Muscular development in the urinary tract

Early investigations into improving bowel and bladder function in fetal ovine myelomeningocele repair

INTRODUCTION

Fetal myelomeningocele (MMC) repair improves lower extremity motor function. We have previously demonstrated that augmentation of fetal MMC repair with placental mesenchymal stromal cells (PMSCs) seeded on extracellular matrix (PMSC-ECM) further improves motor function in the ovine model. However, little progress has been made in improving bowel and bladder function, with many patients suffering from neurogenic bowel and bladder. We hypothesized that fetal MMC repair with PMSC-ECM would also improve bowel and bladder function.

METHODS

MMC defects were surgically created in twelve ovine fetuses at median gestational age (GA) 73 days, followed by defect repair at GA101 with PMSC-ECM. Fetuses were delivered at GA141. Primary bladder function outcomes were voiding posture and void volumes. Primary bowel function outcome was anorectal manometry findings including resting anal pressure and presence of rectoanal inhibitory reflex (RAIR). Secondary outcomes were anorectal and bladder detrusor muscle thickness. PMSC-ECM lambs were compared to normal lambs (n = 3).

RESULTS

Eighty percent of PMSC-ECM lambs displayed normal voiding posture compared to 100% of normal lambs (p = 1). Void volumes were similar (PMSC-ECM 6.1 ml/kg vs. normal 8.8 ml/kg, p = 0.4). Resting mean anal pressures were similar between cohorts (27.0 mmHg PMSC-ECM vs. normal 23.5 mmHg, p = 0.57). RAIR was present in 3/5 PMSC-ECM lambs that underwent anorectal manometry and all normal lambs (p = 0.46). Thicknesses of anal sphincter complex, rectal wall muscles, and bladder detrusor muscles were similar between cohorts.

CONCLUSION

Ovine fetal MMC repair augmented with PMSC-ECM results in near-normal bowel and bladder function. Further work is needed to evaluate these outcomes in human patients.

Developmental pathology of congenital kidney and urinary tract anomalies

Congenital anomalies of the kidneys or lower urinary tract (CAKUT) are the most common causes of renal failure in children and account for 25% of end-stage renal disease in adults. The spectrum of anomalies includes renal agenesis; hypoplasia; dysplasia; supernumerary, ectopic or fused kidneys; duplication; ureteropelvic junction obstruction; primary megaureter or ureterovesical junction obstruction; vesicoureteral reflux; ureterocele; and posterior urethral valves. CAKUT originates from developmental defects and can occur in isolation or as part of other syndromes. In recent decades, along with better understanding of the pathological features of the human congenital urinary tract defects, researchers using animal models have provided valuable insights into the pathogenesis of these diseases. However, the genetic causes and etiology of many CAKUT cases remain unknown, presenting challenges in finding effective treatment. Here we provide an overview of the critical steps of normal development of the urinary system, followed by a description of the pathological features of major types of CAKUT with respect to developmental mechanisms of their etiology.

The molecular biology of pelvi-ureteric junction obstruction

Over recent years routine ultrasound scanning has identified increasing numbers of neonates as having hydronephrosis and pelvi-ureteric junction obstruction (PUJO). This patient group presents a diagnostic and management challenge for paediatric nephrologists and urologists. In this review we consider the known molecular mechanisms underpinning PUJO and review the potential of utilising this information to develop novel therapeutics and diagnostic biomarkers to improve the care of children with this disorder.

British Association of Paediatric Urologists consensus statement on the management of the primary obstructive megaureter

INTRODUCTION

It is well-known that the majority of congenital megaureters may be managed conservatively, but the indications and surgical options in patients requiring intervention are less well defined. Hence this topic was selected for discussion at the 2012 consensus meeting of the British Association of Paediatric Urologists (BAPU). Our aim was to establish current UK practice and derive a consensus management strategy.

METHODS

An evidence-based literature review on a predefined set of questions on the management of the primary congenital megaureter was presented to a panel of 56 Consultant Surgeon members of the British Association of Paediatric Urologists (BAPU), and current opinion and practice established. Each question was discussed, and a show of hands determined whether the panel reached a consensus (two-thirds majority).

