A vascular network closely linked to the epithelium of the urinary bladder of the rat

Characterization of Urothelial Inclusions in Male Wistar Han Rats Treated Orally With the Novel α2A-Adrenoceptor Agonist Tasipimidine

Intracellular inclusions were observed in urinary bladder epithelium of male Wistar rats, following oral treatment with high doses of the α_2A-adrenoceptor agonist tasipimidine for 28 days. No cell death or inflammation was associated with the brightly eosinophilic inclusions. Electron microscopy (EM) studies showed that the inclusions represented intact or fragmented red blood cells (RBC) resulting from erythrophagocytosis, further supported by the presence of iron in urothelial cells. In addition, scattered iron-positive macrophages were observed in the submucosa and muscle layer, indicating microvascular leakage, as no major hemorrhage was evident. Despite the presence of inclusions, the urothelium showed normal uroplakin III distribution, normal cell turnover, and an absence of α-2u-globulin. It is, therefore, concluded that the inclusions were not associated with urothelial damage or increased renewal of the epithelium. This finding shows also that urothelial cells have the capability to phagocytize and break down RBCs originating from submucosal microvascular leakage. Similar changes were not observed in tasipimidine-treated beagle dogs (28 days), suggesting these findings were rat specific. The leakage of RBCs into the urothelium is suggested to be a consequence of exaggerated pharmacology leading to vasoconstriction of submucosal blood vessels in combination with transient increased bladder distension and pressure.

A Method to Isolate Pericytes From the Mouse Urinary Bladder for the Study of Diabetic Bladder Dysfunction

Purpose

Pericytes surround the endothelial cells in microvessels and play a distinct role in controlling vascular permeability and maturation. The loss of pericyte function is known to be associated with diabetic retinopathy and erectile dysfunction. This study aimed to establish a technique for the isolation of pericytes from the mouse urinary bladder and an in vitro model that mimics in vivo diabetic bladder dysfunction.

Methods

To avoid contamination with epithelial cells, the urothelial layer was meticulously removed from the underlying submucosa and detrusor muscle layer. The tissues were cut into multiple pieces, and the fragmented tissues were settled by gravity into collagen I-coated culture plates. The cells were cultured under normal-glucose (5 mmol/L) or high-glucose (30 mmol/L) conditions, and tube formation, cell proliferation, and TUNEL assays were performed. We also performed hydroethidine staining to measure superoxide anion production.

Results

We successfully isolated high-purity pericytes from the mouse urinary bladder. The cells were positively stained for platelet-derived growth factor receptor-β and NG2 and negatively stained for smooth muscle cell markers (desmin and myosin) and an endothelial cell marker (CD31). The number of tubes formed and the number of proliferating cells were significantly lower when the pericytes were exposed to high-glucose conditions compared with normal-glucose conditions. In addition, there were significant increases in superoxide anion production and the number of apoptotic cells when the pericytes were cultured under high-glucose conditions.

Conclusions

To the best of our knowledge, this is the first study to isolate and culture pericytes from the mouse urinary bladder. Our model would be a useful tool for screening the efficacy of therapeutic candidates targeting pericyte function in diabetic bladder dysfunction and exploring the functional role of specific targets at the cellular level.

The Urothelium: Life in a Liquid Environment

The urothelium, which lines the renal pelvis, ureters, urinary bladder, and proximal urethra, forms a high-resistance but adaptable barrier that surveils its mechanochemical environment and communicates changes to underlying tissues including afferent nerve fibers and the smooth muscle. The goal of this review is to summarize new insights into urothelial biology and function that have occurred in the past decade. After familiarizing the reader with key aspects of urothelial histology, we describe new insights into urothelial development and regeneration. This is followed by an extended discussion of urothelial barrier function, including information about the roles of the glycocalyx, ion and water transport, tight junctions, and the cellular and tissue shape changes and other adaptations that accompany expansion and contraction of the lower urinary tract. We also explore evidence that the urothelium can alter the water and solute composition of urine during normal physiology and in response to overdistension. We complete the review by providing an overview of our current knowledge about the urothelial environment, discussing the sensor and transducer functions of the urothelium, exploring the role of circadian rhythms in urothelial gene expression, and describing novel research tools that are likely to further advance our understanding of urothelial biology.

