Tissue alterations in urethral and vaginal walls related to multiparity in rabbits

Vaginal host response to polycarbonate urethane, an alternative material for the repair of pelvic organ prolapse

Complications following surgical repair of pelvic organ prolapse (POP) with polypropylene mesh (PPM) are common. Recent data attributes complications, in part, to stiffness mismatches between the vagina and PPM. We developed a 3D printed elastomeric membrane (EM) from a softer polymer, polycarbonate urethane (PCU). EMs were manufactured with more material given the low inherent material strength of PCU. We hypothesized that the EMs would be associated with an improved host response as compared to PPM. A secondary goal was to optimize the material distribution (fiber width and device thickness) within EMs, in regards to the host response. EM constructs (2 × 1 cm2) with varied polymer stiffness, fiber width, and device thickness were implanted onto the vagina of New Zealand white rabbits for 12 weeks and compared to similarly sized PPMs. Sham implanted animals served as controls. Mixed effects generalized linear models were used to compare the effect of construct type accounting for differences in independent variables. EMs had an overall superior host response compared to PPM as evidenced by preservation of vaginal smooth muscle morphology (p-values<0.01), decreased total cellular response to construct fibers (p-values<0.001), and a reduced percent of macrophages (p-values<0.02) independent of how the material was distributed. Both PPM and EMs negatively impacted vaginal contractility and glycosaminoglycan (GAG) content relative to Sham (all p-values<0.001) with EMs having less of an impact on GAGs (p-values<0.003). The results suggest that softer PCU EMs made with more material are well tolerated by the vagina and comprises a future material for POP repair devices. STATEMENT OF SIGNIFICANCE: Prolapse is a debilitating condition in which loss of support to the vagina causes it and the organs supported by it to descend from their normal position in the pelvis. Surgical solutions to rebuild support involves the use of polypropylene mesh which is orders of magnitude stiffer than the vagina. This mismatch results in complications including exposure of the mesh into the vagina and pain. To provide an innovative solution for women, we have developed an elastomeric membrane from a soft polymer that matches the stiffness of the vagina. Here, we show in a rabbit animal model that this device incorporates better into the vagina and is associated with an overall improved host response as compared to polypropylene mesh.

Multiparity Reduces Urethral and Vaginal Pressures Following the Bulboglandularis Muscle Stimulation in Rabbits

Unlike male mammals showing a well-delimited external urethral sphincter, female mammals have urogenital sphincters shaped by muscles like the urethrovaginal sphincter. Childbirth-related injuries affect morphometry and function of urogenital sphincters in women, which frequently underlies pelvic floor disorders, including stress urinary incontinence and pelvic organ prolapse. The bulboglandularis muscle (Bgm) seems to shape a urogenital sphincter in rabbits. We determined herein the effect of multiparity on urethral and vaginal pressures generated by the Bgm stimulation in age-matched nulliparous and multiparous chinchilla-breed rabbits to stimulate the Bgm with trains of ascending frequencies (from 1 to 100 Hz; 4 s duration each). Subsequently, the Bgm was excised, measured in width, and weighed. Significant differences (P ≤ 0.05) were determined with Mann-Whitney U or Student t-tests or repeated measures two-way ANOVA followed by Tukey tests. Spearman's partial coefficients were calculated to investigate the correlation between the highest pressure (urethral or vaginal) and the Bgm width. Multiparity reduced the weight and the width in the Bgm origin and medial regions. Urethral and vaginal pressures increased in response to the electrical stimulation of Bgm with frequencies from 20 to 100 Hz. Multiparas showed significant reductions in both types of pressures. We detected a strong correlation (conditioned by multiparity) between the medial Bgm width and the highest vaginal pressure. Our present findings demonstrate that multiparity impairs the function of Bgm, resulting in diminished urethral and vaginal pressures. Furthermore, the significant narrowness of the Bgm was correlated with the vaginal pressure recorded.

Animal models for pelvic organ prolapse: systematic review

INTRODUCTION AND HYPOTHESIS

We aimed to summarize the knowledge on the pathogenesis of pelvic organ prolapse (POP) generated in animal models.