RESULTS

The BAPU defined a ureteric diameter over 7 mm as abnormal. The recommendation was for newborns with prenatally diagnosed hydroureteronephrosis to receive antibiotic prophylaxis and be investigated with an ultrasound scan and micturating cystourethrogram, followed by a diuretic renogram once VUR and bladder outlet obstruction had been excluded. Initial management of primary megaureters is conservative. Indications for surgical intervention include symptoms such as febrile UTIs or pain, and in the asymptomatic patient, a DRF below 40% associated with massive or progressive hydronephrosis, or a drop in differential function on serial renograms. The BAPU recommended a ureteral reimplantation in patients over 1 year of age but recognized that the procedure may be challenging in infancy. Proposed alternatives were the insertion of a temporary JJ stent or a refluxing reimplantation.

CONCLUSION

A peer-reviewed consensus guideline for the management of the primary megaureter has been established. The guideline is based on current evidence and peer practice and the BAPU recognized that new techniques requiring further studies may have a role in future management.

Is the pelviureteric junction an anatomical entity?

OBJECTIVE

The concept of the pelviureteric junction has existed for more than a century and yet there is no clear anatomical definition of this junction. This systematic review addresses the question of whether the human pelviureteric junction is a discrete anatomical entity.

METHODS

A systematic literature review was undertaken to investigate the normal gross and microscopic anatomy of the pelviureteric junction using the electronic databases MEDLINE, PubMed, Cochrane Library and Google Scholar.

RESULTS

In most individuals there is a gradual transition between the renal pelvis and ureter with no external features indicating the presence of a discrete pelviureteric 'junction'. Internally, however, luminal mucosal folds are prominent in this region. There is no consensus on the arrangement of muscle fibers at the pelviureteric junction (which may be age-dependent) although some studies suggest a focal thickening in the muscle wall consistent with physiological observations suggesting a high pressure zone capable of regulating urine flow. Studies of innervation have shown no evidence of specialization at this site.

CONCLUSIONS

There is some evidence that a pelviureteric region can be delineated anatomically and physiologically. However, although it may be a useful clinical concept, there is no sound anatomical basis for an actual pelviureteric junction.

The roles of extracellular matrix proteins, apoptosis and c-kit positive cells in the pathogenesis of ureteropelvic junction obstruction

AIM

To investigate histopathological changes in ureteropelvic junction obstruction (UPJO) from an etiological perspective.

PATIENTS AND METHODS

Medical records of patients with UPJO were reviewed and pathological specimens collected. Nephrectomy materials from forensic autopsies were taken as controls. Specimens were assessed with light microscopy. Fibronectin, type 4 collagen, laminin, Bax and Bcl-2 expression for apoptosis, together with interstitial cells of Cajal determination with c-kit were determined immunohistochemically. Staining scores were evaluated semiquantitatively. Results were evaluated using Mann-Whitney U-test.

RESULTS

Control group comprised 14 children (median age, 3.5 years; 6 months-17 years). Study group comprised 22 children with UPJO (median age, 9 months; 1 month-10 years). Light microscopy revealed non-specific inflammation, epithelial proliferation and atrophy with fibrosis in the smooth muscle of the UPJ in all patients. Fibronectin, type 4 collagen and laminin were found to be significantly increased in UPJO at the intrafascicular space of smooth muscle and the matrix of stroma. Bcl-2 expression was increased in UPJO. c-Kit was unable to stain interstitial cells of Cajal, but staining for mast cells was significant.

CONCLUSIONS

High expression of fibronectin, laminin and type 4 collagen may indicate a relation to the pathogenesis of UPJO. Defective kidney morphogenesis, during branching and tubulogenesis of ureteric bud, may be responsible for this congenital pathology.

CONGENITAL URINARY BLADDER OUTLET OBSTRUCTION

The term congenital ‘bladder outlet obstruction (BOO)’ describes the collection of conditions in which the normal, urethral egress of urine from the fetal bladder is impaired. The term is interchangeable with fetal ‘lower urinary tract obstruction’, as used by other authors. After considering normal urinary tract embryology, we describe the epidemiology of congenital BOO and the primary anatomical disorders associated with it. We then proceed to describe its fetal and postnatal clinical manifestations and then consider therapies and interventions which have been used to manage the condition. We not only focus on urethral and bladder disease with constitutes BOO itself, but also describe associated kidney disorders which, via chronic renal excretory failure, are important causes of morbidity. Rather than provide an exhaustive review, we emphasise studies published in the last decade, and therefore readers are referred to other reviews citing numerous earlier references.

