FORMATION AND BREAKDOWN OF COLLAGEN AND ELASTIN IN THE HUMAN UTERUS DURING PREGNANCY AND POST-PARTUM INVOLUTION

The smaller firstborn: exploring the association of parity and fetal growth

PURPOSE

To investigate the association of parity with a range of neonatal anthropometric measurements in a cohort of uncomplicated term singleton pregnancies.

METHODS

Retrospective cohort study of patients with a singleton term birth at a single tertiary center (2014-2020) was carried out. The primary exposure was parity. The following neonatal anthropometric measures were considered: birthweight, head circumference, length, ponderal index, and neonatal body mass index (BMI).

RESULTS

A total of 8134 patients met the study criteria, 1949 (24.0%) of whom were nulliparous. Compared with multiparous patients, infants of nulliparous patients had a lower mean percentile for birthweight (43.1 ± 26.4 vs. 48.3 ± 26.8 percentile, p < 0.001), head circumference (44.3 ± 26.4 vs. 48.1 ± 25.5 percentile, p < 0.001), length (52.6 ± 25.1 vs. 55.5 ± 24.6 percentile, p < 0.001), ponderal index (34.4 ± 24.0 vs. 37.6 ± 24.2 percentile, p < 0.001), and BMI (39.1 ± 27.1 vs. 43.9 ± 27.3 percentile, p < 0.001). In addition, infants of nulliparous patients had higher odds of having a small (< 10th percentile for gestational age) birthweight (aOR 1.32 [95% CI 1.12-1.56]), head circumference (aOR 1.54 [95% CI 1.29-1.84]), length (aOR 1.50 [95% CI 1.16-1.94]), ponderal index (aOR 1.30 [95% CI 1.12-1.51]), and body mass index (aOR 1.42 [95% CI 1.22-1.65]). Most neonatal anthropometric measures increased with parity until a parity of 2, where it seemed to reach a plateau.

CONCLUSION

Parity has an independent impact on a wide range of neonatal anthropometric measures, suggesting that parity is associated with both fetal skeletal growth and body composition. In addition, the association of parity with fetal growth does not follow a continuous relationship but instead reaches a plateau after the second pregnancy.

Equilibrium Tension and Compression Mechanical Properties of the Human Uterus

A successful pregnancy relies on the proper cellular, biochemical, and mechanical functions of the uterus. A comprehensive understanding of uterine mechanical properties during pregnancy is key to understanding different gynecological and obstetric disorders such as preterm birth, placenta accreta, leiomyoma, and endometriosis. This study sought to characterize the macro-scale equilibrium material behaviors of the human uterus in non-pregnancy and late pregnancy under both compressive and tensile loading. Fifty human uterine specimens from 16 patients (8 nonpregnant [NP] and 8 pregnant [PG]) were tested using spherical indentation and uniaxial tension coupled with digital image correlation (DIC). A three-level incremental load-hold protocol was applied to both tests. A microstructurally-inspired material model considering fiber architecture was applied to this dataset. Inverse finite element analysis (IFEA) was then performed to generate a single set of mechanical parameters to describe compressive and tensile behaviors. The freeze-thaw effect on uterine macro mechanical properties was also evaluated. PG tissue exhibits decreased overall stiffness and increased fiber network extensibility compared to NP uterine tissue. Under indentation, ground substance compressibility was similar between NP and PG uterine tissue. In tension, the fiber network of the PG uterus was found to be more extensible and dispersed than in nonpregnancy. Lastly, a single freeze-thaw cycle did not systematically alter the macro-scale material behavior of the human uterus.

Uterine Cesarean Scar Tissue-An Immunohistochemical Study

Background and Objectives: Wound healing encompasses a multitude of factors and entails the establishment of interactions among components of the basement membrane. The quantification of particle concentrations can serve as valuable biomarkers for assessing biomechanical muscle properties. The objective of this study was to examine the immunoexpression and immunoconcentration of myometrial collagen type VI, elastin, alpha-smooth muscle actin, and smooth muscle myosin heavy chain, as well as the expression of platelets and clusters of differentiation 31 in the uterine scar following a cesarean section (CS). Materials and Methods: A total of 177 biopsies were procured from a cohort of pregnant women who were healthy, specifically during the surgical procedure of CS. The participants were categorized into seven distinct groups. Group 1 consisted of primiparas, with a total of 52 individuals. The subsequent groups were organized based on the duration of time that had elapsed since their previous CS. The analysis focused on the immunoexpression and immunoconcentration of the particles listed. Results: No significant variations were observed in the myometrial immunoconcentration of collagen type VI, elastin, smooth muscle myosin, and endothelial cell cluster of differentiation 31 among the analyzed groups. The concentration of alpha-smooth muscle actin in the myometrium was found to be significantly higher in patients who underwent CS within a period of less than 2 years since their previous CS, compared to those with a longer interval between procedures. Conclusions: Our findings indicate that the immunoconcentration of uterine myometrial scar collagen type VI, elastin, smooth muscle myosin heavy chain, alpha-smooth muscle actin, and endothelial cell marker cluster of differentiation 31 remains consistent regardless of the duration elapsed since the previous CS. The findings indicate that there are no significant alterations in the biomechanical properties of the uterine muscle beyond a period of 13 months following a CS.

Material properties of nonpregnant and pregnant human uterine layers

The uterus has critical biomechanical functions in pregnancy and undergoes dramatic material growth and remodeling from implantation to parturition. The intrinsic material properties of the human uterus and how they evolve in pregnancy are poorly understood. To address this knowledge gap and assess the heterogeneity of these tissues, the time-dependent material properties of all human uterine layers were measured with nanoindentation. The endometrium-decidua layer was found to be the least stiff, most viscous, and least permeable layer of the human uterus in nonpregnant and third-trimester pregnant tissues. In pregnancy, the endometrium-decidua becomes stiffer and less viscous with no material property changes observed in the myometrium or perimetrium. Additionally, uterine material properties did not significantly differ between third-trimester pregnant tissues with and without placenta accreta. The foundational data generated by this study will facilitate the development of physiologically accurate models of the human uterus to investigate gynecologic and obstetric disorders.

Uterine Collagen Cross-Linking: Biology, Role in Disorders, and Therapeutic Implications

Collagen is an essential constituent of the uterine extracellular matrix that provides biomechanical strength, resilience, structural integrity, and the tensile properties necessary for the normal functioning of the uterus. Cross-linking is a fundamental step in collagen biosynthesis and is critical for its normal biophysical properties. This step occurs enzymatically via lysyl oxidase (LOX) or non-enzymatically with the production of advanced glycation end-products (AGEs). Cross-links found in uterine tissue include the reducible dehydro-dihydroxylysinonorleucine (deH-DHLNL), dehydro-hydroxylysinonorleucine (deH-HLNL), and histidinohydroxymerodesmosine (HHMD); and the non-reducible pyridinoline (PYD), deoxy-pyridinoline (DPD); and a trace of pentosidine (PEN). Collagen cross-links are instrumental for uterine tissue integrity and the continuation of a healthy pregnancy. Decreased cervical cross-link density is observed in preterm birth, whereas increased tissue stiffness caused by increased cross-link density is a pathogenic feature of uterine fibroids. AGEs disrupt embryo development, decidualization, implantation, and trophoblast invasion. Uterine collagen cross-linking regulators include steroid hormones, such as progesterone and estrogen, prostaglandins, proteoglycans, metalloproteinases, lysyl oxidases, nitric oxide, nicotine, and vitamin D. Thus, uterine collagen cross-linking presents an opportunity to design therapeutic targets and warrants further investigation in common uterine disorders, such as uterine fibroids, cervical insufficiency, preterm birth, dystocia, endometriosis, and adenomyosis.

