Muscarinic stimulation of the rat isolated whole bladder: pathophysiological models of detrusor overactivity

Spontaneous Activity and the Urinary Bladder

The urinary bladder has two functions: to store urine, when it is relaxed and highly compliant; and void its contents, when intravesical pressure rises due to co-ordinated contraction of detrusor smooth muscle in the bladder wall. Superimposed on this description are two observations: (1) the normal, relaxed bladder develops small transient increases of intravesical pressure, mirrored by local bladder wall movements; (2) pathological, larger pressure variations (detrusor overactivity) can occur that may cause involuntary urine loss and/or detrusor overactivity. Characterisation of these spontaneous contractions is important to understand: how normal bladder compliance is maintained during filling; and the pathophysiology of detrusor overactivity. Consideration of how spontaneous contractions originate should include the structural complexity of the bladder wall. Detrusor smooth muscle layer is overlain by a mucosa, itself a complex structure of urothelium and a lamina propria containing sensory nerves, micro-vasculature, interstitial cells and diffuse muscular elements.Several theories, not mutually exclusive, have been advanced for the origin of spontaneous contractions. These include intrinsic rhythmicity of detrusor muscle; modulation by non-muscular pacemaking cells in the bladder wall; motor input to detrusor by autonomic nerves; regulation of detrusor muscle excitability and contractility by the adjacent mucosa and spontaneous contraction of elements of the lamina propria. This chapter will consider evidence for each theory in both normal and overactive bladder and how their significance may vary during ageing and development. Further understanding of these mechanisms may also identify novel drug targets to ameliorate the clinical consequences of large contractions associated with detrusor overactivity.

Testosterone-induced benign prostatic hyperplasia rat and dog as facile models to assess drugs targeting lower urinary tract symptoms

Benign prostatic hyperplasia (BPH) is an age-related disease, affecting a majority of elderly men worldwide. Medical management of BPH is an alternative to surgical treatment of this disease. Currently, α1-adrenergic receptor (α1-AR) antagonists are among the first line drugs to treat BPH by reducing the tension of urinary track and thus the obstructive symptoms in voiding. In drug development, old male dogs with spontaneous BPH are considered the golden standard of the animal models. However, old dogs (>6 years) are expensive and not all old dogs develop BPH. So it is necessary to develop more accessible animal models for drug efficacy evaluation. Here we describe the development of testosterone-induced BPH models in both rats and young adult dogs and their applications in the in vivo evaluation of α1-AR antagonist. The BPH rats and dogs induced by chronic testosterone treatment have significantly increased micturition frequency and reduced mean voided volume, very similar to the clinical symptoms of BPH patients. Silodosin, an α1-AR antagonist, significantly reduces the urinary frequency and increases the voided volume in BPH model animals in a dose-dependent manner. The results demonstrate that testosterone-induced BPH rat and dog models might provide a more efficient way to evaluate micturition behavior in anti-BPH drug studies.

Incidence and risk factors of recurrence of overactive bladder symptoms after discontinuation of successful medical treatment

Purpose

To identify incidence and risk factors of recurrence after discontinuation of successful antimuscarinic therapy in patients with overactive bladder (OAB).

Materials and Methods

This was a prospective, multicenter trial. Patients who had antimuscarinic agents for more than 12 weeks and showed successful response were enrolled. Successful response was defined as answering 'benefit' for patient perception of treatment benefit and answer lesser than 3 points in patient's perception of bladder condition (PPBC). The enrolled patients discontinued the antimuscarinics, and we evaluated their recurrence with PPBC and OAB symptom score (OABSS) at 1, 3, 6, and 12 months. Primary purpose was to identify the recurrence rate and secondary purpose was to reveal risk factors.

Results

Four hundred forty-one patients enrolled and 371 patients completed 6-month follow-up. The enrolled patients showed 1.6 points in PPBC, 2.9 points in OABSS and 1.4 points in IPSS (quality of life) which represented successful response after using antimuscarinics. The cumulative rates of recurrence were 25.6%, 42.3%, and 52.2% at 1, 3, 6 months, respectively. Among 177 patients who did not show recurrence at 6 months, 41 patients were followed up and 4 patients of the 41 patients (9.7%) showed recurrence at 12 months. On univariate and multivariate analyses of recurrence, OAB wet was the risk factor for recurrence after 6 months of discontinuation.