Analysis of TSHZ2 and TSHZ3 genes in congenital pelvi-ureteric junction obstruction

BACKGROUND

Congenital pelvi-ureteric junction obstruction (PUJO) affects 0.3% of human births. It may result from aberrant smooth muscle development in the renal pelvis, resulting in hydronephrosis. Mice that are null mutant for the Teashirt3 (Tshz3) gene exhibit congenital PUJO with defective smooth muscle differentiation and absent peristalsis in the proximal ureter.

METHODS

Given the phenotype of Tshz3 mutant mice, we considered that Teashirt genes, which code for a family of transcription factors, might represent candidate genes for human PUJO. To evaluate this possibility, we used in situ hydridization to analyse the three mammalian Tshz genes in mouse embryonic ureters and determined whether TSHZ3 was expressed in the human embryonic ureter. TSHZ2 and TSHZ3 were sequenced in index cases with non-syndromic PUJO.

RESULTS

Tshz2 and Tshz3 genes were detected in mouse ureters and TSHZ3 was expressed in the human embryonic renal pelvis. Direct sequencing of TSHZ2 and TSHZ3 did not identify any mutations in an initial cohort of 48 PUJO index cases, excluding these genes as a major cause of this condition. A polymorphic missense change (E469G) in TSHZ3 was identified at a residue highly conserved throughout evolution in all Teashirt proteins, although subsequently no significant difference between the E469G allele frequency in Albanian and Macedonian PUJO index cases (3.2%) versus 633 control individuals (1.7%) was found (P = 0.18).

CONCLUSIONS

Mutations in TSHZ2 and TSHZ3 are not a major cause of PUJO, at least in Albanian and Macedonian populations. Expression of these genes in the human fetal ureter emphasizes the importance of analysing these genes in other groups of patients with renal tract malformations.

Ureter myogenesis: putting Teashirt into context

After the basic shape of the mammalian ureter is established, its epithelia mature and a coat of smooth muscle cells differentiate around nascent urothelia. The ureter actively propels tubular fluid from the renal pelvis to the bladder, and this peristalsis, which starts in the fetal period, requires coordinated smooth muscle contraction. Teashirt-3 (Tshz3) is expressed in smooth muscle cell precursors that form the wall of the forming mammalian ureter. The Teashirt gene family was first identified in Drosophila where Teashirt (Tsh) protein acts as a transcription factor directing embryonic anterior-posterior patterning and leg and eye development. In fly embryonic renal tubules, Tsh is expressed in mesodermally derived stellate cells intercalating between principal cells, and a paralogue, tiptop, is expressed in forming tubules. Teashirt is a component of several gene networks in flies and it is notable that similar networks control mammalian renal tract development. Null mutation of Tshz3 in mice leads to failure of functional muscularization in the top of the ureter and this is followed by congenital hydronephrosis. A signaling pathway can be envisaged, starting with sonic hedgehog secreted by the nascent ureteric urothelium and ending with ureteric smooth muscle cell differentiation, with Tshz3 downstream of bone morphogenetic protein 4 and upstream of myocardin and smooth muscle cell contractile protein synthesis. The phenotype of Tshz3 mutant mice resembles that of human congenital pelviureteric junction obstruction, and we suggest these individuals may have mutations of genes encoding molecules in the differentiation pathway mediated by Tshz3.

Upper urinary tract dilatation: prenatal diagnosis, management and outcome

Upper urinary tract dilatation is one of the most common abnormalities detected on prenatal ultrasound scanning. It is commonly due to transient urine flow impairment (UFI) at the level of the pelvi-ureteric and vesico-ureteric junctions, which improves with time in most cases. It is usually in the neonatal period that the diagnosis is confirmed and during the first 18 months of life that the prognosis of the dilatation is defined.

