An in-vivo model to examine the electromyographic activity of isolated myometrial tissue from pregnant sheep

Strips (2.5 x 3.5 cm) of myometrium alone (MYO) or endometrium/myometrium (ENDO/MYO) were removed from the pregnant horn of sheep (Day 110 of gestation) and transplanted to sites within the omental fat. These explants developed regular bursts of electromyographic (EMG) activity over a period of 7-10 days, as well as a dose-dependent stimulatory response to oxytocin (50-200 mU i.v.). The frequency (per 2 h) of EMG bursts in the MYO (5.3 +/- 0.2) and ENDO/MYO (5.2 +/- 0.3) explants was significantly greater (P less than 0.05) than that of the uterine myometrium (3.0 +/- 0.1), while burst duration (min) in MYO (4.1 +/- 0.2) and ENDO/MYO (4.1 +/- 0.2) explants was significantly (P less than 0.05) less than in the uterine myometrium (7.3 +/- 0.1). The EMG bursts were asynchronous between the explants and uterus, although systemic administration of oxytocin produced a synchronous burst of EMG activity in all three tissues. No differences in EMG activity or responsiveness were apparent between MYO and ENDO/MYO explants. Histological examination of the explant tissue revealed the presence of smooth muscle fibres regularly orientated into two layers; some loss of endometrial tissue was apparent in ENDO/MYO explants. To validate the mechanical integrity of this model we examined the in-vitro contractile activity of myometrial strips prepared from the explants. The strips developed regular spontaneous contractions and demonstrated a dose-dependent stimulation in response to the addition of oxytocin (10(-10) to 10(-4) M) to the bath fluid. These results suggest that spontaneous contractures during pregnancy are probably not due to pulsatile release of stimulants into the systemic circulation, or the direct diffusion of stimulants from intrauterine tissues to the myometrium but are probably caused by factors within the myometrium itself.     

Evidence for an intrinsic control of myometrial contractile periodicity in sheep during pregnancy.

Reduction in concentration of prostaglandins in plasma by administration of sodium meclofenamate to pregnant sheep failed to alter the frequency or duration of electromyographic activity bursts or the response to oxytocin of myometrial tissue transplanted to the omentum. However, a significant (P < 0.05) delay (8.6 +/- 3.8 versus 1.3 +/- 0.3 min) in the myometrial response to oxytocin was observed when the hormone was administered 1 min after a spontaneous burst of electromyographic activity compared with 15 min after a burst, indicating a period of refractoriness. Similarly, the myometrial threshold for electrical stimulation was higher at 10-25% of the interval between contractions than close to the expected time of the next contraction. Stimulation of the myometrium at intervals of 30 s revealed a cycling of the electrical stimulation threshold: significantly higher voltages were required to elicit responses between spontaneous bursts of electromyographic activity (18.0 +/- 2.2 V) than during bursts (11.3 +/- 1.6 V). In contrast, there was no voltage differential in animals close to labour (< 24 h). These data provide no evidence to support a role for prostaglandins in the generation of contractions during pregnancy, but suggest that periodicity of contractions is associated with inherent changes in myometrial responsiveness to stimulation, which could occur as a result of a cycling of the resting membrane potential.     

Role of the sympathetic innervation on uterine electromyographic activity in nonpregnant ovariectomized sheep under estrogen supplementation.

The aims of the present study were to characterize the sympathetic innervation of the nonpregnant sheep uterus, to determine the catecholamine content in myometrium (MYO) and endometrium, and to study the effects of chemical sympathectomy (CHSPX) on uterine catecholamine content and on uterine electromyographic (EMG) activity recorded from the MYO and mesometrium (MESO) in the nonpregnant ovariectomized sheep. After synchronization of estrus, 9 nonpregnant sheep were anesthetized with halothane, ovariectomized, and fitted with vascular catheters and EMG electrodes. Estradiol-17 beta was administered intravascularly at a rate of 50 micrograms/24 h for 10 days. CHSPX was induced with 6-hydroxy dopamine (20 mg/kg). Uterine tissues were obtained for determination of catecholamine content by HPLC and for immunocytochemical staining using an antibody against tyrosine hydroxylase (TH). In nonpregnant ovariectomized sheep, TH immunostaining was present in nerve fibers located in endometrium and MYO. In all layers of the uterus, catecholamine fibers were found in the proximity of blood vessels as well as in defined regions of the parenchyma. Throughout the uterus, norepinephrine content and TH immunostaining were dramatically decreased after CHSPX. CHSPX decreased uterine short EMG event activity in both MYO and MESO. Contracture-type activity was not affected in MYO and was increased in MESO. We conclude that sympathetic innervation modulates the MYO and MESO EMG activity in nonpregnant ovariectomized sheep under estradiol supplementation, and that the removal of the sympathetic innervation induces a decrease in the spontaneous activity.     

