3D kidney organoids for bench-to-bedside translation

The kidneys are essential organs that filter the blood, removing urinary waste while maintaining fluid and electrolyte homeostasis. Current conventional research models such as static cell cultures and animal models are insufficient to grasp the complex human in vivo situation or lack translational value. To accelerate kidney research, novel research tools are required. Recent developments have allowed the directed differentiation of induced pluripotent stem cells to generate kidney organoids. Kidney organoids resemble the human kidney in vitro and can be applied in regenerative medicine and as developmental, toxicity, and disease models. Although current studies have shown great promise, challenges remain including the immaturity, limited reproducibility, and lack of perfusable vascular and collecting duct systems. This review gives an overview of our current understanding of nephrogenesis that enabled the generation of kidney organoids. Next, the potential applications of kidney organoids are discussed followed by future perspectives. This review proposes that advancement in kidney organoid research will be facilitated through our increasing knowledge on nephrogenesis and combining promising techniques such as organ-on-a-chip models.

Aberrant differentiation of urothelial cells in patients with ureteropelvic junction obstruction

AIM

To investigate the urothelial changes in the pathogenesis of ureteropelvic junction obstruction (UPJ-O).

METHODS

A total of 12 patients of UPJ-O were respectively studied. The expression of Annexin A7, Annexin A11, EGFR, Keratin 5, uroplakin III, and SMA in the urothelium of obstructed UPJ segment and of the normal ureter below the obstructed segment were determined by immunofluorescence. Transmission electron microscopy was used to determine the morphological changes in UPJ epithelium in compared to normal ureteral epithelium.

RESULTS

We found that Annexin A7, Annexin A11, EGFR, Keratin 5, and SMA were upregulated, while uroplakin III was downregulated in the urothelium of UPJ-O patients. Furthermore, ultrastructural analyses showed that intercellular spaces between urothelial cells were dilated and the number of microvilli on superficial cells was increased in UPJ-O patients.

CONCLUSIONS

We propose that a disrupted urothelial barrier in UPJ-O may results in urothelial inflammatory response and truncated differentiated urothelial cells, which may play an important role in the development and pathogenesis of UPJO.

Imaging tools for analysis of the ureteric tree in the developing mouse kidney

The structure of the ureteric tree in developing mouse and rat kidneys has previously been quantified in two dimensions. While this type of analysis may provide evidence of changes in ureteric growth, these measurements are effectively inaccurate, as the ureteric tree is a three-dimensional (3D) object. Here we describe a method for measuring the ureteric tree in three dimensions. This technique involves (1) culture of the metanephric kidney at embryonic day 12 (mouse) or 14 (rat), (2) whole-mount immunofluorescence to selectively stain ureteric tree epithelium, (3) confocal microscopy to obtain a complete Z series through the ureteric tree, and (4) image analysis algorithms to binarize, skeletonize, and measure individual branch lengths in 3D. This method has been extended to analysis of the same ureteric tree over time (4D). The results obtained provide accurate and precise quantitation of ureteric tree growth in the developing mouse or rat kidney.

[Scanning electron microscopy of resected ureters in children with ureterohydronephrosis]

Using scanning electron microscopy, various portions of the ureter in reflux and obstructive ureterohydronephrosis in children were evaluated. In the first case, architectonics of the distal portions is preserved, while in the second case connective tissue is proliferated. Differences in the structure of proximal and distal portions in both forms of ureterohydronephrosis consist in inflammatory changes and violation of the integrity of the epithelial lining, edema and infiltration of the underlying layers, especially the inner muscle layer of the distal portion. The wall of the ureter in proximal part is much thinner, especially the muscular and mucous layers.

Analysis of 3D branching pattern: hematoxylin and eosin method

Accurate analysis of the three-dimensional (3D) architecture of developing organs is critical to understanding how developmental defects can be linked with structural abnormalities. Here, we describe a 3D reconstruction technique of the developing kidney including the outer kidney capsule, ureteric epithelium, and developing nephrons. This 3D reconstructive process involves generating serial sections of the developing kidney, followed by histological staining. Each serial image is projected on the monitor and each tissue lineage or structure is traced. The kidney tracings are aligned and a 3D image is rendered. Each reconstructed tissue/lineage can then be subjected to quantitative analysis (e.g., surface area or volume). The reconstructed ureteric epithelium can be skeletonized to determine the branching architecture.

Ureteric branching morphogenesis in BMP4 heterozygous mutant mice

Exogenous bone morphogenetic protein 4 (BMP4) inhibits ureteric branching morphogenesis and amplifies the already existing branching asymmetry in the developing mouse kidney in vitro. In the present study we examined ureteric branching morphogenesis in BMP4/lacZ heterozygous (BMP4(+/-)) mice in vitro under control conditions and in the presence of exogenous BMP4 using three-dimensional image analysis software. The relative expression of BMP4 mRNA was determined in BMP4(+/-) and wildtype urogenital ridges using real-time PCR. Embryonic day 12.5 (E12.5) BMP4(+/-) and wildtype mouse metanephroi were cultured for 48 h with or without 260 ng mL(-1) recombinant human BMP4 (rhBMP4) and were then wholemount immunostained in order to identify the ureteric epithelium, which was quantified in three dimensions. Despite a significant reduction in BMP4 mRNA in BMP4(+/-) mice, qualitative and quantitative studies identified no differences in ureteric branching morphogenesis between phenotypically normal BMP4(+/-) and wildtype metanephroi in either BMP4-treated or control cultures. Both BMP4(+/-) and wildtype metanephroi cultured in the presence of BMP4 showed a decrease in total ureteric length, branch number and ureteric volume, and increased average branch length compared with control cultures. A marked anterior-posterior asymmetry in both ureteric length, branch number and average branch length was observed in BMP4-treated metanephroi from both genotypes. A similar asymmetry was revealed in control metanephroi from both genotypes. This asymmetry is the result of reduced ureteric branching morphogenesis but not elongation in the posterior region of the kidney. These results suggest that despite reduced endogenous BMP4 mRNA levels, most BMP4(+/-) embryos can still facilitate normal ureteric branching morphogenesis during development. In addition, reduced endogenous levels of BMP4 do not alter the inhibitory effects of exogenous BMP4 on ureteric branching or amplification of normal renal asymmetry.

An electron microscopic examination of the intravesical ureter in children with primary vesico-ureteric reflux

OBJECTIVE

To determine the structure of the intravesical distal ureteric wall of patients with primary vesico-ureteric reflux (VUR), and to compare the findings with previous reports.

MATERIALS AND METHODS

Specimens of the distal intravesical ureteric segments were taken surgically from children undergoing ureteric reimplantation surgery for primary VUR. There were 24 distal intravesical ureteric specimens from 15 children (nine female and six male). Ultra-thin sections were cut from the specimens and examined with a transmission electron microscope.

