Animal models of female stress urinary incontinence

Multiparity causes uncoordinated activity of pelvic- and perineal-striated muscles and urodynamic changes in rabbits

Temporal and coordinated activation of pelvic- (pubococcygeous) and perineal- (bulbospongiosus and ischiocavernosus) striated muscles occurs during micturition in female rabbits. We have hypothesized that the coordinated activation of pelvic and perineal muscles is modified during the micturition of young multiparous rabbits. Young virgin and multiparous female chinchilla rabbits were used to simultaneously record cystometrograms and electromyograms of the pubococcygeous, ischocavernosus, and bulbospongiosus muscles. Bladder function was assessed using standard urodynamic variables. The temporal coordination of pelvic- and perineal-striated muscle activity was changed in multiparous rabbits. The cystometrogram recordings were different than those obtained from virgin rabbits, as seen in alterations of the threshold volume, the residual volume, the voiding duration, and the maximum pressure. In rabbits, we find that multiparity causes uncoordinated activity of pubococcygeous, ischiocavernosus, and bulbospongiosus muscles and modifies the urodynamics.

Vulnerability of continence structures to injury by simulated childbirth

The goal of this study was to examine acute morphological changes, edema, muscle damage, inflammation, and hypoxia in urethral and vaginal tissues with increasing duration of vaginal distension (VD) in a rat model. Twenty-nine virgin Sprague-Dawley rats underwent VD under anesthesia with the use of a modified Foley catheter inserted into the vagina and filled with saline for 0, 1, 4, or 6 h. Control animals were anesthetized for 4 h without catheter placement. Urogenital organs were harvested after intracardiac perfusion of fixative. Tissues were embedded, sectioned, and stained with Masson's trichrome or hematoxylin and eosin stains. Regions of hypoxia were measured by hypoxyprobe-1 immunohistochemistry. Within 1 h of VD, the urethra became vertically elongated and displaced anteriorly. Edema was most prominent in the external urethral sphincter (EUS) and urethral/vaginal septum within 4 h of VD, while muscle disruption and fragmentation of the EUS occurred after 6 h. Inflammatory damage was characterized by the presence of polymorphonuclear leukocytes in vessels and tissues after 4 h of VD, with the greatest degree of infiltration occurring in the EUS. Hypoxia localized mostly to the vaginal lamina propria, urethral smooth muscle, and EUS within 4 h of VD. Increasing duration of VD caused progressively greater tissue edema, muscle damage, and morphological changes in the urethra and vagina. The EUS underwent the greatest insult, demonstrating its vulnerability to childbirth injury.

Quantification of neurological and other contributors to continence in female rats

Smooth muscle, striated muscle, their central and peripheral innervations and control, and mucosal coaptation contribute to maintenance of continence. We used manual leak point pressure (mLPP) testing and electrical stimulation LPP (eLPP) testing in female rats to quantify the contribution of these factors to urethral resistance, a measure of continence. Abdominal muscles were electrically stimulated to induce leakage for eLPP. A Crede maneuver was applied for mLPP. These were repeated after complete T8 spinal cord injury (SCI) and/or bilateral pudendal nerve transection (PNT). After euthanasia, mLPP was repeated. MLPP was not significantly affected by opening the abdomen, suggesting that intra-abdominal pressure transmission contributes little to continence during slow pressure changes. ELPP was significantly higher than mLPP in intact rats, after PNT, and after SCI+PNT, suggesting that abdominal pressure transmission contributes to continence during rapid increases in intra-abdominal pressure. MLPP decreased significantly after PNT, indicating that urethral striated muscles contribute significantly to continence. ELPP decreased significantly after PNT with and without SCI, suggesting that supraspinal control significantly affects continence during rapid pressure changes, but not during slow pressure changes. MLPP after euthanasia was significantly decreased compared to mLPP after SCI+PNT, suggesting that urethral mucosal seal coaptation and tissue elasticity also contribute to continence. The urethra is a complex organ that maintains continence via a highly organized and hierarchical system involving both the central and peripheral nervous systems.

