Gap junctions: their presence and necessity in myometrium during parturition

PGE2 functions in ovoviviparous teleost black rockfish (Sebastes schlegelii): evolutionary status between parturition and ovulation†

Fish have evolved various reproductive strategies including oviparity, viviparity, and ovoviviparity, which undoubtedly affect the survival of the whole species continuity. As the final step in reproduction, parturition in viviparous vertebrate and ovulation in oviparous teleost seem to share a similar mechanism, when prostaglandins (PGs) act as the trigger to launch the whole process. In the present study, ovoviviparous teleost black rockfish (Sebastes schlegelii) is employed as the research object. Intraperitoneal injection showed that PGE2 (500 μg/kg) could activate the delivery reactions in perinatal black rockfish. RNA-seq data of ovary in perinatal period revealed transcriptional change in cell junction, inflammation, and apoptosis, which is related to mammal parturition and teleost ovulation. Further results proved the positive correlation between ptger EP2 and previous mentioned pathways. Subsequent experiment proved that PGE2 was able to induce the ovulation and spawning in unfertilized individuals, which had a bilayer follicular structure compared to monolayer follicular in perinatal period black rockfish. Both unfertilized and perinatal ovary matrix could response to PGE2 stimulation. In conclusion, the function of PGE2 in activating both parturition and ovulation in a relatively different pathways conserved with viviparity or oviparity provided novel evidence of the evolutionary status of ovoviviparous vertebrates.

Pathophysiological Implications of Interstitial Cajal-like Cells (ICC-like) in Uterus: A Comparative Study with Gastrointestinal ICCs

The main function of interstitial cells of Cajal (ICCs) is to regulate gastrointestinal peristalsis by acting as a "pacemaker" cell by generating spontaneous slow electrical waves. In 2005, electron microscopy revealed a cell type similar to ICCs (ICC-like) outside the gastrointestinal tract, with contractile activity and c-Kit+ immunohistochemistry shared with ICCs. Among the locations where ICC-like cells have been observed, it is in the uterus where they have a significant functional and pathophysiological role. These cells are involved in obstetric phenomena of contractile action, such as ascending sperm transport, embryo implantation, pregnancy, delivery, and the expulsion of menstrual debris. Within the pathophysiology related to these cells, we find obstetric alterations such as recurrent miscarriages, premature deliveries, abolition of uterine contractions, and failures of embryo implantation, in addition to other common conditions in the fertile age, such as endometriosis and leiomyoma.

The In Vitro Contractile Response of Canine Pregnant Myometrium to Oxytocin and Denaverine Hydrochloride

In pregnant bitches, the response to oxytocin and denaverine hydrochloride in dystocia management is usually poor. To better understand the effect of both drugs on myometrial contractility, the circular and longitudinal muscle layers were examined in an organ bath. For each layer, three myometrial strips were stimulated twice, each with one of three oxytocin concentrations. The effect of denaverine hydrochloride was studied once in direct combination with oxytocin and alone with subsequent oxytocin administration. Contractions were recorded and evaluated for average amplitude, mean force, area under the curve (AUC), and frequency. Effects of different treatments were analyzed and compared within and between layers. In the circular layer, oxytocin significantly increased amplitude and mean force compared to untreated controls regardless of stimulation cycles or concentrations. In both layers, high oxytocin concentrations caused tonic contractions, while the lowest concentration created regular rhythmic contractions. Longitudinal layer tissue responded to oxytocin with a significantly decreased contractility when stimulated twice, presumably a sign of desensitization. Denaverine hydrochloride neither affected oxytocin induced contractions nor showed a priming effect to subsequent oxytocin. Thus, no benefit of denaverine hydrochloride on myometrial contractility was found in the organ bath. Our results suggest a better efficiency of low-dose oxytocin in canine dystocia management.

Monitoring uterine contractions during labor: current challenges and future directions

Organ-level models are used to describe how cellular and tissue-level contractions coalesce into clinically observable uterine contractions. More importantly, these models provide a framework for evaluating the many different contraction patterns observed in laboring patients, ideally offering insight into the pitfalls of currently available recording modalities and suggesting new directions for improving recording and interpretation of uterine contractions. Early models proposed wave-like propagation of bioelectrical activity as the sole mechanism for recruiting the myometrium to participate in the contraction and increase contraction strength. However, as these models were tested, the results consistently revealed that sequentially propagating waves do not travel long distances and do not encompass the gravid uterus. To resolve this discrepancy, a model using 2 mechanisms, or a "dual model," for organ-level signaling has been proposed. In the dual model, the myometrium is recruited by action potentials that propagate wave-like as far as 10 cm. At longer distances, the myometrium is recruited by a mechanotransduction mechanism that is triggered by rising intrauterine pressure. In this review, we present the influential models of uterine function, highlighting their main features and inconsistencies, and detail the role of intrauterine pressure in signaling and cervical dilation. Clinical correlations demonstrate the application of organ-level models. The potential to improve the recording and clinical interpretation of uterine contractions when evaluating labor is discussed, with emphasis on uterine electromyography. Finally, 7 questions are posed to help guide future investigations on organ-level signaling mechanisms.

Inflammatory Amplification: A Central Tenet of Uterine Transition for Labor

In preparation for delivery, the uterus transitions from actively maintaining quiescence during pregnancy to an active parturient state. This transition occurs as a result of the accumulation of pro-inflammatory signals which are amplified by positive feedback interactions involving paracrine and autocrine signaling at the level of each intrauterine cell and tissue. The amplification events occur in parallel until they reach a certain threshold, ‘tipping the scale’ and contributing to processes of uterine activation and functional progesterone withdrawal. The described signaling interactions all occur upstream from the presentation of clinical labor symptoms. In this review, we will: 1) describe the different physiological processes involved in uterine transition for each intrauterine tissue; 2) compare and contrast the current models of labor initiation; 3) introduce innovative models for measuring paracrine inflammatory interactions; and 4) discuss the therapeutic value in identifying and targeting key players in this crucial event for preterm birth.

Molecular signatures of labor and nonlabor myometrium with parsimonious classification from 2 calcium transporter genes

Clinical phenotyping of term and preterm labor is imprecise, and disagreement persists on categorization relative to underlying pathobiology, which remains poorly understood. We performed RNA sequencing (RNA-seq) of 31 specimens of human uterine myometrium from 10 term and 21 preterm cesarean deliveries with rich clinical context information. A molecular signature of 4814 transcripts stratified myometrial samples into quiescent (Q) and nonquiescent (NQ) phenotypes, independent of gestational age and incision site. Similar stratifications were achieved using expressed genes in Ca²⁺ signaling and TGF-β pathways. For maximal parsimony, we evaluated the expression of just 2 Ca²⁺ transporter genes, ATP2B4 (encoding PMCA4) and ATP2A2 (coding for SERCA2), and we found that their ratio reliably distinguished NQ and Q specimens in the current study, and also in 2 publicly available RNA-seq data sets (GSE50599 and GSE80172), with an overall AUC of 0.94. Cross-validation of the ATP2B4/ATP2A2 ratio by quantitative PCR in an expanded cohort (by 11 additional specimens) achieved complete separation (AUC of 1.00) of NQ versus Q specimens. While providing additional insight into the associations between clinical features of term and preterm labor and myometrial gene expression, our study also offers a practical algorithm for unbiased classification of myometrial biopsies by their overall contractile program.

