Pubo-urethral ligament transection causes stress urinary incontinence in the female rat: a novel animal model of stress urinary incontinence

The female urethral closure mechanism during physical stress

The closure of the urethra under the condition of stress is the result of a reflex contraction of the urethral rhabdosphincter and pelvic floor muscles. This is likely induced by activity of the abdominal muscles due to a sudden increase in abdominal pressure. This reflex contraction with an increase of urethral pressure occurs a few milliseconds before an increase in intraabdominal pressure. The urethral pressure increase during stress is only possible with fixation of the urethra by the pubourethral ligaments (PUL), facilitating urethral kinking. The highest and most important increase in pressure and resistance occurs in the distal urethra due to this kinking of the urethra.

An estimation of the biomechanical properties of the continent and incontinent woman bladder via inverse finite element analysis

Stress urinary incontinence often results from pelvic support structures' weakening or damage. This dysfunction is related to direct injury of the pelvic organ's muscular, ligamentous or connective tissue structures due to aging, vaginal delivery or increase of the intra-abdominal pressure, for example, defecation or due to obesity. Mechanical changes alter the soft tissues' microstructural composition and therefore may affect their biomechanical properties. This study focuses on adapting an inverse finite element analysis to estimate the in vivo bladder's biomechanical properties of two groups of women (continent group (G1) and incontinent group (G2)). These properties were estimated based on MRI, by comparing measurement of the bladder neck's displacements during dynamic MRI acquired in Valsalva maneuver with the results from inverse analysis. For G2, the intra-abdominal pressure was adjusted after applying a 95% impairment to the supporting structures. The material parameters were estimated for the two groups using the Ogden hyperelastic constitutive model. Finite element analysis results showed that the bladder tissue of women with stress urinary incontinence have the highest stiffness (α1 = 0.202 MPa and µ1 = 7.720 MPa) approximately 47% higher when compared to continent women. According to the bladder neck's supero-inferior displacement measured in the MRI, the intra-abdominal pressure values were adjusted for the G2, presenting a difference of 20% (4.0 kPa for G1 and 5.0 kPa for G2). The knowledge of the pelvic structures' biomechanical properties, through this non-invasive methodology, can be crucial in the choice of the synthetic mesh to treat dysfunction when considering personalized options.

The Maximal Urethral Pressure at Rest and during Normal Bladder Filling Is Only Determined by the Activity of the Urethral Smooth Musculature in the Female

The aim of this opinion paper is to determine the entities that define the maximal urethral pressure (MUP) during rest and during bladder filling that is needed to guarantee continence in females. For the development of this opinion, the literature was searched for via the Pubmed database and historic sources. Animal studies indicate that the maximal urethral pressure is determined by the smooth muscle activity in the mid-urethra. Additionally, during increased smooth muscle tone development, the largest sympathetic responses are found in the middle part of the urethra. This could be confirmed in human studies that are unable to find striated EMG activity in this area. Moreover, the external urethral striated sphincter is situated at the distal urethra, which is not the area with the highest pressure. The external urethral sphincter only provides additional urethral pressure in situations of exertion and physical activity. From a physics point of view, the phasic pressure of the external striated sphincter at the distal urethra cannot be added to the tonic pressure generated by the smooth muscle in the mid-urethra. The assertion that mid-urethral pressure is the result of different pressure forces around the urethra, including that of the external striated sphincter, is not supported by basic research evidence combined with physical calculation and should therefore be considered a misconception in the field of functional urology.

Review of Animal Models to Study Urinary Bladder Function

Simple Summary

The treatment of urinary bladder dysfunction requires the knowledge of bladder function, which involves physiology, pathology, and even psychology. Several animal models are available to study a variety of bladder disorders. These models include animals from rodents, such as mice and rats, to nonhuman primates, such as rabbits, felines, canines, pigs, and mini pigs. This review adapted animal models to study bladder function according to facility, priority, and disease.

Abstract

The urinary bladder (UB) serves as a storage and elimination organ for urine. UB dysfunction can cause multiple symptoms of failure to store urine or empty the bladder, e.g., incontinence, frequent urination, and urinary retention. Treatment of these symptoms requires knowledge on bladder function, which involves physiology, pathology, and even psychology. There is no ideal animal model for the study of UB function to understand and treat associated disorders, as the complexity in humans differs from that of other species. However, several animal models are available to study a variety of other bladder disorders. Such models include animals from rodents to nonhuman primates, such as mice, rats, rabbits, felines, canines, pigs, and mini pigs. For incontinence, vaginal distention might mimic birth trauma and can be measured based on leak point pressure. Using peripheral and central models, inflammation, bladder outlet obstruction, and genetic models facilitated the study of overactive bladder. However, the larger the animal model, the more difficult the study is, due to the associated animal ethics issues, laboratory facility, and budget. This review aims at facilitating adapted animal models to study bladder function according to facility, priority, and disease.