Material Properties of Nonpregnant and Pregnant Human Uterine Layers

The uterus has critical biomechanical functions in pregnancy and undergoes dramatic material growth and remodeling from implantation to parturition. The intrinsic material properties of the human uterus and how they evolve in pregnancy are poorly understood. To address this knowledge gap and assess the heterogeneity of these tissues, the time-dependent material properties of all human uterine layers were measured with nanoindentation. The endometrium-decidua layer was found to be the least stiff, most viscous, and least permeable layer of the human uterus in nonpregnant and third-trimester pregnant tissues. In pregnancy, endometrium-decidua becomes stiffer and less viscous with no material property changes observed in the myometrium or perimetrium. Additionally, uterine material properties did not significantly differ between third-trimester pregnant tissues with and without placenta accreta. The foundational data generated by this study will facilitate the development of physiologically accurate models of the human uterus to investigate gynecologic and obstetric disorders.

Growth and development of syphilis-exposed and -unexposed uninfected children during their first 18 months of life in Suzhou, China: a nested case-control study with propensity score matching

Background

With the successful implementation of Prevention of Mother-to-Child Transmission (PMTCT) policies, the proportion of infants with exposure to both syphilis and antibiotic medication in utero has increased in China, but there is limited evidence about the early growth and development of such infants.

Methods

We conducted a retrospective nested case-control study based on data from the China PMTCT program conducted in Suzhou from 2016 to 2021. Propensity score matching (PSM) was employed to extract 826 syphilis-exposed but uninfected (SEU) infants and 1,652 syphilis-unexposed uninfected (SUU) infants from a total of 712,653 infants. Maternal characteristics were collected through questionnaires, such as parity, age, education level, smoking and drinking habits during pregnancy. Infantile characteristics were retrieved from medical records or via questionnaires, such as gestational age, gender, mode of delivery, Apgar scores, birth weight and length, outdoor time, vitamin D intake, and feed pattern. Mixed effects models, adjusting for potential influencing factors, were used to investigate the early infantile growth pattern of SEU and SUU infants. All statistical analysis were conducted using R (version 4.2.0).

Results

Length and weight were slightly higher in SEU infants than in the SUU infants at some time points (months 0 and 18 for length, p-values <0.05; months 0, 6, and 18 for weight, p < 0.05). In the mixed effects model, SEU group was found to be associated with higher weight [exponentiated beta exp.(β) = 1.15, 95% Confidence Interval (CI) = 1.06, 1.25], length [exp(β) = 1.42, 95% CI = 1.14, 1.77], and BMI z-score [exp(β) = 1.09, 95% CI = 1.00, 1.19].

Conclusion

With the effective prevention of congenital syphilis under the PMTCT program, SEU infants have non-inferior growth patterns during their first 18 months of life compared with SUU controls in Suzhou, China.

Birthweight of the subsequent singleton pregnancy following a first twin or singleton pregnancy

INTRODUCTION

Birthweight is an important pregnancy indicator strongly associated with infant, child, and later adult life health. Previous studies have found that second-born babies are, on average, heavier than first-born babies, indicating an independent effect of parity on birthweight. Existing data are mostly based on singleton pregnancies and do not consider higher order pregnancies. We aimed to compare birthweight in singleton pregnancies following a first twin pregnancy relative to a first singleton pregnancy.

MATERIAL AND METHODS

This was a prospective registry-based cohort study using maternally linked offspring with first and subsequent pregnancies registered in the Medical Birth Registry of Norway between 1967 and 2020. We studied offspring birthweights of 778 975 women, of which 4849 had twins and 774 126 had singletons in their first pregnancy. Associations between twin or singleton status of the first pregnancy and birthweight (grams) in subsequent singleton pregnancies were evaluated by linear regression adjusted for maternal age at first delivery, year of first pregnancy, maternal education, and country of birth. We used plots to visualize the distribution of birthweight in the first and subsequent pregnancies.

RESULTS

Mean combined birthweight of first-born twins was more than 1000 g larger than mean birthweight of first-born singletons. When comparing mean birthweight of a subsequent singleton baby following first-born twins with those following first-born singletons, the adjusted difference was just 21 g (95% confidence interval 5-37 g).

CONCLUSIONS

Birthweights of the subsequent singleton baby were similar for women with a first twin or a first singleton pregnancy. Although first twin pregnancies contribute a greater combined total offspring birthweight including more extensive uterine expansion, this does not explain the general parity effect seen in birthweight. The physiological reasons for increased birthweight with parity remain to be established.

Collagen and elastic fiber remodeling in the pregnant mouse myometrium†

The myometrium undergoes progressive tissue remodeling from early to late pregnancy to support fetal growth and transitions to the contractile phase to deliver a baby at term. Much of our effort has been focused on understanding the functional role of myometrial smooth muscle cells, but the role of extracellular matrix is not clear. This study was aimed to demonstrate the expression profile of sub-sets of genes involved in the synthesis, processing, and assembly of collagen and elastic fibers, their structural remodeling during pregnancy, and hormonal regulation. Myometrial tissues were isolated from non-pregnant and pregnant mice to analyze gene expression and protein levels of components of collagen and elastic fibers. Second harmonic generation imaging was used to examine the morphology of collagen and elastic fibers. Gene and protein expressions of collagen and elastin were induced very early in pregnancy. Further, the gene expressions of some of the factors involved in the synthesis, processing, and assembly of collagen and elastic fibers were differentially expressed in the pregnant mouse myometrium. Our imaging analysis demonstrated that the collagen and elastic fibers undergo structural reorganization from early to late pregnancy. Collagen and elastin were differentially induced in response to estrogen and progesterone in the myometrium of ovariectomized mice. Collagen was induced by both estrogen and progesterone. By contrast, estrogen induced elastin, but progesterone suppressed its expression. The current study suggests progressive extracellular matrix remodeling and its potential role in the myometrial tissue mechanical function during pregnancy and parturition.