Uterine contractions in rodent models and humans

Aberrant uterine contractions can lead to preterm birth and other labour complications and are a significant cause of maternal morbidity and mortality. To investigate the mechanisms underlying dysfunctional uterine contractions, researchers have used experimentally tractable small animal models. However, biological differences between humans and rodents change how researchers select their animal model and interpret their results. Here, we provide a general review of studies of uterine excitation and contractions in mice, rats, guinea pigs, and humans, in an effort to introduce new researchers to the field and help in the design and interpretation of experiments in rodent models.

Anoctamin 1 antagonism potentiates conventional tocolytic-mediated relaxation of pregnant human uterine smooth muscle

BACKGROUND

Currently available tocolytic agents are not effective treatment for preterm labor beyond 48 h. A major reason is the development of maternal side effects which preclude the maintenance of an effective steady-state drug concentration. One strategy that can mitigate these side effects is utilizing synergistic drug combinations to reduce the drug concentrations necessary to elicit a clinical effect. We have previously shown that three anoctamin 1 (ANO1) antagonists mediate potent relaxation of precontracted human uterine smooth muscle (USM). In this study, we aimed to determine whether a combination of sub-relaxatory doses of tocolytic drugs in current clinical use [the L-type voltage-gated calcium channel (VGCC) blocker, nifedipine (NIF); and the β2-adrenergic (β2AR) agonist, terbutaline (TRB)] will potentiate USM relaxation with two ANO1 antagonists [benzbromarone (BB) and MONNA (MN)].

OBJECTIVE

This study sought to examine the synergistic potency and mechanistic basis of two ANO1 antagonists with currently available tocolytic drugs. Functional endpoints assessed included relaxation of pre-contracting pregnant human USM tissue, inhibition of intracellular calcium release, and reduction of spontaneous transient inward current (STIC) recordings in human uterine smooth muscle cells.

METHODS

Human myometrial strips and primary human USM cells were used in organ bath and calcium flux experiments with different combinations of sub-threshold doses of ANO1 antagonists and terbutaline or nifedipine to determine if ANO1 antagonists potentiate tocolytic drugs.

RESULTS

The combination of sub-threshold doses of two ANO1 antagonists and current tocolytic drugs demonstrate a significant degree of synergy to relax human pregnant USM compared to the effects achieved when these drugs are administered individually.

CONCLUSION

A combination of sub-threshold doses of VGCC blocker and β2AR agonist with ANO1 antagonists potentiates relaxation of oxytocin-induced contractility and calcium flux in human USM ex vivo. Our findings may serve as a foundation for novel tocolytic drug combinations.

Uterine Excitability and Ion Channels and Their Changes with Gestation and Hormonal Environment

We address advances in the understanding of myometrial physiology, focusing on excitation and the effects of gestation on ion channels and their relevance to labor. This review moves through pioneering studies to exciting new findings. We begin with the myometrium and its myocytes and describe how excitation might initiate and spread in this myogenic smooth muscle. We then review each of the ion channels in the myometrium: L- and T-type Ca²⁺ channels, K_ATP (Kir6) channels, voltage-dependent K channels (Kv4, Kv7, and Kv11), twin-pore domain K channels (TASK, TREK), inward rectifier Kir7.1, Ca²⁺-activated K⁺ channels with large (KCNMA1, Slo1), small (KCNN1-3), and intermediate (KCNN4) conductance, Na-activated K channels (Slo2), voltage-gated (SCN) Na⁺ and Na⁺ leak channels, nonselective (NALCN) channels, the Na K-ATPase, and hyperpolarization-activated cation channels. We finish by assessing how three key hormones- oxytocin, estrogen, and progesterone-modulate and integrate excitability throughout gestation.

Review and Study of Uterine Bioelectrical Waveforms and Vector Analysis to Identify Electrical and Mechanosensitive Transduction Control Mechanisms During Labor in Pregnant Patients

The bioelectrical signals that produce uterine contractions during parturition are not completely understood. The objectives are as follows: (1) to review the literature and information concerning uterine biopotential waveforms generated by the uterus, known to produce contractions, and evaluate mechanotransduction in pregnant patients using electromyographic (EMG) recording methods and (2) to study a new approach, uterine vector analysis, commonly used for the heart: vectorcardiography analysis. The patients used in this study were as follows: (1) patients at term not in labor (n = 3); (2) patients during the 1st stage of labor at cervical dilations from 2 to 10 cm (n = 30); and (3) patients in the 2nd stage of labor and during delivery (n = 3). We used DC-coupled electrodes and PowerLab hardware (model no. PL2604, ADInstruments, Castle Hill, Australia), with software (LabChart, ADInstruments) for storage and analysis of biopotentials. Uterine and abdominal EMG recordings were made from the surface of each patient using 3 electrode pairs with 1 pair (+ and -, with a 31-cm spacing distance) placed in the right/left position (X position) and with 1 pair placed in an up/down position (Y position, also 31 cm apart) and with the third pair at the front/back (Z position). Using signals from the three X, Y, and Z electrodes, slow (0.03 to 0.1 Hz, high amplitude) and fast wave (0.3 to 1 Hz, low amplitude) biopotentials were recorded. The amplitudes of the slow waves and fast waves were significantly higher during the 2nd stage of labor compared to the 1st stage (respectively, p = 9.54 × e^-3 and p = 3.94 × e^-7). When 2 channels were used, for example, the X vs. Y, for 2-D vector analysis or 3 channels, X vs. Y vs. Z, for 3-D analysis, are plotted against each other on their axes, this produces a vector electromyometriogram (EMMG) that shows no directionality for fast waves and a downward direction for slow waves. Similarly, during the 2nd stage of labor during abdominal contractions ("pushing"), the slow and fast waves were enlarged. Manual applied pressure was used to evoke bioelectrical activity to examine the mechanosensitivity of the uterus. Conclusions: (1) Phasic contractility of the uterus is a product of slow waves and groups of fast waves (bursts of spikes) to produce myometrial contractile responses. (2) 2-D and 3-D uterine vector analyses (uterine vector electromyometriogram) demonstrate no directionality of small fast waves while the larger slow waves represent the downward direction of biopotentials towards the cervical opening. (3) Myometrial cell action event excitability and subsequent contractility likely amplify slow wave activity input and uterine muscle contractility via mechanotransduction systems. (4) Models illustrate the possible relationships of slow to fast waves and the association of a mechanotransduction system and pacemaker activity as observed for slow waves and pacemakers in gastrointestinal muscle. (5) The interaction of these systems is thought to regulate uterine contractility. (6) This study suggests a potential indicator of delivery time. Such vector approaches might help us predict the progress of gestation and better estimate the timing of delivery, gestational pathologies reflected in bioelectric events, and perhaps the potential for premature delivery drug and mechanical interventions.