Prenatal and Postnatal Neuromuscular Development of the Ureterovesical Junction

PURPOSE

The mechanisms underlying functional maturation of the ureterovesical junction during infancy are still not fully understood. We analyzed the development of smooth muscle components of the ureterovesical junction and their nerve supply in the fetal, newborn and adolescent pig.

MATERIALS AND METHODS

Bladder specimens were obtained from porcine fetuses at gestational ages 60 days (5) and 90 days (5), newborn piglets (5) and 6-month-old pigs (4). Serial sections of the ureterovesical junction were investigated by Masson's trichrome, and hematoxylin and eosin histological staining, enzyme immunohistochemistry for alpha-smooth muscle actin and desmin, as well as double immunofluorescence staining using the neuronal marker peripherin and smooth muscle actin.

RESULTS

At day 60 the detrusor muscle already consisted of distinctive muscle bundles with rich innervation, while the smooth muscle coat of the extravesical ureter and subsequently the intravesical ureter had only started to differentiate. At day 60 innervation of the extravesical ureteral smooth muscle was well developed, while the innervation of the intramural part did not mature until birth. Muscle fibers of the periureteral sheath were well distinguishable at day 60 but innervation of these fibers was sparse during fetal life and showed a remarkable increase during the postnatal period. All smooth muscle components showed a striking increase in muscle bulk between the neonatal and adolescent stages.

CONCLUSIONS

Our findings show that the smooth muscle components and innervation of the ureterovesical junction continue to mature during the postnatal period. This may have implications for managing ureterovesical junction disorders.

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.

An anatomical description of the male and female urethral sphincter complex

PURPOSE

We performed a detailed study of the lower urinary tract of the male and female human fetus to elucidate the anatomy of the urethral sphincter complex in both sexes and its relationship to the surrounding organs and tissues.

MATERIALS AND METHODS

A total of 12 male and 14 female normal human pelvic specimens ranging from 17.5 to 38 weeks of gestation were studied by serial sections and immunohistochemical analysis. Three-dimensional reconstructions were created from serial sections to demonstrate the anatomy of the lower urogenital tract and urethral sphincter in both sexes. Specific attention was directed to the sphincteric muscle of the urethra.

RESULTS

The urinary continence mechanism is formed by a combination of detrusor, trigone and urethral sphincter muscles with distinctive histological characteristics in both sexes. In males the external urethral sphincter covers the ventral surface of the prostate as a crescent shape above the verumontanum, horseshoe shape below the verumontanum and crescent shape along the proximal bulbar urethra. The levator ani muscles form an open circle around the external sphincter with a hiatus at the ventral aspect. In females the external urethral sphincter covers the ventral surface of the urethra in a horseshoe shape. Caudally the same horseshoe-shaped external sphincter increases in size to envelop the distal vagina. The levator ani muscles do not support the proximal urethra. The smooth and striated muscle components of the urethral sphincter complex are inseparable in both sexes.

CONCLUSIONS

The developmental anatomy of the urethral sphincter complex is analogous in both sexes. The male and female urinary sphincter mechanism is composed of detrusor, trigone and urethral muscles, each of different muscular origins. The levator ani does not surround the ventral aspect of the urethra and may not have an active role in continence in both sexes. This new concept in the anatomy of male and female sphincter morphology may help to refine our reconstructive and ablative surgical techniques.