Effect of 48-hour infusion of the synthetic oxytocin antagonist, [1-beta-mercapto(beta-(CH2)5)1(OMe)Tyr2,Orn8]-oxytocin, on myometrial activity of pregnant sheep at 139-140 days of gestation.

Currently there is considerable interest in the actions of oxytocin antagonists on the pregnant myometrium. Few studies have been conducted involving long-term infusions of oxytocin antagonists to late-pregnant experimental animals. We set out to determine whether continuous infusion of an oxytocin antagonist ([1-beta-mercapto(beta-(CH2)5)1(OMe)Tyr2,Orn8]-oxytocin) would influence basal levels of myometrial activity of the contracture type and maternal prostaglandins in pregnant sheep. The antagonist was infused into a uterine vein at 80 micrograms.h-1 for 48 h starting at 139 days of gestational age. The antagonist significantly reduced total myometrial electromyogram activity and the frequency of contractures but did not change contracture duration. Antagonist infusion did not produce any significant alterations in maternal carotid or uterine vein 13,14-dihydro-15 keto prostaglandin F2 alpha concentrations. Contractures probably represent an intrinsic instability of the resting membrane potential of uterine muscle and these results suggest that oxytocin may play a role in regulating their frequency in sheep during the last third of gestation.     

Poor spontaneous and oxytocin-stimulated contractility in human myometrium from postdates pregnancies

Prolongation of pregnancy i.e. going more than 10 days over the estimated due date, complicates up to 10% of all pregnancies and is associated with increased risk to both mother and fetus. Despite the obvious need for contractions of the uterus to end pregnancy, there have been no studies directly examining the role of uterine smooth muscle, myometrium, in the aetiology of prolonged pregnancy. This study tested the hypothesis that the intrinsic contractile characteristics of myometrium taken from women with prolonged pregnancy (>41 weeks and 3 days) was reduced compared to those delivering at term (39-41 weeks). We recruited women undergoing Caesarean Section (CS) delivery either pre-labour (n = 27) or in labour (n = 66) at term or postdates. The contractile ability of the postdates myometrium, whether spontaneous or elicited by oxytocin or high-K solution, was significantly reduced compared to term myometrium. These differences remained when adjusted for parity and other maternal characteristics. The findings remained significant when expressed per cross sectional area. Histological examination revealed no differences between the two groups. The contractile differences were however related to intracellular Ca transients suggesting an effect of [Ca] on reduced force production in the postdates group. In summary, myometrium from prolonged pregnancies contracts poorly in vitro even when stimulated with oxytocin and in active labour. Responses to high K(+) and measurements of Ca suggest that alterations in excitation contraction coupling, rather than any histological changes of the myometrium, may underlie the differences between term and postdates myometrium. We show that postdates pregnancy is associated with poor myometrial activity and suggest that this may contribute to increased myometrial quiescence and hence, prolonged gestation.     