Conclusions

Discontinuation of antimuscarinic therapy after successful treatment resulted in high recurrence rate with time and OAB wet was the independent risk factor for recurrence.

Development of an Improved Animal Model of Overactive Bladder: Transperineal Ligation versus Transperitoneal Ligation in Male Rats

Purpose

We compared a transperineal ligation model and a transperitoneal ligation model in male rats to determine which animal model of overactive bladder (OAB) was more useful based on cystometrography, estimations of oxidative stress, and measurements of pro-inflammatory cytokine levels.

Materials and Methods

Male rats were randomly divided into three groups (n=15 in each): the control group, the transperineal ligation group, and the transperitoneal ligation group. Four weeks after the ligation procedure, cystometrography was performed and oxidative stress, pro-inflammatory cytokine levels, and histologic changes were evaluated. Oxidative stress was assessed by measuring 8-hydroxy-20-deoxyguanosine and superoxide dismutase, and pro-inflammatory cytokine activity was investigated by measuring levels of interleukin (IL)-6, IL-8, and tumor necrosis factor-α.

Results

The transperineal model led to results similar to those observed for the transperitoneal model, namely (1) increased voiding frequency and reductions in the non-voiding contraction interval and the maximal vesical pressure, (2) increased levels of oxidative stress markers, (3) increased pro-inflammatory cytokine levels, and (4) fibrotic changes in the bladder tissue.

Conclusions

We suggest that the transperineal procedure can be used as an alternative OAB model in male rats.

Effects of Gegen (Puerariae lobatae Radix) water extract on improving detrusor overactivity in spontaneously hypertensive rats

AIM

Ex vivo experiments showed that the water extract of Puerariae lobatae Radix (named Gegen in Chinese) induced detrusor relaxation. The aim of this study was to prove the in vivo efficacy of Gegen on improving detrusor overactivity and its possible synergism with darifenacin (a first-line muscarinic receptor-3 inhibitor) in spontaneously hypertensive rats (SHR), a rat model exhibiting symptoms of detrusor overactivity.

METHOD

After daily oral administration of Gegen 30 (Gegen, 30mg/kg); Gegen 300 (Gegen, 300mg/kg); Low_Dar (darifenacin, 3mg/kg); High_Dar (darifenacin, 30mg/kg) Low_Dar+Gegen 30 or High_Dar+Gegen 30 for 3 weeks, bladder detrusor strips of the rats were isolated and assessed with different stimulators for the measurement of tonic and phasic contractile activities (including phasic amplitude and frequency). Modes of stimulation included the use of carbachol, isoprenaline and electrical field stimulation (EFS).

RESULTS

All drug treatments significantly reduced carbachol-stimulated tonic contractile activities, but did not change the phasic amplitude. Meanwhile, the treatments with Gegen 300; Low_Dar; Low_Dar+Gegen 30; and High_Dar+Gegen 30 decreased carbachol-stimulated phasic frequency. Gegen 300 and Low_Dar+Gegen 30 showed stronger potency on lowering EFS-induced responses. Under isoprenaline-induced relaxation, only Gegen 300 significantly enhanced this relaxation by decreasing tonic contraction; Gegen 300; Low_Dar; Low_Dar+Gegen 30; and High_Dar+Gegen 30 increased the reduction of phasic frequency, but all treatment did not alter their phasic amplitude. Combination Index (CI) showed that the combination with Low_Dar and Gegen 30 had very strong synergism (CI <0.1) on inhibiting EFS-induced contractile response.

CONCLUSION

Gegen improved detrusor overactivity through neurogenic and anti-muscarinic mechanisms. Gegen and darifenacin together attained synergism for detrusor overactivity treatment via the neurogenic pathway.