Development of visceral smooth muscle

The development of the smooth musculature of viscera has attracted the interest of only relatively few investigators, and thus the field appears somewhat underexplored. The major emphasis on histochemical evidence--at the expense of ultrastructural and functional studies--may have limited the progress in this area. Mature tissue is formed through the differentiation of precursors into muscle cells and through the organization of these cells into a complex tissue where distribution and orientation of muscle cells, deployment of abundant extracellular materials and addition of other cellular elements (interstitial cells, fibroblasts, nerves, blood vessels) are characteristic and specific features. The precursor cells are found at sites where a muscle develops, and they derive predominantly from the mesoderm, but also from the neuroectoderm and from the endoderm. The process starts at different times in different organs. The earliest stages of differentiation are characterized by the precursor cells aggregating and becoming elongated; their longitudinal axis lies in a position similar to the one they will have in the mature muscle. Both the cytological and the histochemical differentiation follow distinct patterns in various muscles, with characteristic temporal sequences in the appearance of key features. This process must impart distinct functional properties to a muscle cell at each stage of its development. However, the chronological correspondence between ultrastructural and histochemical development is poorly understood. Histochemical studies have detected gradients of maturation of the muscle cells, for example, across the thickness of the gizzard musculature and along the length of the small intestine; ultrastructural studies have not yet confirmed the existence of these gradients. Muscle growth is accounted for by muscle cell enlargement (without nucleus duplication) and an increase in muscle cell number by mitosis of pre-existing differentiated muscle cells. De-differentiation and division of muscle cells, migration of muscle cells and late development of muscle cell precursors have all also been considered as possible mechanisms for muscle growth. Several authors have described the presence of precursor cells within developing smooth muscles, and they have described late differentiation of some muscle cells or waves of differentiation that would give rise to phenotypic heterogeneity of the mature muscle cell population. In contrast, other studies, mainly by electron microscopy, have suggested that, within large visceral muscles, the muscle cells differentiate synchronously. There are interesting data on the influence of adjacent tissues on the development of a smooth muscle, but the interplay of these and other factors has not been fully investigated. Smooth muscles contract from early in their development, hence mechanical factors are likely to influence development: on the one hand, passive stresses imposed on the muscle by other tissues, such as adjacent muscles or the contents of the viscera and, on the other hand, active forces generated by the muscle itself. The very attraction of visceral smooth muscles in the study of cellular morphogenesis--an attraction that has not yet been highlighted or exploited in scientific studies, either descriptively or experimentally--is that, onto a single type of cell, a large range of factors interact, such as the genetic expression, chemical influences (from other muscles, endocrine glands, nerves, other intramuscular cells) and mechanical factors.

Sonic hedgehog regulates proliferation and differentiation of mesenchymal cells in the mouse metanephric kidney

Signaling by the ureteric bud epithelium is essential for survival,proliferation and differentiation of the metanephric mesenchyme during kidney development. Most studies that have addressed ureteric signaling have focused on the proximal, branching, ureteric epithelium. We demonstrate that sonic hedgehog is expressed in the ureteric epithelium of the distal, non-branching medullary collecting ducts and continues into the epithelium of the ureter— the urinary outflow tract that connects the kidney with the bladder. Upregulation of patched 1, the sonic hedgehog receptor and a downstream target gene of the signaling pathway in the mesenchyme surrounding the distal collecting ducts and the ureter suggests that sonic hedgehog acts as a paracrine signal. In vivo and in vitro analyses demonstrate that sonic hedgehog promotes mesenchymal cell proliferation, regulates the timing of differentiation of smooth muscle progenitor cells, and sets the pattern of mesenchymal differentiation through its dose-dependent inhibition of smooth muscle formation. In addition, we also show that bone morphogenetic protein 4 is a downstream target gene of sonic hedgehog signaling in kidney stroma and ureteral mesenchyme, but does not mediate the effects of sonic hedgehog in the control of mesenchymal proliferation.

Morphogenesis of the ureterovesical junction:a histologic and microanatomic study in the rat

OBJECTIVES

To investigate the development of the ureterovesical junction in rats.

METHODS

A total of 110 albino rats (50 prenatal and 60 newborn) with a gestation of 21 days were studied at the age of 17 days after conception until 5 days after birth. The lower urinary tract was microdissected. Microphotography (110 animals), histologic examination (44 animals), and scanning electron microscopy (66 animals) of the ureterovesical junction were performed. Urea and creatinine from the amniotic fluid of 20 fetuses and from the urine of 10 neonates were measured.

RESULTS

At day 17 after conception, separate penetration of the mesonephric duct and ureter into the wall of the urogenital sinus was observed. Continuity between the lumen of the ureter and the urogenital sinus was established on day 19 after conception. The straight passage of the intramural ureter into the urogenital sinus at day 17 after conception changed to the definitive L-shape with a vertical entry into the bladder on day 5 after birth. In the distal ureter, the change of the mesenchymal tissue into immature smooth muscle was first observed at birth, and the muscle became mature on the fifth postnatal day. At birth, Waldeyer's sheath was recognized. The creatinine and urea levels were stable prenatally (average 22.4 micromol/L and 6.88 mmol/L, respectively) and rose significantly postnatally (average 133 micromol/L and 32.65 mmol/L, respectively).

