PATHOLOGY AND PATHOPHYSIOLOGY OF DETRUSOR IN INCONTINENCE

Evidence for a common mechanism for spontaneous rhythmic contraction and myogenic contraction induced by quick stretch in detrusor smooth muscle

Detrusor smooth muscle exhibits myogenic contraction in response to a quick stretch (QS) as well as spontaneous rhythmic contraction (SRC); however, whether the same population of actomyosin crossbridges with a common regulatory mechanism is responsible for these two types of contraction has not been determined. Detrusor strips from New Zealand white rabbit bladders were allowed to develop SRC at a reference muscle length (L_ref), or rhythmic contraction (RC) was induced with tetraethylammonium (TEA). Multiple 10-msec stretches of 15% L_ref were then imposed at L_ref randomly during the rhythm cycle, and the nadir-to-peak (NTP) tension amplitude of the resulting myogenic contraction was measured. The amplitude and period of the rhythm cycle were measured prior to each QS. NTP was larger when a QS was imposed during a portion the cycle when tension was smaller (n = 3 each SRC and TEA-induced RC). These data suggest that when the rhythmic mechanism was mostly inactive and tension was near a minimum, a larger portion of a shared population of crossbridges was available to produce a myogenic response to a QS. Rho kinase, cyclooxygenase-1, and cyclooxygenase-2 inhibitors (H-1152, SC-560, and NS-398) affected SRC amplitude and NTP amplitude following a QS to the same degree (n = 3 each drug), providing additional evidence to support the hypothesis that a common mechanism is responsible for SRC and myogenic contraction due to QS. If a common mechanism exists, then QS is a potential mechanical probe to study SRC regulation and its alteration in overactive bladder.

Stimulated calcium entry and constitutive RhoA kinase activity cause stretch-induced detrusor contraction

Urinary bladder wall muscle (i.e., detrusor smooth muscle; DSM) contracts in response to a quick-stretch, but this response is neither fully characterized, nor completely understood at the subcellular level. Strips of rabbit DSM were quick-stretched (5 ms) and held isometric for 10 s to measure the resulting peak quick-stretch contractile response (PQSR). The ability of selective Ca(2+) channel blockers and kinase inhibitors to alter the PQSR was measured, and the phosphorylation levels of myosin light chain (MLC) and myosin phosphatase targeting regulatory subunit (MYPT1) were recorded. DSM responded to a quick-stretch with a biphasic response consisting of an initial contraction peaking at 0.24+/-0.02-fold the maximum KCl-induced contraction (F(o)) by 1.48+/-0.17 s (PQSR) before falling to a weaker tonic (10 s) level (0.12+/-0.03-fold F(o)). The PQSR was dependent on the rate and degree of muscle stretch, displayed a refractory period, and was converted to a sustained response in the presence of muscarinic receptor stimulation. The PQSR was inhibited by nifedipine, 2-aminoethoxydiphenyl borate (2-APB), 100 microM gadolinium and Y-27632, but not by atropine, 10 microM gadolinium, LOE-908, cyclopiazonic acid, or GF-109203X. Y-27632 and nifedipine abolished the increase in MLC phosphorylation induced by a quick-stretch. Y-27632, but not nifedipine, inhibited basal MYPT1 phosphorylation, and a quick-stretch failed to increase phosphorylation of this rhoA kinase (ROCK) substrate above the basal level. These data support the hypothesis that constitutive ROCK activity is required for a quick-stretch to activate Ca(2+) entry and cause a myogenic contraction of DSM.

The elusive electromyogram in the overactive bladder: a spark of understanding

It has been said that a technique capable of recording a urinary bladder electromyogram could be useful in the clinical evaluation of the detrusor neuropathies and myopathies implicated in the generation of lower urinary tract symptoms. However, in contrast to electromyography of skeletal and cardiac muscle, detrusor smooth muscle electromyography has remained in its infancy despite 50 years of scientific effort. The principal problems appear to be isolation of the real signal from artefacts, and the doubtful existence of electromyographic activity during cholinergic muscle contraction. The discovery of purinergic neuromuscular transmission in the overactive human bladder has renewed interest in detrusor electromyography as, in contrast to cholinergic mechanisms, purinergic mechanisms can generate extracellular electrical activity. In this paper, the development and validation of a novel technique for recording electrical activity from neurologically intact guinea-pig and human detrusor in vitro is described. A purinergic electromyographic signal is characterised and it is shown that detrusor taken from overactive human bladders has a greater propensity to generate electromyographic activity than normal by virtue of an aberrant purinergic mechanism.

