Urethral function and histopathology in aged female rats as a stress urinary incontinence model

Animal models, treatment options, and biomaterials for female stress urinary incontinence

In the quest to tackle stress urinary incontinence (SUI), the synthesis of cutting-edge biomaterials and regenerative materials has emerged as a promising frontier. Briefly, animal models like vaginal distension and bilateral ovariectomy serve as crucial platforms for unraveling the intricacies of SUI, facilitating the evaluation of innovative treatments. The spotlight, however, shines on the development and application of novel biomaterials-ranging from urethral bulking agents to nano-gel composites-which aim to bolster urethral support and foster tissue regeneration. Furthermore, the exploration of stem cell therapies, particularly those derived from adipose tissues and urine, heralds a new era of regenerative medicine, offering potential for significant improvements in urinary function. This review encapsulates the progress in biomaterials and regenerative strategies, highlighting their pivotal role in advancing the treatment of SUI, thereby opening new avenues for effective and minimally invasive solutions.

Assessment of the Effectiveness of the Sonofeedback Method in the Treatment of Stress Urinary Incontinence in Women-Preliminary Report

Urinary incontinence is a common problem that affects postmenopausal women. This ailment has a negative impact on many aspects of life, significantly limiting everyday functioning related to professional work, physical activity or the intimate sphere. The aim of the study was to assess the effectiveness of the sonofeedback method in reducing the severity of urinary incontinence in postmenopausal women with a urinary incontinence problem. A total of 60 patients aged 45–65 with stress urinary incontinence, confirmed by a gynecologist, were qualified for the study. All persons qualified for the study were randomly assigned to study group A (n = 20), comparative B (n = 20) and control C (n = 20). Patients from group A were treated with sonofeedback of the pelvic floor muscles. In group B, the combined electrostimulation method was used with biofeedback training. Group C was a control group in which only the measured parameters were measured at the same time interval as those carried out in groups A and B. In all patients, three times: before the therapy, after the fifth procedure and after the end of the therapy, the incidence and severity of stress urinary incontinence were assessed—Gaudenz questionnaire and the intensity of urinary incontinence—a modified 1 h pad test. The obtained results have an application value giving the possibility of using effective therapy with sonofeedback in women in whom the recommended electrostimulation method cannot be used due to health and behavioral reasons.

Age is associated with reduced urethral pressure and afferent activity in rat

Age-related changes in the lower urinary tract (LUT) can affect the coordination of reflexes and increase the incidence of bladder disorders in elderly. This study examines the age-related loss of urethral signaling capability by measuring the afferent activity directly. We find that less urethral pressure develops in response to fluid flow in old rats compared to young rats and that pressure and flow evoke less urethral afferent activation. These findings are consistent with our previous study demonstrating that the urethra-to-bladder reflex, which is required for efficient voiding, becomes weaker with age. We measured the pudendal afferent response in young (4-7 months) and old (18-24 months) rats to fluid flow in the urethra across a range of flow rates. We used paraffin embedding and hematoxylin and eosin staining to quantify age-related changes in the sensory branch of the pudendal nerve. Urethral afferent signaling in response to the same urethral flow rates was weaker in older animals. That is, the sensitivity of urethra afferents to flow decreased with age, and higher flow rates were required in older animals to recruit urethra afferents. There was also a reduction in the myelin thickness of pudendal afferents in old rats, which is a possible contributing factor to the sensory activity. Furthermore, the same flow rates evoked less pressure in the urethras of old animals, indicating there is an age-related change of the urethral tissue that reduces the pressure stimulus to which these afferents respond. These results help characterize the underlying changes in LUT system with age.