Expression of enzymes of cyclooxygenase pathway and secretion of prostaglandin E2 and F2alpha by porcine myometrium during luteolysis and early pregnancy

Past studies of uterine prostaglandin (PGs) and pig reproduction have focused on endometrial rather than myometrial PGs. This study documents the synthesis and secretion of myometrial prostaglandins (PGs) in pigs and the involvement of oxytocin (OT) in these processes. Cyclooxygenase-2 (COX-2) expression was similar in myometrial explants from cyclic and pregnant pigs (days 14-16) and OT (10(-7) M) in vitro significantly increased COX-2 protein regardless of reproductive state. Basal expression of prostaglandin E2 synthase (PGES) was higher during pregnancy than during luteolysis. Conversely, prostaglandin F synthase (PGFS) was highest during luteolysis and lower in myometrium from gravid animals. OT had no influence on the expression of PGES and PGFS. In another tissue culture experiment, myometrial slices produced more PGE2 than PGF2alpha regardless of reproductive state of the female. OT stimulated PGE2 production in myometrium harvested during luteolysis and increased PGF2alpha production in all tissues examined. Progesterone (P4; 10(-5) M) blocked stimulatory effect of OT on myometrial PG release. Myometrial OTr mRNA was higher (P=0.03) during luteolysis than during pregnancy. In conclusion: (1) oxytocin increases myometrial COX-2 expression, but does not influence the expression of terminal enzymes of PGs synthesis (PGES and PGFS); (2) porcine myometrium preferentially produces PGs during early pregnancy and secretes more PGE2 than PGF2alpha; (3) myometrial OT and OTr support secretion of PGs from myometrium during luteolysis.     

Cervical diameter in relation to uterine and cervical EMG activity in early postpartum dairy cows with retained placentas after PGF2alpha induced calving

The cervix must regain its normal diameter after parturition. Until now, little has been known about the pattern of cervical closure and the possible influences of myometrial and cervical contractions in this process. We continuously measured the cervical diameter with ultrasound cervimetry during the first 48h after calving in six cows with retained fetal membranes, while uterine (n=6) and cervical outer muscular layer (n=4) electromyographic (EMG) activity was measured with bipolar EMG electrodes. We found that the cervical diameter which was 6.2cm (+/-0.7) at 1.4h after calving, initially increased to 9.0cm (+/-1.0) during the first 14.8h (+/-2.8) postpartum. After this time, the diameter decreased gradually to 5.3cm (+/-1.0) at 48h after calving. The overall EMG activity after parturition decreased by 59% (+/-6) and 35% (+/-17) for the uterus and cervix, respectively. The decrease in EMG activity was due to a 50% (+/-7) decrease in EMG amplitudes of the myometrium; the EMG amplitudes of the cervix decreased by only 8% (+/-21) (P>0.05). At the same time in the cervix, burst frequency decreased by 69% (+/-17), while the decrease in burst frequency of the myometrium was only 11% (+/-5) (P>0.05). Uterine myometrial and cervical EMG activity after parturition showed burst patterns. These contractions of the uterus and cervix were accompanied by and correlated with transient dilatations of the caudal cervix. This could have functional relevance in the evacuation of the uterus.     

Loss of myometrial oxytocin receptors during oxytocin-induced and oxytocin-augmented labour

Oxytocin is used widely for the induction and augmentation of labour, but there is little information about the dynamics of oxytocin receptors in human myometrium during parturition, and the possible effect of oxytocin infusion. This information is important because G protein-coupled receptors, such as the oxytocin receptor, undergo desensitization after prolonged or repeated stimulation. The concentration of myometrial oxytocin receptors and the steady state of its mRNA were measured in patients undergoing Caesarean sections before or during spontaneous or induced labour. The concentration of receptors before labour was 477 (175-641) fmol mg(-1) protein (median, quartile range), and decreased to 140 (72-206; P < 0.05) and 118 (69-75; P < 0.01) fmol mg(-1) protein during prolonged oxytocin-augmented and oxytocin-induced labour, respectively. The corresponding oxytocin receptor mRNA concentrations decreased by 60- and 300-fold, respectively. The decrease in receptor binding and mRNA in women receiving oxytocin infusion indicates that homologous receptor desensitization occurs in vivo.     

Further characterization of the electromyographic activity of the myometrium and mesometrium in nonpregnant sheep under estrogen supplementation.

