P=0.740) and there were also no differences in the Vv of the connective tissue in females (40.52-60.40%; mean=50.69%) and males (38.84-70.16%; mean=57.04%) (P=0.0506). There were no differences observed in the distribution of the nerves and collagen between the genders.

CONCLUSION

The histological analysis of the smooth muscle, collagen, nerves and connective tissue of the developing bladders revealed that there are no gender differences during weeks 13-23 of gestation.

Fetal surgery for severe lower urinary tract obstruction

Fetal interventions have been proposed for treatment of severe lower urinary tract obstruction (LUTO), as this condition is associated with high rates of perinatal mortality and postnatal renal impairment. The rationale for in utero treatment for those cases is based on the possibility of relieving the obstruction, improving the amniotic fluid volume, and preventing renal and bladder damage. Candidates for fetal intervention should be rigorously selected based on the confirmation of severe LUTO (dilated bladder and bilateral hydronephrosis), oligohydramnios or anyhydramnios and 'favorable' fetal urinalysis (dependent on gestational age). Nowadays there are two different therapeutic options with specific technical approaches. Vesico-amniotic shunting is an easier procedure, but with a higher frequency of related complications. Fetal cystoscopy can be used for diagnostic purpose and for treatment of posterior urethral valves, with suggestive advantage of allowing a more physiological release of the obstruction. According to the literature, estimated survival rates and postnatal normal renal function frequencies are approximately 40 and 50% after vesico-amniotic shunting and 75 and 65% after fetal cystoscopy, respectively.

Bladder development following bladder outlet obstruction in fetal lambs: optimal timing of fetal therapy

BACKGROUND

Lower urinary tract obstruction causes both renal failure and bladder dysfunction after birth. This study examined the early bladder wall changes after creating an obstructive uropathy focusing on bladder wall thickness and muscle integrity.

METHODS

We created obstructive uropathy in fetal lambs at 60 days' gestation, ligating the urethra and urachus. The fetuses (n = 28) were delivered at 48 hours and 3, 4, 5, 7, and 14 days after obstruction and at term (145 days' gestation). Sham-operated lambs were used as controls (n = 20). Histology samples were stained using α-smooth muscle actin) immunohistochemistry and also hematoxylin-eosin, Masson trichrome, and colloidal Fe stain.

RESULTS

The bladder wall initially expanded and stretched. By day 4, the bladder wall became thicker. Histologically, the bladder in obstructed lambs demonstrated a prominent submucosal fibrotic change by 7 days. The mean bladder wall thickness at 14 days after obstruction was thicker than controls, and fibrosis was prominent.

CONCLUSION

The initial changes in the bladder wall were expansion of the muscle component followed by fibrosis. The bladder wall thickness dramatically increased 4 to 7 days after obstruction. We conclude that shunting operations to preserve bladder function may be needed earlier than expected.

Fetal lower urinary tract obstruction

The authors present an overview of the prenatal diagnosis, evaluation, contemporary intervention, and antenatal management of lower urinary tract obstruction. They review early experimental models that confirmed the relation between urinary tract obstruction and renal fibrocystic dysplasia and that early in utero relief of the obstruction could prevent irreversible renal injury. Subsequent studies of the electrolyte and protein concentrations in fetal urine from human cases established prognostic threshold values and helped to develop an algorithm to select candidates for antenatal therapy. Although shunting has improved survival, long-term morbidities remain a significant challenge.

Can a pressure-limited vesico-amniotic shunt tube preserve normal bladder function?

INTRODUCTION

We have previously shown that a vesico-amniotic shunt (V-A shunt) produces fibrotic bladders with poor compliance in normal fetal lambs. We hypothesized that using a ventriculo-peritoneal shunt (V-P shunt) as a V-A shunt in normal bladders may preserve the filling/emptying cycle and normal bladder development.

MATERIALS AND METHODS

The V-A shunting in normal fetal lambs was performed at 74 days of gestation using a V-P shunt (group A) and a free-draining shunt tube (group B). Sham-operated lambs were used as controls (group C). They were all delivered at term (145 days), and the pressure-volume curve, bladder volume, and histologic features of the bladder wall were compared.

RESULT

The mean bladder volume in group B (n = 5), 5 +/- 2.4 mL, was significantly smaller (P < .01) than that in group A (n = 6), 53 +/- 14 mL, and group C (n = 10), 57.3 +/- 12 mL. The bladder wall thickness in group A was 338 + 94.2 microm; group B, 741 +/- 128 microm; and group C, 374 +/- 120 microm. Group B bladders had very poor compliance with thick bladder wall (P < .01). Histologically, group B bladders showed prominent submucosal fibrotic change, but group A bladders were similar to controls.

