Pregnancy- and delivery-induced biomechanical changes in rat vagina persist postpartum

Effect of nonsteroidal anti-inflammatory drugs on pelvic floor muscle regeneration in a preclinical birth injury rat model

BACKGROUND

Pelvic floor muscle injury is a common consequence of vaginal childbirth. Nonsteroidal anti-inflammatory drugs are widely used postpartum analgesics. Multiple studies have reported negative effects of these drugs on limb muscle regeneration, but their impact on pelvic floor muscle recovery following birth injury has not been explored.

OBJECTIVE

Using a validated rat model, we assessed the effects of nonsteroidal anti-inflammatory drug on acute and longer-term pelvic floor muscle recovery following simulated birth injury.

STUDY DESIGN

Three-month old Sprague Dawley rats were randomly assigned to the following groups: (1) controls, (2) simulated birth injury, (3) simulated birth injury+nonsteroidal anti-inflammatory drug, or (4) nonsteroidal anti-inflammatory drug. Simulated birth injury was induced using a well-established vaginal balloon distension protocol. Ibuprofen was administered in drinking water (0.2 mg/mL), which was consumed by the animals ad libitum. Animals were euthanized at 1, 3, 5, 7, 10, and 28 days after birth injury/ibuprofen administration. The pubocaudalis portion of the rat levator ani, which, like the human pubococcygeus, undergoes greater parturition-associated strains, was harvested (N=3-9/time point/group). The cross-sectional areas of regenerating (embryonic myosin heavy chain+) and mature myofibers were assessed at the acute and 28-day time points, respectively. The intramuscular collagen content was assessed at the 28-day time point. Myogenesis was evaluated using anti-Pax7 and anti-myogenin antibodies to identify activated and differentiated muscle stem cells, respectively. The overall immune infiltrate was assessed using anti-CD45 antibody. Expression of genes coding for pro- and anti-inflammatory cytokines was assessed by quantitative reverse transcriptase polymerase chain reaction at 3, 5, and 10 days after injury.

RESULTS

The pubocaudalis fiber size was significantly smaller in the simulated birth injury+nonsteroidal anti-inflammatory drug compared with the simulated birth injury group at 28 days after injury (P<.0001). The median size of embryonic myosin heavy chain+ fibers was also significantly reduced, with the fiber area distribution enriched with smaller fibers in the simulated birth injury+nonsteroidal anti-inflammatory drug group relative to the simulated birth injury group at 3 days after injury (P<.0001), suggesting a delay in the onset of regeneration in the presence of nonsteroidal anti-inflammatory drugs. By 10 days after injury, the median embryonic myosin heavy chain+ fiber size in the simulated birth injury group decreased from 7 days after injury (P<.0001) with a tight cross-sectional area distribution, indicating nearing completion of this state of regeneration. However, in the simulated birth injury+nonsteroidal anti-inflammatory drug group, the size of embryonic myosin heavy chain+ fibers continued to increase (P<.0001) with expansion of the cross-sectional area distribution, signifying a delay in regeneration in these animals. Nonsteroidal anti-inflammatory drugs decreased the muscle stem cell pool at 7 days after injury (P<.0001) and delayed muscle stem cell differentiation, as indicated by persistently elevated number of myogenin+ cells 7 days after injury (P<.05). In contrast, a proportion of myogenin+ cells returned to baseline by 5 days after injury in the simulated birth injury group. The analysis of expression of genes coding for pro- and anti-inflammatory cytokines demonstrated only transient elevation of Tgfb1 in the simulated birth injury+nonsteroidal anti-inflammatory drug group at 5 but not at 10 days after injury. Consistently with previous studies, nonsteroidal anti-inflammatory drug administration following simulated birth injury resulted in increased deposition of intramuscular collagen relative to uninjured animals. There were no significant differences in any outcomes of interest between the nonsteroidal anti-inflammatory drug group and the unperturbed controls.

CONCLUSION

Nonsteroidal anti-inflammatory drugs negatively impacted pelvic floor muscle regeneration in a preclinical simulated birth injury model. This appears to be driven by the negative impact of these drugs on pelvic muscle stem cell function, resulting in delayed temporal progression of pelvic floor muscle regeneration following birth injury. These findings provide impetus to investigate the impact of postpartum nonsteroidal anti-inflammatory drug administration on muscle regeneration in women at high risk for pelvic floor muscle injury.

Retrospective study to assess the effect of epidural analgesia on labor progress and women's pelvic floor muscle from the perspective of electromyography

OBJECTIVE

Epidural analgesia has been widely used as a form of pain relief during labor and its safety has been gradually recognized. However, few studies of the effect of epidural analgesia on the pelvic floor are known. Thus, we aim to analyze the effect of epidural analgesia on labor progress and women's pelvic floor muscle from the perspective of electromyography systematically. In addition, obstetric risk factors for dysfunction of pelvic floor muscle after vaginal delivery were also evaluated.

METHODS

Childbirth data of 124 primiparas who gave first birth vaginally in our hospital and their pelvic floor function assessment results at postpartum 7 weeks were retrospectively collected. Pelvic floor muscle electromyogram screenings were performed by a biofeedback electro-stimulant therapy instrument.

RESULTS

There was no significant difference in the percentage of episiotomy, forceps, artificial rupturing membrane, and the application of oxytocin, except perineal laceration. Woman who implemented epidural analgesia experienced a longer stage of labor. Statistically, there was no significant difference in the total score and pelvic floor muscle strength. The risk factors for the value of the pre-rest phase include the age of pregnant women, the fetal weight, and the length of the second stage while the value of the post-rest phase was only associated with the fetal weight and the length of the second stage. In addition, the value of type I muscles was associated with the gravida and fetal weight while the value of type II muscles was only associated with forceps. The sustained contraction was correlated with the gravida and the total scores had a significant correlation with forceps.

CONCLUSION

Epidural analgesia during labor is approved to be a safe and effective procedure to relieve pain with very low side effects on the mode of labor and pelvic floor muscle. The assessment of pelvic floor muscle before pregnancy is beneficial in guiding the better protection of pelvic floor muscle function. According to the evaluation results, the doctors can control the associated risk factors as much as possible to reduce the injury of pregnancy and parturition to the pelvic floor.

Effects of mesenchymal stem cells and heparan sulfate mimetics on urethral function and vaginal wall biomechanics in a simulated rat childbirth injury model

INTRODUCTION AND HYPOTHESIS

New treatments are needed for pelvic floor disorders. ReGeneraTing Agent® (RGTA®) is a promising regenerative therapy. Therefore, the objective of this study was to compare regenerative abilities of mesenchymal stem cells (MSCs) and RGTA® on regeneration after simulated childbirth injury in rats.

METHODS

Rats underwent pudendal nerve crush and vaginal distension (PNC+VD) or sham injury. Rats that underwent PNC+VD were treated intravenously with vehicle, MSCs or RGTA® 1 h, 7 days, and 14 days after surgery. Sham rats received 1 ml vehicle at all time points. After 21 days, urethral function and pudendal nerve function were tested. Vaginal tissues were harvested for biomechanical testing and histology. Biaxial testing was performed to measure tissue stiffness.