RESULTS

The appearance of the muscular layers of the specimens of different grades differed markedly. There were intercellular oedematous areas in the muscular layer in specimens from patients with grade 2 and 3 VUR. In specimens from grade 4 VUR there were also intracytoplasmic vacuoles in the smooth muscle cells. The most marked and striking changes were in the specimens from children with grade 5 VUR, in which there were large intercellular oedematous areas and prominent large intracytoplasmic vacuoles.

CONCLUSION

Refluxing ureters differ from normal ureters in having disorganized smooth muscle fibres and altered smooth muscle cell structure, leading to incompetence of the valve mechanism. Although we cannot confirm that these pathological changes in the smooth muscle layer of the intravesical ureteric wall are caused by VUR we conclude that, with increasing degrees of reflux, the degree of smooth muscle damage increases, and that the rate of spontaneous resolution decreases.

Rho kinase acts at separate steps in ureteric bud and metanephric mesenchyme morphogenesis during kidney development

In this study, five different in vitro assays, which together recapitulate much of kidney development, were used to examine the role of the Rho-associated protein serine/threonine kinase (ROCK) in events central to ureteric bud (UB) and metanephric mesenchyme (MM) morphogenensis, in isolation and together. ROCK activity was found to be critical for (1) cell proliferation, growth, and development of the whole embryonic kidney in organ culture, (2) tip and stalk formation in cultures of isolated UBs, and (3) migration of MM cells (in a novel MM migration assay) during their condensation at UB tips (in a UB/MM recombination assay). Together, the data indicate selective involvement of Rho/ROCK in distinct morphogenetic processes necessary for kidney development and that the coordination of these events by Rho/ROCK provides a potential mechanism to regulate overall branching patterns, nephron formation, and thus, kidney architecture.

Transient hydroureteronephrosis caused by a Foley's catheter tip in the right ureter

We report a case of unilateral hydronephrosis following urethral catheterization in a patient with T6 complete paraplegia at the Physical Medicine and Rehabilitation Department in a tertiary care teaching hospital, India. Diagnosis was established by an abdominal ultrasound. The misplaced catheter tip was withdrawn from the ureteric orifice and hydronephrosis was resolved. Foley's catheterization, a widely practiced clinical procedure, is not without its attendant risks of an inadvertent placement in the ureter leading to transient hydronephrosis. Inadequate drainage through a catheter should thus alert one to this potentially hazardous complication that can be diagnosed by an early ultrasound. This complication can be avoided by gently tugging on the catheter after inflating the catheter bulb.

Spatiotemporal regulation of morphogenetic molecules during in vitro branching of the isolated ureteric bud: toward a model of branching through budding in the developing kidney

In search of guiding principles involved in the branching of epithelial tubes in the developing kidney, we analyzed branching of the ureteric bud (UB) in whole kidney culture as well as in isolated UB culture independent of mesenchyme but in the presence of mesenchymally derived soluble factors. Microinjection of the UB lumen (both in the isolated UB and in the whole kidney) with fluorescently labeled dextran sulfate demonstrated that branching occurred via smooth tubular epithelial outpouches with a lumen continuous with that of the original structure. Epithelial cells within these outpouches cells were wedge-shaped with actin, myosin-2 and ezrin localized to the luminal side, raising the possibility of a "purse-string" mechanism. Electron microscopy and decoration of heparan sulfates with biotinylated FGF2 revealed that the basolateral surface of the cells remained intact, without the type of cytoplasmic extensions (invadopodia) that are seen in three-dimensional MDCK, mIMCD, and UB cell culture models of branching tubulogenesis. Several growth factor receptors (i.e., FGFR1, FGFR2, c-Ret) and metalloproteases (i.e., MT1-MMP) were localized toward branching UB tips. A large survey of markers revealed the ER chaperone BiP to be highly expressed at UB tips, which, by electron microscopy, are enriched in rough endoplasmic reticulum and Golgi, supporting high activity in the synthesis of transmembrane and secretory proteins at UB tips. After early diffuse proliferation, proliferating and mitotic cells were mostly found within the branching ampullae, whereas apoptotic cells were mostly found in stalks. Gene array experiments, together with protein expression analysis by immunoblotting, revealed a differential spatiotemporal distribution of several proteins associated with epithelial maturation and polarization, including intercellular junctional proteins (e.g., ZO-1, claudin-3, E-cadherin) and the subapical cytoskeletal/microvillar protein ezrin. In addition, Ksp-cadherin was found at UB ampullary cells next to developing outpouches, suggesting a role in epithelial-mesenchymal interactions. These data from the isolated UB culture system support a model where UB branching occurs through outpouching possibly mediated by wedge-shaped cells created through an apical cytoskeletal purse-string mechanism. Additional potential mechanisms include (1) differential localization of growth factor receptors and metalloproteases at tips relative to stalks; (2) creation of a secretory epithelium, in part manifested by increased expression of the ER chaperone BiP, at tips relative to stalks; (3) after initial diffuse proliferation, coexistence of a balance of proliferation vs. apoptosis favoring tip growth with a very different balance in elongating stalks; and (4) differential maturation of the tight and adherens junctions as the structures develop. Because, without mesenchyme, both lateral and bifid branching occurs (including the ureter), the mesenchyme probably restricts lateral branching and provides guidance cues in vivo for directional branching and elongation as well as functioning to modulate tubular caliber and induce differentiation. Selective cadherin, claudin, and microvillar protein expression as the UB matures likely enables the formation of a tight, polarized differentiated epithelium. Although, in vivo, metanephric mesenchyme development occurs simultaneously with UB branching, these studies shed light on how (mesenchymally derived) soluble factors alone regulate spatial and temporal expression of morphogenetic molecules and processes (proliferation, apoptosis, etc.) postulated to be essential to the UB branching program as it forms an arborized structure with a continuous lumen.

[Structural-functional organization of dark and light smooth myocytes in the musculature of visceral organs]

Using electron microscopy, the smooth musculature of human and laboratory animal bronchi, intestine and ureters was found to contain smooth myocytes of light and dark types, which had the cytoplasm of different electron density. Both types of myocytes are characterized by a high degree of differentiation. The significant differences between light and dark myocytes were detected in the ultrastructural organization of their contractile elements. On the basis of data obtained, light and dark myocytes should be considered as mature cells in different phases of their functional activity. Some part of them, light myocytes, are in the state of "passive" contraction and may serve as a tissue functional reserve. Mutual transformation of light and dark myocytes seems to be possible and may be caused by functional requirements, which are realized at the level of tissue regulation.