CONCLUSION

This study shows that a pressure-limited shunt tube for V-A shunting preserves the normal fetal bladder development.

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.

Stereological study of collagen and elastic system in the detrusor muscle of bladders from controls and patients with infravesical obstruction

OBJECTIVE

Compare detrusor muscle of normal and patients with infravesical obstruction, quantifying the collagen and elastic system fibers.

MATERIALS AND METHODS

We studied samples taken from bladders of 10 patients whose ages ranged from 45 to 75 years (mean = 60 years), who underwent transvesical prostatectomy for treatment of BPH. Control material was composed of 10 vesical specimens, removed during autopsies performed in cadavers of accident victims, with ages between 18 and 35 years (mean = 26 years).

RESULTS

The results of collagen and elastic fibers quantification (volumetric density) demonstrated the following results in percentage (mean +/- standard deviation): collagen in BPH patients = 4.89 +/- 2.64 and 2.32 +/- 1.25 in controls (p < 0.0001), elastin in BPH patients = 10.63% +/- 2.00 and 8.94% +/- 1.19 in controls (p < 0.0001).

CONCLUSION

We found that the components of connective tissue, collagen and elastic system fibers are increased in the detrusor muscle of patients with infravesical obstruction, when compared to controls.

Gender Specific Chronological and Morphometric Assessment of Fetal Bladder Wall Development

PURPOSE

To enhance our understanding of sonographically visible alterations in bladder wall thickness, we delineated phenotypic changes occurring in developing smooth muscle cells of the fetal and postnatal bladder with respect to gender specific differences.

MATERIALS AND METHODS

Bladders of 30 male and 18 female fetuses and 4 stillborn infants were immunostained with an alpha-smooth muscle actin antibody. Morphological and morphometric assessment was performed with the assistance of an image analysis system.

RESULTS

Alpha-smooth muscle actin expression in fetal bladder wall was detectable at 9 weeks of gestation. Bladder wall thickness and mean profile area of smooth muscle bundles increased significantly with advancing gestation, mediated by linear growth patterns. Fetal bladder wall development occurred uniformly, unrelated to gender.

CONCLUSIONS

Although the lower urinary tract emerges in a gender specific way, our results suggest that in normal fetal growth detrusor muscle formation proceeds independent of genital sex.

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.

The Impact of Late Presentation of Posterior Urethral Valves on Bladder and Renal Function

PURPOSE

We retrospectively reviewed the records of patients with late presentation of PUVs, and compared bladder and renal function to that in patients with an early diagnosis of PUVs.

MATERIALS AND METHODS

We retrospectively reviewed the charts of 36 males (mean age at diagnosis 8.8 years, range 5 to 14) with late presentation of PUVs who were treated at our institution between 1986 and 2004. Of these patients 20 had undergone urodynamic evaluation during followup (mean age 10.65 years, range 5 to 23). We chose as controls 19 age matched children with PUVs who were diagnosed and treated before age 5 years and underwent urodynamic evaluation during followup (mean age at urodynamic evaluation 8.52 years, range 6 to 15). Urodynamic parameters were compared between the 2 patient groups. Renal function in the late presenting cases was also compared to controls.

RESULTS

The most common symptoms at presentation were diurnal enuresis (17 patients, 47.2%) poor stream (7, 19.4%) and urinary retention (5, 13.9%). Overall, urodynamic bladder abnormalities were detected in 17 of 20 patients (85%), detrusor overactivity in 3 (15%), significant post-void residual in 9 (45%) and bladder capacity greater than expected for age in 9 (45%). No significant difference in bladder capacity, compliance or post-void residual was demonstrated between the late presenting and control groups. Only detrusor overactivity was significantly lower in the late presenting group (p = 0.013). After a mean followup of 67.03 months age specific creatinine levels were increased in 13 of 27 patients (48.1%), including 7 (25.9%) with ESRD. Renal function was significantly impaired in the late presenting group compared to controls (48.1% vs 13.7%, p = 0.001).

CONCLUSIONS

We found a significantly lower rate of detrusor overactivity (15%) in patients with late presenting PUVs. Comparison of urodynamic parameters between the early and late presenting groups did not reveal any significant difference. This similar pattern of bladder dysfunction, independent of age at relief of obstruction, may indicate a common pathophysiological etiology for bladder dysfunction in all patients with PUVs. Also, renal function was significantly impaired in the late presenting group in this series.