The effects of estrogen administration on uterine contractility varies with animal species. In nonpregnant ovariectomized sheep, estrogen administration has been reported either to inhibit, inhibit then stimulate, or only stimulate uterine contractility. The aim of the present study was to determine the effects of prolonged estrogen administration in the electromyographic (EMG) activity recorded from the myometrium and mesometrium in nonpregnant ovariectomized sheep after estrous synchronization by inserting vaginal progesterone sponges 14 days before surgery. Surgery was performed on four ewes under halothane anesthesia. Bilateral oophorectomy was performed, and stainless steel EMG electrodes were sewn to the mesometrium and myometrium in both left and right horns of the uterus. Blood samples were taken at 1000 h from the uterine vein for 13,14-dihydro-15-keto-prostaglandin F2 alpha determination, and from the femoral artery for estradiol determination. Starting on Day 7 after surgery, estradiol 17 beta (50 micrograms/24 h) was infused continuously into the jugular vein. Estrogen administration had a different effect on the EMG activity recorded from myometrium and mesometrium. The myometrial response to estrogen was an increase in the frequency of short EMG events from 19.0 +/- 8.7 to 57.0 +/- 5.0 (p less than 0.05) for events less than 60 sec, and from 2.70 +/- 0.83 to 10.30 +/- 1.36 (p less than 0.05) for events lasting greater than 60 sec but less than less than 180 sec. In contrast, there was no stimulatory effect of estrogen on mesometrial EMG for both types of short events less than 60 sec, and greater than 60 but less than less than 180 sec.(ABSTRACT TRUNCATED AT 250 WORDS)     

Uterine activity, sperm transport, and the role of boar stimuli around insemination in sows

This paper describes changes in spontaneous myometrial activity around estrus, factors that affect myometrial activity, and the possible role of uterine contractions in the process of (artificial) insemination, sperm transport and fertilization. Myometrial activity in the sow increases during estrus. The activity is myogenic in origin, but several factors have been shown to affect myometrial activity. Natural mating stimulates uterine contractions through several mechanisms. The presence of a boar, rather than the act of mating, induces central oxytocin release in the sow and thus increases uterine activity. Estrogens in the ejaculate of a boar can trigger prostaglandin release by the endometrium and thus increase uterine activity. Tactile stimulation of the genital tract (cervix) or tactile stimulation of the back and flanks of the sow during artificial insemination does not cause a release of oxytocin. There is hardly any evidence for the effects of these latter stimuli on uterine activity, and if they are present at all, the effects are very small. Evidence for the effects of synthetic boar odor on oxytocin release and/or uterine activity is inconsistent. The mere presence of a boar during insemination, in contrast, clearly stimulates uterine activity through the release of oxytocin. Hormonal stimulation (intrauterine) of uterine activity with estrogens, prostaglandins, or oxytocins before, during or after insemination generally improves fertilization rate, especially in situations with reduced fertility. Therefore, uterine contractions are believed to play an important role in the transport of sperm cells to the oviducts after insemination. Whether uterine contractions are absolutely necessary for sperm transport through the uterine horns, however, is not clear. Intensive stimulation of uterine contractions using hormones can also reduce the fertilization rate, probably by increasing the reflux of sperm cells during insemination. In this respect, the presence of a boar during AI seems more adequate, as only sows with a low level of uterine activity show an increase in uterine activity in response to this stimulus.     

Inhibition of tissue transglutaminase 2 attenuates contractility of pregnant human myometrium

Premature delivery remains a serious risk factor in pregnancy, with currently licensed tocolytics unable to offer significant improvement in neonatal outcome. Further understanding of the regulators of uterine contractility is required to enable the development of novel and more effective tocolytic therapies. The transglutaminase family is a class of calcium-dependent, transamidating enzymes, of which tissue transglutaminase 2 is a multifunctional enzyme with roles in cell survival, migration, adhesion, and contractility. The aim of the present study was to investigate the role of this enzyme in regulating the contractility of pregnant human myometrium. Tissue strips from biopsy samples obtained at elective cesarean section were either allowed to contract spontaneously or induced to contract with oxytocin, phenylephrine, or bradykinin. Activity integrals, used to measure contractile activity, were taken following cumulative additions of the reversible, polyamine transglutaminase inhibitors cystamine and mono-dansylcadaverine and the irreversible, site-specific transglutaminase inhibitors N-benzyloxycarbonyl-l-phenylalanyl-6-dimethylsulfonium-5-oxo-L-norleucine and 1,3-dimethyl-2[(oxopropyl)thio]imidazolium. The ability of cystamine and mono-dansylcadaverine to affect oxytocin-mediated calcium mobilization within primary cultured myometrial cells was also measured utilizing a calcium indicator. All inhibitors attenuated myometrial contractions in a concentration-dependent manner independent of the method of contraction stimulus. Similarly cultured myometrial cells preincubated with cystamine and mono-dansylcadaverine displayed an altered calcium response to oxytocin stimulation. Our findings demonstrate a potential role for tissue transglutaminase 2 in regulating uterine contractility in pregnant human myometrium that may be associated with the calcium signaling cascade required for contraction.     