Protease activities of vaginal Porphyromonas species disrupt coagulation and extracellular matrix in the cervicovaginal niche

Porphyromonas asaccharolytica and Porphyromonas uenonis are common inhabitants of the vaginal microbiome, but their presence has been linked to adverse health outcomes for women, including bacterial vaginosis and preterm birth. However, little is known about the pathogenesis mechanisms of these bacteria. The related oral opportunistic pathogen, Porphyromonas gingivalis, is comparatively well-studied and known to secrete numerous extracellular matrix-targeting proteases. Among these are the gingipain family of cysteine proteases that drive periodontal disease progression and hematogenic transmission to the placenta. In this study, we demonstrate that vaginal Porphyromonas species secrete broad-acting proteases capable of freely diffusing within the cervicovaginal niche. These proteases degrade collagens that are enriched within the cervix (type I) and chorioamniotic membranes (type IV), as well as fibrinogen, which inhibits clot formation. Bioinformatic queries confirmed the absence of gingipain orthologs and identified five serine, cysteine, and metalloprotease candidates in each species. Inhibition assays revealed that each species' proteolytic activity can be partially attributed to a secreted metalloprotease with broad substrate specificity that is distantly related to the P. gingivalis endopeptidase PepO. This characterization of virulence activities in vaginal Porphyromonas species highlights their potential to alter the homeostasis of reproductive tissues and harm human pregnancy through clotting disruption, fetal membrane weakening, and premature cervical remodeling.

A mathematical model of maternal vascular growth and remodeling and changes in maternal hemodynamics in uncomplicated pregnancy

The maternal vasculature undergoes tremendous growth and remodeling (G&R) that enables a > 15-fold increase in blood flow through the uterine vasculature from conception to term. Hemodynamic metrics (e.g., uterine artery pulsatility index, UA-PI) are useful for the prognosis of pregnancy complications; however, improved characterization of the maternal hemodynamics is necessary to improve prognosis. The goal of this paper is to develop a mathematical framework to characterize maternal vascular G&R and hemodynamics in uncomplicated human pregnancies. A validated 1D model of the human vascular tree from the literature was adapted and inlet blood flow waveforms at the ascending aorta at 4 week increments from 0 to 40 weeks of gestation were prescribed. Peripheral resistances of each terminal vessel were adjusted to achieve target flow rates and mean arterial pressure at each gestational age. Vessel growth was governed by wall shear stress (and axial lengthening in uterine vessels), and changes in vessel distensibility were related to vessel growth. Uterine artery velocity waveforms generated from this model closely resembled ultrasound results from the literature. The literature UA-PI values changed significantly across gestation, increasing in the first month of gestation, then dramatically decreasing from 4 to 20 weeks. Our results captured well the time-course of vessel geometry, material properties, and UA-PI. This 1D fluid-G&R model captured the salient hemodynamic features across a broad range of clinical reports and across gestation for uncomplicated human pregnancy. While results capture available data well, this study highlights significant gaps in available data required to better understand vascular remodeling in pregnancy.

Histological response and expression of collagen, metalloproteinases MMP-1 and MMP-9 and tissue inhibitors of metalloproteinases TIMP-1 and TIMP-2 in fetal membranes following open intrauterine surgery: an experimental study

Objective: To characterize aspects of the repair process by evaluating the tissue collagen density, metalloproteinases and tissue inhibitor of matrix metalloproteinases in the fetal membranes following open fetal surgery for myelomeningocele (MMC).Design: Experimental.Setting: Two Brazilian hospitals in 2013-2014.Population: 30 fetal membranes collected after elective cesarean deliveries, in patients who underwent open fetal surgery for MMC intrauterine repair.Methods: Regions within and surrounding the scar area and regions distant from the surgical site were evaluated for collagen concentration and expression of MMP-1, MMP-9, TIMP-1 and TIMP-2.Results: Collagen was increased in regions of scar formation (14.4 ± 2.7%) as compared to unaffected regions (8.0 ± 1.9%) (p < .001). The mean score of MMP-9 in the area of both the scar and suture was also increased above that observed in normal regions (p < .05). Conversely, MMP-1 was reduced in the scar when compared to the normal region and the area adjacent to the scar (suture region) (p < .05). TIMP-1 was increased in the suture region compared to the normal region (p < .05) while TIMP-2 was reduced in the scar region when compared to the other two regions (p < .05). The membrane repair process was also influenced by the number of previous pregnancies and gestational age at the time of surgery.Conclusion: Reparative activity of the fetal membrane after open fetal surgery involves up-regulation of collagen production and differential involvement of MMPs and TIMPs.

Alterations of elastin in female reproductive tissues arising from advancing parity

Female reproductive tissues undergo significant alterations during pregnancy, which may compromise the structural integrity of extracellular matrix proteins. Here, we report on modifications of elastic fibers, which are primarily composed of elastin and believed to provide a scaffold to the reproductive tissues, due to parity and parturition. Elastic fibers from the upper vaginal wall of virgin Sprague Dawley rats were investigated and compared to rats having undergone one, three, or more than five pregnancies. Optical microscopy was used to study fiber level changes. Mass spectrometry, ¹³C and ²H NMR, was applied to study alterations of elastin from the uterine horns. Spectrophotometry was used to measure matrix metalloproteinases-2,9 and tissue inhibitor of metalloproteinase-1 concentration changes in the uterine horns. Elastic fibers were found to exhibit increase in tortuosity and fragmentation with increased pregnancies. Surprisingly, secondary structure, dynamics, and crosslinking of elastin from multiparous cohorts appear similar to healthy mammalian tissues, despite fragmentation observed at the fiber level. In contrast, elastic fibers from virgin and single pregnancy cohorts are less fragmented and comprised of elastin exhibiting structure and dynamics distinguishable from multiparous groups, with reduced crosslinking. These alterations were correlated to matrix metalloproteinases-2,9 and tissue inhibitor of metalloproteinase-1 concentrations. This work indicates that fiber level alterations resulting from pregnancy and/or parturition, such as fragmentation, rather than secondary structure (e.g. elastin crosslinking density), appear to govern scaffolding characteristics in the female reproductive tissues.

Effects of elastase digestion on the murine vaginal wall biaxial mechanical response

Although the underlying mechanisms of pelvic organ prolapse (POP) remain unknown, disruption of elastic fiber metabolism within the vaginal wall extracellular matrix has been highly implicated. It has been hypothesized that elastic fiber fragmentation correlates to decreased structural integrity and increased risk of prolapse; however, the mechanisms by which elastic fiber damage may contribute to prolapse are poorly understood. Further, the role of elastic fibers in normal vaginal wall mechanics has not been fully ascertained. Therefore, the objective of this study is to investigate the contribution of elastic fibers to murine vaginal wall mechanics. Vaginal tissue from C57BL/6 female mice were mechanically tested using biaxial extension-inflation protocols before and after intraluminal exposure to elastase. Elastase digestion induced marked changes in the vaginal geometry, and biaxial mechanical properties, suggesting that elastic fibers may play an important role in vaginal wall mechanical function. Additionally, a constitutive model that considered two diagonal families of collagen fibers with a slight preference towards the circumferential direction described the data reasonably well before and after digestion. The present findings may be important to determine the underlying structural and mechanical mechanisms of POP, and aid in the development of growth and remodeling models for improved assessment and prediction of changes in structure-function relationships with prolapse development. Keywords: vaginal wall, women's health, mechanical testing, pelvic floor disorders, elastic fibers Disclosures: none.

Gestation-Specific Changes in the Anatomy and Physiology of Healthy Pregnant Women: An Extended Repository of Model Parameters for Physiologically Based Pharmacokinetic Modeling in Pregnancy

BACKGROUND

In the past years, several repositories for anatomical and physiological parameters required for physiologically based pharmacokinetic modeling in pregnant women have been published. While providing a good basis, some important aspects can be further detailed. For example, they did not account for the variability associated with parameters or were lacking key parameters necessary for developing more detailed mechanistic pregnancy physiologically based pharmacokinetic models, such as the composition of pregnancy-specific tissues.

