Possible role of gap junctions in activation of myometrium during parturition

Progesterone control of myometrial contractility

During pregnancy, the primary function of the uterus is to be quiescent and not contract, which allows the growing fetus to develop and mature. A uterine muscle layer, myometrium, is composed of smooth muscle cells (SMCs). Before the onset of labor contractions, the uterine SMCs experience a complex biochemical and molecular transformation involving the expression of contraction-associated proteins. Labor is initiated when genes in SMCs are activated in response to a combination of hormonal, inflammatory and mechanical signals. In this review, we provide an overview of molecular mechanisms regulating the process of parturition in humans, focusing on the hormonal control of the myometrium, particularly the steroid hormone progesterone. The primary reason for discussing the regulation of myometrial contractility by progesterone is the importance of the clinical problem of preterm birth. It is thought that the hormonal mechanisms regulating premature uterine contractions represent an untimely triggering of the normal events occurring during term parturition. Yet, our knowledge of the complex and redundant hormonal pathways controlling uterine contractile activity leading to delivery of the neonate remains incomplete. Finally, we introduce recent animal studies using a novel class of drugs, Selective Progesterone Receptor Modulators, targeting progesterone signaling to prevent premature myometrial contractions.

Physiology and Pathology of Contractility of the Myometrium

Uterine atony is a serious obstetrical complication since it is the leading cause of postpartum hemorrhage. Postpartum hemorrhage (PPH) is one of the 5 major causes of postpartum mortality; therefore, it requires immediate medical intervention, independent of whether delivery occurs normally or with a cesarean section. While in the past years most cases of postpartum hemorrhage were caused due to uterine atony following vaginal delivery, in recent years most PPH cases indicate a significant association with cesarean delivery. There are several methods used in order to avoid such a life-threatening complication, ranging from risk assessment to prevention, and finally medical intervention and management, if such an event occurs. In this scientific paper emphasis is given on the so-called "uterotonic" agents that are currently used, including oxytocin among others. It is, therefore, important to be familiar with these agents as well as understand the physiological mechanism by which they work, since they are used in everyday practice, not only for managing but also for preventing PPH. There are several potential questions that arise from the use of such "uterotonic" agents, and most specifically of oxytocin. Maybe one of the most important issues is the determination of optimal dosing of oxytocin in order to avoid PPH after a cesarean section.

Vaginal bacterial community composition and concentrations of estradiol at the time of artificial insemination in Brangus heifers

The knowledge surrounding the bovine vaginal microbiota and its implications on fertility and reproductive traits remains incomplete. The objective of the current study was to characterize the bovine vaginal bacterial community and estradiol concentrations at the time of artificial insemination (AI). Brangus heifers (n = 78) underwent a 7-d Co-Synch + controlled internal drug release estrus synchronization protocol. At AI, a double-guarded uterine culture swab was used to sample the anterior vaginal tract. Immediately after swabbing the vaginal tract, blood samples were collected by coccygeal venipuncture to determine concentrations of estradiol. Heifers were retrospectively classified as pregnant (n = 29) vs. nonpregnant (n = 49) between 41 and 57 d post-AI. Additionally, heifers were classified into low (1.1 to 2.5 pg/mL; n = 21), medium (2.6 to 6.7 pg/mL; n = 30), and high (7.2 to 17.6 pg/mL; n = 27) concentration of estradiol. The vaginal bacterial community composition was determined through sequencing of the V4 region from the 16S rRNA gene using the Illumina Miseq platform. Alpha diversity was compared via ANOVA and beta diversity was compared via PERMANOVA. There were no differences in the Shannon diversity index (alpha diversity; P = 0.336) or Bray-Curtis dissimilarity (beta diversity; P = 0.744) of pregnant vs. nonpregnant heifers. Overall, bacterial community composition in heifers with high, medium, or low concentrations of estradiol did not differ (P = 0.512). While no overall compositional differences were observed, species-level differences were present within pregnancy status and estradiol concentration groups. The implications of these species-level differences are unknown, but these differences could alter the vaginal environment thereby influencing fertility and vaginal health. Therefore, species-level changes could provide better insight rather than overall microbial composition in relation to an animal's reproductive health.

Reprint of: Myometrial activation: Novel concepts underlying labor

Term labour is a state of physiological inflammation orchestrated by multiple uterine tissues (both fetal and maternal). This physiological inflammation preceding and accompanying labour onset is characterized by an increase in cytokine and chemokine secretion by the fetal membranes, as well as uterine tissues (i.e., decidua and myometrium). Pro-inflammatory cytokines and chemokines activate circulating maternal peripheral leukocytes as well as the uterine vascular endothelium to permit leukocyte infiltration into the uterus. This inflammatory milieu, in the absence of infection, is required for the initiation of labour as the uterine-infiltrated leukocytes secrete matrix metalloproteinases to induce fetal membrane rupture and cervical ripening as well as various labour mediators, which promote contractions of the myometrium. Myometrial activation at term and the onset of labour contractions are directly related to the changes in the ovarian/placental hormone progesterone and its downstream mediators (i.e., the progesterone receptors, PRA/B), which are also critical for maintenance of pregnancy. Our recent data provides direct evidence in support of local and functional P4 withdrawal in the uterine muscle (myometrium) via the activator protein-1 (AP-1) mediated pathway. This review outlines known mechanisms regulating activation of human labour, including progesterone and cytokine signaling. Understanding of the molecular mechanism of myometrial activation and labour onset could facilitate the development of new therapeutics for high-risk pregnant women to prevent premature uterine activation and preterm birth.

Myometrial activation: Novel concepts underlying labor

Term labour is a state of physiological inflammation orchestrated by multiple uterine tissues (both fetal and maternal). This physiological inflammation preceding and accompanying labour onset is characterized by an increase in cytokine and chemokine secretion by the fetal membranes, as well as uterine tissues (i.e., decidua and myometrium). Pro-inflammatory cytokines and chemokines activate circulating maternal peripheral leukocytes as well as the uterine vascular endothelium to permit leukocyte infiltration into the uterus. This inflammatory milieu, in the absence of infection, is required for the initiation of labour as the uterine-infiltrated leukocytes secrete matrix metalloproteinases to induce fetal membrane rupture and cervical ripening as well as various labour mediators, which promote contractions of the myometrium. Myometrial activation at term and the onset of labour contractions are directly related to the changes in the ovarian/placental hormone progesterone and its downstream mediators (i.e., the progesterone receptors, PRA/B), which are also critical for maintenance of pregnancy. Our recent data provides direct evidence in support of local and functional P4 withdrawal in the uterine muscle (myometrium) via the activator protein-1 (AP-1) mediated pathway. This review outlines known mechanisms regulating activation of human labour, including progesterone and cytokine signaling. Understanding of the molecular mechanism of myometrial activation and labour onset could facilitate the development of new therapeutics for high-risk pregnant women to prevent premature uterine activation and preterm birth.