A proliferation-dependent bystander effect in primary porcine and human urothelial explants in response to targeted irradiation

The aim of this study was to test whether radiation-induced bystander effects are involved in the response of multicellular systems to targeted irradiation. A primary explant technique was used that reconstructed the in vivo microarchitecture of normal urothelium with proliferating and differentiated cells present. Sections of human and porcine ureter were cultured as explants and irradiated on day 7 when the urothelial outgrowth formed a halo around the tissue fragment. The Gray Cancer Institute charge particle microbeam facility allowed the irradiation of individual cells within the explant outgrowth with a predetermined exact number of (3)He(2+) ions (which have very similar biological effectiveness to alpha-particles). A total of 10 individual cell nuclei were irradiated with 10 (3)He(2+) ions either on the periphery, where proliferating cells are located, or at the centre of the explant outgrowth, which consisted of terminally differentiated cells. Samples were fixed 3 days after irradiation, stained and scored. The fraction of apoptotic and micronucleated cells was measured and a significant bystander-induced damage was observed. Approximately 2000-6000 cells could be damaged by the irradiation of a few cells initially, suggesting a cascade mechanism of cell damage induction. However, the fraction of micronucleated and apoptotic cells did not exceed 1-2% of the total number of the cells within the explant outgrowth. It is concluded that the bystander-induced damage depends on the proliferation status of the cells and can be observed in an in vitro explant model.

Microscopic and ultrastructural lesions of the ureter and renal pelvis in sows with regard to Actinobaculum suis infection

Tissues from ureter and renal pelvis of 18 sows naturally (n = 15) and experimentally (n = 3) infected with Actinobaculum suis (former Actinomyces, Eubacterium suis) were studied using light and scanning as well as transmission electron microscopy. The results were compared with the findings from 11 clinically healthy sows as controls. The lesions in both the ureter and renal pelvis of naturally and experimentally infected animals were similar. In severe cases there were necrotizing ureteritis and pyelitis with accumulation of bacterial colonies in some cases. Several superficial epithelial cells were found phagocytosing necrotic debris. In mild cases the main lesions included epithelial cell hyperplasia, desquamation of the superficial epithelial cells and goblet cell metaplasia with intraepithelial cyst formation. The goblet cells were found in the superficial as well as in the intermediate cell layers. Generally, it was observed that severe purulent ureteritis and pyelitis/ pyelonephritis in sows were to be expected only in mixed infection of A. suis with other bacteria. The findings were compared and discussed with the changes in the infected urinary bladder of sows and the alterations induced by urinary tract infection in man.

Fine structural aspects of the urothelium in the mouse ureter with special reference to cell kinetics

The present study aimed at clarifying the cell kinetics of the mouse ureteral epithelium by focusing on vesicle maturation in the cells and labeling with bromodeoxyuridine (BrdU). Electron microscopically, superficial cells were characterized by concave plaques in the apical plasma membrane and numerous fusiform vesicles in the cytoplasm. Intermediate cells were laden with ellipsoid vesicles, and basal cells had a few or no round vesicles. From the difference in number and form of vesicles among the three types of cells, it can be inferred that intermediate cells are immature in comparison with superficial cells, and likewise basal cells in comparison with intermediate cells. When BrdU was injected intraperitoneally once a day for seven days, most BrdU-labeled cells were located in the basal layer. Twelve days after the last injection, BrdU was detected in the intermediate or superficial layer in addition to the basal layer. These findings suggest that the basal cell is a progenitor cell giving rise to daughter cells that migrate upward to replace intermediate and superficial cells.

The three-dimensional structure of the neonatal mouse kidney as revealed by scanning electron microscopy after KOH treatment

The shape and arrangement of the developing nephrons were studied three-dimensionally by scanning electron microscopy (SEM) of the neonatal mouse kidney. The specimens were treated with the KOH digestion method in order to remove extracellular connective tissue components, thus enabling the direct observation of the developing nephrons at various stages. At the subcapsular region of the renal cortex, the ureteric ducts were observed as branched tubules with terminal swellings or ampullae. Newly formed blood vessels were often associated with terminals of these ureteric ducts. The cup-shaped renal corpuscles had aggregations of mesangial cells with blood vessels in the groove. At the vascular pole of mature nephrons, extraglomerular mesangial cells were observed as a cellular sheet, which was continuous with the smooth muscle layer of afferent and efferent blood vessels. The present study also demonstrated the shape of the immature podocytes in relation to the endothelial morphology of glomerular capillaries.

ATP is released from guinea pig ureter epithelium on distension

Distension of the perfused guinea pig ureter at pressures from 20 to 700 cmH(2)O increased the amount of ATP released from the epithelium in a pressure-dependent manner. During basal perfusion (40 microl/min), the perfusate contained 10 pmol/ml ATP; this increased 10- to 50-fold at various distending pressures. ATP was released from epithelial cells during distension as mechanical removal of the urothelium blocked release. No lactate dehydrogenase was detected in the perfusate, and scanning electron microscopy confirmed an intact urothelium after distension. ATP was not released due to the activation of stretch-activated channels, as gadolinium (10 microM) failed to affect ATP release. Glibenclamide (10 microM), known to inhibit two members of the ATP-binding cassette (ABC) protein family, did not affect ATP release after distension; nor did verapamil (10 microM). In contrast, both monensin (100 microM) and brefeldin A (10 microM), which interfere with vesicular formation or trafficking, inhibited distension-evoked ATP release, which was Ca(2+)-dependent. This suggests that ATP release from the ureter epithelium might be mediated by vesicular exocytosis. The role of ATP released by distension of hollow visceral organs is discussed in relation to the concept of purinergic mechanosensory transductions, with special reference to nociception and the activation of P2X(3) receptors on the subepithelial sensory nerves.

[Reactive restructuring of ureteral smooth muscle tissue during development of urinary vesico-ureteral reflux in children]

By means of target cell dissociation we studied the cells of smooth muscle tissue from the wall of intact ureter in children in the course of compensatory-adaptive reactions in the vesico-ureteral reflux. Three types of ureteral myocytes differing by structural-metabolic parameters are distinguished. A comparative analysis of the intact and reactively altered ureteral smooth muscle tissue has revealed changes in the population structure manifesting with high optic density of DNA from myocytic nuclei and high activity of synthetic processes in the cytoplasm.

Characterization of the spontaneous electrical and contractile activity of smooth muscle cells in the rat upper urinary tract

PURPOSE

We morphologically and electrophysiologically identified the cells that generate the electrical activity underlying the peristaltic contractions of the rat upper urinary tract.

