ALTERED RESPONSE TO PARTIAL BLADDER OUTLET OBSTRUCTION IN MICE LACKING INDUCIBLE NITRIC OXIDE SYNTHASE

Role of circadian rhythms and melatonin in bladder function in heath and diseases

The circadian system modulates all visceral organ physiological processes including urine storage and voiding. The "master clock" of the circadian system lies within suprachiasmatic nucleus of the hypothalamus while "peripheral clocks" are found in most peripheral tissue and organs, including the urinary bladder. Disruptions of circadian rhythms can cause organ malfunction and disorder or exacerbate pre-existing ones. It has been suggested that nocturia, which develops mostly in the elderly, could be a circadian-related disorder of the bladder. In the bladder, many types of gap junctions and ion channels in the detrusor, urothelium and sensory nerves are likely under strict local peripheral circadian control. The pineal hormone, melatonin, is a circadian rhythm synchroniser capable of controlling a variety of physiological processes in the body. Melatonin predominantly acts via the melatonin 1 and melatonin 2 G-protein coupled receptors expressed in the central nervous system, and many peripheral organs and tissues. Melatonin could be beneficial in the treatment of nocturia and other common bladder disorders. The ameliorating action of melatonin on bladder function is likely due to multiple mechanisms which include central effects on voiding and peripheral effects on the detrusor and bladder afferents. More studies are warranted to determine the precise mechanisms of circadian rhythm coordination of the bladder function and melatonin influences on the bladder in health and diseases.

Astragaloside IV Protects Detrusor from Partial Bladder Outlet Obstruction-Induced Oxidative Stress by Activating Mitophagy through AMPK-ULK1 Pathway

Aims

Bladder outlet obstruction (BOO) and the consequent low contractility of detrusor are the leading causes of voiding dysfunction. In this study, we aimed to evaluate the pharmacological activity of astragaloside IV (AS-IV), an antioxidant biomolecule that possess beneficial effect in many organs, on detrusor contractility and bladder wall remodeling process.

Methods

Partial BOO (pBOO) was created by urethral occlusion in female rats, followed by oral gavage of different dose of AS-IV or vehicle. Cystometric evaluation and contractility test were performed. Bladder wall sections were used in morphology staining, and bladder tissue lysate was used for ELISA assay. Primary smooth muscle cells (SMCs) derived from detrusor were used for mechanism studies.

Results

Seven weeks after pBOO, the bladder compensatory enlarged, and the contractility in response to electrical or chemical stimuli was reduced, while AS-IV treatment reversed this effect dose-dependently. AS-IV also showed beneficial effect on reversing the bladder wall remodeling process, as well as reducing ROS level. In mechanism study, AS-IV activated mitophagy and alleviated oxidative stress via an AMPK-dependent pathway.

Conclusion

Out data suggested that AS-IV enhanced the contractility of detrusor and protected the bladder from obstruction induced damage, via enhancing the mitophagy and restoring mitochondria function trough an AMPK-dependent way.

Effects of nitric oxide inhibitors in mice with bladder outlet obstruction

PURPOSE

To investigate the lower urinary tract changes in mice treated with L-NAME, a non-selective competitive inhibitor of nitric oxide synthase (NOS), or aminoguanidine, a competitive inhibitor of inducible nitric oxide synthase (iNOS), after 5 weeks of partial bladder outlet obstruction (BOO), in order to evaluate the role of constitutive and non-constitutive NOS in the pathogenesis of this experimental condition.

MATERIALS AND METHODS

C57BL6 male mice were partially obstructed and randomly allocated into 6 groups: Sham, Sham + L-NAME, Sham + aminoguanidine, BOO, BOO + L-NAME and BOO + aminoguanidine. After 5 weeks, bladder weight was obtained and cystometry and tissue bath contractile studies were performed.

RESULTS

BOO animals showed increase of non-voiding contractions (NVC) and bladder capacity, and also less contractile response to Carbachol and Electric Field Stimulation. Inhibition of NOS isoforms improved bladder capacity and compliance in BOO animals. L-NAME caused more NVC, prevented bladder weight gain and leaded to augmented contractile responses at muscarinic and electric stimulation. Aminoguanidine diminished NVC, but did not avoid bladder weight gain in BOO animals and did not improve contractile responses.

CONCLUSION

It can be hypothesized that chronic inhibition of three NOS isoforms in BOO animals leaded to worsening of bladder function, while selective inhibition of iNOS did not improve responses, what suggests that, in BOO animals, alterations are related to constitutive NOS.