Reconstruction of Cell Surface Densities of Ion Pumps, Exchangers, and Channels from mRNA Expression, Conductance Kinetics, Whole-Cell Calcium, and Current-Clamp Voltage Recordings, with an Application to Human Uterine Smooth Muscle Cells

Uterine smooth muscle cells remain quiescent throughout most of gestation, only generating spontaneous action potentials immediately prior to, and during, labor. This study presents a method that combines transcriptomics with biophysical recordings to characterise the conductance repertoire of these cells, the ‘conductance repertoire’ being the total complement of ion channels and transporters expressed by an electrically active cell. Transcriptomic analysis provides a set of potential electrogenic entities, of which the conductance repertoire is a subset. Each entity within the conductance repertoire was modeled independently and its gating parameter values were fixed using the available biophysical data. The only remaining free parameters were the surface densities for each entity. We characterise the space of combinations of surface densities (density vectors) consistent with experimentally observed membrane potential and calcium waveforms. This yields insights on the functional redundancy of the system as well as its behavioral versatility. Our approach couples high-throughput transcriptomic data with physiological behaviors in health and disease, and provides a formal method to link genotype to phenotype in excitable systems. We accurately predict current densities and chart functional redundancy. For example, we find that to evoke the observed voltage waveform, the BK channel is functionally redundant whereas hERG is essential. Furthermore, our analysis suggests that activation of calcium-activated chloride conductances by intracellular calcium release is the key factor underlying spontaneous depolarisations.

A well-known problem in electrophysiologal modeling is that the parameters of the gating kinetics of the ion channels cannot be uniquely determined from observed behavior at the cellular level. One solution is to employ simplified “macroscopic” currents that mimic the behavior of aggregates of distinct entities at the protein level. The gating parameters of each channel or pump can be determined by studying it in isolation, leaving the general problem of finding the densities at which the channels occur in the plasma membrane. We propose an approach, which we apply to uterine smooth muscle cells, whereby we constrain the list of possible entities by means of transcriptomics and chart the indeterminacy of the problem in terms of the kernel of the corresponding linear transformation. A graphical representation of this kernel visualises the functional redundancy of the system. We show that the role of certain conductances can be fulfilled, or compensated for, by suitable combinations of other conductances; this is not always the case, and such “non-substitutable” conductances can be regarded as functionally non-redundant. Electrogenic entities belonging to the latter category are suitable putative clinical targets.

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.

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.

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.

Prediction and prevention of spontaneous preterm birth in twin gestations

The incidence of twin gestation has increased significantly over the past 30 years. One of the most significant public health implications of this trend is the increased incidence of preterm birth (PTB). Efforts to improve neonatal outcomes must address the rate of PTB, particularly among multiple gestations, which contribute a disproportionate share to the burden of PTB and neonatal morbidity. There is evidence that sonographic cervical length assessment and fetal fibronectin testing can identify twin pregnancies at risk for PTB, but, to date, there are no proven interventions for prevention of PTB in this population. Perhaps the most promising is vaginal progesterone, which has been shown to reduce the risk of PTB in a cohort of women that included twin gestations. However, the study lacked statistical power to definitively answer this question. Identification of an appropriate treatment for twin gestations recognized to be at increased risk for prematurity will help to decrease overall rate of PTB, a significant public health problem in the United States.

Elevated levels of uterine anti-apoptotic signaling may activate NFKB and potentially confer resistance to caspase 3-mediated apoptotic cell death during pregnancy in mice

Preserving the uterus in a state of relative quiescence is vital to the maintenance of a successful pregnancy. Elevated cytoplasmic levels of uterine caspase 3 during pregnancy have been proposed as a potential regulator of uterine quiescence through direct targeting and disabling of the uterine contractile architecture. However, despite highly elevated levels of uterine caspase 3 during pregnancy, there is minimal evidence of apoptosis. This current study defines the mechanism whereby the pregnant uterine myocyte may harness the tocolytic activity of active caspases while avoiding apoptotic cell death. Using the pregnant mouse model, we have analyzed the uterus for changes in pro- and antiapoptotic signaling patterns associated with the advancing stages of pregnancy. Briefly, we have found that members of the IAP family, such as SURVIVIN and XIAP, and the Bcl2 family members, such as MCL1, are elevated in the uterine myocyte during late gestation. The IAP family members are the only endogenous inhibitors of active caspase 3, and MCL1 limits activation of caspase 3 by suppressing proapoptotic signaling. Elevated XIAP levels partner with SURVIVIN, resulting in increased levels of the antiapoptotic MCL1 via NFKB activation; these together have the potential to limit both the activity and level of active caspase 3 in the pregnant uterus as term approaches. We propose that modification of these antiapoptotic signaling partners allows the pregnant uterus to escape the apoptotic action of elevated active caspase 3 levels but also functions to limit the levels of active uterine caspase 3 near term.

Progesterone-regulated caspase 3 action in the mouse may play a role in uterine quiescence during pregnancy through fragmentation of uterine myocyte contractile proteins

The appropriate timing of the onset of labor is critical to a successful pregnancy, with potentially devastating consequences resulting to both the mother and child with the onset of preterm labor. In this study, we tested the central hypothesis that progesterone maintains uterine quiescence through regulation of active uterine caspase 3. Using the mouse as our model system, we examined, by Western blot analysis, levels of active caspase 3 and its association with the degradation of uterine contractile proteins during pregnancy. Our data demonstrate that caspase 3-specific cleavage fragments of uterine myocyte contractile proteins are elevated in late gestation. Prior to the onset of labor, active caspase 3 levels and fragmentation of the uterine myocyte contractile proteins decline. We postulate that uterine caspase 3 acts as an anticontractile agent maintaining uterine quiescence through degradation of uterine contractile proteins during late pregnancy. We propose that decreased progesterone action during the final days of pregnancy controls the timing of the onset of uterine contractions by removing the anticontractile action of the apoptotic protein caspase 3 locally in the pregnant myometrium.