MATERIALS AND METHODS

Electron microscopy and tension recording techniques were used to characterize the smooth muscle cells underlying spontaneous contractions in the wall of the rat ureter, and proximal and distal renal pelvis. Intracellular microelectrodes, containing 4% neurobiotin were used to record data from the cells of the renal pelvis, which were later viewed on a confocal microscope.

RESULTS

Spontaneous myogenic contractions (average 22.3 +/- 2.2 minutes(-1)) originated in the proximal renal pelvis and propagated into the distal renal pelvis and ureter in 6 preparations. Smooth muscle cells in the renal pelvis and ureter were typical in appearance with greater than 85% of their sectional area containing clumped contractile filaments. In contrast, contractile fibrils occupied only 65% of the sectional area of the smooth muscle cells within the most proximal region of the renal pelvis (pelvicaliceal junction). In strips of the renal pelvis spindle shaped cells 83 to 200 microm. long fired spontaneous action potentials (6 minutes(-1)) consisting of an initial spike, a quiescent plateau phase and abrupt hyperpolarization to a peak diastolic potential of -60 mV. Other spindle shaped cells 94 to 112 microm. long displayed small membrane transients (15 minutes(-1)) 9 to 19 mV. in amplitude, firing from a diastolic potential of -40 mV.

CONCLUSIONS

It is likely that the spontaneous contractile activity of the rat upper urinary tract arises from the discharge of action potentials in typical smooth muscle cells of the proximal renal pelvis that are directly driven by the spontaneous membrane oscillations of atypical smooth muscle cells.

Three-dimensional analysis of nephrogenesis in the neonatal rat kidney: light and scanning electron microscopic studies

In order to clarify the process of renal development more precisely than previously, the present study observed the rat neonatal kidney by scanning electron microscopy (SEM) of KOH digested tissue as well as by light microscopy of plastic sections. In the subcapsular region, aggregation of the mesenchymal cells was closely associated with the upper side of the ureteric duct ampulla. These mesenchymal cells projected a number of fine irregular processes at the basal portion facing the ureteric duct. A spherical cluster transformed from the mesenchymal cell aggregation was found on the lower side of the terminal ampulla, and was differentiated into the renal vesicle. Some cells at the top of the renal vesicle formed a cone-shaped projection and invaded the ureteric duct ampulla, forming a connection with it. In the advanced stage, a shallow transverse cleft appeared on the outer lateral side of the renal vesicle, and a second cleft was formed on the opposite side close to the junction between the renal vesicle and the ampulla. As the two clefts deepened, the vesicle assumed the well-known S-shaped body. In the advanced S-shaped body, the lower limb became cup-shaped, while the segment between the middle and lower limbs of the "S" elongated to form a tubular structure (i.e., the prospective proximal tubule and Henle's loop). The upper limb of the "S" also increased its length to form a distal tubule. The middle limb of the "S", however, was attached firmly to the cup-shaped lower limb (i.e., the prospective renal corpuscle) and was considered to become the macula densa of the mature nephron. In the maturing renal corpuscle, irregularly shaped cells were observed as a sheet-like aggregation at its vascular pole and were continuous with the vascular smooth muscle cells. These findings will help toward a better understanding of the morphological complexities of nephrogenesis.

Mucinous vacuolar change of porcine urothelium induced by regional embolism or cryoablation

Porcine urinary tract epithelium responds to systemic infections with an increase in mucin secretion that has been called "mucinous degeneration." Here we describe similar changes in calyceal, pelvic, and ureteric urothelium in pig renal tracts 14 days after local embolism and cryoablation (four kidneys) or cryoablation alone (six kidneys). Large mucin-filled vacuoles surrounded by smaller cytoplasmic vesicles were present in the affected urothelium but were rare in calyceal urothelium of normal kidneys. These mucinous vacuolar changes were proportional to the extent of renal necrosis and could be important in the pathologic responses of xenotransplanted pig kidneys.

A new self-expanding lined stent-graft in the dog ureter: radiological, gross, histopathological and scanning electron microscopic findings

Recurrent or intractable ureteral strictures pose a significant problem for the practicing urologist. Metallic stents have been used sparingly for this problem with varying success. We investigated the use of a stent-graft consisting of a metal stent lined with a porous biocompatible polymer to determine if the liner would prevent urothelial ingrowth. One ureter of each of 11 dogs was treated with either a metallic woven stent or stent-graft inserted retrograde via a midline cystotomy. Six bare wire stents (controls) and five lined with a new, porous, biocompatible, polycarbonate elastomer liner (Corethane) were placed. The animals were followed radiographically with intravenous urography (IVP) at 6 weeks and just prior to sacrifice (12 to 22 weeks). Gross, histological, and electron microscopic analyses were performed. The results demonstrate that all of the bare metal stented animals developed moderate to severe hydroureteronephrosis with significant urothelial hyperplasia and ingrowth through the spaces between the metal wires. The animals implanted with lined stents showed one instance of mild hydroureteronephrosis (observed radiographically but not grossly at time of sacrifice) and virtually no papillary in-growths of urothelium through the stent interstices. This obstructive phenomenon was prevented by the porous polymer lining. There was no evidence of biodegradation of the liner on scanning electron microscopy. Based upon these findings, the marriage of a biocompatible polymer which provokes minimal tissue reaction, and metallic stents which provide tremendous strength, seems to offer significant advantages when placed into the urinary tract to maintain ureteral luminal patency.

The morphology of the ureter in the duck (Anas platyrhynchos)

The morphology of the ureter of the duck was investigated, using histological, SEM and TEM techniques. The inner perimeter, the total thickness of the ureteral wall and the thickness of each uretral layer were measured. The epithelium was tall columnar and pseudostratified along all the tracts of the ureter and showed a high muco-secretive activity. The lamina propria contained numerous capillaries and aggregates of leucocytes and macrophages. Throughout the lamina propria there was a dense plexus of nerves. Some denuded single nerve fibres were observed between the epithelial basal cells. A plexus of nerves was also observed in the tunica muscularis. The ostium cloacale ureteris opened on a well-developed papilla in the dorsal region of the urodeum. The total thickness of the ureteral wall, the thickness of the lamina propria and the tunica muscularis, and the inner perimeter progressively increased towards the ostium. The above observations suggest that the avian ureter plays an important role in the modification of the urine coming from medullary cones, and in emission of the urine into the cloaca.

Free ureteral replacement in rats: regeneration of ureteral wall components in the acellular matrix graft

OBJECTIVES

To evaluate ureteral replacement by a free homologous graft of acellular matrix in a rat model.

METHODS

In 30 male Sprague-Dawley rats, a 0.3 to 0.8-cm midsegment of the left ureter was resected and replaced with an acellular matrix graft of equal length placed on a polyethylene stent. The animals were killed at varying intervals, and the grafted specimens were prepared for light and electron microscopy.

