Inhibition of cyclooxygenase-2 prevents inflammation-mediated preterm labor in the mouse

Prostaglandins (PGs) have proven important during parturition, but inhibition of PG production treating preterm labor (PTL) results in significant maternal and fetal side effects. We hypothesize that specific inhibition of either cyclooxygenase (COX)-1 or -2 may result in separation of therapeutic and toxic effects. We demonstrate that COX-2, but not COX-1, is induced during inflammation-mediated PTL caused by lipopolysaccharide (LPS) administration. A two- to threefold increase in uterine and ovarian PG concentrations coincides with this induction of COX-2. The COX-2-selective inhibitor SC-236 proved effective in stopping preterm delivery and the increases in PGs. The COX-1-selective inhibitor SC-560 also attenuated uterine and ovarian PG production after LPS but did not inhibit PTL as efficiently as SC-236. COX-1-deficient mice, which show delay in the onset of term labor, exhibited no delay in onset of PTL after LPS. These findings suggest that the mechanisms for initiation of inflammation-mediated PTL and term labor differ and that selective COX-2 inhibition may provide a means of stopping inflammation-induced PTL in humans.     

Study of oxytocin receptor: II. oxytocin and prostaglandin F2 alpha receptors in human myometria and amnion-decidua complex during pregnancy and labor

Oxytocin receptors (OXT-R) and prostaglandin F2 alpha receptors (PGF2 alpha-R) in human myometrium, amnion and decidua during pregnancy and at parturition were examined in an effort to clarify their role in the initiation and maintenance of uterine contractions. The number of binding sites for OXT in myometria showed an increase as gestation advance (Ist trimester v.s. at term; 205 +/- 90 v.s. 671 +/- 98 fmol/mg protein, N = 5, p less than 0.01), and a rapid decrease following the onset of labor (254 +/- 60 fmol/mg protein, N = 5, p less than 0.02). On the other hand the number of PGF2 alpha-R, remained unchanged throughout pregnancy and in labor. This myometrial PGF2 alpha binding capacity was approximately 1/20 to 1/30 that of the OXT binding, while binding affinity was almost equal. The OXT-R both in amnion and decidua, which was 1/6 to 1/7 that in myometrium, showed no significant changes throughout pregnancy or after the onset of labor. Binding affinity for each tissue was almost the same and appeared to increase towards term but no statistical significance was detected. Present data confirmed the presence of OXT as well as PGF2 alpha receptors in the three functionally distinct entities of pregnant human uterus; myometrium, amnion, and decidua. Among the components, the OXT binding increased only in the myometrium during pregnancy, suggesting this tissue specifically responds to OXT. In contrast, there was a constant binding in myometria for PGF2 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)     

Induction of human labor at term: uterine activity, inducibility, duration and neonatal jaundice

A total of 821 patients, 39-40 weeks pregnant, was obstetrically normal at admission. In 212 of them intra-uterine pressure (IUP) was monitored before and during inducing labor by oxytocin, in 212 patients delivery was also induced by oxytocin but not monitored, in 197 by combining oxytocin and amniotomy, and 200 had spontaneous delivery. Inducibility could be predicted by uterine baseline activity and a 50 mu i.v. shot of oxytocin, together with determination of cervical status and placental location. The duration of labour induction was affected by parity, placental location and cervical status, but was predicted only to a minor degree by baseline activity and uterine oxytocin sensitivity. Amniotomy did not affect caesarean, section rate. The newborn child benefited from IUP monitoring: fewer transfers to pediatrics were necessary, there was less neonatal jaundice and fewer blood exchanges. It is assumed that if labor is not monitored through IUP, oxytocin may cause neonatal hyperbilirubinaemia through episodes of increased uterine resting pressure.     