Physiology of myometrial function: intercellular coupling and its role in uterine contractility

The mammalian uterus is composed of a preponderance of small smooth muscle cells usually aligned in two layers. The number of muscle cells in the human uterus at term is estimated at 200 billion, each minute fusiform cell measuring about 5–10μm in diameter and about 200μm in length. The main function of the uterus is to harbour the developing fetus during pregnancy and then to contract vigorously during labour to expel the products of conception. In order for the uterus to contract rhythmically and forcefully, a mechanism must exist to allow interaction between muscle cells in order to achieve synchronous activity. Phasic or cyclical patterns of contractile activity of the uterus cannot be accounted for by stimulation or inhibition from the nervous or endocrine systems. Since myometrial cells are dependent upon action potentials for their contractile processes, some system must be present between the muscle cells for the propagation of action potentials between them. The observation that gap junctions occur in large numbers between myometrial cells during parturition is thought to be significant in this regard and they are considered to play an essential role in parturition and in the control and co-ordination of uterine contractility. In this brief review, we will discuss the role of gap junctions in the modulation of myometrial contractility and the mechanisms that regulate their synthesis and permeability.

The role of voltage-gated potassium channels in the regulation of mouse uterine contractility

BACKGROUND

Uterine smooth muscle cells exhibit ionic currents that appear to be important in the control of uterine contractility, but how these currents might produce the changes in contractile activity seen in pregnant myometrium has not been established. There are conflicting reports concerning the role of voltage-gated potassium (Kv) channels and large-conductance, calcium-activated potassium (BK) channels in the regulation of uterine contractility. In this study we provide molecular and functional evidence for a role for Kv channels in the regulation of spontaneous contractile activity in mouse myometrium, and also demonstrate a change in Kv channel regulation of contractility in pregnant mouse myometrium.

METHODS

Functional assays which evaluated the effects of channel blockers and various contractile agonists were accomplished by quantifying contractility of isolated uterine smooth muscle obtained from nonpregnant mice as well as mice at various stages of pregnancy. Expression of Kv channel proteins in isolated uterine smooth muscle was evaluated by Western blots.

RESULTS

The Kv channel blocker 4-aminopyridine (4-AP) caused contractions in nonpregnant mouse myometrium (EC50 = 54 micromolar, maximal effect at 300 micromolar) but this effect disappeared in pregnant mice; similarly, the Kv4.2/Kv4.3 blocker phrixotoxin-2 caused contractions in nonpregnant, but not pregnant, myometrium. Contractile responses to 4-AP were not dependent upon nerves, as neither tetrodotoxin nor storage of tissues at room temperature significantly altered these responses, nor were responses dependent upon the presence of the endometrium. Spontaneous contractions and contractions in response to 4-AP did not appear to be mediated by BK, as the BK channel-selective blockers iberiotoxin, verruculogen, or tetraethylammonium failed to affect either spontaneous contractions or 4-AP-elicited responses. A number of different Kv channel alpha subunit proteins were found in isolated myometrium from both nonpregnant and term-pregnant mice, and one of these proteins - Kv4.3 - was found to disappear in term-pregnant tissues.

CONCLUSION

These findings suggest a role for Kv channels in the regulation of uterine contractility, and that changes in the expression and/or function of specific Kv channels may account for the functional changes seen in pregnant myometrium.

Preterm labour. Myometrial function in prematurity

The primary function of the uterus during gestation is to harbour the growing conceptus in a largely quiescent environment. Upon maturation of the fetus to a point sufficient for extrauterine survival, the uterus must remodel itself sufficiently to generate forceful contractions during labour. During preterm delivery, the process of remodelling of the myometrium occurs early due to a number of different causes, although the underlying basis for myometrial contraction remains the same. This review summarises the anatomical, physiological and molecular basis for contraction. We describe the fibre structure of the human uterus and how this relates to the spread of electrical excitation during a contraction. The process of excitation within a single myometrial cell is described, as well as how this relates to contraction. We then focus on how excitation-contraction coupling is modulated by intercellular communication, pharmacomechanical-coupling and hormonal milieu. Lastly, we consider the actions of the commonly accepted uterine agonists oxytocin, prostaglandin F(2alpha), and prostaglandin E(2), and the tocolytic ritodrine.

2,2'-Dichlorobiphenyl decreases amplitude and synchronization of uterine contractions through MAPK1-mediated phosphorylation of GJA1 (connexin43) and inhibition of myometrial gap junctions

The present study examined the hypothesis that inhibition of myometrial gap junctions through MAPK1-induced phosphorylation of GJA1 (connexin43) leads to inhibition of spontaneous phasic uterine contractions by 2,2'-dichlorobiphenyl (2,2'-DCB). Uterine strips from Gestation Day 10-pregnant rats exposed in muscle baths to 2,2'-DCB exhibited increased oscillatory frequency and decreased amplitude and synchronization of contractions. To assess effects on gap junctions, Lucifer yellow was injected into myometrial cells and transfer to adjacent cells was scored. After a 1-h treatment, 100 microM 2,2'-DCB decreased Lucifer yellow intercellular transfer in a concentration-dependent manner. The MAP2K1 inhibitor PD98059 increased percentage of dye transfer to adjacent myometrial cells from 18% in cultures exposed for 1 h to 100 microM 2,2'-DCB alone to 48% in cultures cotreated with 50 microM PD98059 and 100 microM 2,2'-DCB. In contrast, the conventional PRKC inhibitor Gö6976 (10 microM) had no significant effect on 2,2'-DCB-induced inhibition of dye transfer. Western blotting showed about a 4.5-fold increase in phosphorylation of GJA1 at S255, a MAPK1 site, after exposure to 100 microM 2,2'-DCB compared to untreated and solvent controls. However, there was no difference in phosphorylation of GJA1 at S368, a PRKC site. Cells treated with 2,2'-DCB increased phosphorylated MAPK1, implicating the increase of activation of MAPK1. Cotreatment with 100 microM 2,2'-DCB and 5 microM PD98059 reversed 2,2'-DCB-induced modification of uterine contractions and increase of pGJA1(S255) in uterine strips. Therefore, this study suggests that 2,2'-DCB decreases amplitude and synchronization of uterine contractions mediated through MAPK1-mediated phosphorylation of GJA1 and subsequent inhibition of myometrial gap junctions.