Deletion of neuropilin 2 enhances detrusor contractility following bladder outlet obstruction

Chronic urethral obstruction and the ensuing bladder wall remodeling can lead to diminished bladder smooth muscle (BSM) contractility and debilitating lower urinary tract symptoms. No effective pharmacotherapy exists to restore BSM contractile function. Neuropilin 2 (Nrp2) is a transmembrane protein that is highly expressed in BSM. Nrp2 deletion in mice leads to increased BSM contraction. We determined whether genetic ablation of Nrp2 could restore BSM contractility following obstruction. Partial bladder outlet obstruction (pBOO) was created by urethral occlusion in mice with either constitutive and ubiquitous, or inducible smooth muscle-specific deletion of Nrp2, and Nrp2-intact littermates. Mice without obstruction served as additional controls. Contractility was measured by isometric tension testing. Nrp2 deletion prior to pBOO increased force generation in BSM 4 weeks following surgery. Deletion of Nrp2 in mice already subjected to pBOO for 4 weeks showed increased contractility of tissues tested 6 weeks after surgery compared with nondeleted controls. Assessment of tissues from patients with urodynamically defined bladder outlet obstruction revealed reduced NRP2 levels in obstructed bladders with compensated compared with decompensated function, relative to asymptomatic controls. We conclude that downregulation of Nrp2 promotes BSM force generation. Neuropilin 2 may represent a novel target to restore contractility following obstruction.

Muro-Neuro-Urodynamics; a Review of the Functional Assessment of Mouse Lower Urinary Tract Function

Background: Mouse urodynamic tests are fundamental to understanding normal lower urinary tract (LUT) function. These experiments also contribute to our understanding of neurological dysfunction, pathophysiological processes, and potential mechanisms of therapy.

Objectives: Systematic assessment of published evidence on urodynamics, advantages and limitations of different urodynamic measurements in mice, and consideration of potential implications for the clinical field.

Methods: A search using specific search-terms for urodynamic studies and mice was conducted on PubMed (from inception to 1 July 2016).

Results: We identified 55 studies examining or describing mouse neuro-urodynamics. We summarize reported features of mouse urodynamic function deriving from frequency-volume chart (FVC) measurements, voiding spot assays, filling cystometry, and pressure-flow studies. Similarly, an influence of the diurnal cycle on voiding is observed in mice and should be considered when interpreting rodent urodynamic studies, especially FVC measurements and voiding spot assays. Anaesthesia, restraint conditions, or filling rate influence mouse neuro-urodynamics. Mouse cystometric studies have observed intravesical pressure oscillations that accompany urine flow, attributed to high frequency opening and closing of the urethra. This characterization is not seen in other species, except rats. In contrast to human clinical urodynamics, the terminology of these examinations has not been standardized although many rodent urodynamic studies have been described.

Conclusion: Mice have many anatomical and physiological similarities to humans and they are generally cost effective, and allow investigation of the effects of aging because of their short lifespan. There are some differences between mouse and human urodynamics. These must be considered when interpreting LUT function in mice, and translational value of murine disease models.

Functional consequences of chronic bladder ischemia

The pathophysiology of lower urinary tract symptoms (LUTS), particularly in the elderly, seems to be multifactorial. One of the factors involved may be chronic ischemia of the bladder caused by bladder outflow obstruction (male) or atherosclerosis (male/female). The mechanisms by which chronic ischemia initiates and causes LUTS and progressive bladder dysfunction, and the time course of the effects, are incompletely known. Bladder ischemia and repeated ischemia/reperfusion during a micturition cycle may produce oxidative stress, leading to denervation of the bladder and the expression of tissue damaging molecules in the bladder wall. This may be responsible for the development of detrusor overactivity progressing to detrusor underactivity and inability to empty the bladder. The extent of bladder dysfunction in chronic bladder ischemia may depend on the degree and duration of ischemia. To prevent chronic bladder ischemia caused by atherosclerosis and to treat its consequences, more pathophysiological knowledge is needed. Several animal models of atherosclerosis-induced chronic bladder ischemia are available and should be useful tools for further research.