METHODS

We searched MEDLINE, Embase, Cochrane and the Web of Science to establish what animal models are used in the study of suggested risk factors for the development of POP, including pregnancy, labor, delivery, parity, aging and menopause. Lack of methodologic uniformity precluded meta-analysis; hence, results are presented as a narrative review.

RESULTS

A total of 7426 studies were identified, of which 51 were included in the analysis. Pregnancy has a measurable and consistent effect across species. In rats, simulated vaginal delivery induces structural changes in the pelvic floor, without complete recovery of the vaginal muscular layer and its microvasculature, though it does not induce POP. In sheep, first vaginal delivery has a measurable effect on vaginal compliance; measured effects of additional deliveries are inconsistent. Squirrel monkeys can develop POP. Denervation of their levator ani muscle facilitates this process in animals that delivered vaginally. The models used do not develop spontaneous menopause, so it is induced by ovariectomy. Effects of menopause depend on the age at ovariectomy and the interval to measurement. In several species menopause is associated with an increase in collagen content in the longer term. In rodents there were no measurable effects of age apart of elastin changes. We found no usable data for other species.

CONCLUSION

In several species there are measurable effects of pregnancy, delivery and iatrogenic menopause. Squirrel monkeys can develop spontaneous prolapse.

Bladder and urethral dysfunction in multiparous and mature rabbits correlates with abnormal activity of pubococcygeus and bulbospongiosus muscles

AIMS

To evaluate the combined effect of age and multiparity on the micturition reflex, including pelvic floor muscle activation.

METHODS

Young and mature nulliparous rabbits were compared to young and mature multiparas (n = 6 per group). Cystometrograms and urethral pressure (UP) were performed while simultaneously recording the electromyogram (EMG) activity of the pubococcygeus and bulbospongiosus muscles to establish their functional correlation to urological function.

RESULTS

Multiparity and age significantly influence the bladder and UP affecting the voiding efficiency and intercontraction interval. Such interaction also reduced the UP threshold, timing, and duration. Other bladder and urethral variables were predominantly affected only by age. Urodynamic alterations correlated with abnormal patterns or absent EMG activity of the pubococcygeus and bulbospongiosus muscles.

CONCLUSIONS

The present findings strongly suggest that multiparity and age affects specific pelvic floor muscle reflex activation during micturition, and may contribute to alterations in bladder and urethral function. This data broadens our understanding of the critical role of the appropriate activity of the individual pelvic floor muscles in micturition.

Is Mode of Delivery Associated With Sexual Response? A Pilot Study of Genital and Subjective Sexual Arousal in Primiparous Women With Vaginal or Cesarean Section Births

INTRODUCTION

Although postpartum sexual concerns are common, limited data exist on postpartum sexual response. Furthermore, the physiological process of vaginal birth may negatively impact genital response compared with unlabored cesarean section (C-section), but this hypothesis has yet to be tested.

AIM

To (i) compare genital and subjective sexual response and sexual concordance by mode of delivery with inclusion of a control group, (ii) compare groups on self-reported sexual function over the past month, (iii) examine the relationship between laboratory measurement of sexual response and self-reported sexual function, and (iv) investigate association between obstetrical factors and breastfeeding and between sexual response and self-reported sexual function.

METHODS

3 groups of cisgender women were recruited from the community: primiparous women who delivered via vaginal birth within the past 2 years (VB group; n = 16), primiparous women who delivered via unlabored C-section within the past 2 years (CS group, n = 15), and age-matched nulliparous women (NP group, n = 18). Laser Doppler imaging was used to assess genital response while participants watched a neutral and erotic film.

MAIN OUTCOME MEASURES

The main outcome measures were change in flux units from neural to erotic video as a measure of genital response, subjective sexual arousal rated continuously throughout films, perceived genital response rated after films, and Female Sexual Function Index (FSFI).

RESULTS

Women in the VB group had significantly lower change in flux units than women in the CS (P = .005, d = 1.39) and NP (P < .001, d = 1.80) groups. Groups did not differ on their subjective indices of sexual response or in sexual concordance. Women in both postpartum groups reported lower FSFI scores than women in the NP group. No relationship was determined between FSFI scores and sexual response in the laboratory. Results suggested that genital trauma and breastfeeding may negatively impact FSFI scores, but they were not related to genital response or subjective sexual arousal as measured in the laboratory.