Urodynamic characteristics of rats with detrusor instability

The purpose of the present study is to investigate urodynamic characteristics of rats with detrusor instability (DI) induced by different causes. Forty-eight adult female Sprague-Dawly rats were randomly divided into 4 groups: cyclophosphamide group, bladder outlet obstruction group, lipopolysaccharide group and control group. The BL-410 model bio-function experimental system was applied to monitor bladder pressure and a number of urodynamic parameters were recorded and calculated, including the frequency of detrusor instability, maximum voiding pressure (MVP), maximum cystometric capacity (MCC), intercontraction interval (ICI), voiding time (VT), postvoid residual (PVR) and bladder compliance (BC). The positive rates of DI in cyclophosphamide group, bladder outlet obstruction group and lipopolysaccharide group were 83.33%, 75.00% and 58.33%, respectively. And correspondingly the frequency of DI was 10.00±2.00, 4.87±1.24 and 3.50±1.00tmin(-1), which was significantly higher than those of the control group (P<0.05). Compared with the control group, the decrease of MVP, MCC, ICI, VT and BC was noted in the cyclophosphamide group and lipopolysaccharide group. Increased PVR, MVP, MCC, VT and BC were presented in the bladder outlet obstruction group. Therefore, we suggested that the urodynamic parameters could reflect the pathophysiological characteristics of DI induced by different causes, which could systematically benefit the diagnosis and treatment of overactive bladder.

Voiding difficulties in the elderly

Voiding difficulties are more common in the elderly. This occurs because of physiological changes such as replacement of muscle fibres with collagen, from life effect insults such as the effects of childbirth, lead to a reduction in contractility and changes in the nerve supply from cholinergic to NANC fibres lead to a change in sensation leading to a delay in first sensation. Symptoms are often similar to those of overactive bladder and the history in older women should include those of hesitancy and poor flow. Likewise, the diagnosis should be considered in women presenting with recurrent urinary tract infections. A failure to consider voiding difficulties can precipitate a crisis and simple strategies such as teaching self-catheterization and using estrogen cream may prevent problems occurring. When acute problems occur, catheterization is required and a review of precipitating factors may identify medications contributing to the condition. The mainstay for treatment, however, remains draining with an indwelling catheter or clean intermittent clean catheterisation.

Adjustable passive stiffness in mouse bladder: regulated by Rho kinase and elevated following partial bladder outlet obstruction

Detrusor smooth muscle (DSM) contributes to bladder wall tension during filling, and bladder wall deformation affects the signaling system that leads to urgency. The length-passive tension (L-T(p)) relationship in rabbit DSM can adapt with length changes over time and exhibits adjustable passive stiffness (APS) characterized by a L-T(p) curve that is a function of both activation and strain history. Muscle activation with KCl, carbachol (CCh), or prostaglandin E(2) at short muscle lengths can increase APS that is revealed by elevated pseudo-steady-state T(p) at longer lengths compared with prior T(p) measurements at those lengths, and APS generation is inhibited by the Rho Kinase (ROCK) inhibitor H-1152. In the current study, mouse bladder strips exhibited both KCl- and CCh-induced APS. Whole mouse bladders demonstrated APS which was measured as an increase in pressure during passive filling in calcium-free solution following CCh precontraction compared with pressure during filling without precontraction. In addition, CCh-induced APS in whole mouse bladder was inhibited by H-1152, indicating that ROCK activity may regulate bladder compliance during filling. Furthermore, APS in whole mouse bladder was elevated 2 wk after partial bladder outlet obstruction, suggesting that APS may be relevant in diseases affecting bladder mechanics. The presence of APS in mouse bladder will permit future studies of APS regulatory pathways and potential alterations of APS in disease models using knockout transgenetic mice.

The role of c-kit-positive interstitial cells in mediating phasic contractions of bladder strips from streptozotocin-induced diabetic rats

OBJECTIVE

• To investigate the role of c-kit-positive interstitial cells (ICCs) in mediating muscarinic receptor-induced phasic contractions of isolated bladder strips from streptozotocin(STZ)-induced diabetic rats and to confirm the expression and location of ICCs in the rat bladder.