Prevalence and related factors of urinary incontinence among Hebei women of China

BACKGROUND/AIMS

The aim of this study was to assess the prevalence and related factors of different types of urinary incontinence (UI) among Hebei women in China.

METHODS

A total of 2,500 women aged 20 years or more were sampled and interviewed face-to-face by well-trained interviewers.

RESULTS

Among these women, 35.2% (862/2,448) had UI. The prevalence of stress, urge, and mixed UI was 26.4% (647/2,448), 1.9% (47/2,448), and 6.9% (168/2,448), respectively. In multivariable logistic regression, age, constipation, pelvic organ prolapse, number of abortions, and cesarean sections were associated with both stress and mixed UI; body mass index, dysmenorrhea, vaginitis and cervicitis, fetal weight, and dystocia were associated with stress UI only; age of menarche and dystocia were associated with urge UI only, and living in a city or countryside, a history of pelvic operation, urinary infection, diseases of the respiratory system, heart disease, and alcohol consumption with mixed UI.

CONCLUSIONS

UI is a highly prevalent condition among women in Hebei Province, PR China. Stress, urge, and mixed UI not only have some related factors in common but also have some different ones. Economic condition and a lack of UI-related knowledge are factors keeping patients from seeing a doctor.

Animal models of stress urinary incontinence

Stress urinary incontinence (SUI) is a common health problem significantly affecting the quality of life of women worldwide. Animal models that simulate SUI enable the assessment of the mechanism of risk factors for SUI in a controlled fashion, including childbirth injuries, and enable preclinical testing of new treatments and therapies for SUI. Animal models that simulate childbirth are presently being utilized to determine the mechanisms of the maternal injuries of childbirth that lead to SUI with the goal of developing prophylactic treatments. Methods of assessing SUI in animals that mimic diagnostic methods used clinically have been developed to evaluate the animal models. Use of these animal models to test innovative treatment strategies has the potential to improve clinical management of SUI. This chapter provides a review of the available animal models of SUI, as well as a review of the methods of assessing SUI in animal models, and potential treatments that have been tested on these models.

Bone marrow mesenchymal stromal cell therapy for external urethral sphincter restoration in a rat model of stress urinary incontinence

OBJECTIVE

To assess the effect of intra-sphincteric injections of bone marrow mesenchymal stromal cells (MSCs) on Valsalva leak point pressure (VLPP) changes in an animal model of stress urinary incontinence (SUI).

MATERIALS AND METHODS

Twenty-four female Sprague-Dawley rats underwent bilateral pudendal nerve section to induce SUI. Six rats were SUI controls, 6 received periurethral injection of Plasma-Lyte (SUI placebo control) and 12 were given periurethral injection of PKH26-labeled MSCs. Four weeks after injection, conscious cystometry was undertaken in animals and VLPP recorded. All groups were sacrificed, and frozen urethra sections were submitted to pathology and immunohistochemistry assessment.

RESULTS

Rat MSCs were positive for the cell surface antigens CD44, CD73, CD90, and RT1A, and negative for CD31, CD45, and RT1B, confirming their stem cell phenotype. In vitro, differentiated MSCs expressed α-smooth muscle actin (SMA) and desmin, markers of smooth and striated muscles in vivo. Immunohistochemistry of rat urethras revealed PKH26-labeled MSCs in situ and at the injection site. LPP was significantly improved in animals injected with MSCs. Mean LPP was 24.28 ± 1.47 cmH(2) O in rats implanted with MSCs and 16.21 ± 1.26 cmH(2) O in SUI controls (P<0.001). Atrophic urethras with implanted MSCs were positively stained for myosin heavy chain and desmin.

CONCLUSION

Rat MSCs have the ability to differentiate and skew their phenotype towards smooth and striated muscles, as demonstrated by SMA up-regulation and desmin expression. Periurethral injection of MSCs in an animal model of SUI restored the damaged external urethral sphincter and significantly improved VLPP.