RESULTS

PNC+VD decreased urethral and pudendal nerve function compared with sham. Vaginal wall stiffness was significantly decreased in longitudinal and transverse tissue axes after PNC+VD compared with sham. MSC or RGTA® did not restore urethral or pudendal nerve function. However, MSC treatment resolved loss in vaginal wall stiffness in both tissue axes and improved collagen content within the vaginal wall. RGTA® treatment increased vaginal wall anisotropy by increasing relative stiffness in the longitudinal direction. PNC+VD (with vehicle or MSCs) enhanced elastogenesis, which was not observed after RGTA® treatment.

CONCLUSIONS

Treatment with MSCs facilitated recovery of vaginal wall biomechanical properties and connective tissue composition after PNC+VD, whereas treatment with RGTA® resulted in anisotropic biomechanical changes. This indicates that MSCs and RGTA® promote different aspects of vaginal tissue regeneration after simulated childbirth injury.

History-Dependent Deformations of Rat Vaginas under Inflation

The vagina is a highly inhomogeneous, anisotropic, and viscoelastic organ that undergoes significant deformations in vivo. The mechanical attributes of this organ facilitate important physiological functions during menstruation, intercourse, and birthing. Despite the crucial mechanical role that the vagina plays within the female reproductive system, the deformations that the organ can sustain over time under constant pressure, in both the longitudinal direction (LD) and circumferential direction (CD), have not been fully characterized. This experimental study focuses on quantifying the creep properties of the vagina via ex vivo inflation testing using the rat as animal model. Toward this end, rat vaginas were subjected to three consecutively increasing constant luminal pressures (28 kPa, 55 kPa, and 83 kPa) using a custom-built experimental setup and the resulting inhomogeneous deformations were measured using the digital image correlation (DIC) method. The vagina was found to deform significantly more in the CD than the LD at any constant pressure, suggesting that the organ primarily adapts to constant pressures by significantly changing the diameter rather that the length. The change in deformation over time (i.e., creep) was significantly higher during the 1st inflation test at a constant pressure of 28 kPa than over the 2nd and 3rd inflation tests at constant pressures of 55 kPa and 83 kPa, respectively. The findings of this study on the mechanical behavior of the vagina could serve to advance our limited knowledge about the physiology and pathophysiology of this important reproductive organ.

Mechanisms governing protective pregnancy-induced adaptations of the pelvic floor muscles in the rat preclinical model

BACKGROUND

The intrinsic properties of pelvic soft tissues in women who do and do not sustain birth injuries are likely divergent. However, little is known about this. Rat pelvic floor muscles undergo protective pregnancy-induced structural adaptations-sarcomerogenesis and increase in intramuscular collagen content-that protect against birth injury.

OBJECTIVE

We aimed to test the following hypotheses: (1) the increased mechanical load of a gravid uterus drives antepartum adaptations; (2) load-induced changes are sufficient to protect pelvic muscles from birth injury.

STUDY DESIGN

The independent effects of load uncoupled from the hormonal milieu of pregnancy were tested in 3- to 4-month-old Sprague-Dawley rats randomly divided into the following 4 groups, with N of 5 to 14 per group: (1) load-/pregnancy hormones- (controls), (2) load+/pregnancy hormones-, (3) reduced load/pregnancy hormones+, and (4) load+/pregnancy hormones+. Mechanical load of a gravid uterus was simulated by weighing uterine horns with beads similar to fetal rat size and weight. A reduced load was achieved by unilateral pregnancy after unilateral uterine horn ligation. To assess the acute and chronic phases required for sarcomerogenesis, the rats were sacrificed at 4 hours or 21 days after bead loading. The coccygeus, iliocaudalis, pubocaudalis, and nonpelvic tibialis anterior musles were harvested for myofiber and sarcomere length measurements. The intramuscular collagen content was assessed using a hydroxyproline assay. An additional 20 load+/pregnancy hormones- rats underwent vaginal distention to determine whether the load-induced changes are sufficient to protect from mechanical muscle injury in response to parturition-associated strains of various magnitude. The data, compared using 2-way repeated measures analysis of variance followed by pairwise comparisons, are presented as mean±standard error of mean.

RESULTS

An acute increase in load resulted in significant pelvic floor muscle stretch, accompanied by an acute increase in sarcomere length compared with nonloaded control muscles (coccygeus: 2.69±0.03 vs 2.30±0.06 μm, respectively, P<.001; pubocaudalis: 2.71±0.04 vs 2.25±0.03 μm, respectively, P<.0001; and iliocaudalis: 2.80±0.06 vs 2.35±0.04 μm, respectively, P<.0001). After 21 days of sustained load, the sarcomeres returned to operational length in all pelvic muscles (P>.05). However, the myofibers remained significantly longer in the load+/pregnancy hormones- than the load-/pregnancy hormones- in coccygeus (13.33±0.94 vs 9.97±0.26 mm, respectively, P<.0001) and pubocaudalis (21.20±0.52 vs 19.52±0.34 mm, respectively, P<.04) and not different from load+/pregnancy hormones+ (12.82±0.30 and 22.53±0.32 mm, respectively, P>.1), indicating that sustained load-induced sarcomerogenesis in these muscles. The intramuscular collagen content in the load+/pregnancy hormones- group was significantly greater relative to the controls in coccygeus (6.55±0.85 vs 3.11±0.47 μg/mg, respectively, P<.001) and pubocaudalis (5.93±0.79 vs 3.46±0.52 μg/mg, respectively, P<.05) and not different from load+/pregnancy hormones+ (7.45±0.65 and 6.05±0.62 μg/mg, respectively, P>.5). The iliocaudalis required both mechanical and endocrine cues for sarcomerogenesis. The tibialis anterior was not affected by mechanical or endocrine alterations. Despite an equivalent extent of adaptations, load-induced changes were only partially protective against sarcomere hyperelongation.

CONCLUSION

Load induces plasticity of the intrinsic pelvic floor muscle components, which renders protection against mechanical birth injury. The protective effect, which varies between the individual muscles and strain magnitudes, is further augmented by the presence of pregnancy hormones. Maximizing the impact of mechanical load on the pelvic floor muscles during pregnancy, such as with specialized pelvic floor muscle stretching regimens, is a potentially actionable target for augmenting pregnancy-induced adaptations to decrease birth injury in women who may otherwise have incomplete antepartum muscle adaptations.

International Urogynecological Consultation (IUC): pathophysiology of pelvic organ prolapse (POP)

INTRODUCTION AND HYPOTHESIS

This manuscript is the International Urogynecology Consultation (IUC) on pelvic organ prolapse (POP) chapter one, committee three, on the Pathophysiology of Pelvic Organ Prolapse assessing genetics, pregnancy, labor and delivery, age and menopause and animal models.