Biphasic effect of a prostacyclin methyl ester analog on uterine contractility in the chronically catheterized pregnant rhesus monkey in late gestation

We determined the in vivo effects of a prostacyclin methyl ester analog (PGI2) administration on myometrial activity in twelve chronically- catheterized pregnant rhesus monkeys during the last third of pregnancy under three different states of myometrial contractility: postsurgical contractions, spontaneous contractures and oxytocin induced contractions. Prostacyclin (200 micrograms) was administered to four monkeys 2-3 h after surgery, to eight monkeys having only contractures, and to four monkeys having oxytocin induced contractions. Vehicle administration was performed in six animals having contractures and to four having oxytocin induced contractions. In all three experimental paradigms PGI2 administration elicited a biphasic response in uterine contractility. An initial increase in the 5 min average intrauterine pressure (IUP) value from 2.3 +/- 1.29 to 5.8 +/- 2.29; 3.6 +/- 2.38 to 7.6 +/- 3.59; and 2.3 +/- 0.65 to 8.6 +/- 0.72 (SD); was observed in the post-surgical, spontaneous contracture and oxytocin induced contraction groups respectively (mmHg, P less than 0.05). This increase was followed by a fall in the 5 min average IUP from 2.3 +/- 1.29 to 0.6 +/- 0.49; 3.6 +/- 2.38 to 1.3 +/- 0.86; and 2.3 +/- 0.65 to 0.1 +/- 0.11 in the post-surgical, spontaneous contracture and oxytocin induced contraction groups respectively (mmHg, P less than 0.05). A fall in mean arterial blood pressure from 89 +/- 9.0 to 55 +/- 10.9 (mmHg, P less than 0.05) and a compensatory tachycardia from 108 +/- 18.2 to 164 +/- 56.2 (beats.min-1, P less than 0.05) was observed by 10 min after PGI2 administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relation between fetal arterial PO2 and oxytocin-induced uterine contractions in pregnant sheep

The relation between oxytocin-induced type A uterine contractions and fetal arterial PO2, measured continuously with an intravascular oxygen electrode, was studied in nine chronically catheterized sheep during late pregnancy. Oxytocin provoked dose-related increases in intrauterine pressure (IUP) and decreases in fetal PaO2. There was a significant positive relationship between changes in IUP and the maximum decrease in fetal PaO2 (average r = 0.696, df = 92; P less than 0.001). We conclude that changes in uterine activity contribute to transient fetal hypoxemia, and that administration of exogenous oxytocin provides an experimental paradigm to examine the consequences of this relationship.     

Macrophages infiltrate the human and rat decidua during term and preterm labor: evidence that decidual inflammation precedes labor

Preterm delivery is the leading cause of perinatal mortality and morbidity. Current tocolytics target myometrial contractions, a late step in the labor cascade. Identifying earlier events in parturition may lead to more effective therapeutic strategies. We hypothesized that inflammatory events in decidua (the maternal-fetal interface), characterized by leucocyte infiltration, are an early event during term and preterm labor (PTL). Leucocyte abundance in decidua of human pregnancies was quantified following term labor and PTL (idiopathic and infection associated), in conjunction with investigation of temporal inflammatory events in rat uterus during the perilabor period and in PTL induced by mifepristone. In human decidua, macrophage numbers were 4-fold higher in term labor (P < 0.01) and 2.5-fold higher in non-infection-associated PTL (P < 0.05) than in term nonlaboring samples. Neutrophil abundance was unchanged with labor but elevated in PTL with infection (5- to 53-fold increase; P < 0.01). T and NK cells were more abundant in idiopathic PTL than TL (P < 0.05). In rat, decidual macrophage infiltration increased 4.5-fold 12 h prior to labor and remained elevated during labor and early postpartum (P < 0.01). Decidual infiltration preceded that of the myometrium and was 4-fold higher (P < 0.01). In rat PTL, decidual macrophage numbers were also elevated (P < 0.01) and exceeded those of the myometrium (P < 0.05). These studies show for the first time that leucocytes infiltrate decidua during labor at term and preterm, supporting a role for leucocyte-derived inflammatory mediators in decidual activation. In the rat, this occurred prior to labor, suggesting it is an early event during parturition and thus a potential target for intervention.     