ULTRASTRUCTURE OF THE BLADDER IN CLASSIC EXSTROPHY: CORRELATION WITH DEVELOPMENT OF CONTINENCE

PURPOSE

Successful initial surgical management of bladder exstrophy does not always lead to continence. We evaluated the ultrastructure of the exstrophic bladder using electron microscopy (EM) at various stages of reconstruction to determine whether morphology could correlate with the potential for continence.

MATERIALS AND METHODS

Bladder specimens obtained from 32 patients undergoing various stages of exstrophy reconstruction were evaluated by EM. Specimens were obtained at primary newborn closure (group 1-10), reclosure following failure (group 2-2), bladder neck reconstruction (group 3-9) and augmentation cystoplasty (group 4-11). Evaluation was performed by a single anatomist with experience with EM. Biopsies were separated into those with good, intermediate or poor ultrastructural parameters and then correlated clinically.

RESULTS

In group 1, 4 children had good and 2 had intermediate parameters. All showed increased bladder volumes at followup. Four patients had poor parameters and poor bladder growth. The 2 group 2 children had poor parameters and bladder growth. In group 3, 7 of 9 patients had good and 1 had intermediate parameters. Eight of the 9 patients are doing well. Only 3 of the 11 group 4 children had good parameters and an additional 2 had intermediate parameters.

CONCLUSIONS

Ultrastructural evaluation can identify changes in the bladder that may portend a poor prognosis for eventual continence. Although the correlation was good at bladder closure, some patients with good parameters still had failed reconstruction. Since this is a small study, we continue to recommend reconstruction in all patients who have an adequate bladder template.

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.

Physiology of incontinence

The physiology of incontinence is related to the normal physiologic mechanisms of aging and to abnormal pathologic changes that recently have become better understood. Further research is needed to develop new methods of pharmacologic treatment.

Management of detrusor dysfunction in the elderly: changes in acetylcholine and adenosine triphosphate release during aging

Numerous studies have detailed age-related changes in the structure and function of the bladder that may contribute to the high prevalence of overactive bladder (OAB) in the elderly population, but the relation of these changes to OAB symptoms remains unclear. Physiologic and neurochemical studies have been conducted in human detrusor strips obtained from people of different ages, focusing on potential changes in cholinergic and purinergic neurotransmission, as well as the release and actions of acetylcholine (ACh) from nonneuronal bladder cells. Results from physiologic and microdialysis experiments indicate that purinergic transmission increases with age, whereas cholinergic transmission decreases. These effects are most likely because of decreased release of ACh and increased release of adenosine triphosphate (ATP) from postganglionic parasympathetic axons innervating the bladder. Immunohistochemical experiments showed that choline acetyltransferase in the human detrusor is contained not only in parasympathetic axons, but also in cells of the urothelium. The release of nonneuronal ACh increases with age and detrusor stretch. The age-related increase in purinergic transmission in the detrusor and other data indicating that responses to ATP are increased in detrusor overactivity suggest that purinergic receptor antagonists may provide a useful complement to muscarinic receptor antagonists in the treatment of older patients with OAB. Nonneuronal ACh release may play a key role in the storage phase of the micturition reflex, and this may explain, at least in part, the effectiveness of antimuscarinic agents for the treatment of OAB.

Positive response to ice water test associated with high-grade bladder outlet obstruction in patients with benign prostatic hyperplasia

OBJECTIVES

To elucidate the clinical significance of detrusor overactivity (DO) that is probably due to C-fiber activation caused by bladder outlet obstruction (BOO), we examined the responses to the ice water test (IWT) in patients with benign prostatic hyperplasia (BPH) and assessed the results with reference to the clinical manifestations and urodynamic findings.

METHODS

A total of 127 patients without neurologic disease, who were older than 50 years of age, with an International Prostate Symptom Score of 8 points or greater and a quality of life index of 2 or more points, were enrolled in this study. We tested the response to ice water instillation by monitoring the intravesical pressure in all cases and assessed the results with reference to the findings of International Prostate Symptom Score and quality of life index questionnaires, BOO indexes, 48-hour frequency volume charts, prostate volume, and data from free-flowmetry and pressure flow studies for detecting DO. Twenty patients with neurogenic bladder dysfunction underwent IWT as a control group.