Biphasic lindane-induced oxidation of glutathione and inhibition of gap junctions in myometrial cells

The insecticide lindane (gamma-hexachlorocyclohexane) inhibits gap junction intercellular communication in rat myometrial cells by a mechanism involving oxidative stress. We hypothesized that oxidation of reduced glutathione (GSH) to glutathione disulfide (GSSG) and subsequent S-glutathionylation provide a mechanistic link between lindane-induced oxidative stress and lindane's inhibition of myometrial gap junction communication. Gap junction communication between cultured rat myometrial myocytes was assessed by Lucifer yellow dye transfer after microinjection. A biphasic pattern was confirmed, with dye transfer nearly abolished after 1 h of exposure to 100 microM lindane followed initially by recovery after lindane removal, and then the development 4 h after termination of lindane exposure of a delayed-onset, sustained inhibition that continued for 96 h. As measured by HPLC, cellular GSH varied over a 24-h period in a biphasic fashion that paralleled lindane-induced inhibition of dye transfer, whereas GSSG levels increased in a manner inversely related to GSH. In accordance, GSH/GSSG ratios were depressed at times when GSH and dye transfer were low. Lindane substantially increased S-glutathionylation in a concentration-dependent manner, measured biochemically by GSSG reductase-stimulated release of GSH from precipitated proteins. Furthermore, treatments that promoted accumulation of GSSG (50 microM diamide and 25 microM 1,3-bis(2-chloroethyl)-1-nitrosourea [BCNU]) inhibited Lucifer yellow dye transfer between myometrial cells. Findings that lindane induced GSH oxidation to GSSG with increased S-glutathionylation, together with the diamide and BCNU results, suggest that oxidation of GSH to GSSG is a component of the mechanism by which lindane inhibits myometrial gap junctions.

Tissue-level bioelectrical signals as the trigger for uterine contractions in human pregnancy

OBJECTIVE

To investigate the relationship between tissue-level bioelectrical signals and tension development during oxytocin-stimulated contractions of human myometrium.

METHODS

We performed in vitro muscle bath experiments on human myometrial tissue strips while simultaneously monitoring bioelectrical activity with two loose-contact electrodes. Tissue was obtained by myometrial biopsy from term pregnant women at the time of cesarean delivery. Tissue strips (1 x 1 x 10 mm) were hung vertically and maintained in culture in media while suspending a 400-mg weight. The tissue exhibited strong isometric contractions in response to 5-nM oxytocin even after 10 to 14 days in culture. The electrodes were separated by 4 mm, and allowed us to distinguish between local and tissue-level bioelectrical signals. Electrical activity was monitored using two, independent AC-coupled amplifiers.

RESULTS

Following exposure to oxytocin, the tissue contracted periodically every 3.5 to 6 minutes, with each contraction lasting 50 to 60 seconds. Near the beginning of each contraction, synchronized spike-like bioelectrical signals were observed in both channels. These bioelectrical signals from each electrode lasted approximately 2 seconds and demonstrated unique fingerprints that were repetitive and remarkably similar over 18 contractions. In each of the contractions, the onset of rapid force increases was synchronized with the bioelectrical signals. Cell recruitment continued during the plateau phase of each contraction even though other tissue-level bioelectrical signals were not observed.

CONCLUSION

These findings suggest that the trigger for the initiation of each contraction is a tissue-level bioelectrical event, and some cells are initially recruited to participate in each contraction by excitation-contraction coupling. After the initial phase of the contraction, cells are recruited by a nonelectrical mechanism.

Normal labor associated with changes in uterine heparan sulfate proteoglycan expression and localization

HYPOTHESIS

Proteoglycans are well-known modulators of intercellular communication and signaling. Remodeling of the proteoglycans in the human uterus occurs throughout pregnancy, and during labor. We therefore hypothesize that heparan sulfate proteoglycans (HSPGs) play an important role in establishing normal labor. In this study HSPGs were characterized and localized in human uterine tissue.

METHODS

Uterine biopsies were obtained from four nonpregnant women, four women during elective cesarean section and four during emergency cesarean section. The biopsies were extracted using 4 m guanidinium hydrochloride (GuHCL). HSPGs were then purified by repeated ion-exchange chromatography on dehydroepiandrosterone (DEAE)-cellulose after digestion with chondroitinase ABC and finally precipitated with Alcian blue. HSPGs were identified by agarose gel electrophoresis and Western blotting. Controlled degradation of the heparan sulfate (HS) side-chains was performed using heparitinase or deglycosylation with trifluoromethanesulfonic acid (TFMS). The resulting core proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and visualized by Coomassie staining. HSPGs were localized in uterine tissue by immunohistochemistry.

RESULTS

SDS-PAGE after deglycosylation indicated the presence of multiple distinct core proteins tentatively identified as syndecans 1-4 and glypican 1. Western blots confirmed the presence of these proteoglycans and also perlecan. Immunohistochemistry revealed that the HSPGs were localized mainly in the smooth muscle with few in the extracellular matrix (ECM). Syndecan 3, the dominant proteoglycan, showed the most pronounced changes during pregnancy and labor.

CONCLUSION

For the first time several heparan sulfate proteoglycans have been identified and localized in the human uterus and shown to vary in expression during pregnancy and labor. Syndecan 3 had the most outstanding features in this respect.

Sustained inhibition of rat myometrial gap junctions and contractions by lindane

BACKGROUND

Gap junctions increase in size and abundance coincident with parturition, forming an intercellular communication network that permits the uterus to develop the forceful, coordinated contractions necessary for delivery of the fetus. Lindane, a pesticide used in the human and veterinary treatment of scabies and lice as well as in agricultural applications, inhibits uterine contractions in vitro, inhibits myometrial gap junctions, and has been associated with prolonged gestation length in rats. The aim of the present study was to investigate whether brief exposures to lindane would elicit sustained inhibition of rat uterine contractile activity and myometrial gap junction intercellular communication.

METHODS

To examine effects on uterine contraction, longitudinal uterine strips isolated from late gestation (day 20) rats were exposed to lindane in muscle baths and monitored for changes in spontaneous phasic contractions during and after exposure to lindane. Lucifer yellow dye transfer between myometrial cells in culture was used to monitor gap junction intercellular communication.

RESULTS

During a 1-h exposure, 10 micro M and 100 micro M lindane decreased peak force and frequency of uterine contraction but 1 micro M lindane did not. After removal of the exposure buffer, contraction force remained significantly depressed in uterine strips exposed to 100 micro M lindane, returning to less than 50% basal levels 5 h after cessation of lindane exposure. In cultured myometrial myocytes, significant sustained inhibition of Lucifer yellow dye transfer was observed 24 h after lindane exposures as brief as 10 min and as low as 0.1 micro M lindane.