RESULTS

In all animals, the acellular matrix graft remained in its original position without evidence of incrustation or infection, and histologic examination showed complete epithelialization and progressive infiltration by vessels. At 10 weeks, smooth muscle fibers were observed; at 12 weeks, nerve fibers were first detected; at 4 months, smooth muscle cells had assumed regular configuration.

CONCLUSIONS

The ureteral acellular matrix graft appears to promote the regeneration of all ureteral wall components.

Experimental infection of native human ureteral tissue with Neisseria gonorrhoeae: adhesion, invasion, intracellular fate, exocytosis, and passage through a stratified epithelium

The exact mechanisms by which Neisseria gonorrhoeae invades the mucosal lining to cause local and disseminated infections are still not fully understood. The ability of gonococci to infect the human ureter and the mechanism of gonococcal infection in a stratified epithelium were investigated by using distal ureters excised from healthy adult kidney donors. In morphological terms, this tissue closely resembles parts of the urethral proximal epithelium, a site of natural gonococcal infection. Using piliated and nonpiliated variants of N. gonorrhoeae MS11, we demonstrated the importance of pili in the attachment of gonococci to native epithelial cells as well as their association with epithelial damage. By electron microscopy we elucidated the different mechanisms of colonization and invasion of a stratified epithelium, including adherence to surface cells, invasion and eventual release from infected cells, disintegration of intercellular connections followed by paracellular tissue infiltration, invasion of deeper cells, and initiation of cellular destruction and exfoliation resulting in thinning of the mucosa.

Influence of furosemide on the ureteric damage in a rat model of obstructive uropathy

Furosemide has been used in the diuretic renography and diuretic radionuclide scan to evaluate the severity of hydroureter and hydronephrosis. To elucidate the influence of furosemide on obstructed ureters, unilateral ligation of ureter was performed in 45 rats. Twenty-four of the rats received intramuscular injections of furosemide (6 mg/kg/day) after the third day postligation. Eight rats were sacrificed for examination on days 7, 10 and 14 after ligation, respectively. The remaining 21 untreated rats were also sacrificed for comparison. The severity of hydroureter and hydronephrosis in the ligated side of the furosemide-treated rats was significantly higher than that of the untreated rats. However, the histological changes in the treated and untreated rats showed no significant difference. The ultrastructural alterations aggravated along the course of ureteric obstruction. Intriguingly, the ultrastructural changes were significantly milder in the treated rats. We conclude that the administration of furosemide might increase the severity of hydroureter, but it does not accelerate the ureteric damage of the obstructed ureters.

Functions of fibroblast and transforming growth factors in primary organoid-like cultures of normal human urothelium

Previous studies have indicated that growth factors such as epidermal growth factor, transforming growth factor alpha, and fibroblast growth factor 1 (FGF-1) have important regulatory functions in murine urothelial wound healing and tumorigenesis. Immunocytochemical analyses suggest that these factors are also involved in human urothelium. Yet, little is known about the functional effects of these growth factors on human urothelial cells. We established organoid-like primary cultures of normal human urothelium on porous membranes. Direct functional effects of growth factors were examined on confluent cultures reflecting intact urothelium. Immunocytochemistry was performed with a panel of specific antibodies against growth factors and their receptors on both cultures and the corresponding tissue sections. Lacking the appropriate antibodies, we performed reverse transcriptase PCR to detect FGF receptor mRNA in cultures and dissected tissue. The proliferation was stimulated by transforming growth factor alpha, FGF-1, and weakly by FGF-7, but not by FGF-2. TGF beta 1 inhibited proliferation. In contrast to mouse urothelium, none of the growth factors showed an effect on differentiation. The functional data correlate with the urothelial expression of epidermal growth factor receptors, TGF beta receptor types I and II, the (low) protein expression of FGF receptor 1, and the presence of FGF-7 receptor (FGF receptor 2 (IIIb)) mRNA. The organotypic nature of the cultures permits the study of growth factor interactions between urothelial cells. The data indicate that FGF-1, transforming growth factor alpha, and TGF beta 1 contribute differently to the maintenance of human urothelium.

Micronuclei kinetics of exfoliated urothelial cells

Micronuclei observed in exfoliated cells result from DNA-damage of basal epithelium's cells by mutagens. Exfoliated urothelial cells can be collected by non-invasive procedure and may be used as target site to identify genotoxic effects of chemicals. Kinetic studies are important for any biomarker, especially those in which tissue differentiation and maturation processes will heavily influence the time between induction of damage and collection of damaged cells for analysis. This manuscript details the result of a longitudinal study of micronuclei induction in cells isolated from urine samples of 4 healthy women over 6 consecutive days. Three of them were former smokers. Results suggested that micronucleated cell rates were not influenced neither by the day nor by the time of sampling.

Chronic systemic treatment with epidermal growth factor in pigs causes pronounced urothelial growth with accumulation of glycoconjugates

Epidermal growth factor (EGF) is present in large amounts in the urine, but the effects of systemically administered EGF on the urinary tract have not been described previously. In the present paper, we describe a potent growth induction of EGF on the urinary tract. Goettingen minipigs were treated with solvent (n = 5), EGF 30 micrograms/kg/day (n = 6) for 4 weeks, or EGF 30 micrograms/kg/day for 5 weeks followed by 3 weeks of recovery (n = 5). The ureters and bladders were examined by routine histology and electron microscopy and were immunostained for proliferating cell nuclear antigen. Four weeks of EGF treatment increased the median cross sectional area of the ureter fourfold with growth of all wall layers. The urothelium was widened from 5 cell layers in the controls to 10 in the EGF-treated animals. Proliferating cell nuclear antigen immunostaining revealed an increased mitotic activity in the basal zone of the urothelium. In the luminal zone, glycoconjugates accumulated in goblet cells, in cells with intracytoplasmic lumina, and beneath the luminal cell membrane in the umbrella cells. Our studies present a new experimental approach to growth induction of the urinary tract. The findings implicate the EGF system in regulating urothelial growth and glycoconjugate biosynthesis.

The effect of extracorporeal electromagnetic shock waves on the morphology and contractility of rabbit ureter

PURPOSE

Although extracorporeal shock wave lithotripsy (ESWL) is known to cause pathologic changes in various organs, little is known about its effects on the ureter, the target organ in ESWL of ureteral stones in situ. In this study, we sought to determine the short-term effects of ESWL on the ureter.

MATERIALS AND METHODS

Left lower ureteral segments of 21 rabbits were removed to serve as the control group and 2000 shocks were applied to the right lower ureters. Groups of 7 rabbits were sacrificed 1, 3 and 5 days after shock wave exposure. While histomorphological alterations were examined under light and transmission electron microscopy, contractility of all ureters was determined in organ baths.