Uterine motility in the cow during the estrous cycle. I. Spontaneous activity

This study describes a method for measuring intrauterine pressure (IUP) changes and uterine motility in cows. Spontaneous uterine motility was recorded during the estrous cycle in stanchioned, nonlactating dairy cows using a pair of miniature pressure transducers mounted 15 cm apart at the distal end of a dacron catheter placed in one uterine horn via the cervix. Clinical examination of ovarian status and determination of the peripheral plasma levels of estradiol-17beta and progesterone were used to determine the stages of the cycle. The pressure sensors recorded variations in muscular resting tension (tone) and the occurrence, spatial distribution, and force of the uterine contractions. Both tone and uterine activity varied significantly during the cycle. They were minimal during diestrus, increased during proestrus, reached maximal values at estrus, and then decreased. The highest synchronized motor activity with presence of peristaltic-antiperistaltic movements occurred during estrus. The prevailing direction of the uterine contractions during late estrus (immediate preovulatory period) was cervico-tubal.     

Changes in the response to adrenergic drugs on mouse uterine contractions during pregnancy

The effect of isoproterenol (ISO), norepinephrine (NE) and phenylephrine (PHE) on electrically-induced contractions of mice uterine horns was studied during pregnancy. At the different times of gestation adrenergic agonists always inhibited uterine contractions in the following rank order of potency: ISO greater than NE greater than PHE. Cumulative dose-response curves constructed for the effect of these amines during diestrous, and at days 3-7, 10-15, 17-21 of gestation, showed that EC50 values increased gradually as term approached, which could imply a lower capacity of the uterus to respond to adrenergic drugs. Some likely explanations for this phenomenon are proposed. It is suggested that this lower response to catecholamines at the end of pregnancy could be a cause for the reduced success of beta 2-adrenergic drugs to stop premature labor.     

Relationship between timing of ovariectomy and maintenance of pregnancy in the guinea-pig

The effect of ovariectomy (OVX) and OVX + progesterone (P) treatment on the regulatory profile and uterine function of the guinea-pig are described. Before day 23 of gestation in the intact pregnant guinea-pig, the placental contribution to P-content is small in comparison with the increasing ovarian contribution. After day 30, the ovarian P-content starts to decrease and the placental P-content exceeds the ovarian contribution, indicating the “luteo-placental shift” (LPS) in P-biosynthesis. Thus, when 14 guinea-pigs were ovariectomized around day 21 of gestation all started aborting within 53 hours of OVX. A gradual increase in intrauterine pressure (IUP), a decrease in P-levels in heart and uterine vein plasma and in the uterine and placental tissues and an increase in the levels of PGF in uterine vein plasma and uterine tissue were observed in these animals. However, if the OVX was delayed until after day 30 of gestation, to examine the biological consequences of advanced LPS in P-biosynthesis, there was no increase in IUP and the animals did not abort in the next 5 days. Furthermore, P-therapy following OVX in the day 21 pregnant guinea-pigs prevented the increase in IUP and the animals did not abort. These observations establish for the guinea-pig a correlation between the success in pregnancy maintenance and the degree of the LPS in P-biosynthesis. These studies therefore emphasize the indispensable role of progesterone in pregnancy maintenance.     

Prostaglandin-induced luteolysis in pregnant and pseudopregnant rabbits and the resultant effects on the myometrial activity.

The effect of prostaglandin (PG)-induced luteolysis on the myometrial activity in 20--21-day-pregnant and 11--12-day-pseudopregnant rabbits was studied by intrauterine pressure (IUP) recording during PG infusions. The same dose of PG (10 micrograms/h during 8h) was also given to 7 non-pregnant (untreated) does that were used as controls. Peripheral plasma concentration of progesterone and oestradiol-17 beta were measured at 2-h intervals during the infusion. Plasma progesterone level decreased significantly within 2 h or the start of infusion in pregnant and pseudopregnant does and continued to decrease; at the end of 8 h, the concentrations were 31 and 41%, respectively, of the pre-infusion levels. The amplitude of uterine contractions increased significantly after 4 h in pseudopregnant does, increased slightly but insignificantly in the pregnant does and showed no significant change in the non-pregnant does during PG infusion. The amplitudes developed in the pregnant and pseudopregnant does were significantly different. The direct effect of progesterone (1--3 micrograms/h during 4 h) was also studied in 7 non-pregnant rabbits. After 2 h the amplitude of contractions had decreased markedly and the pattern of activity had become irregular. The results support the concept of a myometrial inhibitory factor other than progesterone in rabbit pregnancy and suggest that this factor(s) originates in conceptus.     