The effect of prostaglandin I on the contractility of the term pregnant human myometrium

Small myometrial strips were dissected from the upper and lower segments of the term pregnant human uterus. The specimens were superfused in organ chambers and contractile activity was recorded isometrically. In strips from the upper segment, prostacyclin (PGI2), induced an initial excitatory response followed in the majority of experiments by transient inhibition. In the lower segment the response was generally the same although direct inhibition without initial stimulation occurred in some cases. During the period of inhibition the specimens were refractory to iterated exposure to PGI2. Furthermore, during this period of PGI2-induced inhibition the muscle strip was also refractory to PGE2 but responded to PGF2 alpha and oxytocin by stimulation. After inhibition of spontaneous contractile activity induced by indomethacin PGI2 induced an excitatory response. The results do not indicate any critical change in the myometrial responsiveness of the upper uterine segment to PGI2 during labor. In strips from the lower segment obtained before labor there tended to be a dominance of non-responders and inhibition only as compared to the results during labor. Nevertheless, whether or not PGI2 under physiological or pharmacological conditions has any significant influence on the contractility of the term pregnant human uterus, still remains obscure. As judged from earlier reports from our laboratory and the present study it is evident that the uterine vessels are considerably more sensitive to the action of PGI2 than the myometrium.     

Myometrial activity related to gap junction area in periparturient and in ovariectomized oestrogen treated sheep

Propagation of electrical (EMG) activity in the myometrium may be facilitated by the presence of gap junctions (GJ), leading to improved synchronization of contractility. EMG and mechanical (IUP) activity in relation to GJ area were studied in 9 periparturient and in 2 ovariectomized (OVX) oestradiol-17 beta (E2) treated ewes, chronically instrumented with bipolar electrodes and intrauterine sponge-tip catheters. Myometrial biopsies were taken under epidural anaesthesia at various time intervals around delivery and after intra-arterial administration of 0.1 mg of E2. In pregnant ewes we found a significant increase in the rate of rise and area of IUP cycles during labour. Both were closely related to a significant increase in GJ area. In E2 treated OVX sheep we found a significant increase in GJ area, with a maximum at 24 hours after injection. The increase in GJ area was associated with a significant increase in the rate of rise of IUP cycles. The results of our study support the hypothesis that gap junctions facilitate the spread of EMG activity across the myometrium, which may improve synchronization of uterine contractility during labour.     

Effect of oxytocin receptor blockade on rat myometrial responsiveness to prostaglandin f(2)(alpha)

In the present study we have shown that the genetic expression of prostaglandin (PG)F(2alpha) receptor (R) and cyclooxygenase (COX)-2 increases in laboring rat myometrium. This finding was associated with a relatively weak contractile in vitro response (E:(max)) of isolated uterine strips when challenged with PGF(2alpha). Five days postpartum PGF(2alpha)-R mRNA values exceeded those during labor while COX-2 mRNA was reduced to preparturient values. Maximal contractility of isolated strips stimulated with PGF(2alpha) at this time was enhanced and E:C(50) decreased. Oxytocin treatment of estrogen-primed nonpregnant rats down-regulated uterine contractile responsiveness to PGF(2alpha), leaving mRNA values for this receptor unchanged, whereas oxytocin receptor blockade with atosiban (an oxytocin receptor antagonist) left E:(max) unaltered. In contrast, atosiban treatment of pregnant rats resulted in a 2.5-fold increase in E:(max) and a considerably reduced EC(50) during labor when compared to untreated delivering rats. The increased contractile ability was associated with a threefold increase in PGF(2alpha)-R mRNA production, indicating that the regulation by atosiban of the PGF(2alpha)-induced response is exerted at the genetic level. Based on the present data we suggest that 1) PGF(2alpha)-R stimulation may not primarily exert a contracting role in the normally delivering myometrium, and 2) the presence of the PGF(2alpha)-R system in rat myometrium may explain the apparent functional redundancy of the oxytocinergic system during the process of birth in animals lacking oxytocin or where the oxytocin receptor is blocked. In this context PGF(2alpha) receptor stimulation may, in the absence of oxytocin receptor stimulation, exert the contractile forces needed for proper propulsion of the fetus.     