RESULTS

The epithelial cells disclosed no change after shock wave application. Histologically the muscular layer was the most affected part of the ureter. There was interstitial and intracellular edema on light microscopy and marked chromatin and mitochondrial changes at the subcellular level. The adventitial layer was also edematous. These changes were prominent on days 1 and 3 and returned to normal on day 5. The contractility of the ureters on day 1 was significantly reduced (p < 0.05). However, the contractility of the samples on days 3 and 5 were not significantly different from controls.

CONCLUSION

Our findings demonstrate that electromagnetic shock waves produce reversible morphological and functional changes in rabbit ureteric muscle.

The interaction of laser energy with ureter tissues in a long-term investigation

This study investigates tissue responses after laser irradiation of the rabbit ureter, which serves as an experimental model for rectourogenital fistulae of children. Twenty-five rabbit ureters were irradiated intraluminally by a Nd:YAG laser 1320 nm (2 Watt, 20 seconds and 3 Watt, 8 seconds) via an applicator with radialsymmetrical light distribution. Immediately, 2 weeks, 4 weeks, 8 weeks, and 16 weeks after irradiation, the ureters were X-rayed with contrast solution and prepared for light and transmission electron microscopy. For the parameters employed, no apparent morphological differences could be observed. Immediately, the central laser zone showed a transmural thermonecrosis prevailed by cellular destruction, condensed ground substance and occlusion of most vascular lumina. Peripheral laser zones displayed urothelial vacuolations. Between 2 and 16 weeks, urothelial regeneration and ingrowth of granulation tissue caused a luminal stenosis or occlusion followed by transformation into scar tissue. In some peripheral laser zones, a hydroureter with marked luminal dilatation developed. We conclude that the ureter is occluded if the expanding force of the growing scar tissue exceeds the hydrostatic pressure of the obstructed urine. A laser occlusion of rectourogenital fistulae will be easier to achieve since fistula occlusion does not entail an obstruction of the urine flow.

The temporal relationship between the severity of hydroureter and the dynamic changes of obstructed ureters in a rat model

OBJECTIVE

To investigate dynamic changes in the obstructed rat ureter and to evaluate the usefulness of the rat model in the study of obstructive uropathy.

MATERIALS AND METHODS

Unilateral ligation of the ureter was performed in 26 rats. After ureteric ligation, four to seven rats were killed and examined after 1, 3, 7, 10, and 14 days. The severity of hydroureter and hydronephrosis was assessed by pyelography and the hydroureter-hydronephrosis index. The middle portion of the ureter was prepared for light and electron microscopic observation. Five rats which received a sham operation were also examined as controls.

RESULTS

The severity of hydroureter and hydronephrosis in the ligated ureters progressively increased during the period of obstruction (P < 0.005) and reached a maximum 10-14 days after ligation. Hypertrophy of the smooth muscle layer developed on the third day after ligation and proliferation of submucosal connective tissue occurred on the 10th day after ligation. The changes in smooth muscle and connective tissue layers also progressed consistently during ureteric obstruction (P < 0.001 and < 0.005, respectively). The number and size of granular endoplasmic reticulum and Golgi apparatus in the smooth muscle cells increased after ureteric ligation and then caveolae exocytosis developed. Deposition of collagen fibres between muscle cells became apparent later.

CONCLUSION

The rat model of hydrouropathy demonstrated a clear temporal relationship between the severity of hydroureter and the dynamic changes in the obstructed ureter and could be used as a conventional method for the study of obstructive ureter.

Clonal chromosome changes in non-neoplastic ureters

Cytogenetic analysis was performed on 23 samples from non-neoplastic ureters. Clonal chromosome abnormalities were found in eight. They were: loss of Y chromosome, as a single abnormality (five cases) or associated with trisomy 10 and 20 (one case) or with trisomy 2 (one case); and duplication of Y chromosome (one case). Different numerical and structural sporadic abnormalities were found in nine cases. Immunohistochemical analysis and direct observation using the inverted microscope showed that the cells were mainly of the fibroblastic type. FISH analysis with chromosome 7 alpha-satellite probes failed to detect the presence of trisomy 7 in three epithelial cases tested.

[Vesicoureteropelvic reflux in pregnant animals and its role in the pathogenesis of acute gestational pyelonephritis (experimental research)]

The experiments on naturally pregnant rats have demonstrated that pregnancy contributes to much more frequent occurrence of vesicoureteropelvic reflux (VUPR) which, in its turn, is essential for pathogenesis of acute gestational pyelonephritis (AGP). Dynamic obstruction of the urine flow as a result of reduced function of leiomyocytes of urinary tract muscles, decreased urothelial glycocalyx and consequent adhesion of pathogenic agents comprise parts of this pathogenesis. The conclusion is made that VUPR pregnant females are at risk to develop AGP and should be placed by the urologist on ultrasonic monitoring lasting all pregnancy and postpartum periods.

[The clinical and experimental validation of the role of laser-magnetic therapy in the combined treatment of patients following plastic operations on the ureter]

The paper deals with clinical efficacy of laser magnetic therapy performed in patients following ureteroplasty on distal parts of the ureters. The results were estimated by clinical, biochemical and ultrasound monitoring.

Human bilharzial ureters: IV. Ultrastructural interaction between multinucleate giant cells and the parasite eggs

The ultrastructural interaction between multinucleate giant cells (MGCs) and the Schistosoma haematobium eggs is described at the transmission electron microscopy (TEM) level, in granulomas of the lower ureteral segments of Saudi patients. The MGCs were found only within the parasite empty egg-shells which were embedded in the ureter submucosa and muscularis. For the first time, two morphologically different types of MGCs were recognized: the moderate to electron-dense type I contained two types of 8-12 nuclei and cytoplasm poor in cell organelles which appeared non-functional. Type 1 MGCs were considered to be "old" and non-active cells. The electron-lucent to moderately dense type II MGCs contained 3-4 nuclei of one type, and cytoplasm rich in cell organelles. According to the performance of their organelles, type II MGCs were considered to be "young" and highly active cells. The human type II MGCs did not form the cytoplasmic membranous labyrinths previously described for the free moving MGCs obtained from experimental mice, and were suggested to be involved in the cell motility. As in murine MGCs, type II cells were incorporated in exocytic and endocytic activities aimed the degradation of the inner soft layer of the egg-shell. This study shows that individual macrophages were responsible for eliminating the outer and possibly the middle hard layers of the egg-shell.