MATERIALS AND METHODS

• Bladders were removed from STZ-induced diabetic rats at 1, 4 and 12 weeks after induction of diabetes and from age-matched controls. • To investigate the functional role of ICCs in mediating phasic contractions, bladder strips were isolated from control and diabetic rats and mounted in tissue baths. • Strips were stimulated with low concentrations of the muscarinic receptor agonist carbachol (CCH; 0.1 µm) to induce phasic contractions and the effect of increasing concentrations (1-50 µm) of imatinib (Glivec® or Gleevec®, formerly STI571), a c-kit tyrosine kinase inhibitor, was then investigated. • For molecular studies, to detect expression of the c-kit tyrosine kinase receptor (c-kit), total cellular RNA was extracted from rat bladders and reverse-transcribed to obtain complementary DNA (cDNA). • Reverse transcription-polymerase chain reaction (RT-PCR) was then performed using primers specific to the c-kit sequence and amplified products separated by agarose gel electrophoresis. • Amplified PCR products were excised from the gel, sequenced and compared with the known c-kit sequence to confirm their identity. • For immunohistochemical detection, whole mount preparations of control rat bladders were fixed in acetone and labelled using antibodies directed to the ICC marker c-kit.

RESULTS

• In functional studies, CCH induced phasic contractions in bladder strips from control and diabetic rats. Bladder strips from 1-week diabetic rats showed CCH-induced phasic contractions, which were greater in amplitude, but had lower frequency, than the controls, whilst no such differences were apparent at later time points of diabetes. • Imatinib decreased the amplitude and the frequency of the CCH-induced phasic contractions in both control and diabetic tissues in a concentration-dependent manner, although in diabetic tissues this effect was only seen at the higher concentrations of imatinib. RT-PCR of bladder cDNA yielded a single amplicon of 480 bp. • The sequence of this amplicon showed a 98% homology with the published c-kit sequence, thus confirming c-kit mRNA expression in both control and 1-week diabetic rat bladder. • Expression of c-kit protein was also detected in a network of cells on the edge of and between smooth muscle bundles of control rat bladders by positive immunoreactivity to c-kit specific antibodies.

CONCLUSION

• These data show the presence of c-kit-positive ICCs in rat urinary bladder and their importance in mediating muscarinic receptor-induced phasic contractions of bladder strips from control and diabetic rats. The role of these ICCs does not seem to be significantly altered by the diabetic state.

Animal models in overactive bladder research

Overactive bladder syndrome (OAB) is a symptom-based diagnosis characterised by the presence of urinary urgency. It is highly prevalent and overlaps with the presence of bladder contractions during urine storage, which characterises the urodynamic diagnosis of detrusor overactivity. Animal models are needed to understand the pathophysiology of OAB, but the subjective nature of the symptom complex means that interpretation of the findings in animals requires caution. Because urinary urgency cannot be ascertained in animals, surrogate markers such as frequency, altered toileting areas, and non-micturition contractions have to be used instead. No model can recapitulate the subjective, objective, and related factors seen in the clinical setting. Models used include partial bladder outlet obstruction, the spontaneous hypertensive rat, the hyperlipidaemic rat, various neurological insults and some gene knock-outs. Strengths and weaknesses of these models are discussed in the context of the inherent difficulties of extrapolating subjective symptoms in animals.

Rhythmic contraction generates adjustable passive stiffness in rabbit detrusor

The length-tension (L-T) relationships in airway and vascular smooth muscles have been shown to adapt with length changes over time. Our prior studies have shown that the active and passive L-T relationships in rabbit detrusor smooth muscle (DSM) can adapt and that DSM exhibits adjustable passive stiffness (APS) characterized by a passive L-T curve that is a function of strain and activation history. The present study demonstrates that passive tension due to APS can represent a substantial fraction of total tension over a broad length range. Our previous studies have shown that maximal KCl-induced contractions at short muscle lengths generate APS that is revealed by increased pseudo-steady-state passive tension at longer lengths compared with previous measurements at those lengths. The objective of the present study was to determine the mechanisms involved in APS generation. Increasing the number of KCl-induced contractions or the duration of a contraction increased the amount of APS generated. Furthermore, a fraction of APS was restored in calcium-free solution and was sensitive to the general serine and threonine protein kinase inhibitor staurosporine. Most importantly, rhythmic contraction (RC) generated APS, and because RC occurs spontaneously in human bladder, a physiological role for RC was potentially identified.