Oxytocin and glucose oxidation in the rat uterus

The effects of oxytocin on the biochemical pathways of glucose oxidation were investigated in the rat uterus. In the presence of oxytocin, glucose oxidation in uterine segments obtained from Sprague-Dawley rats at diestrus increased 1.5–2.0-fold above the basal rate. A half-maximal response was observed at about 3 nM oxytocin; the maximum response was equal to or greater than the response to 1.7 nM insulin. In stripped myometrial segments (denuded of the endometrial component), oxytocin stimulated glucose oxidation at estrus only; whereas in intact uterine segments, the stimulation of oxidation was observed at both estrus and diestrus. In contrast, stimulation of oxidation by carbachol in stripped myometrial segments was independent of the estrous state of the tissue. The ratio of [1-¹⁴C]glucose to [6-¹⁴C]glucose oxidation was measured to estimate the relative involvement of the pentose phosphate and the tricarboxylic acid pathways of metabolism. In myometrial tissue, stimulation of glucose oxidation by oxytocin appeared to proceed through the tricarboxylic acid cycle. In intact uterine segments, at diestrus, glucose oxidation involved largely the pentose phosphate pathway (suggesting increased glucose metabolism in endometrial tissue), whereas at estrus, in the intact tissue segments, oxytocin increased glucose oxidation largely via the tricarboxylic acid cycle, and appeared to do so predominantly in the myometrial tissue. Carbachol-stimulated glucose oxidation appeared to proceed mainly via the tricarboxylic cycle in the myometrial tissue, irrespective of the stage of the estrous cycle. In the uterus of the Brattleboro rat (either intact uterine segments or stripped myometrial strips), oxytocin stimulated glucose oxidation only at estrus, predominantly through the tricarboxylic acid cycle. These findings suggest that oxytocin, in addition to its known effect on the contractility of uterine and myoepithelial smooth muscle, may regulate glucose metabolism in both the myometrial and endometrial components of uterine tissue.     

Effect of an inhibitor of prostaglandin synthesis on uterine motility in the ovariectomized ewe during induced oestrus. A preliminary report

The myometrial electromyographic activity (EMG) of three ovariectomized ewes was studied after two consecutive treatments used for inducing oestrus: oestrogen administration and oestrogen plus an inhibitor of prostaglandin synthesis (indomethacin). The myometrial activity preceding treatments was used as a reference. The results of this study demonstrated that indomethacin modified the EMG of the myometrium recorded 24 hours after oestrogen injection. The rhythmic activity normally induced by oestrogens was suppressed, so that there was little or no difference between uterine activity recorded before and 24 hours after oestrogen injection.     

EMG activity of the muscular and stromal layer of the cervix in relation to EMG activity of the myometrium and cervical dilatation in PGF2alpha induced parturition in the cow

The goal of this study was to quantify and characterize the electromyographic (EMG) activities in the cervical outer muscular layer and in the cervical stromal layer, and to characterize their relationship with myometrial EMG activity and cervical dilatation during PGF2alpha-induced parturition in term pregnant cows. We continuously measured the EMG activity of the uterine myometrium and cervical outer muscular layer as well as the cervical stromal layer in five cows using bipolar electrodes while at the same time measuring changes in the cervical diameter with ultrasound cervimetry. This we did from the moment a prostaglandin analogue was injected until the expulsion of the calf. In contrast to the cervical stromal layer, the cervical outer muscular layer showed distinct EMG activity, which began to increase at about the same time as the EMG activity of the myometrium, i.e. some 12 h before the start of cervical dilatation. However, the rate of this increase was lower than in the myometrium and it was not characterized, like in the myometrium, by an increase in maximum EMG amplitude. Although the cervical outer muscular layer showed contracture and contraction like EMG activity in unison with in the myometrium, it was also characterized by a more irregular EMG activity, which occurred independently from the myometrium. These data suggest that while the outer muscular layer of the cervix may be considered to be a caudal continuation of the myometrium, it also displays activity independently from the myometrium. The physiological relevance of this activity remains to be explored.     