Use of an ultrasonic blood flow monitor for determining fetal viability in the rhesus monkey (Macaca mulatta). A preliminary study.

Ultrasonic stethoscopy proved to be a reliable and convenient technique for determing fetal viability in Macaca mulatta. Examinations, begun at day 150 of gestation in 33 monkeys and between days 32 and 58 in four other animals, were repeated at intervals of one to seven days. The earliest time of detecting blood flow in the fetal placenta was 42 days of gestation, fetal heart sounds geing discerned later. Three types of fetal cardiac rhythms were recognized: (1) a constant rate during most of pregnancy, (2) fluctuations associated with uterine contractions during labor, and (3) sudden transient bradycardia during violent rotations of the cephalically presented fetus.     

Regulation of alpha1-adrenoceptor-mediated contractions of uterine arteries by PKC: effect of pregnancy

Protein kinase C (PKC) plays an important role in the regulation of uterine artery contractility and its adaptation to pregnancy. The present study tested the hypothesis that PKC differentially regulates alpha(1)-adrenoceptor-mediated contractions of uterine arteries isolated from nonpregnant (NPUA) and near-term pregnant (PUA) sheep. Phenylephrine-induced contractions of NPUA and PUA sheep were determined in the absence or presence of the PKC activator phorbol 12,13-dibutyrate (PDBu). In NPUA sheep, PDBu produced a concentration-dependent potentiation of phenylephrine-induced contractions and shifted the dose-response curve to the left. In contrast, in PUA sheep, PDBu significantly inhibited phenylephrine-induced contractions and decreased their maximum response. Simultaneous measurement of contractions and intracellular free Ca(2+) concentrations ([Ca(2+)](i)) in the same tissues revealed that PDBu inhibited phenylephrine-induced [Ca(2+)](i) and contractions in PUA sheep. In NPUA sheep, PDBu increased phenylephrine-induced contractions without changing [Ca(2+)](i). Western blot analysis showed six PKC isozymes, alpha, beta(I), beta(II), delta, epsilon, and zeta, in uterine arteries, among which beta(I), beta(II), and zeta isozymes were significantly increased in PUA sheep. In contrast, PKC-alpha was decreased in PUA sheep. In addition, analysis of subcellular distribution revealed a significant decrease in the particulate-to-cytosolic ratio of PKC-epsilon in PUA compared with that in NPUA sheep. The results suggest that pregnancy induces a reversal of PKC regulatory role on alpha(1)-adrenoceptor-mediated contractions from a potentiation in NPUA sheep to an inhibition in PUA sheep. The differential expression of PKC isozymes and their subcellular distribution in uterine arteries appears to play an important role in the regulation of Ca(2+) mobilization and Ca(2+) sensitivity in alpha(1)-adrenoceptor-mediated contractions and their adaptation to pregnancy.     

Expression of alpha5 integrin (Itga5) is elevated in the rat myometrium during late pregnancy and labor: implications for development of a mechanical syncytium

The underlying mechanisms controlling uterine contractions during labor are still poorly understood. Integrins are heterodimeric, transmembrane receptors composed of alpha and beta subunits that can be found in focal adhesions. Because these structures play an important role in the regulation of smooth muscle contractility and cell adhesion, we hypothesized that alpha5 integrin mRNA (Itga5) and protein (ITGA5) expression would be induced in the rat myometrium during late pregnancy and labor. Itga5 mRNA expression was significantly increased (P < 0.05) from Day 17 to labor, noticeably decreasing 1 day postpartum (PP). Immunoblot analysis illustrated a continual increase in ITGA5 levels during pregnancy, labor, and PP, with levels reaching significance at labor (P < 0.05). Analysis of ITGA5 expression by immunocytochemistry demonstrated that it is primarily localized to myometrial cell membranes in the longitudinal muscle layer of the myometrium from before pregnancy to Day 6, and in both the longitudinal and circular muscle layers from Day 15 to PP. Treatment of late-pregnant rats with progesterone blocked labor and resulted in sustained expression of Itga5 mRNA expression to Day 24. In addition, immunocytochemistry experiments showed ITGA5 was detectable at higher levels in cell membranes of both myometrial layers in progesterone-treated animals on Days 23 and 24, compared with vehicle controls. We propose that ITGA5, with its sole known partner, ITGB1, may be important in promoting cellular cohesion during late pregnancy. This process may aid the development of a mechanical syncytium for efficient force transduction during the sustained, coordinated, and powerful contractions of labor.     