OBJECTIVES

The aim of this meta-analysis was to provide an updated and extended database of anatomical and physiological parameters in healthy pregnant women that also accounts for changes in the variability of a parameter throughout gestation and for the composition of pregnancy-specific tissues.

METHODS

A systematic literature search was carried out to collect study data on pregnancy-related changes of anatomical and physiological parameters. For each parameter, a set of mathematical functions was fitted to the data and to the standard deviation observed among the data. The best performing functions were selected based on numerical and visual diagnostics as well as based on physiological plausibility.

RESULTS

The literature search yielded 473 studies, 302 of which met the criteria to be further analyzed and compiled in a database. In total, the database encompassed 7729 data. Although the availability of quantitative data for some parameters remained limited, mathematical functions could be generated for many important parameters. Gaps were filled based on qualitative knowledge and based on physiologically plausible assumptions.

CONCLUSION

The presented results facilitate the integration of pregnancy-dependent changes in anatomy and physiology into mechanistic population physiologically based pharmacokinetic models. Such models can ultimately provide a valuable tool to investigate the pharmacokinetics during pregnancy in silico and support informed decision making regarding optimal dosing regimens in this vulnerable special population.

Pregnancy-Induced Dynamical and Structural Changes of Reproductive Tract Collagen

The tissues and organs of the female reproductive tract and pelvic floor undergo significant remodeling and alterations to allow for fetal growth and birth. In this work, we report on a study of the alterations of murine reproductive tract collagen resulting from pregnancy and parturition by spectrophotometry, histology, and (13)C, (2)H nuclear magnetic resonance (NMR). Four different cohorts of rats were investigated that included virgin, multiparous, two- and fourteen-day postpartum primiparous rats. (13)C CPMAS NMR revealed small chemical shift differences across the cohorts. The measured H-C internuclear correlation times indicated differences in dynamics of some motifs. However, the dynamics of the major amino acids, e.g., Gly, remained unaltered with respect to parity. (2)H NMR relaxation measurements revealed an additional water reservoir in the postpartum and multiparous cohorts pointing to redistribution of water due to pregnancy and/or parturition. Spectrophotometric measurements indicated that the collagen content in virgin rats was highest. Histological analysis of the upper vaginal wall indicated a signature of collagen fiber dissociation with smooth muscle and a change in the density of collagen fibers in multiparous rats.

Dynamic reciprocity between cells and their microenvironment in reproduction

Dynamic reciprocity (DR) refers to the ongoing, bidirectional interaction between cells and their microenvironment, specifically the extracellular matrix (ECM). The continuous remodeling of the ECM exerts mechanical force on cells and modifies biochemical mediators near the cell membrane, thereby initiating cell-signaling cascades that produce changes in gene expression and cell behavior. Cellular changes, in turn, affect the composition and organization of ECM components. These continuous interactions are the fundamental principle behind DR, and its critical role throughout development and adult tissue homeostasis has been extensively investigated. While DR in the mammary gland has been well described, we provide direct evidence that similar dynamic interactions occur in other areas of reproductive biology as well. In order to establish the importance of DR in the adaptive functioning of the female reproductive tract, we present our most current understanding of DR in reproductive tissues, exploring the mammary gland, ovary, and uterus. In addition to explaining normal physiological function, investigating DR may shed new light into pathologic processes that occur in these tissues and provide an exciting opportunity for novel therapeutic intervention.

Regional variation in tissue composition and biomechanical properties of postmenopausal ovine and human vagina

OBJECTIVE

There are increasing numbers of reports describing human vaginal tissue composition in women with and without pelvic organ prolapse with conflicting results. The aim of this study was to compare ovine and human posterior vaginal tissue in terms of histological and biochemical tissue composition and to assess passive biomechanical properties of ovine vagina to further characterise this animal model for pelvic organ prolapse research.

STUDY DESIGN

Vaginal tissue was collected from ovariectomised sheep (n = 6) and from postmenopausal women (n = 7) from the proximal, middle and distal thirds. Tissue histology was analyzed using Masson's Trichrome staining; total collagen was quantified by hydroxyproline assays, collagen III/I+III ratios by delayed reduction SDS PAGE, glycosaminoglycans by dimethylmethylene blue assay, and elastic tissue associated proteins (ETAP) by amino acid analysis. Young's modulus, maximum stress/strain, and permanent strain following cyclic loading were determined in ovine vagina.

RESULTS

Both sheep and human vaginal tissue showed comparable tissue composition. Ovine vaginal tissue showed significantly higher total collagen and glycosaminoglycan values (p<0.05) nearest the cervix. No significant differences were found along the length of the human vagina for collagen, GAG or ETAP content. The proximal region was the stiffest (Young's modulus, p<0.05), strongest (maximum stress, p<0.05) compared to distal region, and most elastic (permanent strain).

CONCLUSION

Sheep tissue composition and mechanical properties showed regional differences along the postmenopausal vaginal wall not apparent in human vagina, although the absolute content of proteins were similar. Knowledge of this baseline variation in the composition and mechanical properties of the vaginal wall will assist future studies using sheep as a model for vaginal surgery.

The association between parity and birthweight in a longitudinal consecutive pregnancy cohort

BACKGROUND

Nulliparity is associated with lower birthweight, but few studies have examined how within-mother changes in risk factors impact this association.

METHODS

We used longitudinal electronic medical record data from a hospital-based cohort of consecutive singleton live births from 2002-2010 in Utah. To reduce bias from unobserved pregnancies, primary analyses were limited to 9484 women who entered nulliparous from 2002-2004, with 23,380 pregnancies up to parity 3. Unrestricted secondary analyses used 101,225 pregnancies from 45,212 women with pregnancies up to parity 7. We calculated gestational age and sex-specific birthweight z-scores with nulliparas as the reference. Using linear mixed models, we estimated birthweight z-score by parity adjusting for pregnancy-specific sociodemographics, smoking, alcohol, prepregnancy body mass index, gestational weight gain, and medical conditions.

RESULTS

Compared with nulliparas', infants of primiparas were larger by 0.20 unadjusted z-score units [95% confidence interval (CI) 0.18, 0.22]; the adjusted increase was similar at 0.18 z-score units [95% CI 0.15, 0.20]. Birthweight continued to increase up to parity 3, but with a smaller difference (parity 3 vs. 0 β = 0.27 [95% CI 0.20, 0.34]). In the unrestricted secondary sample, there was significant departure in linearity from parity 1 to 7 (P < 0.001); birthweight increased only up to parity 4 (parity 4 vs. 0 β = 0.34 [95% CI 0.31, 0.37]).

CONCLUSIONS

The association between parity and birthweight was non-linear with the greatest increase observed between first- and second-born infants of the same mother. Adjustment for changes in weight or chronic diseases did not change the relationship between parity and birthweight.