CONCLUSIONS

The attachment of the ureter to the urogenital sinus and later to the bladder, the modification of its passage, and its mobility within Waldeyer's sheath may be essential in preventing vesicoureteral reflux. The production of urine and its flow does not seem to be the trigger of ureteral smooth muscle formation.

Three-dimensional mapping of smooth muscle in the distal conducting airways of mouse, rabbit, and monkey

Airway smooth muscle remodeling is implicated in a number of constrictive pulmonary diseases such as asthma and may include changes in smooth muscle orientation and abundance. Both factors were compared in the normal distal bronchioles of the mouse, rabbit, and rhesus monkey (respiratory bronchioles included). Airway smooth muscle was measured by using a three-dimensional approach employing confocal microscopy and whole-mount cytochemistry with fluorochrome-conjugated phalloidin, a probe for polymerized actin. Smooth muscle orientation had a wide range of angles along the airway, but the distribution was conserved among species and among distal airway generations. At the bifurcation of proximal bronchioles, smooth muscle was nearly parallel to the longitudinal axis of the airway. Smooth muscle abundance was significantly different between species (abundance was less in the monkey compared with the mouse and rabbit), and there was a trend for abundance to decrease with each more distal airway generation. This study defines the normal distribution of smooth muscle in three test species and provides a basis for future comparisons with the diseased state.

A novel in-vitro system for the simultaneous exposure of bladder smooth muscle cells to mechanical strain and sustained hydrostatic pressure

The novel hydrostrain system was designed in an effort to establish and maintain conditions that simulate the in-vivo mechanical environment of the bladder. In this laboratory system, ovine bladder smooth muscle cells on flexible, 10-cm-dia silastic membranes were exposed simultaneously to hydrostatic pressure (40 cm H2O, a pressure level currently associated with bladder pathologies) and mechanical strains (up to 25 percent) under standard cell culture conditions for 7 h. Under these conditions, Heparin Binding-Epidermal Growth Factor and Collagen Type III mRNA expression were significantly increased (p<0.01 and 0.1, respectively); however, no changes were observed in Collagen Type I mRNA expression. Decreases in the Collagen Type I:Type III ratio following simultaneous exposure of bladder smooth muscle cells to pathological levels of hydrostatic pressure and mechanical strain in vitro are in agreement with clinically observed increases in Collagen Type III with concomitant decreased human bladder compliance. The results of the present study, therefore, provide cellular/molecular level information relevant to bladder pathology that could have significant implications in the field of clinical urology.

The effects of sustained hydrostatic pressure on select bladder smooth muscle cell functions

PURPOSE

Normal bladder development is believed to depend on the active work of the bladder for storing and expelling urine. When high urinary diversion is performed in infants and the bladder no longer undergoes normal filling, bladder development may be altered, ultimately resulting in bladder dysfunction. To help better understand this relationship of bladder function with growth at the cellular level we developed a novel laboratory method for applying hydrostatic pressure to cell cultures, and we characterized the response of neonatal bladder smooth muscle cells to physiological levels of sustained hydrostatic pressure.

MATERIALS AND METHODS

Neonatal ovine smooth muscle cells staining positive for desmin and alpha-smooth muscle actin were exposed to pressures of 0.3 (controls), 2, 4, 6 and 8.5 cm. water for 1, 3, 5 and 7 days. At the end of the experiments the cells were fixed, stained and counted. Mitogenic activity of the supernatant media from bladder smooth muscle cells exposed to 8.5 cm. water for 5 days (conditioned media) was tested before and after treatments of heating, freezing, passing through a heparin-sepharose affinity chromatography column or after the addition of suramin, a nonspecific growth factor inhibitor. Statistical analysis was performed using Student's t test with p <0.05 considered statistically significant.

RESULTS

Exposure of bladder smooth muscle cells to sustained hydrostatic pressures of 4, 6 and 8.5 cm. water resulted in increased cell proliferation. Differences became statistically significant (p <0.05) by day 5. Also, conditioned media contained mitogenic activity that was ablated by heating, freezing, passage through a heparin-sepharose affinity chromatography column or with the addition of suramin.