Large Animal Models for Investigating Cell Therapies of Stress Urinary Incontinence

Stress urinary incontinence (SUI) is a significant health concern for patients affected, impacting their quality of life severely. To investigate mechanisms contributing to SUI different animal models were developed. Incontinence was induced under defined conditions to explore the pathomechanisms involved, spontaneous recovery, or efficacy of therapies over time. The animal models were coined to mimic known SUI risk factors such as childbirth or surgical injury. However, animal models neither reflect the human situation completely nor the multiple mechanisms that ultimately contribute to the pathogenesis of SUI. In the past, most SUI animal studies took advantage of rodents or rabbits. Recent models present for instance transgenic rats developing severe obesity, to investigate metabolic interrelations between the disorder and incontinence. Using recombinant gene technologies, such as transgenic, gene knock-out or CRISPR-Cas animals may narrow the gap between the model and the clinical situation of patients. However, to investigate surgical regimens or cell therapies to improve or even cure SUI, large animal models such as pig, goat, dog and others provide several advantages. Among them, standard surgical instruments can be employed for minimally invasive transurethral diagnoses and therapies. We, therefore, focus in this review on large animal models of SUI.

An animal experimental study on pubourethral ligament restoration with platelet rich plasma for the treatment of stress urinary incontinence

Introduction

Minimally invasive methods for injured ligament and tendon restoration have been developed and gained popularity in recent years. Injury and relaxation of the pubourethral ligament (PUL) can lead to stress urinary incontinence (SUI). The aim of this study was to investigate the impact of injecting platelet rich plasma (PRP) into the PUL following its surgical transection resulting in SUI, confirmed by leak point pressure (LPP) measurements pre- and post-intervention in an experimental animal model.

Material and methods

Twenty female adult Sprague-Dawley rats were assigned in 2 groups: 1) treatment group with transection of the PUL and application of PRP at the time of transection and at one month follow-up and 2) a control group, with transection of the PUL only. Leak point pressures (LPPs) were measured prior to transection, immediately following the transection and at 1 and 2 months in both groups.

Results

The median LPPs for the control group were: LPP – preT: 35.6 (29.8–44.8) cmH₂O, LPP – postT: 14.6 (5.8–19.0) cmH₂O, LPP – 1 month: 27.3 (19.2–33.8) cmH₂O, LPP – 2 months: 29.0 (27.0–34.0) cmH₂O, whereas for the PRP group were: LPP-preT: 40.5 (33.2–46.3) cmH₂O, LPP – postT: 15.7 (3.0–24.0) cmH₂O, LPP – 1month: 31.6 (24.8–37.4) cmH₂O, LPP – 2 months: 36.8 (32.5–45.4) cmH₂O. PRP injections on transected PULs significantly increased LPPs at one month follow-up [31.6 cmH₂O vs. 27.3 cmH₂O, p = .043]. This effect was confirmed at two months [36.8 cmH₂O vs. 29.0 cmH₂O, p <.001].

Conclusions

Injection of PRP into transected PULs significantly improved LPPs at one and two months' follow-up. However, further experimental and clinical research is needed to evaluate the safety and efficacy of this treatment, in clinical practice.

A holistic view of the effects of episiotomy on pelvic floor

Vaginal delivery is commonly accepted as a risk factor in pelvic floor dysfunction; however, other obstetric procedures (episiotomy) are still controversial. In this work, to analyze the relationship between episiotomy and pelvic floor function, a finite element model of the pelvic cavity is used considering the pelvic floor muscles (PFMs) with damaged regions from spontaneous vaginal delivery and from deliveries with episiotomy. Common features assessed at screening of pelvic floor dysfunction are evaluated during numerical simulations of both Valsalva maneuver and contraction. As stated in literature, a weakening of the PFM, represented by damaged regions in the finite element model, would lead to a bladder neck hypermobility measured as a variation between the α angle (angle between the bladder neck and the symphysis pubis line and the midline of the symphysis) during straining and withholding. However, the present work does not associate bladder neck hypermobility to a more damaged muscle, suggesting that other supportive structures also play an important role in the stabilization of the pelvic organs. Furthermore, considering passive behavior of the PFM, independently of the amount of damage considered, the resultant displacements of the pelvic structures are the same. Regarding the PFM contraction, the less the muscle is damaged, the greater the movements of the pelvic organs. Furthermore, the internal organs of the female genital system are the most affected by the unhealthy of the PFM. Additionally, the present study shows that the muscle damage affects more the active muscle component than the passive.