The role of mode of delivery on elastic fiber architecture and vaginal vault elasticity: a rodent model study

We report on an experimental study of the role of mode of delivery and pregnancy on the architecture of vaginal elastic fibers and vaginal vault elasticity in female Sprague-Dawley rats. In primiparous rats submitted to spontaneous or Cesarean delivery and virgin rats submitted to simulated delivery, the tortuosity of elastic fibers (defined as the ratio of length to end-to-end distance) was observed to decrease when measured from two days to two weeks postpartum. In addition, the measured tortuosity of elastic fibers in multiparous rats was greater than that of virgin rats. The tortuosity of elastic fibers of all rats measured at two days postpartum was found to be similar to that of multiparous rats. At two weeks postpartum the measured tortuosity of vaginal elastic fibers was indistinguishable from virgin rats, regardless of the delivery method. Borrowing from the field of polymer physics, a model is suggested that connects elastic fiber tortuosity to the resulting tension under an applied stress; fibers having high tortuosity are expected to provide less structural support than more linear, low tortuosity fibers. To probe the macroscopic effects in elasticity due to architectural changes observed in elastic fibers, we have measured the stiffness of the vaginal vault in each cohort using a pressure-infusion system. The vaginal vault stiffness of all primiparous rats measured two weeks postpartum was greater than that measured two days postpartum. In addition, the vaginal vault of virgin rats was stiffer than that of multiparous rats. These observations confirmed that vaginal vault elastic fibers undergo significant remodeling due to pregnancy and parturition, and that the complex remodeling may be a significant contributor to tissue elasticity. Remarkably, regardless of the mode of delivery or simulated tissue trauma, elastic fiber tortuosity is observed to decrease from two days to two weeks postpartum indicating the onset of repair and recovery of tissue stiffness.

Stereology of human myometrium in pregnancy: influence of maternal body mass index and age

OBJECTIVE

Knowledge of the stereology of human myometrium in pregnancy is limited. Uterine contractile performance may be altered in association with maternal obesity and advanced maternal age. The aim of this study was to investigate the stereology of human myometrium in pregnancy, and to evaluate a potential influence of maternal body mass index (BMI) and age.

STUDY DESIGN

Biopsies of human myometrium were obtained from 57 women at cesarean section (n = 26, n = 13, n = 18 normal, overweight and obese BMI, respectively), and volume fractions of smooth muscle and extracellular matrix were assessed using stereologic techniques.

RESULTS

The smooth muscle constituted 65.2% ± 8.9% (standard deviation) and the extracellular matrix 32.6% ± 7.7% (standard deviation) (n = 57). There was no correlation observed between maternal BMI, age, or parity with the fractional volumes of either smooth muscle or extracellular matrix.

CONCLUSION

These results outline the stereology of human myometrium in pregnancy. Putative functional differences in contractility, pertaining to obese or older mothers, are not related to smooth muscle content.

Elastic fiber assembly in the adult mouse pubic symphysis during pregnancy and postpartum

Impairment of pelvic organ support has been described in mice with genetic modifications of the proteins involved in elastogenesis, such as lysyl oxidase-like 1 (LOXL1) and fibulin 5. During pregnancy, elastic fiber-enriched pelvic tissues are modified to allow safe delivery. In addition, the mouse pubic symphysis is remodeled in a hormone-controlled process that entails the modification of the fibrocartilage into an interpubic ligament (IpL) and the relaxation of this ligament. After first parturition, recovery occurs to ensure pelvic tissue homeostasis. Because ligaments are the main supports of the pelvic organs, this study aimed to evaluate elastogenesis in the IpL during mouse pregnancy and postpartum. Accordingly, virgin, pregnant, and postpartum C57BL/6 mice were studied using light, confocal, and transmission electron microscopy as well as Western blots and real-time PCR. Female mice exhibited the separation of the pubic bones and the formation, relaxation, and postpartum recovery of the IpL. By the time the IpL was formed, the elastic fibers had increased in profile length and diameter, and they consisted of small conglomerates of amorphous material distributed among the bundles of microfibrils. Our analyses also indicated that elastin/tropoelastin, fibrillin 1, LOXL1/Loxl1, and fibulin 5 were spatially and temporally regulated, suggesting that these molecules may contribute to the synthesis of new elastic fibers during IpL development. Overall, this work revealed that adult elastogenesis may be important to assure the elasticity of the pelvic girdle during preparation for parturition and postpartum recovery. This finding may contribute to our understanding of pathological processes involving elastogenesis in the reproductive tract.

Structural disorder and protein elasticity

An emerging class of disordered proteins underlies the elasticity of many biological tissues. Elastomeric proteins are essential to the function of biological machinery as diverse as the human arterial wall, the capture spiral of spider webs and the jumping mechanism of fleas. In this chapter, we review what is known about the molecular basis and the functional role of structural disorder in protein elasticity. In general, the elastic recoil of proteins is due to a combination of internal energy and entropy. In rubber-like elastomeric proteins, the dominant driving force is the increased entropy of the relaxed state relative to the stretched state. Aggregates of these proteins are intrinsically disordered or fuzzy, with high polypeptide chain entropy. We focus our discussion on the sequence, structure and function of five rubber-like elastomeric proteins, elastin, resilin, spider silk, abductin and ColP. Although we group these disordered elastomers together into one class of proteins, they exhibit a broad range of sequence motifs, mechanical properties and biological functions. Understanding how sequence modulates both disorder and elasticity will help advance the rational design of elastic biomaterials such as artificial skin and vascular grafts.

Alteration of vaginal elastin metabolism in women with pelvic organ prolapse

OBJECTIVE

To compare elastin metabolism in the vagina of women with and without pelvic organ prolapse and to define the regulation of this process by hormone therapy (HT).

METHODS

Eighty-seven histologically confirmed full-thickness vaginal biopsies were procured from study participants at time of surgery. Premenopausal women with no prolapse served as controls. Women with prolapse were divided into three groups: premenopausal, postmenopausal not on HT, and postmenopausal on HT. The epithelium was excised leaving the subepithelium, muscularis, and adventitia for analyses. The elastin precursor, tropoelastin, was measured by immunoblotting and mature elastin protein via a desmosine cross-link radioimmunoassay. Matrix metalloproteinases (MMPs)-2 and -9 were quantitated by gelatin zymography. Data were analyzed using Kruskal-Wallis test and post hoc analysis using the Mann-Whitney U test.

RESULTS

Tropoelastin (432%), mature elastin (55%), proMMP-9 (90%), and active MMP-9 (106%) were increased in women with prolapse relative to those in the control group while active MMP-2 (41%) was decreased. Comparison of tropoelastin and mature elastin values obtained from the same women showed them to be independently regulated (r=0.19). Interestingly, the highest amount of both proteins occurred in postmenopausal patients not on HT.

CONCLUSION

Elastin metabolism is altered in the vagina of women with prolapse relative to those in the control group, suggesting that vaginal tissue is rapidly remodeling in response to mechanical stretch. We found that elastin levels are highest in the absence of hormones.