Expression of monocyte chemotactic protein 3 following simulated birth trauma in a murine model of obesity

OBJECTIVE

To determine the effect of obesity on simulated birth trauma in leptin-deficient obese mice as measured by relative monocyte chemotactic protein 3 (MCP-3) expression.

MATERIALS AND METHODS

A total of 25 wild-type and 25 obese C57BL/6 virgin female mice underwent 1 hour of vaginal distension (VD), sham VD, or anesthesia without VD. Pelvic organ tissues were then harvested either immediately or 24-hours post VD and subsequent real-time polymerase chain reaction analysis was performed.

RESULTS

Urethral MCP-3 levels in wild-type mice were elevated from baseline at 0 hours with a return to baseline at 24 hours in both VD and sham VD groups. In obese mice, there was a 6-fold elevation in MCP-3 levels at 0 hours after sham VD vs control (P <.05), which then returned to baseline levels at 24 hours. After undergoing VD, MCP-3 levels increased to 6-fold baseline values (P = .002) at 0 hours, with continued elevation in MCP-3 levels to 15 times control levels (P = .0003) at 24 hours.

CONCLUSIONS

MCP-3 is significantly over-expressed in the urethral tissues of both wild-type and obese mice immediately after any urethral manipulation. At 24 hours, the MCP-3 expression patterns become divergent between VD and sham VD in obese mice. With a greater degree of trauma, MCP-3 continued to rise at 24 hours, suggesting that the underlying obesity resulted in alterations in response to tissue injury, paralleling the degree of injury. Such associations warrant further investigation into the role of MCP-3 as a chemokine for stem cell migration, with implications for subsequent tissue repair mechanisms after birth trauma.

Pudendal nerve injury reduces urethral outlet resistance in diabetic rats

Diabetics have voiding and continence dysfunction to which elevated levels of advanced glycation end products (AGE) may contribute. In addition, pudendal nerve injury is correlated with voiding dysfunction and stress incontinence in rats. The aim of this study was to investigate whether pudendal nerve crush (PNC) in diabetic rats alters urinary function. Female virgin Sprague-Dawley rats (144) were divided equally into diabetic, diuretic, and control groups. Half of the animals in each group were subjected to PNC, and the other half to sham PNC. Diabetes was induced 8 wk before PNC or sham PNC by streptozotocin injection (35 mg/kg). Animals underwent conscious cystometry and leak point pressure (LPP) testing 4 or 13 days after PNC or sham PNC. Tissues of half the animals were tested for levels of AGEs. Qualitative histological assessment was performed in the remaining animals. Diabetic rats 4 days after PNC voided significantly greater volume in a shorter time and with significantly less pressure than after sham PNC, suggesting that diabetic rats have a functional outlet obstruction that is relieved by PNC. LPP was significantly reduced 4 days after PNC in diabetic and diuretic animals and returned to normal 13 days after PNC. Diabetic rats with PNC demonstrated increased muscle fiber disruption and atrophy of the external urethral sphincter. AGEs were significantly elevated in diabetic rats. PNC relieves a functional outlet obstruction in diabetic rats. AGEs are elevated in diabetic rats and could play a role in urinary dysfunction and recovery from PNC.

Postpartum stress urinary incontinence: lessons from animal models

Postpartum stress urinary incontinence (SUI) is associated with chronic SUI in later life, which is 240% more likely to occur in women who deliver vaginally than those who did not. The etiology of SUI is multifactoral and has been associated with defects in both neuromuscular and structural components of continence. Specifically, clinical studies have demonstrated that pudendal nerve damage occurs during vaginal delivery, supporting the concept that neuromuscular damage to the continence mechanism can result in postpartum SUI. Urethral hypermobility and the loss of pelvic floor support, such as that involved in pelvic organ prolapse, have also been associated with SUI. Animal models provide an opportunity to investigate these injuries, individually and in combination, enabling researchers to gain further insight into their relative contributions to the development of SUI and the effectiveness of potential therapies for it. This article discusses the use of animal models of postpartum SUI in addition to the broad insights into treatment efficacy they provide.