Molecular mechanisms of bladder outlet obstruction in transgenic male mice overexpressing aromatase (Cyp19a1)

We investigated the etiology and molecular mechanisms of bladder outlet obstruction (BOO). Transgenic (Tg) male mice overexpressing aromatase (Cyp19a1) under the ubiquitin C promoter in the estrogen-susceptible C57Bl/6J genetic background (AROM+/6J) developed inguinal hernia by 2 months and severe BOO by 9 to 10 months, with 100% penetrance. These mice gradually developed uremia, renal failure, renal retention, and finally died. The BOO bladders were threefold larger than in age-matched wild-type (WT) males and were filled with urine on necropsy. Hypotrophic smooth muscle cells formed the thin detrusor urinae muscle, and collagen III accumulation contributed to the reduced compliance of the bladder. p-AKT and ERα expression were up-regulated and Pten expression was down-regulated in the BOO bladder urothelium. Expression of only ERα in the intradetrusor fibroblasts suggests a specific role of this estrogen receptor form in urothelial proliferation. Inactivation of Pten, which in turn activated the p-AKT pathway, was strictly related to the activation of the ERα pathway in the BOO bladders. Human relevance for these findings was provided by increased expression of p-AKT, PCNA, and ERα and decreased expression of PTEN in severe human BOO samples, compared with subnormal to mild samples. These findings clarify the involvement of estrogen excess and/or imbalance of the androgen/estrogen ratio in the molecular pathogenetic mechanisms of BOO and provide a novel lead into potential treatment strategies for BOO.

Bladder stromal loss of transforming growth factor receptor II decreases fibrosis after bladder obstruction

PURPOSE

Transforming growth factor-beta is a potent stimulator of extracellular matrix production. Several studies show that loss of transforming growth factor-beta signaling decreases kidney, liver and lung fibrosis. However, the role of transforming growth factor-beta signaling in bladder fibrosis is not entirely understood. We investigated the effect of stromal loss of such signaling in mice after partial bladder outlet obstruction.

MATERIALS AND METHODS

We performed partial bladder outlet obstruction by urethral ligation in 5-week-old female Tgfbr2(colTKO) mice. These mice were compared to WT mice with partial bladder outlet obstruction and to WT nonobstructed controls. After 4 weeks and before sacrifice urodynamics were performed. Bladder tissue was harvested, and p-Smad2 and collagen (Masson's trichrome) staining were performed.

RESULTS

Bladder compliance was increased in partially obstructed Tgfbr2(colTKO) mice and decreased in partially obstructed WT mice. The latter had increased smooth muscle hypertrophy and increased collagen deposition between smooth muscle bundles compared to those in Tgfbr2(colTKO) mice and nonobstructed controls. Transforming growth factor-beta responsive collagen promoter activity was significantly decreased in Tgfbr2 knockout bladder stromal cells vs WT stromal cells.

CONCLUSIONS

Stromal loss of transforming growth factor-beta signaling decreased collagen deposition after partial bladder outlet obstruction. In contrast to collagen production by recruited macrophages, stromal transforming growth factor-beta signaling appears to be the primary source of fibrosis after partial bladder outlet obstruction. These findings further support the hypothesis that manipulating transforming growth factor-beta signaling in bladder stromal cells would provide a future avenue for neuropathic bladder and bladder fibrosis treatment.

Pharmacologic responses of the mouse urinary bladder

The aim of the study was to determine pathways involved in contraction and relaxation of the mouse urinary bladder. Mouse bladder strips were set up in gassed Krebs-bicarbonate solution and responses to various drugs and electrical field stimulation were obtained. Isoprenaline (b-receptor agonist) caused a 63% inhibition of carbachol precontracted detrusor (EC50=2nM). Carbachol caused contraction (EC50=0.3µM), responses were antagonised more potently by 4-DAMP (M3-antagonist) than methoctramine (M2-antagonist). Electrical field stimulation caused contraction, which was inhibited by atropine (60%) and less by guanethidine and α,β-methylene-ATP. The neurogenic responses were not potentiated by inhibition of nitric oxide synthase. Presence of an intact urothelium significantly depressed responses to carbachol (p=0.02) and addition of indomethacin and L-NNA to remove prostaglandin and nitric oxide production respectively did not prevent the inhibitory effect of the urothelium. In conclusion, b-receptor agonists cause relaxation and muscarinic agonists cause contraction via the M3-receptor. Acetylcholine is the main neurotransmitter causing contraction while nitric oxide has a minor role. The mouse and human urothelium are similar in releasing a factor that inhibits contraction of the detrusor muscle which is unidentified but is not nitric oxide or a prostaglandin. Therefore, the mouse may be used as a model to study the lower urinary tract.