Reinvestigation of the transitional epithelium (urothelium) of the human ureter

The transitional epithelia (urothelia) of the ureters of 30 patients of different ages were studied by means of light and electron microscopical, histochemical and immunocytochemical methods. A great variability of the normal structural appearance of the urothelium was established. Structural features and the uptake of exogenous peroxidase by the surface epithelial cells provided high endocytotic activity. Urothelial cells take up many low and high molecular weight substances from the urine and further metabolize and transport these toward the subepithelial connective tissue. Lymphocytes, macrophages, monocytes, plasma cells and rarely polymorphonuclear leukocytes are distributed intra- and extraepithelially and are involved in the immunological response to agents which enter the intercellular spaces of the epithelium. These cells are also responsible for the elimination of aged and degenerating superficial squamous cells. The present investigation establishes the existence of immunological defence mechanisms in the adult human urothelium. The results obtained suggest that the human ureter contains three functional barriers directed against aggressive components of the urine: the first represented by structures of the superficial squamous cells, the second by the upper cells of the ureteric intermediate layer and the third comprising epithelial and immunological cells involved in immune defence mechanisms.

Human bilharzial ureters: III. Fine structure of the egg granuloma

The fine structure of egg granuloma forming cells is described in lower ureteral segments of patients chronically infected with Schistosoma haematobium. The infiltrates consisted of monocytes, macrophages, lymphocytes, plasma cells, neutrophils, eosinophils, fibroblasts, mast cells, and blood platelets. The abundant monocytes and macrophages were actively mobile and intensively phagocytic cells. Multinucleate giant macrophages were only seen within empty egg shells. In addition to normal looking lymphocytes and plasma cells, several lymphocyte-like Sezary cells characterized by strikingly convoluted "cerebriform" nuclei were observed. Mature neutrophils and eosinophils were detected in addition to abnormal looking neutrophils; these contained numerous filamentous bundles. Fibroblasts were associated with extracellular collagen fibers and an electron-dense material. The few mast cells seen in proximity to blood vessels have a feature consistent with the onset of degranulation. Few blood platelets with active phagocytic features were among the granuloma cells.

[The inflammatory-reparative processes in the implantation of the ureter into the bladder by using the mechanical forces of permanent magnets]

An anastomosis between the ureter and the bladder using ring magnets was first made in our and foreign countries, Magnetic-compressive systems, based on alloy of samarium and cobalt (CS-37), were developed, taking into account their practical use in pediatric surgery. Morphological studies showed that the magnetic compressive procedure for connecting the ureter with the bladder has some advantages.

An immunohistochemical and electron microscopic study of the peri-ureteric ganglia of the guinea-pig

The neuropeptide- and catecholamine-synthesizing enzyme content and ultrastructure of the peri-ureteric ganglia of guinea-pigs were investigated. Small numbers of neuronal perikarya were present at frequent intervals forming ganglia close to, and along the entire length of, the ureter. Each of these ganglia was surrounded by a connective tissue capsule, and was located in the peri-ureteric connective tissues. Within each ganglion were typical nerve terminals and varicosities containing small, clear synaptic vesicles or synaptic vesicles with an electron-dense core, or a mixture of the two. In the ganglia, immunoreactivity to tyrosine hydroxylase, dopamine beta hydroxylase, neuropeptide tyrosine, or vasoactive intestinal peptide was present in neuronal perikarya; immunoreactivity to substance P or leucine enkephalin was present in nerve terminals and varicosities. Electron-microscopic immunogold studies indicated that there was no coexistence of substance P and enkephalin in the nerve terminals, unlike related ganglia in the pelvis of guinea-pigs.

[Clinical course of primary non-obstructive megaureter: analysis of our series]

Due to the widespread use of obstetrical ultrasonography with concomitant fetal screening, congenital uropathies are usually diagnosed in asymptomatic neonates. The main issue is to distinguish those cases of dilatation which are clearly obstructive and need surgical treatment from those which are within the normal anatomical range. Out of 47 patients with primary megaureter, 23 were nonobstructive, these are the aim of our study. There were 16 males and 7 females; 13 were located on the left side, 7 on the right side and 3 were bilateral, adding up to 26 reno-ureteral units. Prenatal diagnosis was performed in 16 cases, the eldest patient diagnosed was nine. All infants were evaluated with ultrasonography, voiding cystourethrography, excretory urography and diuresis renography. The latter has been the most important test inducing us to adopt a conservative attitude. Differential renal function was more than 40% in 24 units and in 2 was more than 35%. Diuretic renograms were type IIIa (Dilated non obstructed) in 19 cases and IIIb (Dilated partially obstructed) in 7. There were 2 cases with vesicoureteral reflux in the contralateral system. We have performed ultrasonography and diuresis renography during the follow-up. There were 8 cases with type I (Normal) renograms and 17 cases with type IIIa. Only one patient developed an obstruction and was operated on. In every case differential renal function did not deteriorate. In 9 cases urography was performed in order to see the anatomical changes. They have remained asymptomatic during the follow-up except for two cases which presented urinary tract infection. BUN, creatinine and other biochemical figures remained within normal ranges.(ABSTRACT TRUNCATED AT 250 WORDS)

Collagen arrangements in ureter

The collagen fibres of rabbit and human ureter were exposed by digestion with trypsin and hyaluronidase. The fibre structure was examined using an SEM and examples of the inner and outer fibre structures are shown together with the effects of different types of mechanical strain. An interesting difference between the arrangements of the inner fibres of human and rabbit was seen where the human ureter had a cross-ply structure while in the rabbit it was helical.

Human bilharzial ureters. II. Cellular dynamic against deposited eggs

The cellular dynamic against deposited Schistosoma haematobium eggs was studied in the submucosa and muscularis of the lower ureteral segments of Saudi patients with chronic urinary schistosomiasis. This dynamic activity was greatly affected by the damaged phase of the egg embryo. Freshly deposited eggs with "healthy" embryos were entirely surrounded by long cytoplasmic extensions of fibroblasts. Eggs with partially damaged embryos were surrounded by plasma cells which were focally adhered to spines of egg-shells and releasing their granular contents over their surface. Eggs with "dead" embryos, or empty egg-shells, were surrounded by actively mobile macrophages possessing numerous lysosomes, phagocytic vacuoles, and convoluted surface projections. After "peeling" off the outer and intermediate shell layers, macrophages invaded into eggs and fused together forming multinucleate giant macrophages. This study showed that the fibroblastic extensions acted as barriers between the parasite eggs or their products, and the host tissue; the plasma cell secretion over the egg surface may be involved in the migration of macrophages towards deposited eggs; and macrophages were the only dynamic cells responsible for the egg-shell invasion possibly for elimination.

[The functional-morphological changes in the kidney and ureter of patients with congenital ureterohydronephrosis]

Complex methods were used to examine 80 patients with congenital ureterohydronephrosis due to obstruction of the juxtavesical portion of the ureter. It was established that at different stages of the disease the ureteral wall develops intravascular, proper vascular and extravascular disorders, of the hemomicrocirculation and disorders of tissue trophics accompanied by functional changes in the kidney and ureter.