Prolonged labour associated with lower expression of syndecan 3 and connexin 43 in human uterine tissue

Background  

Prolonged labour is associated with greater morbidity and mortality for mother and child. Connexin 43 is a major myometrial gap junction protein found in human myometrium. Syndecan 3 seems to prevail in the human uterus among heparan sulphate proteoglycans, showing the most significant increase during labour. The aims of the present study were to investigate syndecan 3 and connexin 43 mRNA expressions and protein distributions in human uterine tissue during normal and prolonged labour.     

Uterine adrenergic and cholinesterase-positive nerves and myometrial catecholamine concentrations during pregnancy in sheep

Uterine adrenergic and cholinesterase (AChE)-positive innervation of the sheep uterus during anestrus and at 4 stages of pregnancy were examined by histochemical methods. In addition, uterine and cervical myometrium concentrations of norepinephrine (NE) and dopamine (DA) were determined using high-performance liquid chromatography. During anestrus, adrenergic and AChE-positive nerve fibers in the uterine myometrium and endometrium were primarily associated with the vasculature. Innervation of myometrial smooth muscle was almost exclusively by adrenergic fibers. In the endometrium, fibers of both types were observed closely associated with endometrial glands, and adrenergic fibers were observed in the connective tissue beneath the luminal epithelium. Density of uterine innervation decreased by day 65 of pregnancy with an additional decrease by day 105. Myometrial NE concentrations were higher in the cervix than the uterus. Uterine NE concentrations generally were not affected by pregnancy. Although cervical NE per gram of tissue decreased during pregnancy, this effect of pregnancy was not detected when NE was expressed per microgram of DNA. Myometrial DA concentrations were higher in uterine segments than in the cervix. DA concentrations decreased during pregnancy in all tissues except the posterior uterine segment. The DA to NE ratio in the uterus was greater than that for the cervix and was not generally affected by the stage of pregnancy. These results demonstrate that cholinergic and adrenergic nerves supply the sheep uterus. Decreasing fiber density during pregnancy suggests that a majority of the innervation to the sheep uterus is supplied by 'short' nerve fibers whose activity is regulated by steroids of pregnancy. The possible role of DA as a neurotransmitter in the sheep uterus is discussed.     

Prostaglandin e and f receptor expression and myometrial sensitivity at labor onset in the sheep

Prostaglandins (PGs) play a pivotal role in the initiation and progression of term and preterm labor. Uterine activity is stimulated primarily by PGE(2) and PGF(2alpha) acting on prostaglandin E (EP) and prostaglandin F (FP) receptors, respectively. Activation of FP receptors strongly stimulates the myometrium, whereas stimulation of EP receptors may lead to contraction or relaxation, depending on the EP subtype (EP1-4) expression. Thus, the relative expression of FP and EP1-4 may determine the responsiveness to PGE(2) and PGF(2alpha). The aims of this study were to characterize the expression of EP1-4 and FP in intrauterine tissues and placentome, together with myometrial responsiveness to PG, following the onset of dexamethasone-induced preterm and spontaneous term labor. Receptor mRNA expression was measured using quantitative real-time polymerase chain reaction using species-specific primers. There was no increase in myometrial contractile receptor expression at labor onset, nor was there a change in sensitivity to PGE(2) and PGF(2alpha). This suggests expression of these receptors reaches maximal levels by late gestation in sheep. Placental tissue showed a marked increase in EP2 and EP3 receptor expression, the functions of which are unknown at this time. Consistent with previous reports, these results suggest that PG synthesis is the main factor in the regulation of uterine contractility at labor. This is the first study to simultaneously report PG E and F receptor expression in the key gestational tissues of the sheep using species-specific primers at induced-preterm and spontaneous labor onset.