Neural control of the lower urinary tract: peripheral and spinal mechanisms

This review deals with individual components regulating the neural control of the urinary bladder. This article will focus on factors and processes involved in the two modes of operation of the bladder: storage and elimination. Topics included in this review include: (1) The urothelium and its roles in sensor and transducer functions including interactions with other cell types within the bladder wall ("sensory web"), (2) The location and properties of bladder afferents including factors involved in regulating afferent sensitization, (3) The neural control of the pelvic floor muscle and pharmacology of urethral and anal sphincters (focusing on monoamine pathways), (4) Efferent pathways to the urinary bladder, and (5) Abnormalities in bladder function including mechanisms underlying comorbid disorders associated with bladder pain syndrome and incontinence.

Ultrastructure of Cajal-like interstitial cells in the human detrusor

The aim of this ultrastructural study was to examine the human detrusor for interstitial cells of Cajal (ICC)-like cells (ICC-L) by conventional transmission electron microscopy (TEM) and immuno-transmission electron microscopy (I-TEM) with antibodies directed towards CD117 and CD34. Two main types of interstitial cells were identified by TEM: ICC-L and fibroblast-like cells (FLC). ICC-L were bipolar with slender (0.04 microm) flattened dendritic-like processes, frequently forming a branching labyrinth network. Caveolae and short membrane-associated dense bands were present. Mitochondria, rough endoplasmic reticulum and Golgi apparatus were observed in the cell somata and cytoplasmic processes. Intermediate filaments were abundant but no thick filaments were found. ICC-L were interconnected by close appositions, gap junctions and peg-and-socket junctions (PSJ) but no specialised contacts to smooth muscle or nerves were apparent. FLC were characterised by abundant rough endoplasmic reticulum but no caveolae or membrane-associated dense bands were observed; gap junctions and PSJ were absent and intermediate filaments were rare. By I-TEM, CD34 gold immunolabelling was present in long cytoplasmic processes corresponding to ICC-L between muscle fascicles but CD117 gold immunolabelling was negative. Thus, ICC-like cells are present in the human detrusor. They are CD34-immunoreactive and have a myoid ultrastructure clearly distinguishable from fibroblast-like cells. ICC-L may be analogous to interstitial cells of Cajal in the gut.

Glucose-dependent enhancement of diabetic bladder contraction is associated with a rho kinase-regulated protein kinase C pathway

Urinary bladder dysfunction, which is one of the most common diabetic complications, is associated with alteration of bladder smooth muscle contraction. However, details regarding the responses under high-glucose (HG) conditions in diabetes are poorly understood. The objective of this study was to identify a relationship between extracellular glucose level and bladder smooth muscle contraction in diabetes. Bladder smooth muscle tissues were isolated from spontaneously type II diabetic (ob/ob mouse; 16-20 weeks of age, male) and age-matched control (C57BL mouse) mice. Carbachol (CCh) induced time- and dose-dependent contractions in ob/ob and C57BL mice; however, maximal responses differed significantly (14.34 +/- 0.32 and 12.69 +/- 0.22 mN/mm(2) after 30 microM CCh treatment, respectively; n = 5-8). Pretreatment of bladders under HG conditions (22.2 mM glucose; concentration is twice that of normal glucose for 30 min) led to enhancement of CCh-induced contraction solely in diabetic mice (15.9 +/- 0.26 mN/mm(2); n = 5). Basal extracellular glucose-dependent enhancement of bladder contraction in diabetes was documented initially in this study. The correlation between intracellular calcium concentration and contraction was enhanced only in the ob/ob mouse. This enhancement of contraction and total protein kinase C (PKC) activity were inhibited by pretreatment with not only a PKC inhibitor (rottlerin) but also with a rho kinase inhibitor, fasudil [1-(5-isoquinolinesulfonyl)homopiperazine HCl]. These reagents also suppressed the differences between ob/ob and C57BL mouse bladder contractions under HG conditions. The data indicated that glucose-dependent enhancement of contraction in diabetic bladder is involved in the activation of the rho kinase and calcium-independent PKC pathways. This dysfunction may contribute to bladder complications such as detrusor overactivity and reduced bladder capacity in diabetes.