MATERIALS AND METHODS

An international group of urogynecologists and basic scientists performed comprehensive literature searches using pre-specified terms in selected biomedical databases to summarize the current knowledge on the pathophysiology of the development of POP, exploring specifically factors including (1) genetics, (2) pregnancy, labor and delivery, (3) age and menopause and (4) non-genetic animal models. This manuscript represents the summary of three systematic reviews with meta-analyses and one narrative review, to which a basic scientific comment on the current understanding of pathophysiologic mechanisms was added.

RESULTS

The original searches revealed over 15,000 manuscripts and abstracts which were screened, resulting in 202 manuscripts that were ultimately used. In the area of genetics the DNA polymorphisms rs2228480 at the ESR1 gene, rs12589592 at the FBLN5 gene, rs1036819 at the PGR gene and rs1800215 at the COL1A1 gene are significantly associated to POP. In the area of pregnancy, labor and delivery, the analysis confirmed a strong etiologic link between vaginal birth and symptoms of POP, with the first vaginal delivery (OR: 2.65; 95% CI: 1.81-3.88) and forceps delivery (OR: 2.51; 95% CI: 1.24-3.83) being the main determinants. Regarding age and menopause, only age was identified as a risk factor (OR : 1.102; 95% CI: 1.02-1.19) but current data do not identify postmenopausal status as being statistically associated with POP. In several animal models, there are measurable effects of pregnancy, delivery and iatrogenic menopause on the structure/function of vaginal support components, though not on the development of POP.

CONCLUSIONS

Genetics, vaginal birth and age all have a strong etiologic link to the development of POP, to which other factors may add or protect against the risk.

Is there agreement between the preference of examiner and women for unidigital and bidigital vaginal palpation? A qualitative study

INTRODUCTION AND HYPOTHESIS

The International Continence Society recommends vaginal palpation as a method for assessing pelvic floor muscle (PFM) function. Our aim was to analyze the agreement between preferences of examiner and participants according to unidigital and bidigital vaginal palpation during PFM assessment. The second aim was to investigate qualitatively women's perception of vaginal palpation.

METHODS

Maximal voluntary contractions (MVCs) were requested during both types of vaginal palpation and were classified by the Modified Oxford Scale (MOS). Examiner and participants answered if they had preferences regarding vaginal palpation. Women answered qualitatively what they felt during the assessment. Cohen's linear kappa (κ) evaluated the agreement after allocation of the women with a weaker and stronger MVC and qualitative analysis was performed by transcription considering age range (18-35; 36-59; ≥60 years).

RESULTS

Agreement was almost zero for women with weaker and stronger MVC at unidigital (κ = 0.06 and κ = -0.12) and bidigital vaginal palpation (κ = 0.008 and κ = 0.005). Participants associated bidigital palpation with more perception and an easier way of contracting the PFMs. Women between 36 and 59 years associated unidigital palpation with a harder but comfortable way of contracting the PFMs. Subjects aged ≥60 years associated bidigital palpation with an uncomfortable, harder way of contracting PFM, with less space into the vagina.

CONCLUSIONS

Agreement between preferences was almost zero neither between women with a weaker and stronger PFM contraction, nor between the types of vaginal palpation. Bidigital palpation increased women's perception, made the contraction easier, and was associated with less space in the vaginal canal and less comfort.

Changes of pelvic organ prolapse and pelvic floor dysfunction throughout pregnancy in singleton primigravidas: A prospective cohort study

OBJECTIVE

To document the deterioration in pelvic organ support occurring throughout all trimesters during the first pregnancy of women with no known risk factors. Secondarily to make a comprehensive review in order to verify the current findings and methodologies of similar studies in the literature.

STUDY DESIGN

In this prospective study, forty-one primigravid women with a singleton pregnancy were recruited during their first trimester. During follow-up pelvic organ support changes were documented by using Pelvic Organ Prolapse Quantification (POP-Q) system. Additionally, pelvic floor muscle strength examination, by modified Oxford scoring (MOS), and symptom assessment by Pelvic Floor Distress Inventory-Short Form (PFDI-20) were performed at three time points: first (T1), second (T2), and third trimester (T3) (n = 33). The Wilcoxon test was performed to test the significance of pairwise differences. Spearman correlation coefficient was estimated to determine the linear association of the findings.

RESULTS

Both distal and proximal anterior and posterior vaginal walls (Points Aa, Ba, Ap and Bp) with cervix (C) descended towards the hymen, throughout first pregnancy with a significant caudal shift on progressing from T2 to T3 (p ≤ 0.017). Posterior fornix (Point D) made a non-significant cranial shift (p = 0.527). The genital hiatus, perineal body and total vaginal length increased significantly (p ≤ 0.001). No significant difference in MOS was observed throughout pregnancy. The scores of PFDI-20 with all its domains worsened significantly during pregnancy, especially in T3 (p ≤ 0.011). Moderate correlations were observed between posterior vaginal descent and anorectal symptoms (rho 0.427, p < 0.05), and between the changes in genital hiatus and prolapse symptoms (rho 0.406, p < 0.05).

CONCLUSION

A significant descent both in all compartments of vaginal wall and perineum with an increase in total vaginal length, was observed together with an associated pelvic floor dysfunction throughout the first pregnancy of women.

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.

Animal Models and Alternatives in Vaginal Research: a Comparative Review

While developments in gynecologic health research continue advancing, relatively few groups specifically focus on vaginal tissue research for areas like wound healing, device development, and/or drug toxicity. Currently, there is no standardized animal or tissue model that mimics the full complexity of the human vagina. Certain practical factors such as appropriate size and anatomy, costs, and tissue environment vary across species and moreover fail to emulate all aspects of the human vagina. Thus, investigators are tasked with compromising specific properties of the vaginal environment as it relates to human physiology to suit their particular scientific question. Our review aims to facilitate the appropriate selection of a model aptly addressing a particular study by discussing pertinent vaginal characteristics of conventional animal and tissue models. In this review, we first cover common laboratory animals studied in vaginal research-mouse, rat, rabbit, minipig, and sheep-as well as human, with respect to the estrus cycle and related hormones, basic reproductive anatomy, the composition of vaginal layers, developmental epithelial origin, and microflora. In light of these relevant comparative metrics, we discuss potential selection criteria for choosing an appropriate animal vaginal model. Finally, we allude to the exciting prospects of increasing biomimicry for in vitro applications to provide a framework for investigators to model, interpret, and predict human vaginal health.

"Comparative intra- and inter-rater reliability of maximal voluntary contraction with unidigital and bidigital vaginal palpation and construct validity with Peritron manometer"

AIMS

Evaluate the intra- and inter-rater reliability of maximal voluntary contraction (MVC) of pelvic floor muscle (PFM) assessment by unidigital and bidigital vaginal palpation. As a secondary aim, evaluate the construct validity of vaginal palpation and a manometer.