CONCLUSION

Brief in vitro exposures to lindane have long-term effects on myometrial functions that are necessary for parturition, inhibiting spontaneous phasic contractions in late gestation rat uterus and gap junction intercellular communication in myometrial cell cultures.

Effects of RU 486 on electrical activity, on sexual steroid and prostaglandin F2 alpha concentrations in the myometrium at mid-pregnancy in the rat

Effects of RU 486 (10 mg.kg-1, per.os) were assessed at mid-pregnancy in the rat. One hour after RU 486 treatment, myometrial electrical activity stayed low. It increased from the 3rd hour after administration of RU 486 and a perfect synchronization of the bursts of the action potentials was observed from the 6th h to the 24th h. Tissular steroid hormones and PGF2 alpha, evaluated at hour 6 after RU 486 administration, showed a decrease of progesterone concentrations in both myometrium and uterus. Estradiol levels decreased in uterus whereas, PGF2 alpha levels increased in both myometrium and uterus. These results show for the first time that RU 486 strongly increases the myometrial electrical activity in the rat at mid-pregnancy. This action was closely related to E2, P4 and PGF2 alpha concentrations.

Hypothalamic orexin-A-immunpositive neurons express Fos in response to central glucopenia

Reports that glucose antimetabolite treatment elicits hyperphagia and hyperglycemia suggest that decreased oxidation of this energy substrate elicits compensatory responses that enhance cellular fuel availability. Neurons the lateral hypothalamic area (LHA) synthesize the orectic neuropeptide, orexin-A (ORX-A). The present study evaluated the functional responsiveness of orexinergic neurons to glucopenia by investigating whether these cells express the genomic regulatory protein, Fos, in response to glucoprivation. Adult male rats were sacrificed 2h after i.p. (400 mg/kg) or intracerebroventricular (i.c.v.; 100 microg) administration of the antimetabolite, 2-deoxy-D-glucose (2DG) or saline. Sections through the LHA, from the level of the paraventricular nucleus (PVN) to the posterior hypothalamic area (PHA), were processed by dual-label immunocytochemistry for Fos- and OXY-A-immunoreactivity (-ir). Although orexinergic neurons expressed negligible Fos-ir following vehicle administration, dual-labeled ORX-A neurons were observed in the LHA, as well as the dorsomedial hypothalamic nucleus (DMN) and PHA, in both drug-treated groups. Bilateral cell counts from representative levels of the LHA, DMN, and PHA showed that in each structure, a greater proportion of ORX-A neurons were immunostained for Fos in response to systemic than following i.c.v. treatment with 2DG. These results provide evidence for the transcriptional activation of hypothalamic ORX-A neurons by diminished glucose availability, data that suggest that these cells may function within central pathways that govern adaptive responses to deficits of this substrate fuel. The findings also support the view that a proportion of this phenotypic population is responsive to glucoprivic stimuli of central origin.

Antioxidants prevent gamma-hexachlorocyclohexane-induced inhibition of rat myometrial gap junctions and contractions

Lindane (gamma-hexachlorocyclohexane) is a commonly used pesticide that bioaccumulates in mammalian adipose tissue. Lindane inhibits gap junctional intercellular communication and oscillatory contractions of pregnant rat myometrium in vitro. The present study investigated the role of oxidative stress in lindane's inhibition of myometrial function in mid-gestation pregnant rat uteri. Lucifer yellow dye was microinjected into cultured myocytes to assess gap junctional intercellular communication. Lindane exposure (100 microM) resulted in a time-dependent, biphasic inhibition of dye transfer. This pattern of inhibition was also seen upon cell exposure to the pro-oxidant, tert-butyl hydroperoxide (100 microM). Lindane's initial and secondary-onset dye transfer inhibitions were reversed by cotreatment and pretreatment with the antioxidants, alpha-tocopherol (25-100 microM), diphenyl-1,4-phenylene diamine (10-30 microM), and superoxide dismutase (100-400 U/ml). D-mannitol (100-300 mM) also reversed lindane's initial dye transfer inhibition. Nitro blue tetrazolium reduction to formazan (measured spectrophotometrically) was elevated upon exposure of cultured cells to lindane or tert-butyl hydroperoxide, indicating the presence of reducing agents. Lipid peroxidation, assessed as thiobarbituric acid-reactive substances, was also elevated in lindane-exposed cell cultures. alpha-Tocopherol reversed this elevation. Finally, uterine contractility was assessed by measuring isometric contractions of uterine strips hung in standard muscle baths. Pretreatment with alpha-tocopherol prevented lindane's abolishment of uterine contractions in vitro. These data support the hypothesis that lindane inhibits uterine contractility and myometrial gap junctions by establishing an oxidative stress environment.

A prospective evaluation of the pathogenesis of detrusor instability in women, using electron microscopy and immunohistochemistry

OBJECTIVE

To characterize the types of detrusor smooth muscle junctions in the bladders of women with detrusor instability and in a control group without, and to assess whether there are differences in the cell junctions between these groups.

PATIENTS AND METHODS

The study included 13 women with detrusor instability (median age 57 years, range 32-86) and 11 control women (median age 50 years, range 33-62). Bladder biopsies were taken from each participant, processed for electron microscopy and immunohistochemistry (using a labelled antibody to vinculin) and analysed by investigators who were unaware of the patients' diagnoses.

RESULTS

Adherens (intermediate) junctions in classic and rudimentary forms were present in all biopsies from patients and controls. Adherens junctions and dense plaques occupied almost the complete cell border in most samples. Complete immunohistochemistry was possible in seven patients and five controls. In almost every detrusor smooth muscle cell studied, there was staining of the entire cell border with labelled antibody to vinculin in all biopsies.

CONCLUSIONS

This study provides evidence against an ultrastructural basis for idiopathic detrusor instability based on possible differences in detrusor smooth muscle intercellular junctions. Virtually the entire cell membrane of detrusor smooth muscle fibres is occupied by adherens junctions in classic and rudimentary forms, and with dense plaques present in samples from women with an unstable bladder and from controls. There was no junction detected in those with instability that was not present in the control group. The adherens junctions in the bladder facilitate mechanical coupling between cells.