RESULTS

The responders to the IWT accounted for 14 (70%) of the 20 patients with neurogenic bladder dysfunction and 35 (27%) of the 127 patients without neurologic disease. All of these responders showed DO on the pressure flow studies. The patients without neurologic disease who responded to the IWT had higher BOO indexes than did the nonresponders and had a smaller volume at a maximal desire to void on the urodynamic studies. The largest single-voided volume recorded from the 48-hour frequency volume charts was also smaller for the responders than for the nonresponders.

CONCLUSIONS

The patients with BPH clearly showed that DO was mainly due to active C-fibers stimulated by high-grade BOO and that DO was a cause of urgency and frequency-related symptoms with decreased bladder capacity. It will be necessary to assess the inhibitory effect of capsaicin on DO caused by activation of C-fibers and the reversibility of C-fiber activation after surgical treatment for BPH, so that the criteria for decision-making for the treatment of BPH may be clarified with the aid of the IWT.

Urgency, urge incontinence and voiding symptoms in men and women aged 70 years and over

OBJECTIVE

To evaluate the prevalence of urgency, urge incontinence and voiding symptoms, and their associations in older men and women.

SUBJECTS AND METHODS

A population-based cross-sectional survey was conducted involving 171 men and 227 women aged > or = 70 years. The data were collected by interview, with a response rate of 92.8%. Voiding symptoms were defined as weakened and/or intermittent stream. The prevalence of urgency, urge incontinence and voiding symptoms were calculated for men and women aged 70-79 and > or = 80 years. Logistic regression models were used to examine the association of voiding symptoms with urgency, with or without incontinence, adjusted in the separate models for age and in the combined model also for gender.

RESULTS

The prevalence of urge incontinence was higher than urgency alone in both men and women (23.9% vs. 9.8% and 36.4% vs. 8.6%, respectively); 71.9% of the men and 48.3% of the women reported voiding symptoms (P < 0.001). Men and women with voiding symptoms were both significantly more likely to report urgency with or without incontinence than those with no voiding symptoms (odds ratio 3.49, 95% confidence interval 1.42-8.57, and 2.34, 1.31-4.17, respectively). Age had no independent effect in men, and in women the effect was marginal. In the combined model female gender (1.98, 1.25-3.16) increased the risk of urgency with or without incontinence.

CONCLUSION

Urgency, urge incontinence and voiding symptoms are common and associated with each other in older men and women; the association is stronger in men. Women are at greater risk of having urgency with or without incontinence. Because the study was cross-sectional a causal relationship cannot be confirmed.

Evaluation and treatment of the overactive bladder

The overactive bladder is characterized by symptoms of frequency, urgency, and urge incontinence, substantially affecting the quality of life of millions of people throughout the world. The symptoms are associated with significant social, psychological, occupational, domestic, physical, and sexual problems. Despite the considerable impact of this condition on quality of life, sufferers are often unwilling to discuss their problem with family members or health care professionals. This situation is unfortunate, for much can be done to alleviate the symptoms of this distressing condition. It is therefore of utmost importance that medical education about symptoms of the overactive bladder and other related problems be improved to help health care professionals identify and treat patients who will benefit from therapy. This article reviews current thinking regarding definition, epidemiology, quality of life effects, evaluation, and management of the overactive bladder.

The production of nerve growth factor by human bladder smooth muscle cells in vivo and in vitro

OBJECTIVE

To measure the concentrations of nerve growth factor (NGF) in tissue biopsies taken from subjects with a normal bladder and from patients diagnosed to have idiopathic detrusor instability (associated with a reduction in the density of motor nerves), and to use an in vitro model to study the mechanisms of NGF expression.

MATERIALS AND METHODS

Biopsy specimens were obtained during endoscopic and open surgery from patients undergoing routine bladder surgery. The patients were divided into two categories based upon urodynamic characterization. The NGF content in samples from 11 normal bladders and seven idiopathic unstable bladders were measured using an enzyme-linked immunosorbent assay. The mechanisms influencing net NGF production were explored using detrusor cells in vitro.

RESULTS

The mean (SEM) NGF content was significantly higher in unstable tissues, at 0.96 (0.05) pg/microg protein, than in the normal bladder, at 0.53 (0.05) pg/microg protein. In the cell model, acetylcholine (10 micromol/L), noradrenaline (1 and 10 micromol/L) and ATP (1 micromol/L) caused a significant increase in net NGF production; acetylcholine at 1 micromol/L had no effect. Direct stimulation of protein kinase C (PKC) by phorbol ester (33 ng/mL) or elevation of cAMP using forskolin (10 micromol/L) increased NGF, suggesting that at least two intracellular pathways (PKC- and PKA-dependent) are involved. The expression of c-Fos was increased by phorbol 12-myristate 13-acetate added before NGF, suggesting that c-Fos may be involved in regulating NGF production.