CLINICAL IMPLICATIONS

Results underscore the importance of balancing objective and subjective indices of sexual response and function, especially considering the biopsychosocial nature of postpartum sexuality.

STRENGTHS & LIMITATIONS

The present study is the first to apply modern sexual psychophysiological methodology to the study of postpartum sexuality. Cross-sectional methodology limits the ability to make causal inferences, and the strict inclusion criteria limits generalizability.

CONCLUSION

Physiological changes as a result of labor and delivery may have a detrimental impact on genital response; however, these physiological differences may not impact women's subjective experience of postpartum sexuality. Cappell J, Bouchard KN, Chamberlain SM, et al. Is Mode of Delivery Associated With Sexual Response? A Pilot Study of Genital and Subjective Sexual Arousal in Primiparous Women With Vaginal or Cesarean Section Births. J Sex Med 2020; 17:257-272.

Expression of Glial Cell Line-Derived Neurotrophic Factor (GDNF) and the GDNF Family Receptor Alpha Subunit 1 in the Paravaginal Ganglia of Nulliparous and Primiparous Rabbits

PURPOSE

To evaluate the expression of glial cell line-derived neurotrophic factor (GDNF) and its receptor, GDNF family receptor alpha subunit 1 (GFRα-1) in the pelvic (middle third) vagina and, particularly, in the paravaginal ganglia of nulliparous and primiparous rabbits.

METHODS

Chinchilla-breed female rabbits were used. Primiparas were killed on postpartum day 3 and nulliparas upon reaching a similar age. The vaginal tracts were processed for histological analyses or frozen for Western blot assays. We measured the ganglionic area, the Abercrombie-corrected number of paravaginal neurons, the cross-sectional area of the neuronal somata, and the number of satellite glial cells (SGCs) per neuron. The relative expression of both GDNF and GFRα-1 were assessed by Western blotting, and the immunostaining was semiquantitated. Unpaired two-tailed Student t -test or Wilcoxon test was used to identify statistically significant differences (P≤0.05) between the groups.

RESULTS

Our findings demonstrated that the ganglionic area, neuronal soma size, Abercrombie-corrected number of neurons, and number of SGCs per neuron were similar in nulliparas and primiparas. The relative expression of both GDNF and GFRα-1 was similar. Immunostaining for both GDNF and GFRα-1 was observed in several vaginal layers, and no differences were detected regarding GDNF and GFRα-1 immunostaining between the 2 groups. In the paravaginal ganglia, the expression of GDNF was increased in neurons, while that of GFRα-1 was augmented in the SGCs of primiparous rabbits.

CONCLUSIONS

The present findings suggest an ongoing regenerative process related to the recovery of neuronal soma size in the paravaginal ganglia, in which GDNF and GFRα-1 could be involved in cross-talk between neurons and SGCs.

Multiparity modifies contractile properties of pelvic muscles affecting the genesis of vaginal pressure in rabbits

AIMS

To characterize the contractile properties of the bulbospongiosus (Bsm), isquiocavernosus (Ism), and pubococcygeus muscles (Pcm), and their involvement in the genesis of vaginal pressure in nulliparous and multiparous rabbits.

METHODS

Age-matched nulliparous and multiparous rabbits were used to record the isometric contractile responses of each muscle as well as the intravaginal pressure evoked by single square electrical pulses and stimulation trains of ascending frequency. To establish significant differences between groups, two-tail unpaired Student t tests were carried out. The linear correlation between intravaginal pressure and muscle contractile force was analyzed with Pearson correlation tests. For all cases, a P ≤ 0.05 was set as statistically significant.

RESULTS

Multiparity decreased the contractile force of Bsm and Ism generated by high-frequency stimulation trains. The normalized force of the Pcm increased when evoked at 1, 4, and 10 Hz while this decreased at higher frequencies (20, 50, and 100 Hz). The contraction of both Bsm and Ism raised particularly the pressure on the perineal vagina while that of the Pcm increased the pressure in the pelvic vagina. Such a functional segregation is still present in multiparous rabbits albeit it was modified.

CONCLUSIONS

Multiparity induces changes in the contractile responses of Bsm, Ism, and Pcm, which alterates the vaginal pressure.