METHODS

A total of 120 women were recruited and allocated into three groups according to age (group 1 [G1]: 18-35; G2: 36-59; G3: ≥60 years). Examiner A conducted an interview and examiners B and C performed evaluations of PFM function using both unidigital and bidigital vaginal palpation. Seven to 10 days later, examiner B repeated both types of vaginal palpation and measured the MVC pressure with a Peritron. Reliability was analyzed using Cohen's linear weighted Kappa (κ_w ). The construct validity was calculated using the Spearman's correlation (r_s ).

RESULTS

Intra-rater reliability of unidigital and bidigital palpation was κ_w  = 0.75 and κ_w  = 0.58 in G1, κ_w  = 0.59 and κ_w  = 0.73 in G2, and κ_w  = 0.79 and κ_w  = 0.86 in G3, respectively. Inter-rater reliability of unidigital and bidigital palpation was κ_w  = 0.52 and κ_w  = 0.48 in G1, κ_w  = 0.47 and κ_w  = 0.52 in G2, and κ_w  = 0.50 and κ_w  = 0.64 in G3, respectively. Spearman's correlation coefficients were significant at r_s  = 0.79 and r_s  = 0.80 for unidigital and bidigital vaginal palpation, respectively.

CONCLUSIONS

Unidigital or bidigital vaginal palpation were indicated to evaluate G1 and G2 but bidigital palpation was more reliable in G3 when two examiners performed the evaluation. For the assessment conducted by one examiner, unidigital palpation was more reliable in G1 while bidigital palpation was more reliable in G2 and G3. Both unidigital and bidigital palpation have high measures of validity.

Uncovering changes in proteomic signature of rat pelvic floor muscles in pregnancy

BACKGROUND

Structural and functional changes of the rat pelvic floor muscles during pregnancy, specifically, sarcomerogenesis, increase in extracellular matrix content, and higher passive tension at larger strains protect the integral muscle components against birth injury. The mechanisms underlying these antepartum alterations are unknown. Quantitative proteomics is an unbiased method of identifying protein expression changes in differentially conditioned samples. Therefore, proteomics analysis provides an opportunity to identify molecular mechanisms underlying antepartum muscle plasticity.

OBJECTIVE

To elucidate putative mechanisms accountable for pregnancy-induced adaptations of the pelvic floor muscles, and to identify other novel antepartum alterations of the pelvic floor muscles.

MATERIALS AND METHODS

Pelvic floor muscles, comprised of coccygeus, iliocaudalis, and pubocaudalis, and nonpelvic limb muscle, tibialis anterior, were harvested from 3-month-old nonpregnant and late-pregnant Sprague-Dawley rats. After tissue homogenization, trypsin-digested peptides were analyzed by ultra-high-performance liquid chromatography coupled with tandem mass spectroscopy using nano-spray ionization. Peptide identification and label free relative quantification analysis were carried out using Peaks Studio 8.5 software (Bioinformatics Solutions Inc., Waterloo, ON, Canada). Proteomics data were visualized using the Qlucore Omics Explorer (New York, NY). Differentially expressed peptides were identified using the multi-group differential expression function, with q-value cutoff set at <0.05. Proteomic signatures of the pelvic floor muscles were compared to nonpelvic limb muscle and between nonpregnant and pregnant states.

RESULTS

Unsupervised clustering of the data showed clear separation between samples from nonpregnant and pregnant animals along principal component 1 and between pelvic and nonpelvic muscles along principal component 2. Four major gene clusters were identified segregating proteomic signatures of muscles examined in nonpregnant vs pregnant states: (1) proteins increased in the pelvic floor muscles only; (2) proteins increased in the pelvic floor muscles and tibialis anterior; (3) proteins decreased in the pelvic floor muscles and tibialis anterior; and (4) proteins decreased in the pelvic floor muscles alone. Cluster 1 included proteins involved in cell cycle progression and differentiation. Cluster 2 contained proteins that participate in mitochondrial metabolism. Cluster 3 included proteins involved in transcription, signal transduction, and phosphorylation. Cluster 4 comprised proteins involved in calcium-mediated regulation of muscle contraction via the troponin tropomyosin complex.

CONCLUSION

Pelvic floor muscles gain a distinct proteomic signature in pregnancy, which provides a mechanistic foundation for the antepartum physiological alterations acquired by these muscles. Variability in genes encoding these proteins may alter plasticity of the pelvic floor muscles and therefore the extent of the protective pregnancy-induced adaptations. Furthermore, pelvic floor muscles' proteome is divergent from that of the nonpelvic skeletal muscles.

Inflation and rupture of vaginal tissue

Around 80% of women experience vaginal tears during labour when the diameter of the vagina must increase to allow the passage of a full-term baby. Current techniques for evaluating vaginal tears are qualitative and often lead to an incorrect diagnosis and inadequate treatment, severely compromising the quality of life of women. In order to characterize the failure properties of the vaginal tissue, whole vaginal tracts from rats (n = 18) were subjected to free-extension inflation tests until rupture using a custom-built experimental set-up. The resulting deformations were measured using the digital image correlation technique. Overall, the strain and changes in curvature in the hoop direction were significantly larger relative to the axial direction. At a failure pressure of 110 ± 23 kPa (mean ± s.d.), the hoop and axial stresses were computed to be 970 ± 340 kPa and 490 ± 170 kPa, respectively. Moreover, at such pressure, the hoop and axial strains were found to be 12.8 ± 4.4 % and 6.4 ± 3.7 % , respectively. Rupture of the vaginal specimens always occurred in the hoop direction by tearing along the axial direction. This knowledge about the rupture properties of the vaginal tissue will be crucial for the development of clinical approaches for preventing and mitigating vaginal tearing and the associated short- and long-term traumatic conditions.

The increased of MMP-9 and MMP-2 with the decreased of TIMP-1 on the uterosacral ligament after childbirth

Introduction

Pelvic floor dysfunction is one of the causes of morbidity that have very active role in the degradation of collagen and elastin through an intermediary changes in matrix metalloproteinases (MMP) and its regulation. This research to evaluate level of MMP-9, MMP-2 and TIMP-1 expression on uterosacral ligament in women after vaginal delivery.

Methods

This research was conducted by collecting samples in consecutive sampling of biopsy uterosacral ligament from primigravida who underwent cesarean section because of obstructive labor at stage 1 and 2. As control, biopsy samples were taken from uterosacral ligament of primigravida a term who have not entered the labor phase and undergoing elective caesarean section surgery. The method in this study was cross sectional. The examination of MMP-9, MMP-2, and TIMP-1 expression by immunohistochemistry based on comparison of the sample and the control differences.

Results

There are differences in the levels of Matrix Metalloproteinase-9, Matrix Metalloproteinase-2, and TIMP-1 in the uterosacral ligament of primigravida women in labor compared with women who are never in labor.

Conclusion

There are increased levels of Matrix Metalloproteinase-9 and Matrix Metalloproteinase-2 with the decreased of TIMP-1 in the uterosacral ligament of primigravida women who underwent cesarean section because of obstructive labor at stage 1 and 2.