Characteristics of bovine early puerperal uterine contractility recorded under farm conditions

A non-invasive, digital technique was used to measure and quantify intrauterine pressure (IUP) changes in early postpartum dairy cows kept under farm conditions in order to document physiological changes in uterine contractility after uncomplicated calvings. In addition, possible relationships between characteristics of uterine contractility and blood ionized calcium (Ca(2+))-concentrations were investigated. Recordings of uterine contractility were made by using a transcervically inserted open tip catheter in 12 healthy cows during their first 48h after calving. The IUP recording technique appeared easily applicable under farm conditions. Although mean frequency (FREQ), amplitude (AMP) and area under the curve (AUC) of the myometrial contractions significantly decreased due to time, untreated early postpartum cows showed a high variability in characteristics of uterine contractility. There was no correlation between blood Ca2+ -concentrations and any of the contractility parameters.     

Observations of parturition among captive patas monkeys (Erythrocebus patas)

Six cases of labor and delivery by laboratory-housed patas monkeys (Erythrocebus patas) are described. Five of the births occurred during the daytime, and the sixth occurred just after the usual “lights out” time. Although it was impossible to determine the actual onset of labor, the final 1.5–0.5 hr before parturition were observed in all cases. Throughout labor, females tended to begin a contraction every 2–4 min and contractions usually lasted 35–60 sec. Females did not show common patterns of change in contraction frequency or duration as birth neared. It was not possible to describe patas monkey labor and delivery in terms of “stages.” Postpartum, females typically began cleaning their infants within 90 sec and picked them up within 5 min. Placental delivery times varied among females, as did the extent of placental consumption. One “mother-only” - reared female proved to be an inadequate mother.     

Pregnancy reduces RhoA/Rho kinase and protein kinase C signaling pathways downstream of thromboxane receptor activation in the rat uterine artery

During pregnancy, reduced vascular responses to constrictors contribute to decreased uterine and total vascular resistance. Thromboxane A(2) (TxA(2)) is a potent vasoconstrictor that exerts its actions via diverse signaling pathways, and its biosynthesis increases in preeclampsia. In this study, we hypothesized that maternal vascular responses to TxA(2) will be attenuated via Rho kinase, PKC, p38 MAPK, and ERK1/2 signaling pathways. Isolated ring segments of uterine and small mesenteric arteries from late pregnant (19-21 days) and virgin rats were suspended in a myograph, and isometric force was measured. Pregnancy did not affect uterine and mesenteric artery responses to the TxA(2) analog U-46619 (10(-9)-10(-5) M), but transduction signals associated with these contractions were different between pregnant and nonpregnant rats. Inhibition of Rho kinase (10(-6) M Y-27632) reduced sensitivity to U-46619 in virgin uterine vessels but did not inhibit these contractions in pregnant uterine arteries and had no effect on mesenteric vessels. Treatment of arterial segments with a PKC inhibitor (10(-6) M bisindolylmaleimide I) reduced U-46619-induced contractions in virgin uterine and mesenteric arteries and in pregnant mesenteric arteries. Pregnant uterine arteries, however, were unresponsive to PKC inhibition. Inhibition of ERK1/2 (10(-5) M PD-98059) and p38 MAPK (10(-5) M SB-203580) reduced U46619-induced contractions in nonpregnant vessels and in pregnant uterine and mesenteric vessels. These data suggest that normal pregnancy does not affect uterine and mesenteric contractile responses to TxA(2) but reduces the contribution of Rho kinase and PKC signaling pathways to these contractions in the uterine vasculature. In contrast, the role of ERK1/2 and p38 MAPK in U-46619-induced uterine contractions remains unchanged with pregnancy. TxA(2)-associated transduction signals and its regulators might present potential targets for the development of new treatments for preeclampsia and other pregnancy-associated vascular diseases.     