Contraction-associated proteins expression by human uterine smooth muscle cells depends on maternal serum and progranulin associated with gestational weight gain

Pregnant women with obesity are at increased risk of parturition dysfunction; however, the biological mechanism has remained unknown. We hypothesized that molecules circulating in the serum of pregnant women with obesity may induce the aberrant expression of contraction-associated proteins (CAPs), leading to insufficient uterine contractions. This study aimed to investigate the effects of maternal serum on CAPs expression by human uterine smooth muscle cells (UtSMCs) and elucidate the influence of maternal obesity. Blood samples were collected from singleton pregnant women at 36-41 weeks of gestation before the onset of labor. UtSMCs were incubated in the serum, and the mRNA expressions of PTGFR, OXTR, GJA1, and PTGS2 were examined by RT-PCR. Progranulin (PGRN) is a circulating glycoprotein associated with insulin resistance characterized by the accumulation of visceral fat. The serum PGRN levels of the samples were measured by ELISA. After incubated with PGRN (100-1,000 ng/mL), mRNA expression of PTGFR, OXTR, and GJA1 and protein expression of CX43 were examined by RT-PCR and western blotting, respectively. The mRNA expressions of PTGFR, OXTR, and GJA1 showed significantly negative correlations with gestational weight gain (GWG). Serum PGRN levels showed a significantly positive correlation with GWG. High levels of PGRN suppressed the mRNA expression of GJA1 and the protein expression of CX43. The change in maternal serum induced by GWG suppressed the CAPs expression by UtSMCs. PGRN is one of the factors in the serum responsible for inhibiting the expression of CX43.

An application of higher order multivariate cumulants in modelling of myoelectrical activity of porcine uterus during early pregnancy

The analysis of the uterine contraction have become a general practice in an effort to improve the clinical management of uterine contractions during pregnancy and labour in human beings. The fluctuations in uterine activity may occur without affecting progress of gestation, however the painful and fashion contractions may be the first threat of miscarriage. While pigs were considered as an referential preclinical model, the computational modelling of spontaneous myoelectrical activity of complex systems of porcine myometrium in peri-fertilization period has been proposed. The higher order statistic, multivariate cumulants and Joint Skewness Band Selection method, have been applied to study the dependence structure of electromyographic (EMG) signal with an effective EMG feature. Than the model of recognition of multivariate, myoelectricaly changes according to crucial stages for successful fertilization and early pregnancy maintenance has been estimated. We found that considering together time and frequency features of EMG signal was extremely non-Gaussian distributed and the higher order multivariate statistics such as cumulants, have to be used to determine the pattern of myoelectrical activity in reproductive tract. We confirmed the expectance that the probabilistic model changes on a daily base. We demonstrated the changes in proposed model at the crucial time points of in peri-fertilization period. We speculate the activity of the middle of uterine horn and the power (minimum and maximum) and pauses between myoelectrical burst features are essential for the functional role of uterine contractility in peri-fertilization period.

The interplay between electrical and chemical synaptogenesis

Neurons communicate with each other via electrical or chemical synaptic connections. The pattern and strength of connections between neurons are critical for generating appropriate output. What mechanisms govern the formation of electrical and/or chemical synapses between two neurons? Recent studies indicate that common molecular players could regulate the formation of both of these classes of synapses. In addition, electrical and chemical synapses can mutually coregulate each other’s formation. Electrical activity, generated spontaneously by the nervous system or initiated from sensory experience, plays an important role in this process, leading to the selection of appropriate connections and the elimination of inappropriate ones. In this review, we discuss recent studies that shed light on the formation and developmental interactions of chemical and electrical synapses.

Identification of uterine pacemaker regions at the myometrial-placental interface in the rat

KEY POINTS

Coordinated contraction of the uterine smooth muscle is essential to parturition. Histologically and physiologically defined pacemaker structures have not been identified in uterine smooth muscle. Here we report combined electrophysiological and histological evidence of zones associated with pacemaker activity in the rat myometrium. Our method relies crucially on the integration of histological and electrophysiological data in an in silico three-dimensional reconstruction of the rat myometrium at 10 μm resolution. We find that myometrial/placental pacemaking zones are closely related with placental sites and the area of disruptive myometrial remodelling surrounding such sites. If analogues of the myometrial/placental pacemaking zone are present in the human, defining their histology and physiology will be important steps towards treatment of pre-term birth, pre-eclampsia, and postpartum haemorrhage.

ABSTRACT

Coordinated uterine contractions are essential for delivering viable offspring in mammals. In contrast to other visceral smooth muscles, it is not known where excitation within the uterus is initiated, and no defined pacemaking region has hitherto been identified. Using multi-electrode array recordings and high-resolution computational reconstruction of the three-dimensional micro-structure of late pregnant rat uterus, we demonstrate that electrical potentials are initiated in distinct structures within the placental bed of individual implantation sites. These previously unidentified structures represent modified smooth muscle bundles that are derived from bridges between the longitudinal and circular layers. Coordinated implantation and encapsulation by invading trophoblast give rise to isolated placental/myometrial interface bundles that directly connect to the overlying longitudinal smooth muscle layer. Taken together, these observations imply that the anatomical structure of the uterus, combined with site-specific implantation, gives rise to emergent patterns of electrical activity that drive effective contractility during parturition.

Anoctamin Channels in Human Myometrium: A Novel Target for Tocolysis

BACKGROUND

Spontaneous preterm labor leading to preterm birth is a significant obstetric problem leading to neonatal morbidity and mortality. Current tocolytics are not completely effective and novel targets may afford a therapeutic benefit.

OBJECTIVE

To determine whether the anoctamin (ANO) family, including the calcium-activated chloride channel ANO1, is present in pregnant human uterine smooth muscle (USM) and whether pharmacological and genetic modulation of ANO1 modulates USM contraction.

METHODS

Reverse transcription-polymerase chain reaction (RT-PCR), quantitative RT-PCR, and immunohistochemical staining were done to determine which members of the ANO family are expressed in human USM. Uterine smooth muscle strips were studied in an organ bath to determine whether ANO1 antagonists inhibit oxytocin-induced USM contractions. Anoctamin 1 small interfering RNA (siRNA) knockdown was performed to determine its effect on filamentous-/globular (F/G)-actin ratio, a measurement of actin polymerization's role in promoting smooth muscle contraction.

RESULTS

Messenger RNA (mRNA) encoding all members of the ANO family (except ANO7) are expressed in pregnant USM tissue. Anoctamin 1 mRNA expression was decreased 15.2-fold in pregnant USM compared to nonpregnant. Anoctamin 1 protein is expressed in pregnant human USM tissue. Functional organ bath studies with pregnant human USM tissue demonstrated that the ANO1 antagonist benzbromarone attenuates the force and frequency of oxytocin-induced contractions. In human USM cells, siRNA knockdown of ANO1 decreases F-/G-actin ratios.

CONCLUSION

Multiple members of the ANO family, including the calcium-activated chloride channel ANO1, are expressed in human USM. Antagonism of ANO1 by pharmacological inhibition and genetic knockdown leads to an attenuation of contraction in pregnant human USM. Anoctamin 1 is a potentially novel target for tocolysis.