CONCLUSION

These data suggest a role for NGF in the physiology and pathophysiology of the human bladder, and indicate some of the possible mechanisms which might regulate NGF production.

The effect of pregnancy and delivery on the function and ultrastructure of the rat bladder and urethra

OBJECTIVE

To examine the effect of pregnancy and delivery on the function and ultrastructure of the bladder and urethra in rats. Material and methods The study comprised six virgin and 18 pregnant rats; both groups underwent cystometry (at the 19th day of gestation, and 2 days and 6 weeks after parturition). Tissues from the bladder and urethra were collected for electron microscopy, western blotting and immunostaining for caveolin-1 and caveolin-3.

RESULTS

The bladder capacity was greater and the modified leak-point pressures lower in pregnant and 2-day postpartum rats than in virgin and 6-week postpartum rats. The residual volume was significantly higher in the pregnant group. Electron microscopy showed more sarcolemmal caveolae in the smooth muscle cells of both the bladder and urethra of virgin rats than in the other groups. Lipid droplets and subsarcolemmal mitochondria accumulated in pregnant and 2-day postpartum rats. Caveolin-1 protein was detected in the cytoplasmic membrane of urethra and bladder smooth muscle cells. Caveolin-3 was detected in the membrane of striated muscle in the intrinsic sphincter. Western blotting showed increased caveolin-1 protein expression in the bladder and urethra of 2-day postpartum rats; in contrast, levels of caveolin-1 were lower in pregnant rats than in virgin and 6-week postpartum rats.

CONCLUSION

s During pregnancy there was a significant decrease in sarcolemmal caveolae and caveolin-1 in the smooth muscle cells of the rat bladder and urethra. The changes in caveolae and the membrane protein caveolin may play a role in the functional changes associated with pregnancy and after delivery.

The role of collagen in bladder filling

While this model is speculative, it is attractive in that it can account for the physiologic properties of the bladder. It also implies that connections must exist between the tension generating elements, i.e., the smooth muscle cells, and the other components of the bladder. In bladders that become noncompliant, it is likely that there is some interference with the ability of the collagen fibers to elastically and reversibly alter their tortuosity. This, predictably, would reduce total bladder capacity. Further studies will be required to establish the relationship between compliance changes and the passive mechanical elements of the bladder wall that comprise its structural protein matrix.

Focal changes in nerve, muscle and connective tissue in normal and unstable human bladder

OBJECTIVE

To compare and quantify, in a morphological study, the changes that occur in the connective tissue elements (elastin and collagen), muscle fibre diameters and nerve densities between normal, idiopathic and neuropathic bladders.

MATERIALS AND METHODS

Bladder tissue was obtained from 27 patients undergoing cystectomy for carcinoma, from 12 with idiopathic instability and from seven neuropathic patients who were undergoing ileocystoplasty. A combination of histochemical and immunohistochemical techniques were used to detect detrusor muscle, connective tissue and nerve profiles in the bladder tissue.

RESULTS

In both idiopathic and neuropathic bladder tissue the structural changes were highly punctate. From the density of nerve profiles, three areas were defined: (i) apparently unaffected normal fascicles with a high density of nerves, no hypertrophy of the muscle and no infiltration of elastin and collagen. The nerve density in these areas was similar to that in normal bladder tissue. (ii) Fascicles with a low density of nerve profiles, muscle hypertrophy but no connective tissue infiltration. (iii) Areas with few nerve profiles, muscle hypertrophy and extensive elastin and collagen infiltration within the fascicles. The mean (sem) density of nerve profiles in control tissue was 752 (53) nerves/mm2 and in the idiopathic bladders was 905 (91), 81 (20) and 74 (38) nerves/mm2 in the three defined areas, respectively. In the neuropathic tissues the nerve profile densities were 672 (249), 57 (23) and 37 (28) nerves/mm2, respectively. Fibre diameter, elastin and collagen content and nerve density were measured in normal and unstable bladder tissue using these three defined areas. The mean (sem) fibre diameter was 6.81 (0.52) in normal bladder; in idiopathic bladder tissue the fibre diameters in the three areas were 6.72 (0.62), 7.06 (0.62) and 7.34 (1.15) micrometer, respectively, and in neuropathic bladders were 6.75 (0.62), 8.24 (0.62) and 9.35 (0.62) micrometer, respectively. The relative areas of elastin were 0.79 (0.70), 0.56 (0.45) and 18.3 (4.1)% for the control, normal and affected areas of the neuropathic bladders, respectively, and the relative areas of collagen were 3.5 (1.3), 6.15 (3.6) and 15.7 (5. 0)%, respectively. The pattern was similar in idiopathic bladders.