Growth and stretch response of human exstrophy bladder smooth muscle cells: molecular evidence of normal intrinsic function

OBJECTIVE

To establish primary cultures of smooth muscle cells (SMC) from human exstrophic bladders (E-SMC), and determine their in vitro growth dynamics and responses to mechanical stretch.

MATERIALS AND METHODS

Primary cultures of E-SMC from three patients were established from exstrophic bladder tissue using an explant method. Growth dynamics were assessed using tetrazolium-dye uptake. The DNA synthesis rate in response to cyclic stretch-relaxation was determined with thymidine-incorporation assays. Expression of the SMC mitogen heparin-binding epidermal growth factor-like growth factor (HB-EGF) mRNA in response to mechanical stretch was determined using semiquantitative reverse transcription-polymerase chain reaction.

RESULTS

The approximate doubling time of the E-SMC grown in the presence of serum was 4 days, consistent with growth rates of SMC reported previously. E-SMC exposed to stretch had greater DNA synthesis, albeit to a lesser extent than previously seen with non-exstrophic SMC. The expression of HB-EGF was also increased in cells exposed to mechanical stimuli, consistent with our previous finding of stretch-regulated HB-EGF gene expression in bladder SMC.

CONCLUSIONS

E-SMC had growth characteristics similar to those previously reported in non-exstrophic cells. E-SMC also had stretch-induced expression of HB-EGF mRNA. These observations provide evidence that despite development in an abnormal defunctionalized state, E-SMC retain the potential for normal growth, and may modulate this response through mechanisms similar to those operating in normal bladder SMC.

CORRELATION BETWEEN DETRUSOR COLLAGEN CONTENT AND URINARY SYMPTOMS IN PATIENTS WITH PROSTATIC OBSTRUCTION

PURPOSE

We used computerized imaging analysis to compare the collagen content of detrusor specimens between patients affected with symptomatic obstructive benign prostatic hyperplasia (BPH) and asymptomatic controls.

MATERIALS AND METHODS

In our study we enrolled 36 patients with symptomatic urodynamically obstructed BPH undergoing transurethral resection of the prostate. We also enrolled 28 men (mean age 61.3, range 55 to 70) undergoing transurethral resection of the bladder for primitive, singular Ta bladder cancer, with no significant urinary symptoms, as the control group. During the transurethral surgical procedure in controls and in patients with BPH, a biopsy was performed deep through the muscular layer from either of the lateral bladder walls. Computerized morphometric analysis of the stained sections was performed with an image analysis system, and a percentage of collagen fibers was extracted through morphological filtering and expressed as a mean percentage of the total bioptic area.

RESULTS

Collagen content in bladder detrusor specimens was significantly higher in patients with BPH compared to controls (48% and 17% of bioptic area, respectively, p <0.001). Mean detrusor collagen content was clearly higher in patients with severe symptoms than in patients with moderate symptoms (50.45 +/- 8.22% and 43.09% +/- 7.05%, respectively).

CONCLUSIONS

Our study supports the important role of detrusor collagen neo-deposition in determining lower urinary tract symptoms in obstructive BPH. Detrusor collagen content correlates with urodynamic obstruction, the presence and severity of symptoms and, given that collagen neoformation is irreversible could probably have a role in the postoperative persistence of lower urinary tract symptoms in patients undergoing surgery for BPH.

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.

Identification of bladder wall layers by Raman spectroscopy

PURPOSE

We explored the applicability of Raman spectroscopy to in situ investigation of bladder wall tissue.

MATERIALS AND METHODS

Bladder wall tissue was obtained from a guinea pig model and frozen sections were used for Raman spectroscopic investigations. From each section 500 to 700 spectra were obtained in a 2-dimensional grid spanning the urothelium, lamina propria and muscle layer. The data set of spectra was subdivided into groups of similar spectra by a cluster analysis algorithm. With each group assigned a different color Raman maps of frozen sections were constructed based on group membership of measured spectra. These maps were then compared with histological and histochemical data obtained from hematoxylin and eosin and immunohistochemical staining for collagen I and III and for smooth muscle actin to correlate Raman spectral features with bladder wall structure and molecular composition.