Prostaglandin-Endoperoxide Synthase 1 Mediates the Timing of Parturition in Mice Despite Unhindered Uterine Contractility

Cyclooxygenase (COX)-derived prostaglandins stimulate uterine contractions and prepare the cervix for parturition. Prior reports suggest Cox-1 knockout (KO) mice exhibit delayed parturition due to impaired luteolysis, yet the mechanism for late-onset delivery remains unclear. Here, we examined key factors for normal onset of parturition to determine whether any could account for the delayed parturition phenotype. Pregnant Cox-1KO mice did not display altered timing of embryo implantation or postimplantation growth. Although messenger RNAs of contraction-associated proteins (CAPs) were differentially expressed between Cox-1KO and wild-type (WT) myometrium, there were no differences in CAP agonist-induced intracellular calcium release, spontaneous or oxytocin (OT)-induced ex vivo uterine contractility, or in vivo uterine contractile pressure. Delayed parturition in Cox-1KO mice persisted despite exogenous OT treatment. Progesterone (P4) withdrawal, by ovariectomy or administration of the P4-antagonist RU486, diminished the delayed parturition phenotype of Cox-1KO mice. Because antepartum P4 levels do not decline in Cox-1KO females, P4-treated WT mice were examined for the effect of this hormone on in vivo uterine contractility and ex vivo cervical dilation. P4-treated WT mice had delayed parturition but normal uterine contractility. Cervical distensibility was decreased in Cox-1KO mice on the day of expected delivery and reduced in WT mice with long-term P4 treatment. Collectively, these findings show that delayed parturition in Cox-1KO mice is the result of impaired luteolysis and cervical dilation, despite the presence of strong uterine contractions.

Connexin 43 in the development and progression of breast cancer: What's the connection? (Review)

Connexin 43 is a prominent gap junction protein within normal human breast tissue. Thus far, there have been a number of research studies performed to determine the function of connexin 43 in breast tumor formation and progression. Within primary tumors, research suggests that the level of connexin 43 expression in breast tumors is altered when compared to normal human breast tissue. While some reports indicate that connexin 43 levels decrease, other evidence suggests that connexin 43 levels are increased and protein localization shifts from the plasma membrane to the cytoplasm. In either case, the prevailing theory is that breast tumor cells have reduced gap junction intercellular communication within primary tumors. The current consensus appears to be that the loss of connexin 43 gap junction intercellular communication is an early event in malignancy, with the possibility of gap junction restoration in the event of metastasis. However, additional evidence is needed to support the latter claim. The purpose of this report is to review the connexin 43 literature that describes studies using human tissue samples, in order to evaluate the function of connexin 43 protein in normal human breast tissue as well as the role of connexin 43 in human breast tumor formation and metastatic progression.

Optimal routes of administration, vehicles and timing of progesterone treatment for inhibition of delivery during pregnancy

OBJECTIVES

Progestins, notably progesterone (P4) and 17 alpha hydroxyprogesterone caproate, are presently used to treat pregnant women at risk of preterm birth. The aim of this study was to assess the optimal treatment options for progesterone (P4) to delay delivery using a sensitive bioassay for progesterone.

STUDY DESIGN

Pregnant rats, known to be highly sensitive to progestins, were treated with P4, including Prochieve^® (also known as Crinone^®), in various vehicles from day 13 of gestation and in late gestation, days 19 to 22, and delivery times noted. Various routes of administration of P4 and various treatment periods were studied.

RESULTS

Use of micronized P4 by rectal, subcutaneous injection (sc) and topical (transdermal) administration in various oils all significantly (P<0.05-<0.001) delay delivery, but vaginal Prochieve^® did not. Administration of P4 in late gestation also prevented (P<0.001) delivery even when given 8h before delivery.

CONCLUSIONS

Prochieve^® possesses little biological activity to suppress delivery in a sensitive bioassay system and suggests that this preparation may be of little value in prevention and inhibition of preterm birth. Further, this study shows: 1) Inhibition of delivery is increased with P4 treatments when given subcutaneously or topically. 2) P4 in fish oil provides the best vehicle for topical treatment and may be an effective treatment of preterm birth. 3) P4 in fish oil also delays delivery even when treatment begins just prior to normal delivery. 4) To prevent preterm birth in pregnant women, randomized controlled studies are needed with a potent progestin using better formulations and routes of administration.

Biomathematical pattern of EMG signal propagation in smooth muscle of the non-pregnant porcine uterus

Uterine contractions are generated by myometrial smooth muscle cells (SMCs) that comprise most of the myometrial layer of the uterine wall. Aberrant uterine motility (i.e., hypo- or hyper-contractility or asynchronous contractions) has been implicated in the pathogenesis of infertility due to the failure of implantation, endometriosis and abnormal estrous cycles. The mechanism whereby the non-pregnant uterus initiates spontaneous contractions remains poorly understood. The aim of the present study was to employ linear synchronization measures for analyzing the pattern of EMG signal propagation (direction and speed) in smooth muscles of the non-pregnant porcine uterus in vivo using telemetry recording system. It has been revealed that the EMG signal conduction in the uterine wall of the non-pregnant sow does not occur at random but it rather exhibits specific directions and speed. All detectable EMG signals moved along the uterine horn in both cervico-tubal and tubo-cervical directions. The signal migration speed could be divided into the three main types or categories: i. slow basic migration rhythm (SBMR); ii. rapid basic migration rhythm (RBMR); and iii. rapid accessory migration rhythm (RAMR). In conclusion, the EMG signal propagation in smooth muscles of the porcine uterus in vivo can be assessed using a linear synchronization model. Physiological pattern of the uterine contractile activity determined in this study provides a basis for future investigations of normal and pathologicall myogenic function of the uterus.

Myometrial relaxation of mice via expression of two pore domain acid sensitive K(+) (TASK-2) channels

Myometrial relaxation of mouse via expression of two-pore domain acid sensitive (TASK) channels was studied. In our previous report, we suggested that two-pore domain acid-sensing K⁺ channels (TASK-2) might be one of the candidates for the regulation of uterine circular smooth muscles in mice. In this study, we tried to show the mechanisms of relaxation via TASK-2 channels in marine myometrium. Isometric contraction measurements and patch clamp technique were used to verify TASK conductance in murine myometrium. Western blot and immunehistochemical study under confocal microscopy were used to investigate molecular identity of TASK channel. In this study, we showed that TEA and 4-AP insensitive non-inactivating outward K⁺ current (NIOK) may be responsible for the quiescence of murine pregnant longitudinal myometrium. The characteristics of NIOK coincided with two-pore domain acid-sensing K⁺ channels (TASK-2). NIOK in the presence of K⁺ channel blockers was inhibited further by TASK inhibitors such as quinidine, bupivacaine, lidocaine, and extracellular acidosis. Furthermore, oxytocin and estrogen inhibited NIOK in pregnant myometrium. When compared to non-pregnant myometrium, pregnant myometrium showed stronger inhibition of NIOK by quinidine and increased immunohistochemical expression of TASK-2. Finally, TASK-2 inhibitors induced strong myometrial contraction even in the presence of L-methionine, a known inhibitor of stretch-activated channels in the longitudinal myometrium of mouse. Activation of TASK-2 channels seems to play an essential role for relaxing uterus during pregnancy and it might be one of the alternatives for preventing preterm delivery.