Linking hyperelastic theoretical models and experimental data of vaginal tissue through histological data

Mechanical characterization of living tissues and computer-based simulations related to medical issues, has become increasingly important to improve diagnostic processes and treatments evaluation. This work proposes a link between the mechanical testing and the material model predictions through histological data of vaginal tissue. Histological data was used to link tensile testing experiments with material-dependent parameters; the approach was adequate to capture the nonlinear response of ovine vaginal tissue over a large strain range. The experimental data obtained on a previous study, has two main components: tensile testing and histological analysis of the ovine vaginal tissue. Uniaxial tensile test data and histological data were collected from three sheep groups: virgins, pregnant and parous. The distal part of vaginal wall was selected since it is prone to tears induced by vaginal delivery. The HGO (Holzapfel-Gasser-Ogden) model parameters were fitted using a stochastic approach, namely the Simple Genetic Algorithm (SGA). The SGA was able to fit the experimental data successfully (R² > 0.986). The dimensionless coefficient ξ, was highly correlated with histological data. The ratio was seen to increase linearly with increasing collagen content. Coefficient ξ brings a new way of interpreting and understanding experimental data; it connects the nonlinear mechanical behaviour (tensile test) with tissue's morphology (histology). It can be used as an 'inverse' (approximate) method to estimate the mechanical properties without direct experimental measurements, through basic histology. In this context, the proposed methodology appears very promising in estimating the response of the tissue via histological information.

The effect of consecutive pregnancies on the ovine pelvic soft tissues: Link between biomechanical and histological components

BACKGROUND

Pelvic organ prolapse, various types of incontinence (urinary incontinence, defecatory dysfunction), chronic cystourethritis, and sexual dysfunctions remain between the most common disorders in urogynecology. Currently, it is believed that the nature and number of births plays a major role in their development. Moreover, after these events, pelvic floor tissues may not recover to their original statuses. The close anatomical relationship among the vaginal wall, bladder and rectum often contribute to the emergence of anatomical-functional failure of adjacent organs and systems.

BASIC PROCEDURES

The aim of this study was to investigate the effect of consecutive pregnancies on pelvic floor soft tissues, conducting biomechanical and histological analysis. Fifteen Swifter ewes: virgins, parous and pregnant were used. Samples, for uniaxial tension tests and histological analysis, were cut out from fresh tissue. A description of the mechanical properties of native tissue was obtained from the stress-strain curve. Histological samples were stained with Miller's Elastica staining and analyzed using ImageJ software. Collagen, elastin, and smooth muscle contents (%) were analyzed along the full wall thickness of the selected organs. The links between mechanical properties of the soft tissues and histological parameters were analyzed.

MAIN FINDINGS

Mechanically, vaginal wall tissue and cervix of pregnant sheep were more compliant. In contrast, bladder and rectum became stiffer and had the highest total collagen content. Parous sheep rectum and bladder were stiffer, compared to virgin sheep.

PRINCIPAL CONCLUSIONS

Tensile strength appears to be linked to total collagen content. Elastin and smooth muscle show a direct influence on tissue compliance.

Anisotropy of the Passive and Active Rat Vagina Under Biaxial Loading

Pelvic organ prolapse, the descent of the pelvic organs from their normal anatomical position, is a common condition among women that is associated with mechanical alterations of the vaginal wall. In order to characterize the complex mechanical behavior of the vagina, we performed planar biaxial tests of vaginal specimens in both the passive (relaxed) and active (contracted) states. Specimens were isolated from virgin, female Long-Evans rats (n = 16) and simultaneously stretched along the longitudinal direction (LD) and circumferential direction (CD) of the vagina. Tissue contraction was induced by electric field stimulation (EFS) at incrementally increasing values of stretch and, subsequently, by KCl. On average, the vagina was stiffer in the CD than in the LD (p < 0.001). The mean maximum EFS-induced active stress was significantly higher in the CD than in the LD (p < 0.01). On the contrary, the mean KCl-induced active stress was lower in the CD than in the LD (p < 0.01). When comparing the mean maximum EFS-induced active stress to the mean KCl-induced active stress, no differences were found in the CD (p = 0.366) but, in the LD, the mean active stress was much higher in response to the KCl stimulation (p < 0.001). Collectively, these results suggest that the anisotropic behavior of the vaginal tissue is determined not only by collagen and smooth muscle fiber organization but also by the innervation.

Pelvic muscles' mechanical response to strains in the absence and presence of pregnancy-induced adaptations in a rat model

BACKGROUND

Maternal birth trauma to the pelvic floor muscles is thought to be consequent to mechanical demands placed on these muscles during fetal delivery that exceed muscle physiological limits. The above is consistent with studies of striated limb muscles that identify hyperelongation of sarcomeres, the functional muscle units, as the primary cause of mechanical muscle injury and resultant muscle dysfunction. However, pelvic floor muscles' mechanical response to strains have not been examined at a tissue level. Furthermore, we have previously demonstrated that during pregnancy, rat pelvic floor muscles acquire structural and functional adaptations in preparation for delivery, which likely protect against mechanical muscle injury by attenuating the strain effect.

OBJECTIVE

We sought to determine the mechanical impact of parturition-related strains on pelvic floor muscles' microstructure, and test the hypothesis that pregnancy-induced adaptations modulate muscle response to strains associated with vaginal delivery.

STUDY DESIGN

Three-month-old Sprague-Dawley late-pregnant (N = 20) and nonpregnant (N = 22) rats underwent vaginal distention, replicating fetal crowning, with variable distention volumes. Age-matched uninjured pregnant and nonpregnant rats served as respective controls. After sacrifice, pelvic floor muscles, which include coccygeus, iliocaudalis, and pubocaudalis, were fixed in situ and harvested for fiber and sarcomere length measurements. To ascertain the extent of physiological strains during spontaneous vaginal delivery, analogous measurements were obtained in intrapartum rats (N = 4) sacrificed during fetal delivery. Data were compared with repeated measures and 2-way analysis of variance, followed by pairwise comparisons, with significance set at P < .05.

RESULTS

Gross anatomic changes were observed in the pelvic floor muscles following vaginal distention, particularly in the entheseal region of pubocaudalis, which appeared translucent. The above appearance resulted from dramatic stretch of the myofibers, as indicated by significantly longer fiber length compared to controls. Stretch ratios, calculated as fiber length after vaginal distention divided by baseline fiber length, increased gradually with increasing distention volume. Paralleling these macroscopic changes, vaginal distention resulted in acute and progressive increase in sarcomere length with rising distention volume. The magnitude of strain effect varied by muscle, with the greatest sarcomere elongation observed in coccygeus, followed by pubocaudalis, and a smaller increase in iliocaudalis, observed only at higher distention volumes. The average fetal rat volume approximated 3 mL. Pelvic floor muscle sarcomere lengths in pregnant animals undergoing vaginal distention with 3 mL were similar to intrapartum sarcomere lengths in all muscles (P > .4), supporting the validity of our experimental approach. Vaginal distention resulted in dramatically longer sarcomere lengths in nonpregnant compared to pregnant animals, especially in coccygeus and pubocaudalis (P < .0001), indicating significant attenuation of sarcomere elongation in the presence of pregnancy-induced adaptations in pelvic floor muscles.