Antioxidant levels in the pig urinary bladder: distribution within the bladder wall and in the urothelium derived from different bladder regions

This study was designed to determine the antioxidant levels in the urinary bladder wall layers as well as urothelium derived from different bladder regions. Samples of the urothelium, lamina propria, muscularis, and serosa were prepared from the pig's urinary bladder body, while samples used for regional mapping of the urothelium were prepared from trigone, ventral and dorsal middle bladder body, and apex region. Activities of superoxide dismutase, glutathione peroxidase, glutathione reductase, and catalase were determined. Concentrations of ascorbic acid and glutathione were also measured. Antioxidant activities, i.e. concentrations of superoxide dismutase, glutathione peroxidase, glutathione reductase and glutathione, were shown to be highest in the urothelium and progressively lower towards the serosa. Regional mapping of the urothelium singled out apex as the region with the lowest antioxidant activities, i.e. concentrations of glutathione peroxidase, ascorbic acid, and glutathione. The fact that antioxidants are concentrated in the urothelium implies that urothelium functions as a barrier against reactive species. The urothelium derived from the apex is the region with the lowest antioxidant levels and is therefore probably the region most liable to development of oxidative damage.

Biochemical alterations in partial bladder outlet obstruction in mice: up-regulation of the mitogen activated protein kinase pathway

PURPOSE

We evaluated the effect of partial bladder outlet obstruction on bladder weight, protein synthesis, mitotic markers and the mitogen activated protein kinase pathway in a mouse model.

MATERIALS AND METHODS

Mice were divided into 3 groups, including control, sham treated and partially obstructed. Bladders were harvested from the mice in the partially obstructed group 12, 24, 48, 72 and 168 hours after surgical partial outlet obstruction, respectively. Partially obstructed bladders were compared to bladders in the control and sham treated groups by weight, protein content, and expression of proliferating cellular nuclear antigen, cyclin D3, HsP 70, c-jun and phosphorylated c-jun. Bladders were examined histologically for changes occurring with partial obstruction.

RESULTS

We tested 3 groups of mice, including control, sham treated and partially obstructed mice, to understand the pathophysiology of the bladder response to partial obstruction. We found no statistical difference in body weight among the groups. Furthermore, there was a significant increase in bladder weight and protein content in partially obstructed mice compared to those in controls and sham operated mice. There was up-regulation of proliferating cellular nuclear antigen, cyclin D3, HsP70, c-jun and phosphorylated c-jun with partial obstruction. Fibrosis was prominent at 168 hours compared to that in controls.

CONCLUSIONS

Bladder weight and protein content increase with partial bladder outlet obstruction in mice. Cell cycle proteins and elements of the mitogen activated protein kinase pathway are up-regulated during this process.

Effects of l-arginine and N(G)-nitro-l-arginine methyl ester treatments on expression of neuronal nitric oxide synthase in the guinea-pig bladder after partial bladder outlet obstruction

This study was aimed to examine the effects of pharmacological intervention on partial bladder outlet obstruction (PBOO) on expression of neuronal nitric oxide synthase (nNOS) and nitric oxide (NO) production and NO-related free radical damage using nitrotyrosine as a marker in the guinea-pig bladder. Partial urethral ligation was performed in young male guinea pigs which were then intraperitoneally administered l-arginine, N(G)-nitro-l-arginine methyl ester (l-NAME) or vehicle (saline) for 2 or 4 weeks. At the respective time points, the bladder was removed for nNOS immunohistochemistry, Western blot analysis, nitrotyrosine enzyme-linked immunosorbent assay test and NO colorimetric assay. In l-arginine-treated animals killed at 2 and 4 weeks, the total number of nNOS positive intramural neurons was significantly increased when compared with the corresponding control. Some neurons projected long extending fibers that were closely associated with the blood vessels. Furthermore, at 4 weeks, the nNOS protein content and NO production as reflected by the concentration of nitrite and nitrate were drastically elevated as measured by Western blot analysis and NO colorimetric assay, respectively. In l-NAME-treated group killed at 2 weeks, the number of nNOS positive neurons was markedly reduced when compared with the controls, but the change was not significant at 4 weeks. In the latter, however, the NO production as reflected by the concentration of nitrite and nitrate was markedly reduced; in addition, the nitrotyrosine concentration was significantly lower than the control. The present results support the role of NO in the pathophysiological changes following PBOO. We suggest the potential therapeutic application of l-arginine and l-NAME in PBOO; however, ultimately balancing the bidirectional effects of NO would be essential.