An electro-mechanical multiscale model of uterine pregnancy contraction

Detecting preterm labor as early as possible is important because tocolytic drugs are much more likely to delay preterm delivery if administered early. Having good information on the real risk of premature labor also leads to fewer women who do not need aggressive treatment for premature labor threat. Currently, one of the most promising ways to diagnose preterm labor threat is the analysis of the electrohysterogram (EHG). Its characteristics have been related to preterm labor risk but they have not proven to be sufficiently accurate to use in clinical routine. One of the reasons for this is that the physiology of the pregnant uterus is insufficiently understood. Models already exist in literature that simulate either the electrical or the mechanical component of the uterine smooth muscle. Few include both components in a co-simulation of electrical and mechanical aspects. A model that can represent realistically both the electrical and the mechanical behavior of the uterine muscle could be useful for better understanding the EHG and therefore for preterm labor detection. Processing the EHG considers only the electrical component of the uterus but the electrical activity does not seem to explain by itself the synchronization of the uterine muscle that occurs during labor and not at other times. Recent studies have demonstrated that the mechanical behavior of the uterine muscle seems to play an important role in uterus synchronization during labor. The aim of the proposed study is to link three different models of the uterine smooth muscle behavior by using co-simulation. The models go from the electrical activity generated at the cellular level to the mechanical force generated by the muscle and from there to the deformation of the tissue. The results show the feasibility of combining these three models to model a whole uterus contraction on 3D realistic uterus model.

Mechanotransduction mechanisms for coordinating uterine contractions in human labor

This review presents evolving concepts of how the human uterus contracts in pregnancy, with emphasis on the mechanisms of long-distance signaling. Action potential propagation has historically been assumed to be the sole mechanism for signaling and tissue recruitment over both short and long distances. However, data in animals and humans indicate that a single action potential does not travel distances greater than a few centimeters. To address this enigma, a long-distance signaling mechanism based on hydraulic signaling and mechanotransduction is developed. By combining this mechanism for long-distance signaling with the action potential propagation mechanism for signaling over short distances, a comprehensive dual mechanism model (or 'dual model') of uterine function is formulated. Mechanotransduction is an accepted phenomenon of myometrium, but the dual model identifies mechanotransduction as relevant to normal labor. For hydraulic signaling, a local contraction slightly increases intrauterine pressure, which globally increases wall tension. Increased wall tension then mechanically induces additional local contractions that further raise pressure. This leads to robust, positive feedback recruitment that explains the emergence of consistently strong contractions of human labor. Three key components of the dual model - rapid long-distance signaling, mechanical triggering, and electrical activity - converge with the concept of mechanically sensitive electrogenic pacemakers distributed throughout the wall. The dual model retains excitation-contraction coupling and action potential propagation for signaling over short distances (<10cm) and hence is an extension of the action potential model rather than a replacement.

Enhanced Expression of Contractile-Associated Proteins and Ion Channels in Preterm Delivery Model Mice With Chronic Odontogenic Porphyromonas Gingivalis Infection

Inflammation and infection have been reported to induce preterm delivery. We have studied the relationship between inflammation and various ion channels, including the L-type Ca(2+) channel and P2X7 receptor, during acute inflammation of the pregnant rat uterus induced by lipopolysaccharides. Recently, we found that mice with odontogenic Porphyromonas gingivalis (P.g, an important odontogenic pathogen) infection delivered at day 18.3 of gestation (vs. day 20.5 in normal mice). The purpose of this study was to investigate the expression of myometrial contractile-associated proteins inducing contractions and confirm that these mice are useful as a model for preterm delivery induced by chronic inflammation. We examined the expression of the oxytocin receptor, connexin 43, prostaglandin F receptors, L-type Ca(2+) channel, and P2X7 receptor in the myometrium at day 18 of gestation by real-time PCR and western blot analyses. We also measured TNF-α and IL-1β levels in the blood serum, placenta, fetal membrane and myometrium on the same day. mRNA expression of the oxytocin receptor, connexin 43, prostaglandin F receptors, L-type Ca(2+) channel, and P2X7 receptor was elevated by 5.4, 3.2, 2.4, 2.5, and 1.7 fold, respectively, in the P.g-infected mice. Protein levels of the oxytocin receptor and connexin 43 also increased. Serum levels of TNF-α and IL-1β were elevated, showing that systemic inflammation continued during pregnancy. IL-1β levels in the placenta and fetal membrane also increased, suggesting inflammatory reactions were induced. Thus, mice with odontogenic infection may be useful as a model of chronic inflammation-induced preterm delivery.

Alterations in gap junction connexin43/connexin45 ratio mediate a transition from quiescence to excitation in a mathematical model of the myometrium

The smooth muscle cells of the uterus contract in unison during delivery. These cells achieve coordinated activity via electrical connections called gap junctions which consist of aggregated connexin proteins such as connexin43 and connexin45. The density of gap junctions governs the excitability of the myometrium (among other factors). An increase in gap junction density occurs immediately prior to parturition. We extend a mathematical model of the myometrium by incorporating the voltage-dependence of gap junctions that has been demonstrated in the experimental literature. Two functional subtypes exist, corresponding to systems with predominantly connexin43 and predominantly connexin45, respectively. Our simulation results indicate that the gap junction protein connexin45 acts as a negative modulator of uterine excitability, and hence, activity. A network with a higher proportion of connexin45 relative to connexin43 is unable to excite every cell. Connexin45 has much more rapid gating kinetics than connexin43 which we show limits the maximum duration of a local burst of activity. We propose that this effect regulates the degree of synchronous excitation attained during a contraction. Our results support the hypothesis that as labour approaches, connexin45 is downregulated to allow action potentials to spread more readily through the myometrium.

The location of pacemakers in the uteri of pregnant guinea pigs and rats

The pregnant uterus is a smooth muscle organ whose pattern of contraction is dictated by the propagation of electrical impulses. Such electrical activity may originate from one or more pacemakers, but the location of these sites has not yet been determined. To detect the location of the pacemaker in the gravid uterus, two approaches were used: 1) determine the site from where the contraction started using isolated uteri from the pregnant guinea pig, and videotape their contractions; and 2) record, in isolated uteri from pregnant term rats, with 240 extracellular electrodes simultaneously, and determine where the electrical bursts started. In both the contractile and electrophysiological experiments, there was not a single, specific pacemaker area. However, most contractions (guinea pig 87%) and bursts (rat 76%) started close to the mesometrial border (mean 2.7 ± 4.0 mm SD in guinea pigs and 1.3 ± 1.4 mm in rats). In addition, in the rat, most sites of initiations were located closer to the ovarial end of the horn (mean distance from the ovarial end 6.0 ± 6.2 mm SD), whereas such an orientation was not seen in the guinea pig. In both guinea pig and rat uteri at term, there is not one specific pacemaker area. Rather, contractile and electrical activity may arise from any site, with the majority starting close to the mesometrial border. Furthermore, in the rat, most activities started at the ovarial end of the horn. This may suggest a slightly different pattern of contraction in both species.