CONCLUSION

Delivery-related strains lead to acute sarcomere elongation, a well-established cause of mechanical injury in skeletal muscles. Sarcomere hyperelongation resultant from mechanical strains is attenuated by pregnancy-induced adaptations acquired by the pelvic floor muscles prior to parturition.

Transfer of vaginal chloramphenicol to circulating blood in pregnant women and its relationship with their maternal background and neonatal health

Few clinical studies have determined the quantitative transfer of vaginal chloramphenicol to circulating blood in pregnant women. This study aimed to evaluate the plasma concentration of chloramphenicol in pregnant women treated with trans-vaginal tablets and its relationship with maternal background and neonatal health. Thirty-seven pregnant women treated with 100 mg of trans-vaginal chloramphenicol once daily for bacterial vaginosis and its suspected case were enrolled. The plasma concentration of chloramphenicol was determined using liquid chromatography coupled to tandem mass spectrometry at day 2 or later after starting the medication. The correlations between the maternal plasma concentration of chloramphenicol and the background and neonatal health at birth were investigated. Chloramphenicol was detected from all maternal plasma specimens and its concentration ranged from 0.043 to 73.1 ng/mL. The plasma concentration of chloramphenicol declined significantly with the administration period. The plasma concentration of chloramphenicol was lower at the second than the first blood sampling. No correlations were observed between the maternal plasma concentration of chloramphenicol and background such as number of previous births, gestational age at dosing, and clinical laboratory data. Neonatal infant health parameters such as birth-weight, Apgar score at birth, and gestational age at the time of childbearing were not related to the maternal plasma concentration of chloramphenicol. Vaginal chloramphenicol transfers to circulating blood in pregnant women. The maternal plasma concentration of chloramphenicol varied markedly and was associated with the administration day, but not with maternal background or her neonatal health.

Pregnancy-induced adaptations in intramuscular extracellular matrix of rat pelvic floor muscles

BACKGROUND

Birth trauma to pelvic floor muscles is a major risk factor for pelvic floor disorders. Intramuscular extracellular matrix determines muscle stiffness, supports contractile component, and shields myofibers from mechanical strain.

OBJECTIVE

Our goal was to determine whether pregnancy alters extracellular matrix mechanical and biochemical properties in a rat model, which may provide insights into the pathogenesis of pelvic floor muscle birth injury. To examine whether pregnancy effects were unique to pelvic floor muscles, we also studied a hind limb muscle.

STUDY DESIGN

Passive mechanical properties of coccygeus, iliocaudalis, pubocaudalis, and tibialis anterior were compared among 3-month old Sprague-Dawley virgin, late-pregnant, and postpartum rats. Muscle tangent stiffness was calculated as the slope of the stress-sarcomere length curve between 2.5 and 4.0 μm, obtained from a stress-relaxation protocol at a bundle level. Elastin and collagen isoform concentrations were quantified by the use of enzyme-linked immunosorbent assay. Enzymatic and glycosylated collagen crosslinks were determined by high-performance liquid chromatography. Data were compared by the use of repeated-measures, 2-way analysis of variance with Tukey post-hoc testing. Correlations between mechanical and biochemical parameters were assessed by linear regressions. Significance was set to P < .05. Results are reported as mean ± SEM.

RESULTS

Pregnancy significantly increased stiffness in coccygeus (P < .05) and pubocaudalis (P < .0001) relative to virgin controls, with no change in iliocaudalis. Postpartum, pelvic floor muscle stiffness did not differ from virgins (P > .3). A substantial increase in collagen V in coccygeus and pubocaudalis was observed in late-pregnant, compared with virgin, animals, (P < .001). Enzymatic crosslinks decreased in coccygeus (P < .0001) and pubocaudalis (P < .02) in pregnancy, whereas glycosylated crosslinks were significantly elevated in late-pregnant rats in all pelvic floor muscles (P < .05). Correlations between muscle stiffness and biochemical parameters were inconsistent. In contrast to the changes observed in pelvic floor muscles, the tibialis anterior was unaltered by pregnancy.

CONCLUSIONS

In contrast to other pelvic tissues, pelvic floor muscle stiffness increased in pregnancy, returning to prepregnancy state postpartum. This adaptation may shield myofibers from excessive mechanical strain during parturition. Biochemical alterations in pelvic floor muscle extracellular matrix due to pregnancy include increase in collagen V and a differential response in enzymatic vs glycosylated collagen crosslinks. The relationships between pelvic floor muscle biochemical and mechanical parameters remain unclear.

Transplantation of bone marrow-derived mesenchymal stem cells expressing elastin alleviates pelvic floor dysfunction

Background

Pelvic floor dysfunction (PFD) is a group of clinical conditions including stress urinary incontinence (SUI) and pelvic organ prolapse (POP). The abnormality of collagen and elastin metabolism in pelvic connective tissues is implicated in SUI and POP.

Methods

To reconstitute the connective tissues with normal distribution of collagen and elastin, we transduced elastin to bone marrow-derived mesenchymal stem cells (BMSC). Elastin-expressing BMSCs were then differentiated to fibroblasts using bFGF, which produced collagen and elastin. To achieve the sustained release of bFGF, we formulated bFGF in poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NP).

Results

In an in vitro cell culture system of 7 days, when no additional bFGF was administrated, the initial PLGA-loaded bFGF NP induced prolonged production of collagen and elastin from elastin-expressing BMSCs. In vivo, co-injection of PLGA-loaded bFGF NP and elastin-expressing BMSCs into the PFD rats significantly improved the outcome of urodynamic tests. Together, these results provided an efficient model of connective tissue engineering using BMSC and injectable PLGA-loaded growth factors.

Conclusions

Our results provided the first instance of a multidisciplinary approach, combining both stem cell and nanoparticle technologies, for the treatment of PFD.

Impact of parity on ewe vaginal mechanical properties relative to the nonhuman primate and rodent

INTRODUCTION AND HYPOTHESIS

Parity is the leading risk factor for the development of pelvic organ prolapse. To assess the impact of pregnancy and delivery on vaginal tissue, researchers commonly use nonhuman primate (NHP) and rodent models. The purpose of this study was to evaluate the ewe as an alternative model by investigating the impact of parity on the ewe vaginal mechanical properties and collagen structure.

METHODS

Mechanical properties of 15 nulliparous and parous ewe vaginas were determined via uniaxial tensile tests. Collagen content was determined by hydroxyproline assay and collagen fiber thickness was analyzed using picrosirius red staining. Outcome measures were compared using Independent samples t or Mann-Whitney U tests. ANOVA (Gabriel's pairwise post-hoc test) or the Welch Alternative for the F-ratio (Games Howell post-hoc test) was used to compare data with previously published NHP and rodent data.