The link between vascular dysfunction, bladder ischemia, and aging bladder dysfunction

The vascular supply to the human bladder is derived mainly from the superior and inferior vesical arteries, the latter being directly connected to the internal iliac artery. Aging is associated with an impairment of blood vessel function and changes may occur in the vasculature at the molecular, cellular and functional level. Pelvic arterial insufficiency may play an important role in the development of bladder dysfunctions such as detrusor overactivity (DO) and the overactive bladder syndrome. Chronic ischemia-related bladder dysfunction may progress to bladder underactivity and it would be desirable to treat not only lower urinary tract symptoms (LUTS) induced by chronic ischemia, but also the progression of the morphological bladder changes. Studies in experimental models in rabbits and rats have shown that pelvic arterial insufficiency may result in significant bladder ischemia with reduced bladder wall oxygen tension. In turn, this will lead to oxidative stress associated with upregulation of oxidative stress-sensitive genes, increased muscarinic receptor activity, ultrastructural damage, and neurodegeneration. The phosphodiesterase type 5 (PDE5) inhibitor tadalafil, the α₁-adrenoceptor (AR) blocker silodosin, the β₃-AR agonist mirabegron, and the free radical scavenger melatonin, exerted a protecting effect on urodynamic parameters, and on functional and morphological changes of the bladder demonstrable in vitro. Since the agents tested are used clinically for relieving LUTS, the results from the animal models seem to have translational value, and may be of relevance for designing clinical studies to demonstrate if the drugs may prevent progression of ischemia-related functional and morphological bladder changes.

Urethral sensation: basic mechanisms and clinical expressions

A prerequisite for conscious bladder control is adequate sensory input to the central nervous system, and it is well established that changes in sensory mechanisms can give rise to disturbances in bladder function. Impulses related to the desire to void are believed to course through the pelvic nerves, and those for sensation of a full bladder course through the pudendal nerves. The sense of imminent micturition most probably resides in the urethra, and the desire to void comes from stretching the bladder wall. In addition, a variety of structures play an important role in terms of urethral closure (such as the urethral epithelium, vasculature and smooth muscle) that are necessary to maintain continence. This overview will discuss mechanisms related in part to the urethra involved in activation of bladder reflexes and sensation with a discussion on the mucosa (urothelium and underlying lamina propria) and underlying cellular structures.

Urothelial signaling

The urinary bladder "mucosa" or innermost portion of the bladder is composed of transitional epithelium, basement membrane, and the lamina propria. This chapter reviews the specialized anatomy of the bladder epithelium (urothelium) and speculates on possible communication mechanisms from urothelial cells to various cell types within the bladder wall. For example, beyond serving as a simple barrier, there is growing evidence that the urinary bladder urothelium exhibits specialized sensory properties and plays a key role in the detection and transmission of both physiological and nociceptive stimuli. Findings from a number of studies suggest that the urothelium exhibits both "sensor" (expressing receptors/ion channels capable of responding to thermal, mechanical, and chemical stimuli) and "transducer" (ability to release chemicals) properties. Thus, urothelial cells exhibit the ability to sense changes in their extracellular environment including the ability to respond to chemical, mechanical, and thermal stimuli that may communicate the state of the urothelial environment to the underlying nervous and muscular systems.

Microvasculature of the urinary bladder of the dog: a study using vascular corrosion casting

The urinary bladder is an unusual organ in that its normal function includes filling and emptying with alternating changes in internal pressure. Although fluctuations in blood flow to the bladder wall are known to accompany these changes, detailed descriptions of the bladder microvasculature are sparse. The present study uses vascular corrosion casting and scanning electron microscopy to describe the three-dimensional anatomy of the microvasculature of the urinary bladder of the dog. Specialized features of that microvasculature, including collateral circulation, vessel folding, vessel orientation, the presence of valves and sphincters, and mucosal capillary density, that may enhance and control blood flow during normal bladder function, are described and discussed.