Why the heart is like an orchestra and the uterus is like a soccer crowd

The human uterus has no pacemaker or motor innervation, yet develops rhythmic, powerful contractions that increase intrauterine pressure to dilate the cervix and force the fetus through the pelvis. To achieve the synchronous contractions required for labor, the muscle cells of the uterus act as independent oscillators that become increasingly coupled by gap junctions toward the end of pregnancy. The oscillations are facilitated by changes in resting membrane potential that occur as pregnancy progresses. Reductions of potassium channels in the myocyte membranes in late pregnancy prolong myocyte action potentials, further facilitating transmission of signals and recruitment of neighboring myocytes. Late in pregnancy prostaglandin production increases leading to increased myocyte excitability. Also late in pregnancy myocyte actin polymerizes allowing actin-myosin interactions that generate force, following myocyte depolarization, calcium entry, and activation of myosin kinase. Labor occurs as a consequence of the combination of increased myocyte to myocyte connectivity, increased depolarizations that last longer, and activated intracellular contractile machinery. During labor the synchronous contractions of muscle cells raise intrauterine pressure to dilate the cervix in a process distinct from peristalsis. The synchronous contractions occur in a progressively larger region of the uterine wall. As the size of the region increases with increasing connectivity, the contraction of that larger area leads to an increase in intrauterine pressure. The resulting increased wall tension causes myocyte depolarization in other parts of the uterus, generating widespread synchronous activity and increased force as more linked regions are recruited into the contraction. The emergent behavior of the uterus has parallels in the behavior of crowds at soccer matches that sing together without a conductor. This contrasts with the behavior of the heart where sequential contractions are regulated by a pacemaker in a similar way to the actions of a conductor and an orchestra.

Direct electrical stimulation softens the cervix in pregnant and nonpregnant rats

OBJECTIVE

The objective of the study was to determine the effects of electrical stimulation (ES) on cervical ripening in pregnant and nonpregnant rats.

STUDY DESIGN

Timed pregnant and nonpregnant Sprague-Dawley rats (n = 6-7/group) were used. Cervical ES for pregnant rats was performed in vivo on day 15 of gestation by inserting an electrical probe into the vagina in contact with the cervix. Parameters of ES varied from 0.1 to 0.2 mA, 10 pulses per second, 20 milliseconds pulse duration, and repeating pulses for 15, 30, 60, and 120 minutes for pregnant ES groups and similar times for sham control groups with electrode but without ES. Nonpregnant ES groups were stimulated with only 0.2 mA for 30 minutes. Cervical collagen was measured in controls and following ES at various times using light-induced fluorescence (LIF) of collagen. Photographs were taken following ES, and some rats were killed, the cervices were isolated, and cervical extensibility was estimated.

RESULTS

LIF values of pregnant rats are significantly lower (P < .001) and extensibility greater (P < .05) in the ES treatment groups compared with the control groups on days 16 and 17 of pregnancy. Similarly LIF is lower (P < .05) and extensibility values greater (P < .05) in nonpregnant rats treated with ES. No adverse effects, including altered delivery time, pup weights, or damage to cervix, were produced by low current levels of ES needed to soften the cervix.

CONCLUSION

The following conclusions were reached: (1) application of ES rapidly produces softening and ripening of the cervix in pregnant and nonpregnant rats; (2) ES treatment does not produce early delivery; (3) the exact mechanism for ES ripening is not yet known; and (4) ES might be used clinically to ripen the cervix when needed.

The inwardly rectifying K+ channel KIR7.1 controls uterine excitability throughout pregnancy

Abnormal uterine activity in pregnancy causes a range of important clinical disorders, including preterm birth, dysfunctional labour and post-partum haemorrhage. Uterine contractile patterns are controlled by the generation of complex electrical signals at the myometrial smooth muscle plasma membrane. To identify novel targets to treat conditions associated with uterine dysfunction, we undertook a genome-wide screen of potassium channels that are enriched in myometrial smooth muscle. Computational modelling identified Kir7.1 as potentially important in regulating uterine excitability during pregnancy. We demonstrate Kir7.1 current hyper-polarizes uterine myocytes and promotes quiescence during gestation. Labour is associated with a decline, but not loss, of Kir7.1 expression. Knockdown of Kir7.1 by lentiviral expression of miRNA was sufficient to increase uterine contractile force and duration significantly. Conversely, overexpression of Kir7.1 inhibited uterine contractility. Finally, we demonstrate that the Kir7.1 inhibitor VU590 as well as novel derivative compounds induces profound, long-lasting contractions in mouse and human myometrium; the activity of these inhibitors exceeds that of other uterotonic drugs. We conclude Kir7.1 regulates the transition from quiescence to contractions in the pregnant uterus and may be a target for therapies to control uterine contractility.

Propagation of electrical activity in uterine muscle during pregnancy: a review

The uterine muscle (the myometrium) plays its most evident role during pregnancy, when quiescence is required for adequate nourishment and development of the foetus, and during labour, when forceful contractions are needed to expel the foetus and the other products of conception. The myometrium is composed of smooth muscle cells. Contraction is initiated by the spontaneous generation of electrical activity at the cell level in the form of action potentials. The mechanisms underlying uterine quiescence during pregnancy and electrical activation during labour remain largely unknown; as a consequence, the clinical management of preterm contractions during pregnancy and inefficient uterine contractility during labour remains suboptimal. In an effort to improve clinical management of uterine contractions, research has focused on understanding the propagation properties of the electrical activity of the uterus. Different perspectives have been undertaken, from animal and in vitro experiments up to clinical studies and dedicated methods for non-invasive parameter estimation. A comparison of the results is not straightforward due to the wide range of different approaches reported in the literature. However, previous studies unanimously reveal a unique complexity as compared to other organs in the pattern of uterine electrical activity propagation, which necessarily needs to be taken into consideration for future studies to be conclusive. The aim of this review is to structure current variegated knowledge on the properties of the uterus in terms of pacemaker position, pattern, direction and speed of the electrical activity during pregnancy and labour.

Functional and morphological development of the womb throughout life

The uterus undergoes changes throughout a woman's life, beginning with her own embryonic development when she is still in the womb, commencing a monthly cycle at the onset of adulthood, and undergoing dramatic changes during pregnancy and parturition. The impact of preterm labour and other perinatal health problems is significant, both in human and financial terms; therefore the study of the physiological and regulatory changes which the uterus undergoes can be of enormous potential benefit. Here we briefly review the current state of knowledge, with an emphasis on the importance of changes in connectivity in the uterine smooth muscle cell network and on recent mathematical modelling work aimed at elucidating the role of spatial heterogeneity in this connected network.

Anterior placental location influences onset and progress of labor and postpartum outcome

INTRODUCTION

The aim of the study is to evaluate whether placental location at term is associated with delivery outcome.

METHODS

A prospective study including 2354 patients with singleton pregnancy at term admitted for vaginal delivery was conducted. Placental position was determined before delivery by ultrasonographic examination performed transabdominally with women in the supine position. Maternal characteristics and delivery outcome such as premature rupture of membranes, induction of labor, mode and gestational age at delivery, indication for cesarean section, duration of the third stage, postpartum hemorrhage (PPH) and manual removal of placenta were correlated with anterior, posterior or fundal placental locations.