CONCLUSIONS

We have demonstrated a proliferative response of neonatal bladder smooth muscle after exposure to physiological levels of sustained hydrostatic pressure. This response is partially due to 1 or more transferable mitogenic factors. These data support the hypothesis that pressure associated with bladder filling is an important stimulus for detrusor development.

The pathophysiology of UPJ obstruction. Current concepts

It took more than half of a century for urologists to recognize that hydronephrosis is not necessarily equivalent to obstruction. Keeping this important truism in mind, particularly when dealing with antenatal hydronephrosis, one must also remember that hydronephrosis is not a normal condition. It is conceivable that although the initial intrinsic stenosis or ureterovascular obstruction may not be clinically significant in terms of renal functional damage, as compensatory renal pelvic dilatation develops, secondary obstructive elements may be recruited to create an insertional anomaly and peripelvic fibrosis. The individual types of UPJ obstruction that are seen in diagnostic studies or on the operating table may represent isolated "snapshots" of evolving pathophysiologic processes. If this is true, patients with asymptomatic congenital hydronephrosis, although lacking obvious renal function loss, require long-term follow-up.

Developmental expression of interstitial collagen genes in fetal bladders

Bovine bladders at 3 stages during fetal development were examined for expression of collagens by immunohistochemistry as well as by measurement of steady state mRNA levels. Expression of type I and type III collagens during the fetal period was compared with that of adult cows as well as a young animal (heifer). Each bladder was separated into a detrusor and a urothelial-lamina propria sample which were then analyzed separately. Distribution and fiber arrangement of types I and III collagens were different depending upon the region of the bladder wall examined. Type III collagen, in particular, has a "coiled" appearance which is especially prominent within the lamina propria. Collagen gene expression showed a distinctive pattern which was different for both type I and type III collagen. While type I collagen gene expression peaked during the late second to early third trimester, type III collagen expression progressively decreased throughout the fetal period. In addition, expression of both collagens was greater in the urothelial-lamina propria fractions. These data demonstrate that the pattern of collagen gene expression in the developing bladder is developmentally regulated and is unique to each of the two major structural layers.

Airway smooth muscle orientation in intraparenchymal airways

Airway smooth muscle (ASM) shortening is the central event leading to bronchoconstriction. The degree to which airway narrowing occurs as a consequence of shortening is a function of both the mechanical properties of the airway wall as well as the orientation of the muscle fibers. Although the latter is theoretically important, it has not been systematically measured to date. The purpose of this study was to determine the angle of orientation of ASM (theta) in normal lungs by using a morphometric approach. We analyzed the airway tree of the left lower lobes of four cats and one human. All material was fixed with 10% buffered Formalin at a pressure of 25 cmH2O for 48 h. The fixed material was dissected along the airway tree to permit isolation of generations 4-18 in the cats and generations 5-22 in the human specimen. Each airway generation was individually embedded in paraffin. Five-micrometer-thick serial sections were cut parallel to the airway long axis and stained with hematoxylin-phloxine-saffron. Each block yielded three to five sections containing ASM. To determine theta, we measured the orientation of ASM nuclei relative to the transverse axis of the airway by using a digitizing tablet and a light microscope (x250) equipped with a drawing tube attachment. Inspection of the sections revealed extensive ASM crisscrossing without a homogeneous orientation. The theta was clustered between -20 degrees and 20 degrees in all airway generations and did not vary much between generations in any of the cats or in the human specimen. When theta was expressed without regard to sign, the mean values were 13.2 degrees in the cats and 13.1 degrees in the human. This magnitude of obliquity is not likely to result in physiologically important changes in airway length during bronchoconstriction.