LUTS treatment: Future treatment options

Lower urinary tract symptoms (LUTS) are commonly divided into storage, voiding, and postmicturition symptoms, and may occur in both men and women. Male LUTS have historically been linked to benign prostatic hyperplasia (BPH), but are not necessarily prostate related. The focus of treatment for LUTS has thus shifted from the prostate to the bladder and other extraprostatic sites. LUTS include symptoms of the overactive bladder (OAB), which are often associated with detrusor overactivity. Treatment for LUTS suggestive of BPH has traditionally involved the use of alpha(1)-adrenoceptor (AR) antagonists; 5alpha-reductase inhibitors; and phytotherapy-however, several new therapeutic principles have shown promise. Selective beta(3)-adrenoceptor agonists and antimuscarinics are potentially useful agents for treating LUTS, particularly for storage symptoms secondary to outflow obstruction. Other agents of potential or actual importance are antagonists of P2X(3) receptors, botulinum toxin type A, endothelin (ET)-converting enzyme inhibitors, and drugs acting at vanilloid, angiotensin, and vitamin D(3) receptor sites. Drugs interfering with the nitric oxide/cGMP-cAMP pathway, Rho-kinase and COX inhibitors, as well as drugs targeting receptors and mechanisms within the CNS, are also of interest and deserving of further study for the treatment of LUTS.

Null mutation in macrophage migration inhibitory factor prevents muscle cell loss and fibrosis in partial bladder outlet obstruction

Idiopathic detrusor underactivity (DU) and detrusor decompensation which develops following partial bladder outlet obstruction (pBOO) are both associated with smooth muscle degeneration and fibrosis. Macrophage migration inhibitory factor (MIF), an important mediator of bladder inflammation, has been shown to promote fibroblast survival and muscle death in other tissues. We evaluated the hypothesis that MIF has similar actions in the bladder by studying detrusor responses to pBOO or sham surgery in anesthetized female mice rendered null for the mif gene (MIF KO) and in wild-type (WT) controls, all killed 3 wk after surgery. WT mice revealed intense MIF immunoreactivity in urothelial cells which decreased, without change in overall mif mRNA levels. Stereologically sound quantitative morphometric measurements were performed in the middetrusor region of each bladder. MIF KO bladders were normal in appearance, yet were 30–40% heavier, with increased middetrusor collagen and muscle, compared with WT controls. In WT mice, pBOO increased the collagen-to-muscle ratio 1.9-fold and middetrusor collagen 1.8-fold, while nucleated muscle counts were 22% lower. In MIF KO mice, by contrast, pBOO had no significant effect on any of these parameters. In primary bladder muscle cultures, treatment with rMIF protein increased TUNEL staining, raising the proportion of early and late apoptotic cells on flow cytometry. Our studies implicate MIF in the sequence of events leading to detrusor muscle loss and fibrosis in obstruction. They raise the possibility that strategies designed to antagonize MIF synthesis, release, or biological activity could prevent or delay DU and urinary retention.

Pharmacology of the lower urinary tract: basis for current and future treatments of urinary incontinence

The lower urinary tract constitutes a functional unit controlled by a complex interplay between the central and peripheral nervous systems and local regulatory factors. In the adult, micturition is controlled by a spinobulbospinal reflex, which is under suprapontine control. Several central nervous system transmitters can modulate voiding, as well as, potentially, drugs affecting voiding; for example, noradrenaline, GABA, or dopamine receptors and mechanisms may be therapeutically useful. Peripherally, lower urinary tract function is dependent on the concerted action of the smooth and striated muscles of the urinary bladder, urethra, and periurethral region. Various neurotransmitters, including acetylcholine, noradrenaline, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in this neural regulation. Muscarinic receptors mediate normal bladder contraction as well as at least the main part of contraction in the overactive bladder. Disorders of micturition can roughly be classified as disturbances of storage or disturbances of emptying. Failure to store urine may lead to various forms of incontinence, the main forms of which are urge and stress incontinence. The etiology and pathophysiology of these disorders remain incompletely known, which is reflected in the fact that current drug treatment includes a relatively small number of more or less well-documented alternatives. Antimuscarinics are the main-stay of pharmacological treatment of the overactive bladder syndrome, which is characterized by urgency, frequency, and urge incontinence. Accepted drug treatments of stress incontinence are currently scarce, but new alternatives are emerging. New targets for control of micturition are being defined, but further research is needed to advance the pharmacological treatment of micturition disorders.

Urinary bladder contraction and relaxation: physiology and pathophysiology

The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition. These processes are regulated by several external nervous and hormonal control systems, and the detrusor contains multiple receptors and signaling pathways. Functional changes of the detrusor can be found in several clinically important conditions, e.g., lower urinary tract symptoms (LUTS) and bladder outlet obstruction. The aim of this review is to summarize and synthesize basic information and recent advances in the understanding of the properties of the detrusor smooth muscle, its contractile system, cellular signaling, membrane properties, and cellular receptors. Alterations in these systems in pathological conditions of the bladder wall are described, and some areas for future research are suggested.