CONCLUSION

These observations suggest that the primary defect in the idiopathic and neuropathic bladders is a loss of nerves accompanied by a hypertrophy of the cells. These changes may continue with further hypertrophy of the cells and an increased production of elastin and collagen within the muscle fascicles.

Office management of female urinary incontinence

The majority of incontinent women are manageable using office-based techniques. This article reviews the basic causes of per urethram urinary incontinence, and summarizes how to optimally evaluate them from a clinical and urodynamic standpoint in the office setting. Emphasis is made on the progress and efficiency of the wide range of ambulatory treatment options, which include behavioral treatments, pharmacotherapy, periurethral injection of bulking agents, anti-incontinence devises, and the use of absorbent products. The economy-driven trend to decrease hospital management of disease and patient interest in noninvasive techniques will continue to increase the importance of the key role played by the office urologist in the management of female urinary incontinence.

Diagnosis and significance of idiopathic overactive bladder

OBJECTIVES

To offer a critical overview of the basis for the International Continence Society (ICS) classification of detrusor instability, to summarize current diagnostic methodologies, and to outline the etiologic factors that should be excluded in the diagnosis of idiopathic overactive bladder.

METHODS

The current ICS definitions of overactive bladder are discussed. Issues related to the diagnosis of detrusor instability (DI) are addressed through a review of the literature.

RESULTS

The term idiopathic overactive bladder reflects the present lack of knowledge concerning vesicourethral function and dysfunction. The term is used to apply to a wide spectrum of different conditions that may have a common final pathophysiologic pathway. This heterogeneous group of conditions could be subdivided on the basis of presumptive etiopathogenesis, urodynamic patterns, and response to treatment. The diagnosis of DI, its rate of detection, and its urodynamic patterns depend on the type of urodynamic test used and the way the test is performed. The ICS definitions of DI have been called into question by the results of studies using urodynamic tests in addition to, or instead of, provocative cystometry--for instance, ambulatory urodynamics, urethrocystometry, the ice-water test, and evaluation of the voiding phase. The literature supports a broadening of the ICS criteria for excluding all known causes of DI when establishing the diagnosis of idiopathic overactive bladder.

CONCLUSIONS

Appropriate longitudinal studies, using contemporary urodynamic tests and knowledge, are needed to improve the identification of subsets of patients with overactive bladder who have different prognoses and outcomes. The ICS definitions and classification should be updated.

Functional anatomy of the organs of micturition

The anatomy of the organs of micturition has been the subject of study for nearly 150 years. As a result of advances in techniques and methods of clinical and research investigation, studies over the past three decades have intensified and have been increasingly directed at the functional implications and significance of organ anatomy and structure. This has led to revision of many traditional ideas about micturition and the development of new viewpoints and modalities for study of its disorders. This article summarizes the evolution of our thinking and understanding of the functional anatomy of the bladder and urethra over the years, and suggests possible directions for continued clinical study and investigation.

Smooth-muscle physiology

In the last several years, significant advances have been made in the understanding of bladder smooth muscle physiology. This article provides a summary for the clinician of current knowledge about the detrusor smooth muscle cell structure, function, and the relationship of structure to function in terms of bladder storage and physical properties such as compliance. The integration of this basic science knowledge into clinical practice is illustrated in discussion of two common disorders: detrusor instability, and outflow obstruction.

Geriatric incontinence

Regardless of age, mobility, mentation, or institutionalization, incontinence is never normal. By attenuating physiologic reserve, aging increases the likelihood of becoming incontinent in the setting of additional physiologic, pharmacologic, or pathologic insults. Because many of these problems lie outside the urinary tract, so too must the diagnostic and therapeutic focus. Such a strategy, however, coupled with a multifactorial, creative, persistent, and optimistic approach, increases the chances of a successful outcome and generally rewards patient and physician alike.