RESULTS

Vaginal tissue from the nulliparous ewe had a higher tangent modulus and tensile strength compared with the parous ewe (p < 0.025). The parous ewe vagina elongated 42 % more than the nulliparous ewe vagina (p = 0.015). No significant differences were observed in collagen structure among ewe vaginas. The tangent modulus of the nulliparous ewe vagina was not different from that of the NHP or rodent (p = 0.290). Additionally, the tangent moduli of the parous ewe and NHP vaginas did not differ (p = 0.773).

CONCLUSIONS

Parity has a negative impact on the mechanical properties of the ewe vagina, as also observed in the NHP. The ewe may serve as an alternative model for studying parity and ultimately prolapse development.

Pregnancy-induced adaptations in the intrinsic structure of rat pelvic floor muscles

OBJECTIVE

Maternal birth trauma to the pelvic floor muscles (PFMs) is a major risk factor for pelvic floor disorders. Modeling and imaging studies suggest that demands placed on PFMs during childbirth exceed their physiologic limits; however many parous women do not sustain PFM injury. Here we determine whether pregnancy induces adaptations in PFM architecture, the strongest predictor of muscle function, and/or intramuscular extracellular matrix (ECM), responsible for load bearing. To establish if parallel changes occur in muscles outside of the PFM, we also examined a hind limb muscle.

STUDY DESIGN

Coccygeus, iliocaudalis, pubocaudalis, and tibialis anterior of 3-month-old Sprague-Dawley virgin, mid-pregnant, and late-pregnant; 6-month-old virgin; and 4- and 12-week postpartum rats (N = 10/group) were fixed in situ and harvested. Major architectural parameters determining muscle's excursion and force-generating capacity were quantified, namely, normalized fiber length (Lfn), physiologic cross-sectional area, and sarcomere length. Hydroxyproline content was used as a surrogate for intramuscular ECM quantity. Analyses were performed by 2-way analysis of variance with Tukey post hoc testing at a significance level of .05.

RESULTS

Pregnancy induced a significant increase in Lfn in all PFMs by the end of gestation relative to virgin controls. Fibers were elongated by 37% in coccygeus (P < .0001), and by 21% in iliocaudalis and pubocaudalis (P < .0001). Importantly, no Lfn change was observed in the tibialis anterior. Physiologic cross-sectional area and sarcomere length were not affected by pregnancy. By 12 weeks' postpartum, Lfn of all PFMs returned to the prepregnancy values. Relative to virgin controls, ECM increased by 140% in coccygeus, 52% in iliocaudalis, and 75% in pubocaudalis in late-pregnant group, but remained unchanged across time in the tibialis anterior. Postpartum, ECM collagen content returned to prepregnancy levels in iliocaudalis and pubocaudalis, but continued to be significantly elevated in coccygeus (P < .0001).

CONCLUSION

This study demonstrates that pregnancy induces unique adaptations in the structure of the PFMs, which adjust their architectural design by adding sarcomeres in series to increase fiber length as well as mounting a substantial synthesis of collagen in intramuscular ECM.

Maternal adaptations in preparation for parturition predict uncomplicated spontaneous delivery outcome

OBJECTIVE

The objective of the study was to define maternal tissue adaptations in pregnancy associated with uncomplicated spontaneous vaginal delivery using anatomical and biological outcomes.

STUDY DESIGN

Nulliparous gravidas were prospectively enrolled in the first trimester at 2 institutions. Demographic and delivery data were chart abstracted. Vaginal elastase activity (units per milligram of protein) and Pelvic Organ Prolapse Quantification measurements of pelvic organ support were obtained in the first and third trimesters. A subset underwent 3-dimensional ultrasound measures of levator hiatus. Uncomplicated spontaneous vaginal delivery (VD) was defined as no cesarean, forceps, vacuum, shoulder dystocia, third- or fourth-degree perineal laceration, or prolonged second stage labor.

RESULTS

We enrolled 173 women in their first trimester, 50 of whom had ultrasounds. Mean age was 25.5 ± 5.5 years with a body mass index of 28.0 ± 7.3 kg/m(2). Sixty-seven percent were white/Caucasian, 27% black/African American, and 6% Hispanic/Latina. Mean delivery gestational age was 38.5 ± 2.9 weeks, with 23% delivering by cesarean and 59% achieving uncomplicated spontaneous VD. Vaginal support changed significantly over trimesters with posterior vaginal and hiatal relaxation, vaginal lengthening, and increased levator hiatus area during strain. Women achieving uncomplicated spontaneous VD demonstrated significantly greater relaxation on third-trimester Pelvic Organ Prolapse Quantification for anterior, apical, and hiatal measures than those without uncomplicated spontaneous VD. Higher first-trimester vaginal elastase activity was strongly associated with uncomplicated spontaneous VD (geometric mean activity 0.289 ± 0.830 U/mg vs -0.029 ± 0.585 U/mg, P = .009). Higher first-trimester elastase, younger age, lower first-trimester body mass index, and more third-trimester vaginal support laxity in points C and GH were predictive of VD success.

CONCLUSION

Significant maternal adaptations occur in the vagina during pregnancy, presumably in preparation for vaginal delivery. Greater adaptation, including vaginal descent and higher first-trimester elastase activity, is associated with an increased likelihood of uncomplicated spontaneous VD.

Comparison of pelvic muscle architecture between humans and commonly used laboratory species

INTRODUCTION AND HYPOTHESIS

Pelvic floor muscles (PFM) are deleteriously affected by vaginal birth, which contributes to the development of pelvic floor disorders. To mechanistically link these events, experiments using animal models are required, as access to human PFM tissue is challenging. In choosing an animal model, a comparative study of PFM design is necessary, since gross anatomy alone is insufficient to guide the selection.

METHODS

Human PFM architecture was measured using micromechanical dissection and then compared with mouse (n = 10), rat (n = 10), and rabbit (n = 10) using the Architectural Difference Index (ADI) (parameterizing a combined measure of sarcomere length-to-optimal-sarcomere ratio, fiber-to-muscle-length ratio, and fraction of total PFM mass and physiological cross-sectional area (PCSA) contributed by each muscle). Coccygeus (C), iliocaudalis (IC), and pubocaudalis (PC) were harvested and subjected to architectural measurements. Parameters within species were compared using repeated measures analysis of variance (ANOVA) with post hoc Tukey's tests. The scaling relationships of PFM across species were quantified using least-squares regression of log-10-transformed variables.

RESULTS

Based on the ADI, rat was found to be the most similar to humans (ADI = 2.5), followed by mouse (ADI = 3.3). When animals' body mass was regressed against muscle mass, muscle length, fiber length, and PCSA scaling coefficients showed a negative allometric relationship or smaller increase than predicted by geometric scaling.

CONCLUSION

In terms of muscle design among commonly used laboratory animals, rat best approximates the human PFM, followed by mouse. Negative allometric scaling of PFM architectural parameters is likely due to the multifaceted function of these muscles.