Effect of bladder outlet obstruction on detrusor smooth muscle cell: an in vitro study 1, 2 1Presented at the 6th Asian Congress of Urology (6th ACU), Kuala Lumpur, Malaysia, August 12–18, 2002 2This study was supported by a grant from National Natural Science Fund (No. 39970739), China, PRC

BACKGROUND

Although relieving obstruction is generally curative on bladder outlet obstruction (BOO), bladder dysfunction persists in some patients. Repetitive stretch and relaxation applied to cultured bladder smooth muscle (SM) cells in vitro have been used to mimic increases in urodynamic load experienced by the detrusor muscle under conditions of BOO. We first clarified the relationship between phenotype transformation and biomechanical properties of detrusor smooth muscle cell (DSMC) subjected to the cyclic mechanical stretch.

MATERIALS AND METHODS

Cultured rat DSMC were grown on collagen-coated silicone membranes and subjected to continuous cycles of stretch-relaxation. All experiments were performed on cells between passages 2 and 4. Each cycle consists of 5 seconds of stretch and 5 seconds of relaxation. The computer controlled vacuum induced 10% (1), 20% (2), and 30% (3) maximum elongation of the plate membrane at different designed pressures. The deoxyribonucleic acid synthesis rate was assessed by performing tritiated thymidine incorporation assay. The expression of SM-alpha-actin and proliferation of DSMC were analyzed by immunofluorescent assay and flow cytometry. The image analysis and micropipet aspiration systems were used to investigate the single cell contraction and viscoelasticity. Using the 3-element standard linear solid model, the elastic modulus K(1), K(2), and viscoelastic coefficient mu were determined, which show the passive deformation ability of detrusor cells.

RESULTS

As the basic structural changes to mechanical stretch, DSMC undergo phenotypic modulation from their normal contractile phenotype to a "synthetic" phenotype: the DSMC become more proliferative and the actin less organized along the cell's long axis. The cell proliferation index of control and stretched group (10%, 20%, 30% elongation) are 0.24, 0.43, 0.58, and 0.65, respectively. The actin filaments in unstimulated cells were evident and orientated along the major axis of the cell. After mechanical stretch, the well-spread filaments changed their orientation. The function, such as contraction, and viscoelasticity of a single DSMC subjected to stretch both decreased significantly compared with control. The maximum contractile velocity and maximum cell length shortening rate of group 3 (30% elongation) showed significant decreases compared with unstretched control (P < 0.01). K(1) and K(2) were decreased with the increase of mechanical overload. However, there was no statistic difference between groups 2 and 3.

CONCLUSIONS

Functional abnormalitie of BOO have the structural basis: phenotype transformation (i.e., remodeling) of the detrusor cells. Cyclic stretch and relaxation applied to DSMC in vitro can be used to model increases in urodynamic load experienced by the bladder detrusor muscle under conditions of BOO. Phenotype transformation is the structural basis of functional changes of DSMC subjected to periodic overload mechanical stretch.

Inducible nitric oxide synthase promotes pathophysiological consequences of experimental bladder outlet obstruction

PURPOSE

Bladder outlet obstruction leads to histological and functional changes in the bladder over time. We investigated the role of inducible nitric oxide synthase (iNOS) in the progression of pathological changes of the bladder secondary to outlet obstruction in a rat and a mouse model.

MATERIALS AND METHODS

To assess expression of iNOS in the bladder, polymerase chain reaction amplification of mRNA was done. Rats were subjected to sham operation or partial bladder outlet obstruction. They were given the iNOS inhibitor aminoguanidine in drinking water or unmodified water. After 2 weeks, awake cystometric evaluation was performed, the bladders were harvested and the degree of fibrosis was assessed. In another series of experiments mice deficient in the iNOS gene (iNOS -/-) were compared to WT mice for cystometric as well as histological changes in the bladder following partial bladder outlet obstruction or sham operation.

RESULTS

Partial bladder outlet obstruction induced the expression of iNOS mRNA in the mouse bladder. iNOS -/- mice showed a significantly smaller increase in bladder volume at 3 weeks compared with WT. Pharmacological inhibition of iNOS activity significantly attenuated the increase in bladder size and the number of spontaneous bladder contractions in obstructed rats at 2 weeks. Furthermore, genetic and pharmacological decreases in iNOS led to significantly less fibrosis of the bladder after partial bladder outlet obstruction in mice and rats, respectively.