Pelvic floor muscles and the external urethral sphincter have different responses to applied bladder pressure during continence

OBJECTIVES

To determine the functional innervation of the pelvic floor muscles (PFM) and whether there is PFM activity during an external pressure increase to the bladder in female rats.

METHODS

Thirty-one female adult virgin Sprague-Dawley rats received an external increase in bladder pressure until urinary leakage was noted while bladder pressure was recorded (leak point pressure [LPP]) under urethane anesthesia. Six of the rats underwent repeat LPP testing after bilateral transection of the levator ani nerve. Another 6 rats underwent repeat LPP testing after bilateral transection of the pudendal nerve. Simultaneous recordings of PFM (pubo- and iliococcygeus muscles), electromyogram (EMG), and external urethral sphincter (EUS) EMG were recorded during cystometry and LPP testing.

RESULTS

Thirteen rats (42%) showed tonic PFM EMG activity during filling cystometry. Eighteen rats (58%) showed no tonic PFM EMG activity at baseline, but PFM EMG could be activated by pinching the perineal skin. This activity could be maintained unless voiding occurred. The external increase in bladder pressure caused significantly increased EUS EMG activity as demonstrated by increased amplitude and frequency. However, there was no such response in PFM EMG. LPP was not significantly different after levator ani nerve transection, but was significantly decreased after pudendal nerve transection.

CONCLUSIONS

PFM activity was not increased during external pressure increases to the bladder in female rats. Experimental designs using rats should consider this result. The PFM, unlike the EUS, does not contribute to the bladder-to-urethra continence reflex. PFM strengthening may nonetheless facilitate urinary continence clinically by stabilizing the bladder neck.

Autologous bone-marrow-derived mesenchymal stem cell transplantation into injured rat urethral sphincter

OBJECTIVES

To evaluate the functional and histological recovery by autologous bone-marrow-derived mesenchymal stem cell (BMSC) transplantation into injured rat urethral sphincters.

METHODS

BMSC were harvested from female Sprague-Dawley retired breeder rats for later transplantation. The cells were cultured, and transfected with the green fluorescence protein gene. The urethral sphincters were injured by combined urethrolysis and cardiotoxin injection. One week after injury, the cultured BMSC were injected autologously into the periurethral tissues. Controls included sham-operated rats and injured rats injected with cell-free medium (CFM). Abdominal leak point pressures (LPP) were measured before and after surgery during the following 13 weeks. The urethras were then retrieved for histological evaluation. The presence of green-fluorescence-protein-labeled cells and the regeneration of skeletal muscles, smooth muscles, and peripheral nerves were evaluated by immunohistochemical staining.

RESULTS

LPP was significantly reduced in the injured rats. It increased gradually after transplantation, but there was no significant difference between the BMSC and CFM groups. In the BMSC group, transplanted cells survived and differentiated into striated muscle cells and peripheral nerve cells. The proportions of skeletal muscle cells and peripheral nerves in the urethra were significantly greater in the BMSC group compared to the CFM group.

CONCLUSIONS

Despite a clear trend towards recovery of LPP in BMSC-transplanted urethras, no significant effect was detected. Further study is required for clinical applications for the treatment of stress urinary incontinence.

Effects of sphincterotomy and pudendal nerve transection on the anal sphincter in a rat model

PURPOSE

Our objective was to define anal resting pressure and electromyography of the normal rat anal sphincter and investigate the short-term effects of both mechanical trauma to the anal sphincter muscles and pudendal nerve transection.

METHODS

Forty-five virgin female Sprague-Dawley rats were randomly allotted to three groups: controls (n = 21), sphincterotomy (n = 12), and pudendal nerve transection (n = 12). Anal pressure was monitored using a saline-filled balloon connected to a pressure transducer. Anal pressure and electromyography of the anal sphincter with use of a needle electrode were recorded both before and after injury or succinylcholine administration.