Muscle regeneration after endoureteropyelotomy?

Three specimens of ureteropelvic junction, obtained at dismembered pyeloplasty after successful endoureteropyelotomy, were studied. In the regenerative tissue, numerous cells were found with morphological, immunohistochemical and ultrastructural characteristics of mature smooth muscle cells; no regeneration of bundle arrangement was observed.

Binding sites for P and/or type 1-piliated Escherichia coli in human ureter

Adherence sites for uropathogenic Escherichia coli in the excised human ureter were studied by using scanning electron microscopy. P-piliated E. coli adhered to younger epithelial cells which had microvilli on their surfaces, but did not to mature epithelial cells which had microfolds on their surfaces. This adherence was D-mannose resistant and alpha-D-Galactopyranosyl-(1----4)- beta-D-Galactopyranoside sensitive. Type-1 piliated E. coli adhered to both types of epithelial cells, but it was prevented by D-mannose. Entrapment of adherent type 1-piliated E. coli was observed only on the epithelial cells with microfolds. This model system allowed quantitative estimates of bacterial adherence to the luminal surface of the human ureteral mucosa in vitro, and demonstrated different manners of adherence of P and type 1-piliated E. coli.

Incomplete protection mechanism against vesico-ureteral reflux and hydronephrosis in the inbred mouse strain DDD

We have previously reported the occurrence and inheritance mode of hydronephrosis in the inbred mouse strain DDD. The present investigation examined the possibility that hydronephrosis may be caused by a vesico-ureteral reflux (VUR). Bladder pressure was measured under anaesthesia in 3 strains of mice (DDD, ddY and C57BL/6). VUR was demonstrated by lower bladder pressure only in the DDD strain. Loading pressure into the renal pelvis (LPP) was significantly higher in DDD than in C57BL/6 (P less than 0.001). Correlations between LPP and severity of hydronephrosis were significantly positive in DDD and ddY, indicating that mice showing higher LPPs had the severest disease. Scanning electron micrography revealed that the ureteral orifice of DDD (100-300 microns) was much larger than in C57BL/6 (30 microns), and thus offered scant protection against VUR in DDD. These results suggest that DDD hydronephrosis caused by VUR is related primarily to the absence of an adequate protection mechanism in the ureteral orifice.

The microvasculature of the guinea pig ureter. A scanning electron microscopic investigation

In 24 albinotic guinea pigs (Cavia porcellus) the gross vasculature and the microvascular architecture of the ureter were studied by light microscopy of tissue blocks and by scanning electron microscopy of vascular casts. The guinea pig ureter is supplied by the renal artery proximally, by the aorta and the internal iliac artery in its mid-segment, and by the uterine and prostatic as well as by the vesical arteries distally. The main arterial trunks run alongside the ureter before they branch to send perforating arterioles to the muscular coat and the mucosal lining. The draining venules are found on both sides of the ureter and form transverse anastomoses. Communications between the arterioles are also located on both sides, but longitudinally arranged. The capillary network of the mucosal lining shows an undulating pattern with tortuous vessels and lies just below the epithelium. The muscular coat and the adventitia have no prominent capillaries of their own. Large arteries are embedded in the adventitia, large veins in the lamina propria. In analogy to human anatomy the vascular arrangement found suggests that, if the ureters are excised in transplant surgery, a lateral incision should be used for the abdominal portion, while the pelvic portion is best approached by a medial incision.

Effects of maternal bilateral ureteral ligation on the development of the proximal tubule of the kidney in fetal rats: morphometry and electron microscopic study

Development of the proximal tubule in the fetal kidney was studied following ligation of both ureters of pregnant rats. The ligation was performed on days 15, 17, 19, and 21 of gestation and autopsy followed 24 hours after each operation. On fetal days 20 and 22, the proximal tubular length per unit volume (1 mm3) of whole kidney of the fetuses from the ligated mothers was significantly increased, while the ratio of total glomerular volume to total proximal tubular volume was remarkably decreased when compared to that of the fetuses from the non-ligated mothers. Apical vacuoles in proximal tubular cells were increased by the ligation on fetal days 20 and 22. These findings suggest that maternal bilateral ureteral ligation accelerates the growth and differentiation of the proximal tubule in fetal kidney, when the fetal kidney is functional in urine production.

The three-dimensional structure of the musculature and the nerve elements in the rabbit ureter

The three-dimensional arrangement of muscle fibres and nerve elements in the rabbit ureter was examined by scanning electron microscopy after removal of fibrous elements by the HCl-trypsin digestion method. The ureteral muscle coat consisted of an interlacing network of muscle bundles made up of varying numbers of smooth muscle cells. On the outer surface of the muscle coat the muscle bundles predominantly extended transversely but some of them continued longitudinally. Some small bundles diverged from the main bundle and joined up with neighbouring or distant bundles. In most regions of the muscle coat irregular membranous or bifurcating cells were sometimes observed. On the longitudinally cut surface of the ureter, polygonal profiles of the cross-sectioned cells and elongated profiles of the longitudinally-sectioned cells were observed in the same bundle. The variety of these cut profiles suggested the differing directions of the muscle Some small interconnecting bundles extended across the inter-bundle spaces. Neighbouring muscle cells were connected laterally by short processes and were joined by gap junctions and desmosomal junctions; these were seen by transmission electron microscopy in thin sections and by freeze-fracture replicas. Thread-like nerve fibres were seen to be lying individually or in a fasciculus. Their terminals were characterised by varicose swellings. Streaks indicting mesaxonal extensions were exhibited on the Schwann cells enclosing nerve fibres.

Adherence of uropathogenic E. coli to differentiated human uroepithelial cells grown in vitro

A quantitative in vitro model to measure E. coli adherence to differentiated human uroepithelial cells has been developed. Primary cultures of uroepithelial cells were initiated from normal ureteral epithelium. Adherence of uropathogenic 3H-labelled Escherichia coli to postconfluent human uroepithelial cells was directly related to the bacteria:epithelial cell ratio during incubation. Bacterial attachment was inhibited either by mannose or by urine containing anti-E. coli antibodies. Transmission electron microscopy showed that epithelial cells differentiated in vitro to resemble normal uroepithelium in vivo. Furthermore, electron microscopy showed specific adherence of bacteria to the glycocalyx of microvilli of the superficial uroepithelial cells in vitro in a manner which closely mimics the in vivo interaction. This model of bacterial adherence permits in vitro analysis of adhesin-receptor interactions between uropathogenic E. coli and a layer of viable uroepithelial cells similar to those lining the bladder.