Stress urinary incontinence animal models as a tool to study cell-based regenerative therapies targeting the urethral sphincter

Urinary incontinence (UI) is a major health problem causing a significant social and economic impact affecting more than 200million people (women and men) worldwide. Over the past few years researchers have been investigating cell therapy as a promising approach for the treatment of stress urinary incontinence (SUI) since such an approach may improve the function of a weakened sphincter. Currently, a diverse collection of SUI animal models is available. We describe the features of the different models of SUI/urethral dysfunction and the pros and cons of these animal models in regard to cell therapy applications. We also discuss different cell therapy approaches and cell types tested in preclinical animal models. Finally, we propose new research approaches and perspectives to ensure the use of cellular therapy becomes a real treatment option for SUI.

Morphological and functional response to injury to the external urethral sphincter - similarities and differences between male and female rats

AIMS

The objective of this study was to evaluate the similarities and differences of the urethral morphological and functional changes following external urethral sphincter EUS injury in male and female rats.

METHODS

30 female and 30 male age-matched Wistar rats were used in the experiments. Half of them underwent electrocauterization of the surrounding tissues lateral to the urethra at the level of the (EUS) and the others, a sham operation. At 2, 6, and 16 weeks after surgeries they underwent anesthetized cystometry, measurement of leak point pressure (LPP) and their urethras were harvested for morphological analyses.

RESULTS

There were no differences in cystometric parameters between sex-time-matched animals, ensuring normal bladder function in the manipulated animals. The mean LPP in male and female rats was lower compared with sham animals. Age-time-matched sham operated male rats exhibited a higher LPP compared with female rats. The reduction in LPP comparing electrocauterized and sham time-matched animals was more pronounced in male rats than in female rats. Electrocauterization produced urethral collagen deposition and nerve damage in both male and female animals. Muscle atrophy and disruption also occurred, being more evident in female rats.

CONCLUSIONS

The urethras of male and female rats exhibited a similar morphological and functional response to electrocauterization. The time-course evaluation revealed that the male animal model is as reliable, reproducible and long-lasting as the female model. Intact males had a higher LPP than female rats and the nerve injury led to a more drastic impairment of this mechanism.

Stem cell homing factor, CCL7, expression in mouse models of stress urinary incontinence

OBJECTIVES

Animal models of vaginal distention (VD) have demonstrated increased expression of chemokine (C-C motif) ligand 7 (CCL7) In this study, we investigated the expression of CCL7 in mice models of simulated birth trauma-induced urinary incontinence using VD and pudendal nerve transection (PNT).

METHODS

Forty-nine mice were divided into 6 groups: VD, sham VD, PNT, sham PNT, anesthesia, and age-matched controls. The urethra, vagina, and rectum were harvested for the expression of CCL7 immediately or 24 hours after assigned procedure. Venous sampling for quantification of serum CCL7 was also performed. An analysis of variance model was used to compare the relative expression of CCL7 in each group.

RESULTS

Urethral CCL7 expression in the VD group was significantly higher than control group after 24 hours (P < 0.01). There was no difference in the urethral CCL7 expression in PNT, sham PNT, sham VD, or anesthesia groups compared with the controls. No statistically significant difference was noted in the vaginal and rectal expression of CCL7 between any of the groups except for sham PNT. Statistically significant differences were noted in the serum CCL7 expression in the VD, PNT, and sham PNT (P < 0.01 in all) groups after 24 hours compared with the control group.

CONCLUSIONS

This study demonstrates overexpression of urethral CCL7 after VD but not PNT. This suggests that nerve injury does not contribute to the CCL7 overexpression. The overexpression of CCL7 in the serum of mice after VD suggests a translational potential where CCL7 measurement could be used as a surrogate for injury after delivery.

Pathophysiology of urinary incontinence in murine models

Urethral closure mechanisms under stress conditions consist of passive urethral closure involving connective tissues, fascia and/or ligaments in the pelvis and active urethral closure mediated by hypogastric, pelvic and pudendal nerves. Furthermore, we have previously reported that the active urethral closure mechanism might be divided into two categories: (i) the central nervous control passing onto Onuf's nucleus under sneezing or coughing; and (ii) the bladder-to-urethral spinal reflex under Valsalva-like stress conditions, such as laughing, exercise or lifting heavy objects. There are over 200 million people worldwide with urinary incontinence, a condition that is associated with a significant social impact and reduced quality of life. Therefore, basic research for urinary continence mechanisms in response to different stress conditions can play an essential role in developing treatments for stress urinary incontinence. It has been clinically shown that the etiology of stress urinary incontinence is divided into urethral hypermobility and intrinsic sphincter deficiency, which could respectively correspond to passive and active urethral closure dysfunction. In this review, we summarize the representative stress urinary incontinence animal models and the methods to measure leak point pressures under stress conditions, and then highlight stress-induced urinary continence mechanisms mediated by active urethral closure mechanisms, as well as future pharmacological treatments of stress urinary incontinence. In addition, we introduce our previous reports including sex differences in urethral closure mechanisms under stress conditions and urethral compensatory mechanisms to maintain urinary continence after pudendal nerve injury in female rats.