Targeted neuromodulation of pelvic floor nerves in aging and multiparous rabbits improves continence

Pelvic floor muscle stretch injury during pregnancy and birth is associated with the incidence of stress urinary incontinence (SUI), a condition that affects 30-60% of the female population and is characterized by involuntary urine leakage during physical activity, further exacerbated by aging. Aging and multiparous rabbits suffer pelvic nerve and muscle damage, resulting in alterations in pelvic floor muscular contraction and low urethral pressure, resembling SUI. However, the extent of nerve injury is not fully understood. Here, we used electron microscopy analysis of pelvic and perineal nerves in multiparous rabbits to describe the extent of stretch nerve injury based on axon count, axon size, myelin-to-axon ratio, and elliptical ratio. Compared to young nulliparous controls, mid-age multiparous animals showed an increase in the density of unmyelinated axons and in myelin thickness in both nerves, albeit more significant in the bulbospongiosus nerve. This revealed a partial but sustained damage to these nerves, and the presence of some regenerated axons. Additionally, we tested whether electrical stimulation of the bulbospongiosus nerve would induce muscle contraction and urethral closure. Using a miniature wireless stimulator implanted on this perineal nerve in young nulliparous and middle age multiparous female rabbits, we confirmed that these partially damaged nerves can be acutely depolarized, either at low (2-5 Hz) or medium (10-20 Hz) frequencies, to induce a proportional increase in urethral pressure. Evaluation of micturition volume in the mid-age multiparous animals after perineal nerve stimulation, effectively reversed a baseline deficit, increasing it 2-fold (p = 0.02). These results support the notion that selective neuromodulation of pelvic floor muscles might serve as a potential treatment for SUI.

Verification and Defined Dosage of Sodium Pentobarbital for a Urodynamic Study in the Possibility of Survival Experiments in Female Rat

Objectives

To evaluate the effects of pentobarbital dosages on lower urinary tract function and to define an appropriate dosage of sodium pentobarbital that would be suitable for urodynamic studies in which recovery from anesthesia and long term survive were needed for subsequent experiment.

Methods

Twenty-four 8-week-old, female, virgin, Sprague-Dawley rats (200-250 g) were used in this study. Rats in study groups received gradient doses of pentobarbital intraperitoneally, and those in the control group received urethane intraperitoneally. External urethral sphincter electromyography (EUS-EMG) was recorded simultaneously during cystometry and leak point pressure tests. The toe-pinch reflex was used to determine the level of anesthesia.

Results

Micturition was normally induced in both the urethane group and 32 mg/kg pentobarbital group. However, in groups of 40 mg/kg or 36 mg/kg pentobarbital, micturition failed to be induced; instead, nonvoiding contractions accompanied by EUS-EMG tonic activity were observed. There were no significant differences in leak point pressure or EUS-EMG amplitude or frequency between the urethane and 32 mg/kg pentobarbital groups.

Conclusions

This study confirmed significant dose-dependent effects of pentobarbital on lower urinary tract function and 32 mg/kg pentobarbital as an appropriate dosage for recovery urodynamic testing, which enable the achievement of expected essential micturition under satisfactory anesthesia in female rats.

Sensitivity of urethral flow-evoked voiding reflexes decline with age in the rat: insights into age-related underactive bladder

The prevalence of underactive bladder (UAB) increases with age, suggesting a link between age-related processes and lower urinary tract (LUT) symptoms; however, the underlying mechanisms of age-related UAB are poorly understood. Understanding how aging affects LUT reflexes may help in the development of new treatments by identifying mechanistic targets. In this work, we studied the relationship between age and systems-level function of the LUT and tested the hypothesis that aging is related to weakening of reflexes that control voiding. Three groups of anesthetized female rats, young (4–7 mo old), mature (11–14 mo old), and old (18–24 mo old), were used to quantify the effect of aging on LUT reflexes. A double-lumen catheter enabled us to control the bladder volume and urethral flow rate independently, under quasi-isovolumetric bladder conditions. We systematically investigated the reflex bladder contractions evoked by combinations of rates of urethral infusion and bladder fill volumes as a function of age. Urethral infusion with the same flow rate evoked bladder contractions (via the augmenting reflex) in old animals less often than in younger animals. Furthermore, old animals needed more fluid in their bladders (relative to their bladder capacity) before urethra flow-evoked bladder contractions could be triggered at all, suggesting a delay in the switch of the LUT to “voiding mode.” Old rats also showed longer and weaker bladder contractions than young or mature rats. Taken together, this suggests there is an age-related functional weakening and loss of sensitivity in LUT reflexes, which may contribute to age-related UAB symptoms.