Urotheliogenic modulation of intrinsic activity in spinal cord-transected rat bladders: role of mucosal muscarinic receptors

We examined the modulation of intrinsic (i.e., spontaneous) detrusor contractions by the urothelium and the lamina propria through optical mapping approaches. Normal adult and spinal cord-transected (SCT) rat bladders were stained with Ca2+- and voltage-sensitive dyes, and optical activity generated from intrinsic contractions was mapped from the mucosal surface of whole bladder sheets. Both normal adult and SCT rat bladders displayed intrinsic contractions, where normal bladders showed low-amplitude, high-frequency contractions with disorganized patterns of activity. In contrast, in the SCT animals there were high-amplitude, low-frequency contractions that displayed an organized spread of membrane potential and intracellular Ca2+. The difference in contractile activity was mirrored in the Ca2+ and membrane potential maps of bladder sheets. Normal bladders showed multiple initiation sites across the mucosal surface, whereas SCT bladders showed only one or two fixed initiation sites localized to the dome. The magnitude of intrinsic contractions could be enhanced by stretch or low-dose arecaidine (50 nM), a muscarinic-specific agonist. Partial removal of the mucosa decreased the amplitude of the intrinsic contractions and decreased the response to stretch or arecaidine. Optical mapping of mucosa-denuded sheets, where enhanced spontaneous activity was abolished, or application of 1 microM nifedipine to remove smooth muscle signals, but not the mucosal signals, shows that intrinsic activity in pathological bladders is driven by the mucosal layer. In summary, we suggest an urotheliogenic origin for intrinsic activity, where structures within the mucosal layer organize and thereby enhance intrinsic detrusor contractions.

The integrative physiology of the bladder

Normal bladder function is complex, resulting from the co-operative interaction of numerous regulatory cell types, of which the interstitial cells and the peripheral neurones are particularly interesting. Collectively, these comprise the myovesical plexus, which appears to confer structural and functional characteristics on the bladder loosely akin to those of the gut. These include functional modularity, which gives rise to the potential for localised and propagating peristalsis-like movements in the bladder wall according to the prevailing physiological conditions. Localised modular activity during filling may contribute to normal generation of sensation and exaggerated modular activity may give rise to urinary urgency. Enhanced co-ordination of modular activity occurs in various models of detrusor overactivity; it leads to surges of contraction over a large part of the bladder wall, generating phasic changes in intravesical pressure. During voiding, the myovesical plexus sustains detrusor contraction at the behest of the brainstem, monitoring state of bladder fullness as it does so, as a guide to the required duration for which it has to keep up the effort. Accordingly, the bladder wall itself may house structures which render the bladder the effector level in a hierarchy of lower urinary tract regulation. Dysfunction in these vital regulatory structures is an underestimated factor in the pathophysiology of clinical bladder problems.

The extracorporeal perfusion of the female pig detrusor as an experimental model for the study of bladder contractility

AIMS

The objective of the study was to establish an experimental model for the extracorporeal perfusion of the pig detrusor. In order to validate this model we examined some biochemical parameters and determined the effect of carbachol on the contractility of perfused female pig bladders.

METHODS

Twenty-six pig bladders were perfused with Krebs-Ringer bicarbonate-glucose buffer for a period up to 5 hr with the aim to preserve a viable organ, which would be responsive to contraction-inducing agents. The intravesical pressure of the bladder as well as the intraarterial pressure of the vesical arteries were recorded before and after administration of carbachol.

RESULTS

The perfusate pH, lactate, partial carbon dioxide tension, and the ATP content in the perfused tissue, all indicators of tissue ischemia or cell necrosis, showed a good preservation of the organ for up to 5 hr. Carbachol was able to induce contractions of the prefilled bladder with a complete draining of the bladder throughout the whole perfusion period.

CONCLUSIONS

We could demonstrate that this perfusion system was able to preserve the pig bladder in a functional condition, appropriate for the study of physiological questions.