RESULTS

Anal pressure data were consistent with rhythmic pressure contractions. Succinylcholine significantly reduced both pressure and electromyography signals. Electromyography amplitude and frequency decreased after nerve transection but not after sphincterotomy. The histology showed that the rat anal anatomy has muscular components that compare with human anatomy. The sphincterotomy group showed injury to the anal sphincters and the sphincter anatomy of the nerve transection group appeared similar to the control group. The anal pressure wave appears to be created by synergistic activity of both striated and smooth muscle of the anal sphincter.

CONCLUSION

The female rat is a suitable and reliable model for studying effect of direct and indirect injury to the anal sphincters.

Recovery of continence function following simulated birth trauma involves repair of muscle and nerves in the urethra in the female mouse

BACKGROUND

The natural history and the mechanisms behind the alteration of vaginal distension (VD) in a mouse model are not clear.

OBJECTIVE

We examined the temporal sequelae of VD and pudendal nerve transection (PNT) on leak-point pressure (LPP) and the muscular and nerve components of the urethra in mice.

DESIGN, SETTING, AND PARTICIPANTS

Seventy-two virgin female C57BL/6 mice were equally distributed into three groups. The VD group underwent VD for 1h. The PNT group received bilateral PNT. A control group underwent sham VD.

INTERVENTION

Each group was divided into four subgroups of six mice for measurement of LPP at 0, 4, 10, and 20 d after VD or PNT.

MEASUREMENTS

LPP was measured. Morphology and neurofilament-immunoreactive nerve of the urethra were assessed.

RESULTS AND LIMITATIONS

LPP was decreased at 0, 4, and 10 d but not at 20 d after VD. Decreased LPP persisted to 20 d in the PNT group. The external urethral striated muscle appeared disrupted and/or wavy in two mice at 0 d, in three mice at 4 d, in one mouse at 10 d, and in one mouse in 20 d after VD. The density of neurofilament-immunoreactive nerve in the urethra was reduced at 4 and 10 d after VD, but not at 20 d, and at 4, 10, and 20 d after PNT compared with the corresponding values of the sham VD group. The limitation of this animal model is that the pelvic floor structure of the mouse is different from that of female humans. Therefore, results of this study should be carefully applied to human subjects.

CONCLUSIONS

VD causes reversible stress urinary incontinence in female mice. Recovery of continence function following VD is associated with repair of the external urethral sphincter and reinnervation of the urethra. This mouse model will be useful for mechanistic investigation and targeting of therapeutic intervention by taking advantage of genetic manipulation.

Dual simulated childbirth injury delays anatomic recovery

A dual childbirth injury model, including vaginal distension (VD) and pudendal nerve crush (PNC), may best represent the injuries seen clinically. The objective of this study was to investigate urethral function, anatomy, and neurotrophin expression after several simulated childbirth injuries. Groups of 140 rats underwent PNC, VD, PNC+VD, or neither (C). Four days after injury, all injury groups had significantly decreased leak-point pressure (LPP) compared with C rats. Ten days after injury, LPP in PNC and PNC+VD rats remained significantly lower than C rats. Three weeks after injury, LPP in all injury groups had recovered to C values. Histological evidence of injury was still evident in the external urethral sphincter (EUS) after VD and PNC+VD 10 days after injury. Three weeks after injury, the EUS of PNC+VD rats remained disrupted. One day after VD, brain-derived neurotrophic factor (BDNF) expression in the EUS was reduced, while neurotrophin-4 (NT-4) and nerve growth factor (NGF) expression was unchanged. BDNF, NT-4, and NGF expression was dramatically upregulated in the EUS after PNC. After PNC+VD, NGF expression was upregulated, and BDNF and NT-4 expression was upregulated somewhat but not to the same extent as after PNC. Ten days after injury, PNC+VD had the least number of normal nerve fascicles near the EUS, followed by PNC and VD. Twenty-one days after injury, all injury groups had fewer normal nerve fascicles, but without significant differences compared with C rats. PNC+VD therefore provides a more severe injury than PNC or VD alone.