A weak link in metabolism: the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis

In a previous paper, we pointed out that the capability to synthesize glycine from serine is constrained by the stoichiometry of the glycine hydroxymethyltransferase reaction, which limits the amount of glycine produced to be no more than equimolar with the amount of C 1 units produced. This constraint predicts a shortage of available glycine if there are no adequate compensating processes. Here, we test this prediction by comparing all reported fl uxes for the production and consumption of glycine in a human adult. Detailed assessment of all possible sources of glycine shows that synthesis from serine accounts for more than 85% of the total, and that the amount of glycine available from synthesis, about 3 g/day, together with that available from the diet, in the range 1.5-3.0 g/day, may fall significantly short of the amount needed for all metabolic uses, including collagen synthesis by about 10 g per day for a 70 kg human. This result supports earlier suggestions in the literature that glycine is a semi-essential amino acid and that it should be taken as a nutritional supplement to guarantee a healthy metabolism.

Changes in expression of fibulin-5 and lysyl oxidase-like 1 associated with pelvic organ prolapse

OBJECTIVES

Pelvic organ prolapse is associated with defects in connective tissue including elastic fibers. The purpose of this study was to investigate expression of fibulin-5 and lysyl oxidase-like 1, which play an essential role in synthesis and assembly of elastic fibers in the uterosacral ligament, in samples taken from women with advanced pelvic organ prolapse compared with controls.

STUDY DESIGN

Specimens were obtained prospectively during abdominal hysterectomy from 30 women with advanced pelvic organ prolapse and 30 controls matched to the study group for age and parity among postmenopausal women with benign gynecologic pathology. Expression levels of protein and mRNA of fibulin-5 and lysyl oxidase-like 1 in uterosacral ligaments were measured by Western blot analysis and real-time quantitative polymerase chain reactions. For statistical analyses, Student's t-test, chi-square test, Mann-Whitney U test, Fisher's exact test and Spearman's correlation were used.

RESULTS

Significant decrease in the expression of mRNA of fibulin-5 was found in patients with prolapse (P-value=0.042; 0.743+/-0.229 and 1.061+/-0.537). The expression of mRNA of lysyl oxidase-like 1 was increased in the patient group (P-value=0.017; 4.099+/-2.832 and 1.816+/-1.602). Similar results were shown in Western blot analysis. Differences in expression of fibulin-5 and lysyl oxidase-like 1 were noted according to stage of prolapse (P-value=0.037 and 0.009).

CONCLUSIONS

There was decreased expression of fibulin-5 and increased expression of lysyl oxidase-like 1 in uterosacral ligaments in patients with pelvic organ prolapse, which suggests the possibility of defects in elastin synthesis.

Cervical ripening and insufficiency: from biochemical and molecular studies to in vivo clinical examination

To understand cervical ripening and especially the pathophysiology of cervical insufficiency, it is important to know the cervical composition: the cervix is dominated by fibrous connective tissue, consisting predominantly of Type I collagen (70%). Despite many studies of the cervix, we still rely upon relatively crude methods for clinical evaluation of the cervix. If the amount of cervical collagen plays a role in cervical insufficiency and in success of or length of induction of labor, then measurements of cervical collagen may provide an objective means of establishing the diagnosis or prognosis. We have established and reported a non-invasive means, called Collascope, to measure collagen cross-linking using light-induced fluorescence (LIF), and which is specifically designed to assess cervical ripening, and functions by measuring the natural fluorescence of non-soluble collagen in the cervix. Studies conducted in animals and humans in a variety of settings indicate that cervical function can be successfully monitored using the Collascope during pregnancy: LIF correlates negatively with gestational age and positively with time-to-delivery interval, and is predictive of delivery within 24h. Additionally LIF is significantly lower in women with cervical insufficiency. We suggest that the Collascope might be useful to better define management in cases of spontaneous preterm or induced term cervical ripening. From our studies and others, it is clear that in forecasting (pre-)term cervical ripening, the capability of the technologies and bioassays that have been generally accepted into clinical practice are limited. Any devices shown to be superior to the clinically accepted tests currently used should be quite useful for clinicians. The Collascope offers an objective measurement of both the function and state of the cervix, by directly measuring collagen cross-linking using LIF.

Proteinases in connective tissue breakdown

Lysosomal cathepsins B and N complete the depolymerization of native fibrillar collagen in the phagolysosome after prior extracellular fragmentation by collagenase and other neutral proteinases. In vitro studies have confirmed that cathepsins B and N cleave native collagen only at the short non-helical telopeptides, which generate the intermolecular cross-links. This action occurs maximally at pH 3.5 and at 37 degrees C the released monomers denature spontaneously and are susceptible to further breakdown. In the phagolysosome the collagenous debris is already weakened and probably therefore, more easily disrupted by these cathepsins. Complete digestion would then be undertaken by the whole complement of proteases. The lysosomal glycosidases may assist this breakdown by degrading ground substance components which are normally tightly bound to collagen. In certain situations cells may instead generate an acidic pericellular environment that could permit the direct action of secreted lysosomal enzymes. This extracellular action may supersede the action of collagenase and the activity of these different enzymes would thus be regulated by changes in the nature of this microenvironment.

Failure of elastic fiber homeostasis leads to pelvic floor disorders

Pelvic floor disorders, a group of conditions affecting adult women, include pelvic organ prolapse and urinary incontinence. Vaginal childbirth and aging are risk factors, and weakening of the pelvic support structures is a major aspect of the pathology. However, the underlying molecular mechanism remains unknown. Female reproductive organs are rich in elastic fibers that turn over slowly in most adult tissues but undergo massive remodeling in the reproductive organs through pregnancy and birth. Here we show that a failure to maintain elastic fiber homeostasis in mice causes pelvic floor disorders. Lysyl oxidase-like-1 (LOXL1), a protein essential for the postnatal deposition of elastic fibers, was highly expressed and regulated in the reproductive tract of the mouse, and its expression was diminished during aging. LOXL1 deficiency caused an inability of reproductive tissues to replenish elastic fibers after parturition, leading to pelvic organ prolapse, weakening of the vaginal wall, paraurethral pathology, and lower urinary tract dysfunction. These data demonstrate the importance of elastic fibers for maintaining structural and functional integrity of the female pelvic floor. Our findings raise the possibility that a failure of elastic fiber homeostasis, either due to genetic predisposition or advancing age, could underlie the etiology of pelvic floor dysfunction in women.

Urinary excretion of collagen degradation markers by sows during postpartum uterine involution