Mechanisms of disease: involvement of the urothelium in bladder dysfunction

Although the urinary bladder urothelium has classically been thought of as a passive barrier to ions and solutes, a number of novel properties have been recently attributed to urothelial cells. Studies have revealed that the urothelium is involved in sensory mechanisms (i.e. the ability to express a number of sensor molecules or respond to thermal, mechanical and chemical stimuli) and can release chemical mediators. Localization of afferent nerves next to the urothelium suggests that urothelial cells could be targets for neurotransmitters released from bladder nerves or that chemicals released by urothelial cells could alter afferent nerve excitability. Taken together, these and other findings highlighted in this article suggest a sensory function for the urothelium. Elucidation of mechanisms that influence urothelial function might provide insights into the pathology of bladder dysfunction.

Ultrastructural smooth muscle ontogeny of the rat bladder

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

Near-infrared confocal laser scanning microscopy of bladder tissue in vivo

OBJECTIVES

To assess the potential of a near-infrared confocal laser scanning microscope (CLSM) for imaging bladder tissue in vivo.

METHODS

Confocal images of the exposed bladder of male Sprague-Dawley rats were obtained with a CLSM. To minimize tissue motion, the bladder was placed in light contact under an objective lens housing, and the top surface was lightly flattened with a coverslip. Images were obtained from the outer and inner layers of the bladder wall with a lateral resolution of 0.5 to 1 microm and an axial resolution (section thickness) of 3 to 5 microm. The confocal images were later correlated with routine histologic studies.

RESULTS

The CLSM allows imaging of the urothelium, the superficial and deep portions of the lamina propria, the muscularis propria, and the serosa of the bladder wall in vivo. Urothelial cells, collagen bundles and fibers, muscle, and circulating blood cells in capillaries and larger blood vessels are easily visualized. The confocal images correlated well with the histologic studies.

CONCLUSIONS

Confocal microscopy allows real-time, high-resolution, high-contrast imaging of cellular and structural morphologic features to a maximal depth of 300 microm within the bladder wall in vivo. Artifacts caused by tissue motion can be minimized with a bladder-objective lens contact housing.

Microvascular architecture of the human urinary bladder wall: a corrosion casting study

The vascular system of the urinary bladder wall effectively performs its function in spite of considerable spatial changes due to the filling/voiding cycle. However, only a few studies have dealt with the microvascular architecture of the bladder wall and only two, using old-fashioned techniques, were devoted to the human bladder. This study presents the microvasculature of the human bladder wall visualized by scanning electron microscopy of vascular corrosion casts. Postoperative bladder specimens obtained from patients with advanced bladder tumors were filled with small amount (80 ml) of saline and perfused via at least four largest arteries with anticoagulant-containing saline followed by paraformaldehyde/glutaraldehyde fixative and Mercox resin. After polymerization of the resin, the vascular casts were macerated with potassium hydroxide, cleaned with formic acid and water and freeze dried. Only regions of the bladder wall distant to the tumor were examined in light and scanning electron microscopes. The almost empty state of the bladder was manifested by extensive folding of the mucosa and tortuosity of almost all vessels other than capillaries. The branches of main arteries and veins formed an adventitial/serosal plexus which directly supplied/drained the capillary network of the muscularis and sent long perpendicular vessels to the mucosal plexus. These vessels had straight or coiled course depending on whether they terminated at the top or at the base of the mucosal folds. The rich mucosal plexus followed the folds parallel to their surface and gave off short, straight, mostly perpendicular twigs communicating with the subepithelial capillary network. Apart from very few vascular interconnections between the mucosal plexus and the muscularis, the submucosa was generally avascular. The subepithelial capillary network showed extreme density and uneven contours of the capillaries, only in less folded areas of trigone and urethral orifice the network was looser and capillaries thinner. The capillary system of the muscularis was poorly developed. Due to its architecture, tortuosity, and coiling/uncoiling capabilities, the microvasculature of the human urinary bladder wall seems to efficiently accommodate changes associated with cyclic contraction and stretching. Disturbances in blood flow induced by overdistension of the bladder reported in several studies may be due to pressure of the urine affecting the patency of the vessels rather than to the spatial insufficiency of the vascular system.