CONCLUSIONS

Pharmacological or genetic decreases in iNOS resulted in amelioration of functional and fibrotic changes in the bladder after partial bladder outlet obstruction, suggesting that NO contributes to the pathophysiology of bladder outlet obstruction.

Activity and expression of nitric oxide synthase in the hypertrophied rat bladder and the effect of nitric oxide on bladder smooth muscle growth

PURPOSE

We investigated the expression and activity of nitric oxide synthase (NOS) and the localization of cyclic guanosine monophosphate (cGMP) in hypertrophied rat bladder. We also examined whether nitric oxide (NO) has a growth inhibitory effect in bladder smooth muscle cells.

MATERIALS AND METHODS

The urethra was partly ligated and the bladder was removed 3 days, 3 or 6 weeks after obstruction. NOS activity was determined as the conversion of L-[14C]citrulline from L-[14C]arginine (Amersham Life Science, Solna, Sweden). Neuronal NOS (nNOS) expression was studied with Western blot analysis and immunohistochemistry. The expression of inducible NOS (iNOS) and cGMP was evaluated by immunohistochemistry. The effect of NO on isolated bladder smooth muscle cell growth was assessed as protein and DNA synthesis by [3H]-leucine and [3H]-thymidine (NEN Life Science Products, Zaventem, Belgium) incorporation, respectively.

RESULTS

Ca independent iNOS activity increased after short-term obstruction. Immunohistochemical studies in obstructed bladders demonstrated iNOS expression primarily in urothelial and inflammatory cells. Ca dependent nNOS activity decreased after obstruction, as confirmed by Western blot analysis. The cGMP immunoreactive cells were mainly found within the serosal layer of obstructed bladders. The NO donor DETA-NONOate (Alexis Biochemicals, Lausen, Switzerland) (300 microM.) reduced [3H]-leucine and [ H]-thymidine incorporation by a mean of 29% +/- 2% and 95% +/- 2%, respectively, in cultured bladder smooth muscle cells.

CONCLUSIONS

Bladder obstruction caused a small increase in iNOS activity and a decrease in nNOS activity. NO was found to have a growth inhibitory effect in bladder smooth muscle cells, suggesting that changes in NOS activity may influence the progress of bladder hypertrophy.

Increased blood flow after catheterization and drainage in the chronically obstructed rabbit urinary bladder

OBJECTIVES

To determine the effect of drainage on rabbit bladder blood flow after 4 weeks of partial outlet obstruction. Previous studies have shown that catheterization and drainage of the urinary bladder in control rabbits resulted in a significant nitric oxide-induced increase of blood flow to the bladder. It was also shown that 4 weeks' partial outlet obstruction caused a significant decrease in blood flow to the bladder.

METHODS

Male New Zealand White rabbits underwent partial outlet obstruction by standard methods. After 4 weeks, the blood flow to the bladder muscle and mucosa was determined by a microsphere technique. Within 1 to 2 minutes after transurethral catheterization and complete drainage of the bladder, the blood flow was again determined. Unobstructed animals served as controls. Four other control animals underwent a repetitive blood flow study during 10 minutes to determine the time frame of blood flow changes after drainage. Blood flow was also measured in 2 control rabbits after transurethral catheterization without drainage and in 2 control rabbits after drainage by suprapubic puncture. To exclude the possibility that increased intravesical pressure alters the blood flow measurements, the relationship between the intravesical volume and the bladder pressure was examined in the obstructed rabbits.

RESULTS

After drainage of the bladder, the blood flow to the bladder muscle increased 4.5-fold in the decompensated obstructed group (bladder weights greater than 15 g) and 2.5-fold in the compensated animals (bladder weights less than 5 g) and control animals. Blood flow to the mucosa followed the same pattern but without reaching significance. Blood flow returned to near baseline values within 5 minutes. Catheterization without drainage did not alter the blood flow. In contrast, drainage by puncture increased the blood flow significantly. Higher intravesical volumes increased the intravesical pressure slightly, but after opening the abdominal fascia, the intravesical pressure did not change with increasing volumes.

CONCLUSIONS

Although the previously shown decreased blood flow to the bladder smooth muscle may be an etiologic factor in bladder contractile dysfunction secondary to partial outlet obstruction, the bladder does have the ability to increase the blood flow after drainage. This ability could be a compensatory and possibly protective mechanism after outlet obstruction.