Incomplete uterine involution is the putative cause of the increased embryo mortality and reproductive failure often exhibited by sows that lactate for less than 21 days. Since such short lactation lengths are common in American swine production, an effective technique to monitor the postpartum involution process and test this hypothesis might be valuable. Rapid and extensive catabolism of uterine collagen is essential for normal postpartum involution. The objective of this study was to characterize postpartum excretion of two biochemical markers of collagen degradation. In experiment I, urine samples were collected from five sows every other day from the day before parturition (day -1), through a 21-day lactation, to day 8 postweaning. The collagen crosslinks hydroxylysyl pyridinoline (HP), which is present in many tissues, and lysyl pyridinoline (LP), which is primarily concentrated in bone, were assayed by both ELISA and HPLC. Urinary levels of both free (ELISA) and total (HPLC) HP and LP increased (P < 0.001) approximately two-fold during lactation. The mean molar ratio of total HP:LP increased (P < 0.001) from 6.6 +/- 1.6 at day 1 to a maximum of 10.2 +/- 1.5 at day 7 postpartum and averaged 9.1 +/- 0.3 for the entire sampling period. These data are consistent with a postpartum increase of soft tissue collagen catabolism since bone has a low HP:LP ratio of 4 and soft tissues like the uterus have a high HP:LP ratio of >/=20 because they contain only trace amounts of LP. Since HPLC (total) and ELISA (free) crosslinks estimates were highly correlated (r = 0.85-0.91, P < 0.001) in experiment I, only the less technical ELISA technique was used in experiment II. Urine samples were collected from 21 sows every third day from day 1 to 19 of lactation. Sows from this second group exhibited one of four distinct crosslinks excretion patterns: peak on day 1 (n = 3), peak on day 7 (n = 4), peak on day 10, 13 or 16 (n = 7), or no peak (n = 7). This variation of postpartum crosslinks excretion among sows was not related to parity, body weight, lactation body weight change, litter size, or litter birth weight. Overall, data from experiments I and II indicate that urinary HP does increase postpartum in a pattern temporally consistent with uterine involution. However, significant variation among sows in the magnitude and timing of peak HP excretion was evident.

Histochemical and ultrastructural study of collagen fibers in mouse pubic symphysis during late pregnancy

Reference is usually made to the parallel orientation towards the main line of exerted tension at the pubic joint in mice, for supporting forces applied to the joint. Despite the wealth of morphological information about the extracellular matrix in this joint, little is known regarding the involvement of the crimp of collagen fibers in the dramatic transformations occurring in this region during the last 3 days of pregnancy. Examination of the collagenous architecture suggests that the biomechanical properties are directly related to fibril diameters, composition of ground substance and changes in the bundle morphology, particularly in the crimp structure. The purpose of this study was to further describe the transformation of the collagen fibers of the pubic symphysis during late mouse pregnancy. We examined the architecture of collagen fibers in the symphysis and pubic ligament through the Picrosirius-polarization method and also through scanning electron microscopy to directly visualize and measure the crimping from pregnant and virgin mice. The crimp angle and the length of five consecutive crimps were measured according to Patterson-Kane et al. [Connect. Tissue Res. 36 (1997) 253]. It could be demonstrated that the angles progressively decreased and the crimp length increased, denoting that the fibers have untwisted during the relaxation process. Our findings suggest that a disruption of the helical arrangement of the collagen containing fibers may contribute to explaining the rapid remodeling that occurs at the end of pregnancy and that is responsible for an increase in pliancy and length of the pubic ligament in mice.

How to measure the increase in elastic system fibres in the lamina propria of the uterine cervix of pregnant rats

As the uterus enlarges to accommodate the growing fetus during pregnancy, the cervix behaves essentially as a barrier. During ripening and delivery, it needs to become soft and distensible to allow dilation and the passage of the conceptus. As the transformations of the collagen-containing fibres are known to be essential for ripening and delivery, it has been hypothesized that the elastic system fibres, owing to their intrinsic mechanical properties (reversible extensibility), could be involved in the shape-recovering process immediately after delivery. In sections stained by Weigert's resorcin-fuchsin (with previous oxidation), we describe the elastic system fibres in the lamina propria of the rat uterine cervix. They are distributed following different patterns when in the endocervix or in the ectocervical-vaginal region. A third distinctive pattern (named the 'elastic tendon') is described here for the first time in the uterine-cervical transition. A special morphometrical protocol has been designed in order to overcome problems during the quantification process. Using the so-called intercept counting method, it was possible to demonstrate that the elastic system fibres are increased in the cervix at the end of pregnancy. They may be involved in the immediate shape-recovering of the cervix after delivery as well as in helping to strengthen the anchoring of the epithelium to the lamina propria, thus minimizing birth trauma.

Increased Expression of Matrix Metalloproteinases in the Uterine Cervix of Postmenopausal Women

OBJECTIVE.: To determine whether atrophy of the uterine cervix in menopausal women is associated with an increased expression of matrix metalloproteinases (MMP), a decrease in their counter regulatory proteins (tissue inhibitors of matrix metalloproteinase [TIMP]), and a decrease in type I collagen. MATERIALS AND METHODS.: A pilot study was performed on cervical stroma harvested from 10 premenopausal and 9 postmenopausal women undergoing a hysterectomy. The amount of pro-MMP-2 and pro-MMP-9 in protein extracts from the two groups was compared by gelatin zymography. The membrane-type (MT)1-MMP, TIMP-1, and TIMP-2 were quantitated by Western immunoblotting. Total collagen was estimated by measuring hydroxyproline content. A primary fibroblast culture was developed to study estrogen regulation of MMP expression in vitro. RESULTS.: Pro-MMP-2 and pro-MMP-9 were increased in postmenopausal extracts. No difference in the amount of MT1-MMP, TIMP-1, TIMP-2, or total collagen was detected. In primary cervical fibroblast cultures, only active MMP-2 was suppressed by estrogen. CONCLUSIONS.: The protein expression of pro-MMP-2 and pro-MMP-9 is increased in cervical stroma of postmenopausal women relative to premenopausal women.

Basic anatomical and physiological data for use in radiological protection: reference values. A report of age- and gender-related differences in the anatomical and physiological characteristics of reference individuals. ICRP Publication 89

This report presents detailed information on age- and gender-related differences in the anatomical and physiological characteristics of reference individuals. These reference values provide needed input to prospective dosimetry calculations for radiation protection purposes for both workers and members of the general public. The purpose of this report is to consolidate and unify in one publication, important new information on reference anatomical and physiological values that has become available since Publication 23 was published by the ICRP in 1975. There are two aspects of this work. The first is to revise and extend the information in Publication 23 as appropriate. The second is to provide additional information on individual variation among grossly normal individuals resulting from differences in age, gender, race, or other factors. This publication collects, unifies, and expands the updated ICRP reference values for the purpose of providing a comprehensive and consistent set of age- and gender-specific reference values for anatomical and physiological features of the human body pertinent to radiation dosimetry. The reference values given in this report are based on: (a) anatomical and physiological information not published before by the ICRP; (b) recent ICRP publications containing reference value information; and (c) information in Publication 23 that is still considered valid and appropriate for radiation protection purposes. Moving from the past emphasis on 'Reference Man', the new report presents a series of reference values for both male and female subjects of six different ages: newborn, 1 year, 5 years, 10 years, 15 years, and adult. In selecting reference values, the Commission has used data on Western Europeans and North Americans because these populations have been well studied with respect to antomy, body composition, and physiology. When appropriate, comparisons are made between the chosen reference values and data from several Asian populations. The first section of the report provides summary tables of all the anatomical and physiological parameters given as reference values in this publication. These results give a comprehensive view of reference values for an individual as influenced by age and gender. The second section describes characteristics of dosimetric importance for the embryo and fetus. Information is provided on the development of the total body and the timing of appearance and development of the various organ systems. Reference values are provided on the mass of the total body and selected organs and tissues, as well as a number of physiological parameters. The third section deals with reference values of important anatomical and physiological characteristics of reference individuals from birth to adulthood. This section begins with details on the growth and composition of the total body in males and females. It then describes and quantifies anatomical and physiological characteristics of various organ systems and changes in these characteristics during growth, maturity, and pregnancy. Reference values are specified for characteristics of dosimetric importance. The final section gives a brief summary of the elemental composition of individuals. Focusing on the elements of dosimetric importance, information is presented on the body content of 13 elements: calcium, carbon, chloride, hydrogen, iodine, iron, magnesium, nitrogen, oxygen, potassium, sodium, sulphur, and phosphorus.