RESULTS

Urothelium, lamina propria and muscle layers could be clearly distinguished based on Raman spectra. Lamina propria spectra were dominated by signal contributions of collagen and the smooth muscle layer showed strong signal contributions of actin. The urothelium had a relatively strong lipid signal contribution.

CONCLUSIONS

These results and the fact that Raman spectroscopy is rapidly evolving into a technology that can be applied in vivo by thin, flexible fiberoptic catheters indicate that prospects are good for in vivo analysis of the molecular composition of the normal and pathological bladder without biopsies.

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.

Aspirin treatment improves bladder function after outlet obstruction in rabbits

OBJECTIVES

To examine whether bladder smooth muscle dysfunction after outlet obstruction could be altered by treatment with aspirin. Long-term outlet obstruction causes contractile and metabolic dysfunction of the bladder in vivo and in vitro. The evidence is growing that a decrease in bladder perfusion is an important cause of this phenomenon. The platelet aggregation inhibitor, acetylsalicylic acid (aspirin), has been used to improve perfusion of the heart for decades.

METHODS

Ten male New Zealand white rabbits were obstructed for 4 weeks. Five rabbits received no further treatment (Obs), and 5 rabbits received 2 mg/kg/day aspirin (Obs+aspirin), administered by an osmotic pump implanted subcutaneously 1 week before the surgical obstruction. The bleeding time was measured to confirm the effectiveness of the aspirin treatment. Three different control groups were created: sham-operated rabbits, unobstructed rabbits with pumps containing DMSO (vehicle), and unobstructed rabbits with pumps containing aspirin. The contractile responses of bladder strips to field stimulation, adenosine triphosphate, carbachol, and KCl were determined. A section of each detrusor tissue was fixed in formalin and used to determine the smooth muscle and collagen (connective tissue) volume fraction.

RESULTS

No differences were found in the bladder weights or responses to stimuli in the different control groups, which were therefore combined. Partial bladder outlet obstruction caused significant increases in the bladder weight of the obstructed animals (Obs+aspirin, 10.15 +/- 0.87 g; Obs, 10.17 +/- 0.88 g; and controls, 2.87 +/- 0.21 g). The aspirin treatment increased the bleeding time from 1.7 +/- 0.3 minutes to 3.3 +/- 0.1 minutes. The responses to field stimulation were significantly reduced in all of the obstructed rabbits. However, the responses of the bladder strips from the Obs rabbits to field stimulation were impaired to a significantly greater degree than were those from the Obs+aspirin rabbits. The response to 32-Hz stimulation was reduced by 86% in the Obs group but by only 64% in the Obs+aspirin group. The responses to carbachol were significantly reduced by 62% in the strips from the Obs rabbits, but the responses of the strips from the Obs+aspirin rabbits were similar to the responses of the strips from the controls. The responses to KCl and adenosine triphosphate were reduced, although they just failed to achieve statistical significance using Bonferroni's analysis. The ratio of smooth muscle and connective tissue shifted slightly toward smooth muscle after 4 weeks of obstruction, but no difference was found with or without aspirin treatment.

CONCLUSIONS

Low-dose aspirin has a small but significant protective effect on the contractile dysfunction induced by bladder outlet obstruction in rabbits, although the increase in bladder mass was not altered. Bladders of the same weight showed improved responses to all forms of stimulation after pretreatment with aspirin. Already used by millions of patients with heart diseases, aspirin could be a useful protection against contractile dysfunction of the obstructed bladder.

Effect of chronic bladder outlet obstruction on blood flow of the rabbit bladder

PURPOSE

Previous studies have shown that the initial reaction of the rabbit bladder to partial bladder outlet obstruction is increased blood flow at day 1 and a return to baseline blood flow at 1 week. Mucosal and muscle blood flow followed this pattern but mucosal blood flow was always 4 to 5-fold greater. In this study we examined the effect of 4 weeks of outlet obstruction on bladder blood flow and correlated it with the severity of bladder contractile dysfunction.

MATERIALS AND METHODS

A total of 14 male New Zealand White rabbits underwent partial outlet obstruction creation by standard methods. After 4 weeks the rabbits were anesthetized, and blood flow to the muscle and mucosa was determined by standard fluorescent microsphere technique. A section of each detrusor was used for in vitro contractility studies. Contractile responses to field stimulation, carbachol and potassium chloride were determined. A section of each detrusor tissue was fixed in formalin and used to determine the smooth muscle volume fraction.