Labor and inflammation increase the expression of oxytocin receptor in human amnion

The oxytocin/oxytocin receptor (OXT/OXTR) system plays an important role in the regulation of parturition. The amnion is a major source of prostaglandins and inflammatory cytokine synthesis, which increase both before and during labor. Amnion is a noncontractile tissue; therefore, the role played by OXT/OXTR in this tissue will be fundamentally different from the role played in myometrial contractions. In the present study, we demonstrate increased OXTR mRNA and protein concentrations in human amnion epithelial cells associated with the onset of labor. We show that incubation of primary human amnion epithelial cells with IL1B results in a rapid, transient up-regulation of OXTR mRNA expression, which peaks in prelabor samples after 6 h. Incubation of prelabor amnion epithelial cells with OXT results in a marked increase of prostaglandin E(2) synthesis, and we demonstrate that OXT activates the extracellular signal-regulated protein kinase signal transduction pathway to stimulate up-regulation of cyclo-oxygenase 2 in human amnion epithelial cells. The increased ability of human amnion to produce prostaglandins in response to OXT treatment suggests a complementary role for the OXT/OXTR system in the activation of human amnion and the onset of labor.     

Different patterns of myometrial activity and 24-h rhythms in myometrial contractility in the gravid baboon during the second half of pregnancy.

Two clearly distinct epochs of myometrial contractility were observed in 13 pregnant baboons when recorded either as intraamniotic pressure (IAP) or myometrial electromyogram (EMG). Contractures, epochs lasting longer than 3 min, were the characteristic form of myometrial activity throughout pregnancy. Contractures generated only small increases in IAP. Short-lived contractions, generating larger increases in IAP, were characteristic of labor and delivery. Power spectral analysis of IAP and myometrial EMG activity proved to be an effective means whereby periods when the myometrium was in the contractures or contractions mode could be easily distinguished. Concomitantly recorded maternal intraabdominal temperature showed significant 24-h variations. When myometrial activity switched from low-amplitude, long-lasting regular contractures of pregnancy to contractions, the switch always occurred around the onset of darkness. Five baboons went into spontaneous labor, 3 prematurely and 2 at term. In these animals the switch from contractures to contractions occurred for several nights before delivery. The recurrence and timing of the switch from contractures to contractions for several nights before delivery were similar to the pattern we and others have observed in the pregnant rhesus monkey. The presence of 24-h periodicity in the patterns of specific types of myometrial activity in another nonhuman primate lends support to the view that similar 24-h patterns of myometrial activity may occur in pregnant women.     

Modeling Magnetomyograms of Uterine Contractions during Pregnancy Using a Multiscale Forward Electromagnetic Approach

Understanding the mechanisms of uterine contractions during pregnancy is especially important in predicting the onset of labor and thus in forecasting preterm deliveries. Preterm birth can cause serious health problems in newborns, as well as large financial burdens to society. Various techniques such as electromyography (EMG) and magnetomyography (MMG) have been developed to quantify uterine contractions. However, no widely accepted method to predict labor based on electromagnetic measurement is available. Therefore, developing a biophysical model of EMG and MMG could help better understand uterine contractions, interpret real measurements, and detect labor. In this work, we propose a multiscale realistic model of uterine contractions during pregnancy. At the cellular level, building on bifurcation theory, we apply generalized FitzHugh-Nagumo (FHN) equations that produces both plateau-type and bursting-type action potentials. At the tissue level, we introduce a random fiber orientation model applicable to an arbitrary uterine shape. We also develop an analytical expression for the propagation speed of transmembrane potential. At the organ level, a realistic volume conductor geometry model is provided based on magnetic resonance images of a pregnant woman. To simulate the measurements from the SQUID Array for Reproductive Assessment (SARA) device, we propose a sensor array model. Our model is able to reproduce the characteristics of action potentials. Additionally, we investigate the sensitivity of MMG to model configuration aspects such as volume geometry, fiber orientation, and pacemaker location. Our numerical results show that fiber orientation and pacemaker location are the key aspects that greatly affect the MMG as measured by the SARA device. We conclude that sphere is appropriate as an approximation of the volume geometry. The initial step towards validating the model against real MMG measurement is also presented. Our results show that the model is flexible to mimic the limited-propagation magnetic signature during the emergence and decay of a uterine contraction.