Methods and devices for the management of term and preterm labor

In this review, we outline studies showing that the uterus (myometrium) and cervix pass through a conditioning step in preparation for labor. This step is not easily identifiable with present methods designed to assess the uterus or cervix. In the uterus, this seemingly irreversible step consists of changes in the electrical properties that make muscle more excitable and responsive and produce forceful contractions. In the cervix, the step consists of softening of the connective tissue components. Progesterone and nitric oxide appear to have important roles in these processes. The progress of labor can be assessed noninvasively using electromyographic (EMG) signals from the uterus (the driving force for contractility) recorded from the abdominal surface. Uterine EMG bursts detected in this manner characterize uterine contractile events during human and animal pregnancy. A low uterine EMG activity, measured transabdominally throughout most of pregnancy, rises dramatically during labor. EMG activity also increases substantially during preterm labor in humans and rats and may be predictive of preterm labor. A quantitative method for assessing the cervix is also described. A collascope estimates cervical collagen content from a fluorescent signal generated when collagen crosslinks are illuminated with an excitation light of about 340 nm. The system has proved useful in rats and humans at various stages of pregnancy and indicates that cervical softening occurs progressively in the last one-third of pregnancy. In rats, collascope readings correlate with resistance measurements made in the isolated cervix, which may help to assess cervical function during pregnancy and indicate controls and treatments.

Clinical associations with objective menstrual blood volume

OBJECTIVE

To determine the association between simple clinical parameters and objective menstrual blood volume.

STUDY DESIGN

A cohort study, in a London teaching hospital. Women complaining of menorrhagia (207) and those who considered their menstruation to be normal (47) were studied. Those with no demonstrable gynaecological pathology had their menstrual blood loss measured using the alkaline haematin technique.

RESULTS

Only 49% of 207 women complaining of menorrhagia had a loss of 80 ml or more. There was an increasing incidence of objective menorrhagia with increasing duration of bleeding and use of more sanitary protection items. Increasing height, age and number of intrauterine pregnancies were all associated with increasing menstrual blood volume. Haemoglobin fell with increasing menstrual blood loss.

CONCLUSIONS

Despite these clinical associations it is difficult to establish the quantity of menstrual bleeding with certainty without an objective assessment.

Regulation of uterine collagenase gene expression: interactions between serotonin and progesterone

This report seeks to further define the requirements for the previously established induction of collagenase gene expression by serotonin and inhibition by progesterone in primary cultures of rat uterine smooth muscle cells. Detectable increases in collagenase production were observed after as little as 3 h exposure of cells to 5 microM serotonin, with maximal induction occurring after approximately 8 h of exposure. The apparent half-life of collagenase mRNA upon removal of serotonin was estimated to be approximately 12 h, and was not dependent on the duration of induction. Inhibition by either cycloheximide or progesterone showed similar half lives for collagenase mRNA, however a much shorter half-life (6 h) was obtained in the presence of actinomycin D. These experiments suggest that neither serotonin induction nor progesterone inhibition of collagenase synthesis represents a primary effect on collagenase gene transcription. Rather they appear to be secondary to changes that occur at one or more primary intermediate genes whose induction or decay must occur prior to changes in collagenase transcription. The progesterone receptor antagonist, RU-486, abrogates the ability of progesterone to inhibit serotonin-induced collagenase gene expression, indicating that the effects of progestins in this system likely are receptor-mediated. Finally, the present studies demonstrate that pretreatment of cells for times as long as 5 days with medroxyprogesterone in the absence of serotonin is unable to prevent subsequent serotonin-induced collagenase mRNA increases. These data suggest the possibility of a unique interaction between the molecular pathways of inducer and inhibitor, one in which serotonin may help mediate the progesterone-dependent repression of the levels of collagenase mRNA.

Tissue collagenase: serum levels during pregnancy and parturition

Serum levels of tissue collagenase, matrix metalloproteinase-1, were measured in both longitudinal and cross-sectional studies, in 332 pregnant women and 27 non-pregnant volunteers. The enzyme-linked immunosorbent assay (ELISA) used is the first described to measure collagenase in serum directly, is specific, and is rapid and reproducible. Levels were determined throughout pregnancy, during term and preterm labour, and in the post-partum period. Serum tissue collagenase levels were elevated in pregnancy (P < 0.001). There was no difference between levels of serum collagenase prior to labour at term and those observed during labour. Similarly, there was no significant difference in levels obtained during preterm labour and those at a similar gestation in women who subsequently delivered at term. No significant decrease in levels had occurred by the 4th post-partum day. In view of these findings of unaltered matrix metalloproteinase-1 levels in association with labour, previous reports of raised serum collagenase activity in association with the onset of spontaneous labour, at term and preterm gestation periods, may be due to increased neutrophil collagenase activity.

Three-dimensional structures of uterine elastic fibers: scanning electron microscopic studies

We report findings that demonstrate for the first time that the structure of the elastic fibers of the uterus and cervix are characteristic to these tissues. Elastic fibers of the uterine corpus and cervix were studied by scanning electron microscopy (SEM). Elastic tissues were prepared from non-pregnant human uteri and pregnant rat uteri by three different methods: extraction from the tissue homogenates, in situ digestion by autoclaving of sliced tissue, and in situ formic acid digestion of sliced tissue. In addition, in situ formic acid digestion of the glutaraldehyde-fixed uterine wall of pregnant rats was done. Under SEM, the uterine elastic fibers revealed two distinct structures--fibrils and thin sheets of elastic membranes. Isolated fibers and membranes ranged in thickness from 0.1 to 0.4 micron which is thinner than aortic elastic lamellae (1-2.5 microns in thickness). These thin sheets of elastic membranes and elastic fibrils probably allow the uterus to maintain its elasticity without exerting excess pressure on the growing fetus. Formic acid digestion of fixed uterine walls of pregnant rats preserved the structural organization of elastic tissues near in vivo conditions. In these tissues, the fibers were arranged in a honeycomb structure made up largely of membranes, although sparse fibrils were present. These elastic, membranous sheets were arranged parallel to the plane of the uterine surface and interconnected with the threads of the membranes or fibrils. In the rat uterine wall, at least 12 parallel layers of elastic sheets were present. In contrast, at low magnification, the elastic tissues in the non-pregnant human uterus had no specific architectural arrangement and exhibited a sponge-like structure. Elastic fibers of the cervix were also made up of membranes and fibrils, and these fibers were organized into fishnet-like structures. These cervical membranes had fenestrations and pits with a diameter of 3-5 microns. In these studies, the concentrations of insoluble elastin in human uteri were found to be 1.38 and 1.32-1.41% of dry-defatted tissues for uterine body and cervix, respectively. The concentrations of total collagen were 38.8 and 64.3-72.4% of dry-defatted tissues for uterine body and cervix, respectively.