Gap junctions: fates worse than death?

The reasons for the molecular heterogeneity of connexin channels in vivo remain unclear. Functional replacement of one connexin gene with another has now revealed unexpected phenotypes and shows that cellular homeostasis depends not simply on cell-cell communication but also on the correct types of connexin.

Sensitivity of myometrium to CGRP varies during mouse estrous cycle and in response to progesterone

Calcitonin gene-related peptide (CGRP) inhibits contractions of the myometrium. Isometric force measurements on myometrial strips were carried out to monitor the inhibitory capacity of CGRP in the myometrium during the estrous cycle and in response to estrogen and progesterone in ovariectomized mice. CGRP inhibition of KCl-induced contractions was lowest at estrus and significantly increased during metestrus and diestrus. Progesterone treatment of ovariectomized mice resulted in a significant increase in the responsiveness of the myometrium to CGRP. Expression of CGRP-receptor component protein (CGRP-RCP), a marker of CGRP-receptor expression, was quantitated by Western and Northern blot analyses. The levels of inhibition exerted by CGRP during the various stages of the estrous cycle and in response to steroid hormone treatment correlated with the protein levels of CGRP-RCP. The mRNA levels did not change significantly during the estrous cycle or in response to hormone treatment, indicating that the regulation of CGRP-RCP protein does not occur at the transcriptional level. CGRP had an inhibitory effect both when applied before the stimulus for contraction and when applied during a sustained contracture induced by KCl. This suggests that CGRP-induced generation of second messengers can influence late events in electro-/chemomechanical coupling and/or the contractile machinery directly.

Gap junctions in intestinal smooth muscle and interstitial cells of Cajal

This manuscript reviews gap junctions' roles in control of intestinal motility. Gap junctions (GJs) of small intestine (SmIn) are found between circular muscle (CM) cells, between interstitial cells of Cajal (ICC) of deep muscular plexus (DMP) and between them and adjacent outer circular muscle (OCM). GJs between longitudinal muscle (LM) cells or between cells of inner circular muscle (ICM) have not been reported. Occasional GJs have been reported between ICC of the myenteric plexus (MyP) and rarely between these ICC and adjacent LM or CM cells, or between ICC within CM and smooth muscle cells. In the colon (Co) of several species a special network of ICC lines the inner border of CM, the submuscular plexus (SP). GJs are found between ICCs and between them and CM cells. The ICC of MyP of Co are associated with LM and CM; occasional GJs exist between ICC and each muscle layer. Small GJs are missed by electron microscopy or light microscopic Immunocytochemistry. Therefore, GJ coupling may exist without demonstrated GJs. The consequences for the pacemaking functions of ICC networks of varied densities of GJ between ICC and between ICC of MyP or DMP or of SP and CM are considered. Connexins (Cxs) that compose intestinal GJs may affect coupling, but are incompletely known. Understanding of the role of GJs in coordinating intestinal motility requires knowing: (1) what passes through gap junctions to couple ICC to smooth muscle cells; (2) what Cx with what conductances and what modulatory controls connect ICC and smooth muscle cells; (3) whether smooth muscles can generate slow waves independent of ICC networks; and (4) what happens to motility, slow waves, and IJPs when GJs are selectively uncoupled.

Development and plasticity of interstitial cells of Cajal

Interstitial cells of Cajal (ICC) are the pacemakers in gastrointestinal (GI) muscles, and these cells also mediate or transduce inputs from the enteric nervous system. Different classes of ICC are involved in pacemaking and neurotransmission. ICC express specific ionic conductances that make them unique in their ability to generate and propagate slow waves in GI muscles or transduce neural inputs. Much of what we know about the function of ICC comes from developmental studies that were made possible by the discoveries that ICC express c-kit and proper development of ICC depends upon signalling via the Kit receptor pathway. Manipulating Kit signalling with reagents to block the receptor or downstream signalling pathways or by using mutant mice in which Kit or its ligand, stem cell factor, are defective has allowed novel studies into the specific functions of the different classes of ICC in several regions of the GI tract. Kit is also a surface antigen that can be used to conveniently label ICC in GI muscles. Immunohistochemical studies using Kit antibodies have expanded our knowledge about the ICC phenotype, the structure of ICC networks, the interactions of ICC with other cells in the gut wall, and the loss of ICC in some clinical disorders. Preparations made devoid of ICC have also allowed analysis of the consequences of losing specific classes of ICC on GI motility. This review describes recent advances in our knowledge about the development and plasticity of ICC and how developmental studies have contributed to our understanding of the functions of ICC. We have reviewed the clinical literature and discussed how loss or defects in ICC affect GI motor function.

Gap junction currents in cultured muscle cells from human myometrium

OBJECTIVE

The electrophysiologic properties of gap junctions between human myometrial smooth muscle cells were studied.

STUDY DESIGN

Double whole-cell patch clamp recordings were made on pairs of cells from primary cultures of myometrial cells from women undergoing cesarean section. Macroscopic gap junction currents were measured as the change in current in a cell held at a constant voltage while the other member of a pair was subjected to a test pulse of voltage. The blockade by halothane was examined.

RESULTS

Mean junctional conductance between pairs of cells was 23 +/- 14 nanosiemens (n = 57). Instantaneous gap junction conductance was constant as a function of transjunctional voltage. For transjunctional voltages of < or = 50 mV, currents were constant during a 5-second test pulse. For larger voltages, however, the currents showed a time-dependent decay. The currents were blocked completely and reversibly with 3.5 mmol/L halothane. Single-channel conductances of 60 picosiemens and 15 picosiemens were observed.

CONCLUSION

This first study of gap junction currents in human myometrial cells confirms that connexin43 is the major functional constituent. Functional studies of myometrial gap junction channels may suggest new strategies for controlling uterine contractility.