RESULTS

Among women enrolled: i) 1164 had an anterior placenta, ii) 1087 a posterior placenta, iii) 103 a fundal placenta. Women with anterior placenta showed: i) a higher incidence of induction of labor (p = 0.0001), especially for postdate pregnancies and prolonged prelabor rupture of membranes (p < 0.0001), ii) a higher rate of cesarean section rate for failure to progress in labor (p = 0.02), iii) a prolonged third stage (p = 0.01), iv) a higher incidence of manual removal of placenta (p = 0.003) and a higher rate of PPH in vaginal deliveries (p = 0.02).

DISCUSSION

The present study showed the influence of anterior placental location on the course of labor, with a later onset of labor, a higher rate of induction and cesarean section and postpartum complications. The reason for this influence on labor and delivery complications remains to be elucidated.

Fine spatiotemporal activity in contracting myometrium revealed by motion-corrected calcium imaging

Successful childbirth depends on the occurrence of precisely coordinated uterine contractions during labour. Calcium indicator fluorescence imaging is one of the main techniques for investigating the mechanisms governing this physiological process and its pathologies. The effective spatiotemporal resolution of calcium signals is, however, limited by the motion of contracting tissue: structures of interest in the order of microns can move over a hundred times their width during a contraction. The simultaneous changes in local intensity and tissue configuration make motion tracking a non-trivial problem in image analysis and confound many of the standard techniques. This paper presents a method that tracks local motion throughout the tissue and allows for the almost complete removal of motion artefacts. This provides a stabilized calcium signal down to a pixel resolution, which, for the data examined, is in the order of a few microns. As a byproduct of image stabilization, a complete kinematic description of the contraction–relaxation cycle is also obtained. This contains novel information about the mechanical response of the tissue, such as the identification of a characteristic length scale, in the order of 40–50 μm, below which tissue motion is homogeneous. Applied to our data, we illustrate that the method allows for analyses of calcium dynamics in contracting myometrium in unprecedented spatiotemporal detail. Additionally, we use the kinematics of tissue motion to compare calcium signals at the subcellular level and local contractile motion. The computer code used is provided in a freely modifiable form and has potential applicability to in vivo calcium imaging of neural tissue, as well as other smooth muscle tissue.

Vitamin D regulates contractile profile in human uterine myometrial cells via NF-κB pathway

OBJECTIVE

Infection triggers inflammation that, in turn, enhances the expression of contractile-associated factors in myometrium and increases the risk of preterm delivery. In this study, we assessed vitamin D regulation of inflammatory markers, contractile-associated factors, steroid hormone receptors, and NFκB pathway proteins in human uterine myometrial smooth muscle (UtSM) cells that were cultured in an inflammatory environment.

STUDY DESIGN

Inflammatory environment was simulated for UtSM cells by coculturing them with monocyte lineage (THP1) cells. We measured the expression of inflammatory markers, contractile-associated factors, steroid hormone receptors, and NFκB pathway proteins in UtSM cells that were cultured with THP1 cells in the presence and absence of vitamin D by real time polymerase chain reaction and Western blot analysis.

RESULTS

Monocytes secreted monocyte inflammatory protein-1α and -1β, interleukin (IL)-1β and 6, and tumor necrosis factor-α into the conditioned medium. In the UtSM cells that had been cocultured with THP1 cells, there was a significant (P < .05) increase in the expression of inflammatory markers IL-1β, -6, and -13 and tumor necrosis factor-α; the contractile-associated factors connexin-43, Cox-2, and prostaglandin F2α receptor; the estrogen receptor α, and progesterone receptors A and B. Vitamin D treatment of cocultures decreased (P < .05) the expression of inflammatory markers and contractile-associated factors in UtSM cells. Similarly, vitamin D decreased estrogen receptor α and progesterone receptors A-to-B ratio in UtSM cells that were cocultured with THP1 cells. In addition, vitamin D treatment significantly (P < .05) decreased monocyte-induced p-IκBα in cytosol and NFκB-p65 in the nucleus and increased IκBα in cytosol in UtSM cells.

CONCLUSION

Our results suggest that vitamin D treatment decreases inflammation-induced cytokines and contractile-associated factors in the uterine myometrial smooth muscle cells through the NFκB pathway.

Characterization of the tissue-level Ca2+ signals in spontaneously contracting human myometrium

In the labouring uterus, millions of myocytes forming the complex geometrical structure of myometrium contract in synchrony to increase intrauterine pressure, dilate the cervix and eventually expel the foetus through the birth canal. The mechanisms underlying the precise coordination of contractions in human myometrium are not completely understood. In the present study, we have characterized the spatio-temporal properties of tissue-level [Ca(2+)](i) transients in thin slices of intact human myometrium. We found that the waveform of [Ca(2+)](i) transients and isotonic contractions recorded from thin slices was similar to the waveform of isometric contractions recorded from the larger strips in traditional organ bath experiments, suggesting that the spatio-temporal information obtained from thin slices is representative of the whole tissue. By comparing the time course of [Ca(2+)](i) transients in individual cells to that recorded from the bundles of myocytes we found that the majority of myocytes produce rapidly propagating long-lasting [Ca(2+)](i) transients accompanied by contractions. We also found a small number of cells showing desynchronized [Ca(2+)](i) oscillations that did not trigger contractions. The [Ca(2+)](i) oscillations in these cells were insensitive to nifedipine, but readily inhibited by the T-type Ca(2+) channel inhibitor NNC55-0396. In conclusion, our data suggest that the spread of [Ca(2+)](i) signals in human myometrium is achieved via propagation of long-lasting action potentials. The propagation was fast when action potentials propagated along bundles of myocytes and slower when propagating between the bundles of uterine myocytes.

Gap junctions

Gap junctions are essential to the function of multicellular animals, which require a high degree of coordination between cells. In vertebrates, gap junctions comprise connexins and currently 21 connexins are known in humans. The functions of gap junctions are highly diverse and include exchange of metabolites and electrical signals between cells, as well as functions, which are apparently unrelated to intercellular communication. Given the diversity of gap junction physiology, regulation of gap junction activity is complex. The structure of the various connexins is known to some extent; and structural rearrangements and intramolecular interactions are important for regulation of channel function. Intercellular coupling is further regulated by the number and activity of channels present in gap junctional plaques. The number of connexins in cell-cell channels is regulated by controlling transcription, translation, trafficking, and degradation; and all of these processes are under strict control. Once in the membrane, channel activity is determined by the conductive properties of the connexin involved, which can be regulated by voltage and chemical gating, as well as a large number of posttranslational modifications. The aim of the present article is to review our current knowledge on the structure, regulation, function, and pharmacology of gap junctions. This will be supported by examples of how different connexins and their regulation act in concert to achieve appropriate physiological control, and how disturbances of connexin function can lead to disease.