Influence of reproductive status on tissue composition and biomechanical properties of ovine vagina

Objective

To undertake a comprehensive analysis of the biochemical tissue composition and passive biomechanical properties of ovine vagina and relate this to the histo-architecture at different reproductive stages as part of the establishment of a large preclinical animal model for evaluating regenerative medicine approaches for surgical treatment of pelvic organ prolapse.

Methods

Vaginal tissue was collected from virgin (n = 3), parous (n = 6) and pregnant sheep (n = 6; mean gestation; 132 d; term = 145 d). Tissue histology was analyzed using H+E and Masson's Trichrome staining. Biochemical analysis of the extracellular matrix proteins used a hydroxyproline assay to quantify total collagen, SDS PAGE to measure collagen III/I+III ratios, dimethylmethylene blue to quantify glycosaminoglycans and amino acid analysis to quantify elastin. Uniaxial tensiometry was used to determine the Young's modulus, maximum stress and strain, and permanent strain following cyclic loading.

Results

Vaginal tissue of virgin sheep had the lowest total collagen content and permanent strain. Parous tissue had the highest total collagen and lowest elastin content with concomitant high maximum stress. In contrast, pregnant sheep had the highest elastin and lowest collagen contents, and thickest smooth muscle layer, which was associated with low maximum stress and poor dimensional recovery following repetitive loading.

Conclusion

Pregnant ovine vagina was the most extensible, but the weakest tissue, whereas parous and virgin tissues were strong and elastic. Pregnancy had the greatest impact on tissue composition and biomechanical properties, compatible with significant tissue remodeling as demonstrated in other species. Biochemical changes in tissue protein composition coincide with these altered biomechanical properties.

High-frequency micro-ultrasound: a novel method to assess external urethral sphincter function in rats following simulated birth injury

AIMS

We evaluated external urethral sphincter (EUS) function using high-frequency micro-ultrasound (US) in rats that were either uninjured (Control, C) or underwent vaginal distension (VD) as a substitute for vaginal birth injury induced stress urinary incontinence (SUI).

METHODS

Thirteen female nulliparous Sprague-Dawley rats of 12 weeks were divided into two groups, either C (n = 6) or VD (n = 7). Vaginal balloon distension was performed under pentobarbital anesthesia for 4 hours. Five days after the injury, all animals underwent US assessment of the urethra during high-rate bladder filling and urine leakage/voiding. Urinary leakage, the presence, absence, and pattern of EUS bursting during the voiding phase were registered, and pre-determined parameters of intercontraction interval (ICI), length of contraction (LOC), and rate of contraction (ROC) were registered.

RESULTS

Our ultrasound findings consistently showed the presence of rhythmic EUS bursting in all of the C rats (6/6), which were absent in all VD rats (0/7). The mean of ROC, ICI, and LOC in C group were 3.02 ± 0.12 contractions/sec, 471.43 ± 17.9 msec, and 103.41 ± 3.28 msec, respectively.

CONCLUSIONS

Pre-determined parameters of LOC, ICI, and ROC during US provide objective and measurable data on EUS function. US showed the total disappearance of EUS bursting in the VD group as compared to the C group. These results indicate that ultrasound testing may become a valuable non-invasive tool in future translational studies to investigate SUI/urethral function in rat models.

Animal models of female pelvic organ prolapse: lessons learned

Pelvic organ prolapse is a vaginal protrusion of female pelvic organs. It has high prevalence worldwide and represents a great burden to the economy. The pathophysiology of pelvic organ prolapse is multifactorial and includes genetic predisposition, aberrant connective tissue, obesity, advancing age, vaginal delivery and other risk factors. Owing to the long course prior to patients becoming symptomatic and ethical questions surrounding human studies, animal models are necessary and useful. These models can mimic different human characteristics - histological, anatomical or hormonal, but none present all of the characteristics at the same time. Major animal models include knockout mice, rats, sheep, rabbits and nonhuman primates. In this article we discuss different animal models and their utility for investigating the natural progression of pelvic organ prolapse pathophysiology and novel treatment approaches.

Induced Regenerative Elastic Matrix Repair in LOXL1 Knockout Mouse Cell Cultures: Towards Potential therapy for Pelvic Organ Prolapse

Impaired elastic matrix remodeling occurs in reproductive tissues after vaginal delivery. This has been linked to development of pelvic organ prolapse (POP) for which there currently is no pharmacologic therapy. Hyaluronan oligomers and transforming growth factor beta 1 (termed elastogenic factors, EFs) have been shown to significantly enhance tropoelastin synthesis, elastic fiber assembly, and crosslinking by adult vascular smooth muscle cells (SMCs). The goal of this study was to ascertain if these factors similarly improve the quantity and quality of elastic matrix deposition by vaginal SMCs (VSMCs) isolated from lysyl oxidase like-1 knock out (LOXL1 KO) mouse model of POP. Cells isolated from whole vagina of a LOXL1 KO mouse (multiparous, stage 3 prolapse) were cultured and identified as SMCs by their expression of various SMC markers. Passage 2 vaginal SMCs (VSMCs; 3×10⁴/10 cm²) were cultured for 21 days with EFs. Cell layers and spent medium aliquots were assessed for elastin content and quality. EF-treated VSMCs proliferated at a similar rate to untreated controls but synthesized more total elastin primarily in the form of soluble matrix elastin. Elastin mRNA was also increased compared to controls. The elastic matrix was significantly denser in EF-treated cultures, which was composed of more mature, non-interrupted elastic fibers that were absent in controls. The results are promising towards development of a therapy to enhance regenerative elastic matrix repair in post-partum female pelvic floor tissues.

Impact of pregnancy and vaginal delivery on the passive and active mechanics of the rat vagina

Remodeling of vaginal extracellular matrix and smooth muscle likely plays a critical role in reducing the risk of maternal injury during vaginal delivery by altering the mechanical properties to increase distension and reduce stress. Long-Evans rats were divided into five groups to examine the passive mechanical and active contractile properties throughout pregnancy and postpartum: virgin (n=17), mid-pregnant (Day 14-16, n=12), late-pregnant (Day 20-22, n=14), immediate postpartum (0-2 h after delivery, n=14), and 4 week postpartum (n=15). Longitudinal sections of vaginal tissue were loaded to failure uniaxially for passive mechanical or active contractile properties were examined. For passive mechanics, the tangent modulus decreased 45% by mid-pregnancy and immediately postpartum (p<0.001). The ultimate strain continuously increased up to 43% higher than virgin animals (p=0.007) in the immediate postpartum group. For active mechanics, the maximal contractile force was 36-56% lower through immediate postpartum animals, and was significantly more sensitive to K+ throughout pregnancy and postpartum (p=0.003). The changes observed in the passive and active properties of the rat vagina are consistent with what would be expected from a tissue that is remodeling to maximize its ability to distend at the time of vaginal delivery to facilitate passage of the fetus with minimal injury.