Glucoprivic induction of Fos immunoreactivity in hypothalamic dopaminergic neurons

The hypothalamic neurotransmitter dopamine (DA) regulates pituitary secretion of the glucoregulatory hormones, growth hormone (GH) and adrenocorticotropin (ACTH). The glucose antimetabolite, 2-deoxy-D-glucose (2DG), elicits expression of the proto-oncogene product Fos, which is expressed in hypothalamic structures where DA is synthesized. These studies utilized dual-label immunocytochemistry to determine whether discrete DA neuron populations in this region of the brain exhibit Fos immunoreactivity (-ir) in response to glucopenia. Ovariectomized female rats implanted s.c. with exogenous estradiol or vehicle were injected with 2DG (400 mg/kg, i.p.) or saline, and sacrificed 2 h later. Whereas Fos-ir was negligible after saline administration, 2DG induced expression of Fos-ir by TH-ir neurons in the paraventricular (PVN), periventricular (Pe) and arcuate nuclei (ARC), and in the anterior hypothalamic area (AHA). TH-ir neurons in the zona incerta did not express Fos-ir following 2DG. Although mean numbers of co-labeled neurons in the Pe, PVN and AHA did not differ between estradiol- and non-steroid-treated rats, the former group exhibited significantly higher numbers of TH-positive plus Fos-positive neurons in the ARC in response to 2DG. These results reveal the functional responsiveness of discrete DA neuron populations to glucoprivation, and indicate that estradiol enhances cellular accumulation of Fos-ir by ARC DA neurons during this metabolic challenge.

Increase of myometrial activity correlated with variations in 17 beta-estradiol and progesterone uterine concentrations in mid-term pregnant rat: estrogen agonist effect of 4-hydroxytamoxifen

The objective of this investigation was to examine the effects of 4-hydroxytamoxifen on the uterine activity. For this, we evaluated the electrical activity of the myometrium, chronically, in conscious unrestrained rats at mid-pregnancy. We also examined the tissular progesterone and 17 beta-estradiol concentrations in the myometrium and uterus 6 hours after administration of 4-hydroxytamoxifen. Comparison of myometrial electrical activities recorded during the control period with those obtained during the two periods (6 and 24 hours) after administration of 4-hydroxytamoxifen (80 micrograms.kg-1, s.c.) showed an increase in simultaneity of uterine contractions (P < 0.01). Tissular steroid hormone measurement by radioimmunoassay shows a fall of progesterone in the myometrium (P < 0.001) and of 17 beta-estradiol in the uterus (P < 0.01), 6 hours after administration of 4-hydroxytamoxifen. In the myometrium, for 50% of animals, 17 beta-estradiol concentration decreased (P < 0.01) and for 50% of animals it increased (P < 0.05). The decrease in progesterone is significant in the myometrium and in the whole uterus (respectively P < 0.001 and P < 0.01), 24 hours after administration of 4-hydroxytamoxifen. The 17 beta-estradiol concentration significantly decreased for all animals in the myometrium (P < 0.01) and in the uterus (P < 0.01), after this time. It appears that variation in progesterone induces the activation of uterine motility and exerts an effect on some factors involved in the regulation of the rat myometrium at mid-pregnancy.

Voltage-clamp studies of gap junctions between uterine muscle cells during term and preterm labor

Gap junctions between myometrial cells increase dramatically during the final stages of pregnancy. To study the functional consequences, we have applied the double-whole-cell voltage-clamp technique to freshly isolated pairs of cells from rat circular and longitudinal myometrium. Junctional conductance was greater between circular muscle-cell pairs from rats delivering either at term (32 +/- 16 nS, mean +/- SD, n = 128) or preterm (26 +/- 17 nS, n = 33) compared with normal preterm (4.7 +/- 7.6 nS, n = 114) and postpartum (6.5 +/- 10 nS, n = 16); cell pairs from the longitudinal layer showed similar differences. The macroscopic gap junction currents decayed slowly from an instantaneous, constant-conductance level to a steady-state level described by quasisymmetrical Boltzmann functions of transjunctional voltage. In half of circular-layer cell pairs, the voltage dependence of myometrial gap junction conductance is more apparent at smaller transjunctional voltages (< 30 mV) than for other tissues expressing mainly connexin-43. This unusual degree of voltage dependence, although slow, operates over time intervals that are physiologically relevant for uterine muscle. Using weakly coupled pairs, we observed two unitary conductance states: 85 pS (85-90% of events) and 25 pS. These measurements of junctional conductance support the hypothesis that heightened electrical coupling between the smooth muscle cells of the uterine wall emerges late in pregnancy, in preparation for the massive, coordinate contractions of labor.

Gap junction regulation in the uterus and ovaries of immature rats by estrogen and progesterone

The effects of estrogen (E2) and progesterone (P) were examined on the expression levels of multiple gap junction (GJ) gene products (alpha 1 = Cx43, beta 1 = Cx32, beta 2 = Cx26) in the uterus and ovaries of immature rats by immunohistochemistry, electron microscopy and northern blot analysis. E2 induced the expression of alpha 1 connexin in the uterus (specifically in the myometrium and in endometrial stroma proximal to luminal epithelium) and ovaries. The E2-induced alpha 1 expression was completely suppressed by P in the uterus, but only partly in ovaries. Steroid hormones also modulated the quantity, size, and distribution of beta 1 and beta 2 containing junctional plaques along lateral cell borders in polarized luminal and glandular uterine epithelia. Small GJs were detected at basolateral regions in proliferative luminal epithelium following administration of E2. In contrast, large GJs were localized at subapical-lateral cell borders of the secretory epithelium following P-treatment. The co-administration of E2 + P had a synergistic effect on beta 1 and beta 2 expression in the luminal epithelium, but an inhibitory effect on beta 2 expression in glandular epithelium. Myometrial GJs were detected in freeze-fracture replicas as aggregates containing regularly arranged particles with particle free zones. In contrast, GJs in secretory epithelium contained particles which were arranged in a non-crystalline fashion. These GJs contained domains of mixed and segregated beta 1 and beta 2 antigens within a single plaque as revealed by laser scanning confocal microscopy analysis of immuno-double-labeled secretory epithelium. The demonstration of segregated antigens within a single GJ plaque indicates the possibility of multiple channel populations formed by homo-oligomeric connexons. These results suggest that different connexins can be differentially regulated by steroid hormones in different cell types, and that the same steroid hormone can have different effects on the same connexin in different cell types.

Effects of estrogen treatment and inhibition of prostanoid synthesis on myometrial activity and gap junction formation in the oophorectomized ewe

The objective was to elucidate the functional relationship between estradiol-induced changes in myometrial activity, uterine prostanoid synthesis, and gap junction formation in vivo. The study design was as follows. The effects of inhibition of prostanoid synthesis with naproxen on formation of gap junctions and coordination of electrical and mechanical myometrial activity induced by estradiol-17 beta were investigated in 6 chronically instrumented oophorectomized ewes. Prostanoid metabolites were measured in arterial and uterine venous plasma. Myometrial biopsies were obtained to determine gap junction area. The results were that intraarterial administration of 0.1 mg of estradiol-17 beta was followed by a significant increase in maximum rate of rise of the intrauterine pressure cycles and a significant decrease in conduction time of bursts of electrical activity; this response was not altered by pharmacologic inhibition of uterine prostanoid synthesis using naproxen. Estradiol administration during continuous naproxen infusion increased gap junction area. The conclusion is that improved coordination of myometrial activity and formation of myometrial gap junctions induced by estradiol is not mediated by prostaglandins.