Assessment of myometrial transcriptome changes associated with spontaneous human labour by high-throughput RNA-seq

The transition of the human uterus from a quiescent to a contractile state takes place over a number of weeks. On such biological time scales, cellular phenotype is modified by changes in the transcriptome, which in turn is under the control of the underlying endocrine, paracrine, and biophysical processes resulting from the ongoing pregnancy. In this study, we characterize the transition of the human myometrial transcriptome at term from not in labour (NIL) to in labour (LAB) using high throughput RNA sequencing (RNA-seq). RNA was isolated from the myometrium of uterine biopsies from patients at term who were not in labour (n = 5) and at term in spontaneous labour (n = 5) without augmentation. A total of 143.6 million separate reads were sequenced, achieving, on average, ∼13 times coverage of the expressed human transcriptome per sample. Principal component analysis indicated that the NIL and LAB transcriptomes could be distinguished as two distinct clusters. A comparison of the NIL and LAB groups, using three different statistical approaches (baySeq, edgeR, and DESeq), demonstrated an overlap of 764 differentially expressed genes. A comparison with currently available microarray data revealed only a partial overlap in differentially expressed genes. We conclude that the described RNA-seq data sets represent the first fully annotated catalogue of expressed mRNAs in human myometrium. When considered together, the full expression repertoire and the differentially expressed gene sets should provide an excellent resource for formulating new hypotheses of physiological function, as well as the discovery of novel therapeutic targets.

Spatial heterogeneity enhances and modulates excitability in a mathematical model of the myometrium

The muscular layer of the uterus (myometrium) undergoes profound changes in global excitability prior to parturition. Here, a mathematical model of the myocyte network is developed to investigate the hypothesis that spatial heterogeneity is essential to the transition from local to global excitation which the myometrium undergoes just prior to birth. Each myometrial smooth muscle cell is represented by an element with FitzHugh-Nagumo dynamics. The cells are coupled through resistors that represent gap junctions. Spatial heterogeneity is introduced by means of stochastic variation in coupling strengths, with parameters derived from physiological data. Numerical simulations indicate that even modest increases in the heterogeneity of the system can amplify the ability of locally applied stimuli to elicit global excitation. Moreover, in networks driven by a pacemaker cell, global oscillations of excitation are impeded in fully connected and strongly coupled networks. The ability of a locally stimulated cell or pacemaker cell to excite the network is shown to be strongly dependent on the local spatial correlation structure of the couplings. In summary, spatial heterogeneity is a key factor in enhancing and modulating global excitability.

Ultrastructural identification of interstitial cells of Cajal in hen oviduct

The interstitial cells of Cajal (ICC) are widely believed to be neuroeffector cells of smooth muscle activity in all tubular organs, including the oviduct. The avian oviduct involves the secretion, sheathing, and transportation of a large-sized egg, but there is no information available on ICC in this special organ. We have demonstrated the presence of ICC in different segments throughout the oviduct in the laying hen and provided details on their ultrastructure by transmission electron microscopy technique, for the first time. The observed ICC appeared bipolar and multipolar cells of different shapes, with varying nuclear morphologies, a thin rim of electron-dense cytoplasm, and an infrequent basal lamina. They showed moniliform primary processes with one or 2 secondary or terminal processes. We found ICC near smooth muscle cells, nerve fibers, and the epithelia, where they make specialized contacts in the form of close membrane associations or gap-like junctions and peg-and-socket-like junctions. Intricate labyrinthine-type networking contacts were also present in ICC processes. Moreover, we report for the first time, that ICC in avian oviduct make interdigitating contacts with the epithelium. Cytoplasmic organelles identified in ICC include numerous well-developed mitochondria, abundant rough endoplasmic reticulum, and dispersed intermediate filaments. Many caveolae and vesicles were also present. Golgi bodies and centrioles were rare. Fibroblasts, on the other hand, were distinct cells with larger cytoplasmic area, more rough endoplasmic reticulum, and less mitochondrial content. No basal lamina, intermediate filaments, or caveolae were present in fibroblasts. Their processes were shorter and showed no contacts with smooth muscle cells or nerves. We conclude that these ICC might also have a key role in the regulatory mechanisms of motility and transportation in the hen oviduct, as already proved in mammalian oviduct. Such role of ICC might also be responsible for the function of the muscular infundibulum, where the fertilization takes place, and that moves to surround the released ovum, failure of which results in the internal laying.

Immune aspects and myometrial actions of progesterone and CRH in labor

Progesterone and corticotropin-releasing hormone (CRH) have a critical role in pregnancy and labor, as changes related to these hormones are crucial for the transition from myometrial quiescence to contractility. The mechanisms related to their effect differ between humans and other species, thus, despite extensive research, many questions remain to be answered regarding their mediation in human labor. Immune responses to progesterone and CRH are important for labor. Progesterone acts as an immunomodulator which controls many immune actions during pregnancy, and its withdrawal releases the inhibitory action on inflammatory pathways. In humans, a "functional" progesterone withdrawal occurs with onset of labor through changes in progesterone metabolism, progesterone receptors, and other molecules that either facilitate or antagonize progesterone function. Placental CRH acts on the fetal pituitary-adrenal axis to stimulate adrenal production of androgens and cortisol and also acts directly on myometrial cells via its receptors. CRH also affects inflammatory signals and vice versa. Interactions between progesterone and CRH additionally occur during labor. We describe the role of these two hormones in human myometrium and their interactions with the immune system during labor.

Connexins: key mediators of endocrine function

The appearance of multicellular organisms imposed the development of several mechanisms for cell-to-cell communication, whereby different types of cells coordinate their function. Some of these mechanisms depend on the intercellular diffusion of signal molecules in the extracellular spaces, whereas others require cell-to-cell contact. Among the latter mechanisms, those provided by the proteins of the connexin family are widespread in most tissues. Connexin signaling is achieved via direct exchanges of cytosolic molecules between adjacent cells at gap junctions, for cell-to-cell coupling, and possibly also involves the formation of membrane "hemi-channels," for the extracellular release of cytosolic signals, direct interactions between connexins and other cell proteins, and coordinated influence on the expression of multiple genes. Connexin signaling appears to be an obligatory attribute of all multicellular exocrine and endocrine glands. Specifically, the experimental evidence we review here points to a direct participation of the Cx36 isoform in the function of the insulin-producing β-cells of the endocrine pancreas, and of the Cx40 isoform in the function of the renin-producing juxtaglomerular epithelioid cells of the kidney cortex.

Changes in trace elements during follicular atresia in goat (Capra hircus) ovary

Quantitative analysis of follicular fluid and granulosa cells from small, medium and large antral atretic follicles of goat (Capra hircus) ovaries was conducted to study the alterations in trace elements viz zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe). The zinc content was lower in the follicular fluid (0.993 ± 0.001, 0.935 ± 0.002, 1.321 ± 0.001 μg/ml) and granulosa cells (0.867 ± 0.002, 0.801 ± 0.001, 1.073 ± 0.002 μg/mg) of small, medium, and large antral atretic follicles respectively than their respective controls. Copper quantity was higher in the follicular fluid (0.113 ± 0.001, [Formula: see text], 0.224 ± 0.001 μg/ml) and granulosa cells (0.094 ± 0.001, 0.114 ± 0.001, 0.182 ± 0.001 μg/mg) from small, medium, and large antral atretic follicles respectively than their respective controls. Similarly, iron and manganese was also found higher in the follicular fluid and granulosa cells of small, medium, and large antral atretic follicles than their respective controls. The present study provides the basic data on trace elements that can be safely used as atretic marker and will find use in in vitro studies for fertility improvement plan. Thus, help in elevating the number of ovulations and screening of follicles to enhance the success rate in vivo and in vitro fertilization and embryo transfer technology.