RESULTS

Four weeks of partial bladder outlet obstruction caused a significant and variable increase in bladder weight and a decrease in blood flow to bladder muscle without changes in the blood flow to mucosa. There was a clear correlation between the severity of contractile dysfunction, bladder weight and the magnitude of the decrease in blood flow in muscle. The smooth muscle volume fraction remained stable at approximately 40%.

CONCLUSIONS

Bladder decompensation was associated with decreased blood flow to bladder smooth muscle. Because compensated obstructed bladders with relatively normal contractile function are also hypertrophied but have normal blood flow, decreased blood flow in decompensated bladders is not simply a response to bladder hypertrophy. From this study we hypothesize that decreased blood flow to bladder smooth muscle is an etiological factor in bladder contractile dysfunction (bladder decompensation) secondary to partial outlet obstruction.

Ultrastructural smooth muscle ontogeny of the rat bladder

The transmission electron microscope characteristics of developing rat bladder smooth muscle are described at 14 and 18 days of gestation, birth, and adulthood. Caveolae, microfilaments, and dense bodies increase during smooth muscle development. Collagen content in the extracellular matrix also increases. These changes may reflect increased bladder emptying in the rat, and also allow for comparison of smooth muscle cells in studies of bladder wound healing and tissue substitutes.

Fetal interventions for obstructive uropathy

Obstructive uropathy is a significant source of morbidity and mortality in the neonate and infant, despite advances in postnatal management. Diagnosis is typically made early in the second trimester on the basis of sonographic measurements. In utero therapy holds promise for improved outcomes by preventing progressive urinary tract damage and permitting drainage of urine into the amniotic space to minimize the pulmonary sequelae of oligohydramnios. Multiple studies with animal models have showed the benefits of midgestational intervention, but large prospective, randomized studies have not yet been performed to confirm these findings in humans. Standardization of the diagnostic evaluation allows for refined patient selection, resulting in improved postnatal outcomes after fetal vesicoamniotic shunting. Research into the role of specific growth factors and immunoproteins in renal development and function may further improve patient selection and outcome. This article reviews diagnosis, technique, and outcomes for fetal treatment of obstructive uropathy.

Fetal uropathy

Our understanding of the causes, mechanisms, and prenatal management of fetal obstructive uropathy has increased significantly. Improved methods of prenatal evaluation have allowed the better selection of fetuses for invasive therapy, and studies indicate better survival and renal outcomes in carefully selected cases. New biological markers in fetal urine may provide a better understanding of the pathological processes of renal damage, additional prognostic markers, and lead to non-surgical approaches to preventing renal damage.

Stretch activates heparin-binding EGF-like growth factor expression in bladder smooth muscle cells

Cultured rat bladder smooth muscle cells (SMC) were grown on collagen-coated silicone membranes and subjected to continuous cycles of stretch-relaxation. Semiquantitative RT-PCR analysis revealed a time-dependent increase in heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) mRNA levels after stretch, with maximal levels appearing after 4 h. Immunostaining for proHB-EGF revealed higher levels of HB-EGF protein in the stretched than in the nonstretched SMC. The ANG II receptor type 1 antagonist losartan markedly suppressed stretch-activated HB-EGF expression. ANG II levels were 3.3-fold higher in the stretch- than in the non-stretch-conditioned media. Stretch stimulation of bladder SMC that had been transiently transfected with an HB-EGF promoter-luciferase expression construct resulted in an 11-fold increase in reporter activity. Mechanical stretch induced a 4.7-fold increase in tritiated thymidine incorporation rate, and this was reduced by 25% in the presence of losartan. We conclude that mechanical stretch activates HB-EGF gene expression in bladder SMC and that this is mediated in part by autocrine ANG II secretion.

In vitro ligation of ureters and urethra modulates fetal mouse bladder explants development

The compliance of the bladder which accommodates the holding and voiding of urine is influenced by the amount and type of collagen deposited as well as the packing and organization of collagen fiber bundles. During fetal development, the accumulation of urine within the bladder lumen is associated with the maturation of the bladder's wall. Fetal mouse bladders can undergo maturation as organ cultured explants in defined medium. Polarized light optics of Sirius red-stained sections of fetal mouse bladders in organ culture for 4 days showed that the ligation of both ureters and urethra promoted more orderly packing of collagen fiber bundles within the luminal edge of the lamina propria compared to unligated bladder explants. It is proposed that ligation causes differences in the development and organization of the collagen fiber bundles within the bladder wall. These differences are due to either increases in intravesical pressure, the accumulation of growth factors within the lumen or a combination of both.