Morphological and immunohistochemical differentiation patterns of rabbit uterine epithelium in vitro

We describe morphological and immunohistochemical changes of uterine epithelium from immature rabbits in vitro in response to hormonal treatments, using a matrix-coated semipermeable filter. These investigations were compared to in vivo studies of uterine epithelium from immature rabbits treated with estrogen and/or progesterone. In vitro, polarization of the epithelium seems to be best developed under progesterone dominance, and the pattern of cell organelles is similar to those seen in vivo. Two types of apical protrusions could be observed in cultures treated with progesterone, some shaped like domes, containing cell organelles, and some irregular in shape with small lucent vesicles. Both types of apical differentiation are typical for the in vivo situation. In vitro, estrogen leads to a more pseudostratified growth pattern of the cells. They develop apical protrusions with big vesicles probably containing mucin, as in vivo. Treatment with both steroid hormones leads to a heterogeneous response of the uterine epithelial cells in culture, some cells responding more to the estrogen, others to the progesterone whereas in vivo the progesterone-dominant features are obvious. Immunohistochemistry of uteroglobin in monensin-treated cultures gives evidence for uteroglobin secretion in all cultures, but to a lesser extent in the untreated, and this is strongly increased in cultures treated with estrogen and progesterone. These results correspond to observations made in vivo. This in vitro cell culture method seems therefore to provide a useful model for investigating the regulatory mechanisms of sexual steroid hormones and the cell biology of uterine receptivity.

Therapeutic abortion during the 2nd and 3rd trimesters of pregnancy using a synthetic derivative of prostaglandin E2, sulprostone, administrated intravenously. Based upon 182 cases

OBJECTIVE

The purpose of the study is to assess the efficacy of and adverse events linked to the use of intravenous sulprostone during the 2nd or 3rd trimesters of pregnancy for therapeutic abortion.

STUDY DESIGN

One hundred eighty-two patients (70 nulliparous, 112 multiparous) were hospitalized for therapeutic abortion. The route of administration was invariably intravenous and one single dose of sulprostone was used: 1000 micrograms of sulprostone diluted in 1 l of isotonic saline solution given as a 10-h infusion.

RESULT

Expulsion within the first 24 h was obtained in 70% of cases with a mean induction-expulsion interval of 14 h. In three cases, laparotomy was required for hemorrhagic syndromes.

CONCLUSION

Intravenous sulprostone enable evacuation of uterine contents with minimal adverse reaction. Attention should nevertheless be drawn to the existence of hemorrhagic syndromes.

Nickel-induced increases in gap junctional communication in the uterine cell line SK-UT-1

Previous studies have suggested that gap junctions may have a role in various uterine functions, including parturition. Because nickel has been demonstrated to increase uterine contractility in vitro, the effect of nickel (II) chloride on gap junctional communication was assessed in a tumorigenic uterine cell line, SK-UT-1 (ATCC HTB 114). Cells were exposed in vitro to 25 and 50 microM NiCl2 for 24 h or 100 microM NiCl2 for 3, 12, and 24 h, then functional gap junctional communication was measured as the transfer of Lucifer yellow dye from microinjected donor cells to their primary neighbor cells. Dye transfer was significantly increased only in cell cultures exposed to 100 microM NiCl2 for 24 h, compared to untreated controls, lower doses, and shorter exposure periods. This response was inhibited by the simultaneous co-treatment of SK-UT-1 cells with magnesium by adding 100 microM MgSO4 to the dosing medium. Possible mechanisms and implications for these findings are discussed.

Modulation of cell-to-cell coupling between myometrial cells of the human uterus during pregnancy

OBJECTIVE

The purpose of this study was to investigate changes in cell-to-cell coupling of human myometrium during pregnancy to assess the presence and permeability of gap junctions.

STUDY DESIGN

To evaluate the coupling, input resistance was measured and intercellular spread of Lucifer yellow was observed with microelectrode techniques in intact myometrial preparations from four nonpregnant women, 13 women not in labor, and three women in labor. Octanol, isoproterenol, and dibutyryl adenosine 3',5'-cyclic monophosphate were applied to the preparations to assess their effects on cell-to-cell coupling.

RESULTS

Input resistance of myometrial cells was decreased (p less than 0.001) and intercellular spread of Lucifer yellow was increased during pregnancy. Octanol, isoproterenol, and dibutyryl adenosine 3',5'-cyclic monophosphate rapidly and reversibly increased input resistance (p less than 0.001 for all these agents) and blocked Lucifer yellow spread in tissues from pregnant patients.

CONCLUSIONS

Cell-to-cell coupling between human myometrial cells is spontaneously improved during pregnancy because of the presence of gap junctions. The coupling is rapidly and reversibly decreased by octanol, isoproterenol, and dibutyryl adenosine 3',5'-cyclic monophosphate as a result of decreased permeability of gap junctions. These two methods of modulation of gap junctions are suggested to be major mechanisms for control of myometrial contractile activity in the human uterus during pregnancy.

Characteristics and analysis of uterine electromyographic activity in pregnant cows

The electromyographic activity of the cow uterus in the last trimester of pregnancy was investigated. The investigation was performed on 12 animals and the electrical activity was recorded in the last trimester of pregnancy during 11 different periods until the delivery. The duration of the action potential bursts (APB) recorded during the first 7 periods, was small. It did not exceed 2 seconds. A significant increase, however, was recorded at 7 to 9 days before the labor and it involved all the investigated areas in the uterus. The number of APB of the gravid horn was significantly higher than that recorded at other locations in the uterus with the exception of the day of delivery. A significant correlation was found between the number of APB and the level of magnesium in blood serum. The levels of 17-beta estradiol and progesterone were similar during all studied periods with the exception of the last week, in which a dramatic fall in estradiol level and a significant increase in the progesterone concentration were observed. The results showed that it is possible to distinguish three different phases of electric activity in the cow uterus during the last trimester of pregnancy. The features of these phases were discussed.