Histological and histochemical study of the vesicoureteric junction in infancy and childhood

The morphology of the vesicoureteric junction was compared using 19 post mortem specimens obtained from male and female Afro-American and Caucasian children with an age range of 1 to 72 months (mean 4). All specimens were serially sectioned and the tissues processed using standard histological and histochemical techniques (acetylcholinesterase ¿AChE¿ and pseudocholinesterase ¿PChE¿). The results failed to reveal any differences in the structure of the vesicoureteric junction with respect to age, sex and ethnic origins. The vesicoureteric junction comprised 3 histologically and histochemically distinct smooth muscle components. Ureteric muscle formed a complete inner layer rich in PChE which continued beyond the ureteric orifices to merge distally with the superficial trigone. An intermediate layer of muscle was also demonstrated whose constituent muscle cells possessed specific histological features and which was rich in both AChE and PChE, which is distinct from that derived from the ureter and detrusor. The presence of detrusor muscle on the outer aspect of the juxtavesical segment of ureter rich in AChE was also confirmed. While this study, using histochemical studies in infants and children, did not reveal any differences in the structure of the vesicoureteric junction with respect to age, sex or ethnic origin, an intermediate layer of muscle was identified with histochemical characteristics more like that of the male genital tract than that derived from the ureter or detrusor muscle.

A view on the anatomy of the ureterovesical junction

Macro- and microscopic dissection of 8 adult and 2 fetal human bladders was undertaken in two directions as part of a study to evaluate ureterovesical junction function. In the trigonal region the detrusor muscle consists of 3, more or less triangular layers. Both ureters are only loosely enveloped by a fibromuscular sheath of mainly bladder origin. This design allows for easy movement of the ureters on their oblique course through the bladder wall. The ureteral muscle fibers play only a minor part in the sheath or join the detrusor muscle. The majority fan out to end at the bladder mucosa or intermingle with fibers originating from the opposite ureter. Since an intricate muscular structure can be demonstrated, an active anti-reflux muscular component in the normal human bladder seems plausible. A classic ureteral sphincter mechanism does not exist. Our findings are discussed and compared with data from the literature.

Collagen and elastin in the normal fetal bladder

The development of muscle, collagen and elastic fibers was studied histologically in 15 human fetal bladder specimens. Muscle thickness progressively increased and the relative collagen content in the muscle decreased during gestation. The ratio of thick-to-thin collagen fibers also decreased, whereas elastic fibers increased. These findings document the normal process of maturation of the fetal bladder and serve as a basis for comparison with congenitally obstructed fetal bladders.

Histologic, morphometric, and immunocytochemical analysis of myometrial development in rats and mice: I. Normal development

Myometrial development from the prenatal to adult period was examined in rats and mice 1) by histologic and immunocytochemical methods with anti-actin, -vimentin, and -laminin to assess cytodifferentiation of smooth muscle and fibroblastic cells; and 2) by morphometric procedures to assess quantitatively the expression of cellular orientation in the emerging inner circular myometrial layer. Uterine mesenchymal cells initially were uniformly vimentin-positive, undifferentiated, and randomly oriented during the late fetal period. By the early neonatal period, three mesenchymal layers became recognizable histologically, the middle one of which (prospective circular myometrium) developed distinct circular orientation and differentiated into a layer composed of actin-positive smooth muscle cells. The cells of the inner mesenchymal layer initially exhibited radial orientation. By 10 days postpartum, the outer longitudinal mesenchymal layer differentiated into bundles of smooth muscle cells representing the longitudinal myometrium. The inner mesenchymal layer remained vimentin-positive and differentiated into the randomly ordered endometrial stroma. The cells of the middle and outer mesenchymal layers that were destined to form myometrium initially expressed vimentin throughout and then coexpressed vimentin and actin, but with time vimentin staining disappeared in the maturing smooth muscle cells as they expressed actin.

Pathology of ureterorenal units in various ureteral anomalies with particular reference to the genesis of renal dysplasia

Renal morphology of various congenital ureteral anomalies was investigated to gain further insight into the genesis of associated renal dysplasia. Abnormality in the ureteral bud explains the genesis of renal dysplasia as long as the adjoining ureter is cranially ectopic. In caudal ectopy of either single or duplex system, no difference was found in the histologic quality of kidneys with G and H position orifice. In the single system kidneys of H position orifice, however, occurrence of renal dysplasia was not associated with obstruction, suggesting the operation of the "bud theory" even in single system caudal ectopy. In anomalies in which the ureteral orifice was not ectopic, it was suggested that renal parenchymal development was impaired by complete, but not by incomplete obstruction. The association of dysplastic ureter and renal dysplasia was not so frequent as anticipated and the hypodysplastic values of the kidneys with and without dysplastic ureters were similar, suggesting no direct causal relationship between them.