Neurophysiology and therapeutic receptor targets for stress urinary incontinence

Stress urinary incontinence is the most common type of urinary incontinence in women. Stress urinary incontinence involves involuntary leakage of urine in response to abdominal pressure caused by activities, such as sneezing and coughing. The condition affects millions of women worldwide, causing physical discomfort as well as social distress and even social isolation. This type of incontinence is often seen in women after middle age and it can be caused by impaired closure mechanisms of the urethra as a result of a weak pelvic floor or poorly supported urethral sphincter (urethral hypermobility) and/or a damaged urethral sphincter system (intrinsic sphincter deficiency). Until recently, stress urinary incontinence has been approached by clinicians as a purely anatomic problem as a result of urethral hypermobility requiring behavioral or surgical therapy. However, intrinsic sphincter deficiency has been reported to be more significantly associated with stress urinary incontinence than urethral hypermobility. Extensive basic and clinical research has enhanced our understanding of the complex neural circuitry regulating normal function of the lower urinary tract, as well as the pathophysiological mechanisms that might underlie the development of stress urinary incontinence and lead to the development of potential novel strategies for pharmacotherapy of stress urinary incontinence. Therapeutic targets include adrenergic and serotonergic receptors in the spinal cord, and adrenergic receptors at the urethral sphincter, which can enhance urethral reflex activity during stress conditions and increase baseline urethral pressure, respectively. This article therefore reviews the recent advances in stress urinary incontinence research and discusses the neurophysiology of urethral continence reflexes, the etiology of stress urinary incontinence and potential targets for pharmacotherapy of stress urinary incontinence.

Comparative study of three rat models of stress urinary incontinence

The aim of this study was to establish three rat models of stress urinary incontinence (SUI) and investigate the differences in urodynamics and success rate of establishing each model. Sixty healthy female SD rats were randomly divided into 4 groups of 15 rats each: A: control group; B: urethrolysis group; C: ovariectomy with colpectasis group; and D: colpectasis only group. Abdominal leak point pressure (LPP) and maximum bladder capacity (MBC) were calculated. The sneeze test was used to examine whether or not liquid leakage occurred at the urethral meatus in each model. LPP and MBC values were significantly lower in all experimental groups (groups B, C, and D) when compared to the control group A (p < 0.001). Within the experimental groups, the MBC and LPP of group B was the lowest, while these values in groups C and D were relatively higher (p < 0.001). However, there was no significant difference in LPP between groups C and D (p > 0.05). The positive rates of the sneeze test in groups A, B, C, and D were 0%, 86%, 64%, and 40%, respectively. We observed significant differences between the experimental groups and the control group (p < 0.05). Three methods (urethrolysis, colpectasis with an ovariectomy, and colpectasis only) can be successfully used to establish models of SUI in rats. Significant differences in urodynamics and the successful establishment of the model occurred in this study.

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.

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.

Pubo-urethral ligament injury causes long-term stress urinary incontinence in female rats: an animal model of the integral theory

PURPOSE

We examined the long-term effects of pubo-urethral ligament deficiency as a potential model of stress urinary incontinence compared to an established model of stress urinary incontinence.

MATERIALS AND METHODS

A total of 21 female Sprague-Dawley rats were randomly assigned to 1 of 3 groups, including pubo-urethral ligament transection, sham pubo-urethral ligament transection and bilateral pudendal nerve transection. Leak point pressure was measured 28 days later via an implanted suprapubic catheter. After leak point pressure measurement all animals were sacrificed. The pubic arch and pelvic organs were harvested for histological examination. The Wilcoxon rank sum test was used to evaluate differences in leak point pressure among the experimental groups.

RESULTS

At 28 days after pubo-urethral ligament transection mean +/- SD leak point pressure was significantly decreased when comparing pubo-urethral ligament transection and pudendal nerve transection to sham treatment (15.75 +/- 6.46 and 15.10 +/- 4.98 cm H(2)O, respectively, vs 42.56 +/- 11.58, p <0.001). No difference was noted when comparing pubo-urethral ligament transection to pudendal nerve transection (p = 0.76), indicating the long-term durability of pubo-urethral ligament transection on inducing stress urinary incontinence in the female rat. Histological examination of en bloc suprapubic areas demonstrated an absent pubo-urethral ligament in the pubo-urethral ligament transection group, and an intact pubo-urethral ligament in the sham treated and pudendal nerve transection groups.

CONCLUSIONS

Our results show that pubo-urethral ligament deficiency in the female rat induces long-term stress urinary incontinence that is comparable to that in the established stress urinary incontinence model via pudendal nerve transection. Our novel rat model could be used to investigate mechanisms of stress urinary incontinence in females, including the role of urethral hypermobility and potential therapeutic interventions for stress urinary incontinence.