Microvasculature of the rabbit urinary bladder

BACKGROUND

The urinary bladder requires a rich blood supply to maintain its functions, the storage and release of urine. Specialized properties of the bladder vasculature might be anticipated to ensure the integrity of this blood supply, because it is known that blood flow is reduced by distension during bladder filling. However, the bladder vasculature has been described in detail only at the gross level. A comprehensive, three-dimensional view of the blood supply to the bladder wall is presented here.

METHODS

The microvasculature of the bladder of male New Zealand white rabbits was described using the combination of vascular corrosion casting, alkali digestion, light microscopy, and scanning and transmission electron microscopy. Following administration of an anticoagulant and an overdose of anesthetic, the abdominal aorta was cannulated just above the inferior mesenteric artery to permit flushing of the distal vasculature. The bladder vasculature was cleared of blood with buffered saline and then either perfuse-fixed with buffered 2% glutaraldehyde and sectioned, or filled with "Mercox" resin to prepare vascular corrosion casts. Casts were cleaned with NaOH, formic acid, and water. In some cases fixed bladders were partially digested with NaOH to expose the mucosal capillary plexus.

RESULTS

The bladder is supplied with blood by single, left and right vesicular branches of the internal or external iliac arteries. The serpentine vesicular arteries extend along the lateral borders of the bladder from base to apex just deep to the serosal surface and send dorsal and ventral branches to supply the dorsal and ventral bladder walls. Veins accompany the arteries and exhibit numerous valves. A very dense complex of vessels at the apex of the bladder apparently serves to accommodate bladder distension. The muscularis and submucosa contains few vessels, but the mucosa is well vascularized. An especially dense capillary plexus is present in the lamina propria at its junction with the transitional epithelium. In the relaxed bladder these capillaries lie in grooves formed by the basal layers of the epithelium. The endothelial cells of these capillaries display few cytoplasmic vesicles and are continuous or fenestrated. These capillaries are often invested with pericytes. The mucosal capillary plexus may be associated with an epithelial transport function or may be necessary for urothelial metabolism or maintenance of the barrier function of the urothelium. Unusual capillary tufts, possibly associated with vascular lymphatic tissue, are found associated with the main vessels on the lateral walls in the basal half of the bladder.

CONCLUSIONS

These methods present a clear, comprehensive, three-dimensional view of the microvasculature of the bladder wall. They also identify several unique features of this vasculature and provide a basis for studies of the response of this vasculature to pathologic states and experimental manipulation.

Vascular anatomy of the rabbit ureter

BACKGROUND

The success of kidney transplant surgery and ureteral reconstruction requires the preservation of the ureteral blood supply. Because of its potential vulnerability to surgical trauma during transplant and reconstructive surgery, the ureteral vasculature merits a full anatomical description.

METHODS

The microvascular anatomy of the ureter was studied in male New Zealand white rabbits by light microscopy and transmission electron microscopy and scanning electron microscopy of vascular corrosion casts and alkali digested tissue.

RESULTS

The rabbit ureter is supplied predominantly by a branch of the renal artery proximally (cranial ureteral artery) and by a branch of the vesicular artery distally (caudal ureteral artery). Minor vascular continuities are also present between the capillary beds of the ureter and those of the renal pelvis cranially and the bladder wall caudally. There are no external vascular connections to the middle ureter with the exception of a single, small vein which drains into the inferior vena cava. A single group of longitudinal arteries and veins runs the full length of the ureter within the adventitia. Branches of these longitudinal vessels pass tangentially through the muscularis to supply a vascular complex within the lamina propria. This complex in turn supports a rich, mucosal capillary plexus located at the junction between the transitional epithelium and the lamina propria. In the fixed ureter the capillary plexus lies in grooves formed by displacement of the basal layers of the overlying transitional epithelium. The capillaries are continuous or fenestrated, are often invested with pericytes, and are distributed uniformly around the entire circumference of the ureter.

CONCLUSIONS

The ureteral vasculature exhibits several unique features related to its function in urine conduction and its ability to accommodate expansion and contraction. The combination of techniques used provides a clear three-dimensional view of this vasculature. Our findings also confirm that, because of its limited blood supply, the ureter may be very susceptible to injury during renal transplantation or other abdominal surgery.