The decompensated detrusor IV: experimental bladder outlet obstruction and its functional correlation to the expression of the ryanodine and voltage operated calcium channels

PURPOSE

Calcium ion homeostasis has a significant role in smooth muscle function. Its regulation requires complex storage and release mechanisms via ion pumps and channels located within intracellular storage sites (sarcoplasmic reticulum) and at the plasma membrane. A prominent component of the sarcoplasmic reticulum is the ryanodine sensitive ion channel which releases calcium from the sarcoplasmic reticulum into the cytosol. At the level of the plasma membrane the voltage operated calcium channel (dihydropyridine sensitive) serves to allow an influx of extracellular calcium. Our prior studies have shown a loss of sarcoplasmic endoplasmic reticulum Ca++Mg++ATPase expression following outlet obstruction. In this study we correlate ryanodine and voltage operated calcium channel protein expression with bladder function following partial outlet obstruction.

MATERIALS AND METHODS

Standardized partial bladder outlet obstructions were created in adult New Zealand white rabbits, which were divided into control, sham operated and obstructed groups. Muscle strip studies further subcategorized the obstructed group into compensated (force greater than 50% of control) and decompensated (force less than 50% of control) and were correlated with in vivo determinations of voiding frequency and voided volumes. Microsomal membrane protein fractions were prepared from the same bladder tissue and were used for Western blot analysis using specific monoclonal antibodies.

RESULTS

Increased voiding frequency and decreased voided volumes correlated with the definitions of compensated and decompensated. The Western blots revealed a near disappearance of ryanodine expression in the decompensated group with minimal changes in the expression of the voltage operated calcium channel.

CONCLUSIONS

Bladder performance as measured in vivo and in vitro after outlet obstruction is influenced in part by smooth muscle cell ability to maintain calcium homeostasis via the sarcoplasmic reticulum. Bladder decompensation is highly associated with a loss of sarcoplasmic reticulum function with lesser changes taking place in those calcium regulatory proteins at the plasma membrane.

The decompensated detrusor IV: experimental bladder outlet obstruction and its functional correlation to the expression of the ryanodine and voltage operated calcium channels

PURPOSE

Calcium ion homeostasis has a significant role in smooth muscle function. Its regulation requires complex storage and release mechanisms via ion pumps and channels located within intracellular storage sites (sarcoplasmic reticulum) and at the plasma membrane. A prominent component of the sarcoplasmic reticulum is the ryanodine sensitive ion channel which releases calcium from the sarcoplasmic reticulum into the cytosol. At the level of the plasma membrane the voltage operated calcium channel (dihydropyridine sensitive) serves to allow an influx of extracellular calcium. Our prior studies have shown a loss of sarcoplasmic endoplasmic reticulum Ca++Mg++ATPase expression following outlet obstruction. In this study we correlate ryanodine and voltage operated calcium channel protein expression with bladder function following partial outlet obstruction.

MATERIALS AND METHODS

Standardized partial bladder outlet obstructions were created in adult New Zealand white rabbits, which were divided into control, sham operated and obstructed groups. Muscle strip studies further subcategorized the obstructed group into compensated (force greater than 50% of control) and decompensated (force less than 50% of control) and were correlated with in vivo determinations of voiding frequency and voided volumes. Microsomal membrane protein fractions were prepared from the same bladder tissue and were used for Western blot analysis using specific monoclonal antibodies.

RESULTS

Increased voiding frequency and decreased voided volumes correlated with the definitions of compensated and decompensated. The Western blots revealed a near disappearance of ryanodine expression in the decompensated group with minimal changes in the expression of the voltage operated calcium channel.

CONCLUSIONS

Bladder performance as measured in vivo and in vitro after outlet obstruction is influenced in part by smooth muscle cell ability to maintain calcium homeostasis via the sarcoplasmic reticulum. Bladder decompensation is highly associated with a loss of sarcoplasmic reticulum function with lesser changes taking place in those calcium regulatory proteins at the plasma membrane.

Lower urinary tract physiology and pharmacology

This review focuses on what we consider to be the most important findings of the last year relating to the smooth muscle of the lower urogenital system and the different levels of regulation that control its contraction and relaxation. One level is through modulation of the smooth muscle itself or its environment. Recent findings examining myosin isoform composition and collagen content as well as mechanisms that appear to be involved in inducing hyperplasia/hypertrophy of smooth muscle are described. Another method of regulation is via calcium-dependent phosphorylation of the regulatory light chain of myosin, which increases its activity. Interesting results indicating an uncoupling of force from calcium in the bladder are discussed. A third level of regulation is pharmacologic. Thus, the most recent findings related to receptor subtypes, including muscarinic, endothelin, alpha-adrenergic and nicotinic receptors, are presented. In addition, the effects of diabetes, incontinence, and partial bladder outlet obstruction on these modes of contractile regulation are also discussed.