Labor In Rats Research Articles

Does high molecular weight-hyaluronic acid prevent hormone-induced preterm labor in rats?

The aim of our study was to test if oral high hyaluronic acid (HMW-HA) administration was effective in contrasting induced preterm birth (PTB) in female Wistar rats. A total of 24 pregnant rats were pretreated with placebo or low (2.5 mg/day)/high dose (5 mg/day) of HMW-HA (day 15) and then induced to delivery with mifepristone plus prostaglandin E2 (PGE2) (3 mg/100 µL + 0.5 mg/animal) on the 19th day of pregnancy. The delivery time was recorded and the messenger RNA (mRNA) levels of pro-inflammatory cytokines [tumor necrosis factor-α (TNF-α), interleukin (IL)1β, IL-6] were detected in the uterine tissues by real-time polymerase chain reaction (real PCR). Immunohistochemistry was performed alongside. Oral HMW-HA was well absorbed in the body and was able to significantly delay the timing of delivery and decrease mRNA synthesis of pro-inflammatory cytokines. HMW-HA, by acting in the management of PTB, may represent a new approach to protecting physiological pregnancy.

Castor oil Induces Morphological Changes in Endometrium and Biochemical Parameters in Pregnant Wistar Rats

Background: Misoprostol is a synthetic prostaglandin E1 analogue, used for the management of miscarriages and labour. Castor oil is a natural plant extract that has been reported to have some abortifacient Properties Objectives: This study investigated the labour induction and abortifacient properties of castor oil, as well as possible effects on the electrolytes and hormones that regulate pregnancy, as well as to compare these effects with a standard labour inducing drug misoprostol, in Wistar rats. Methods: The study was conducted out in 2 phases. The pregnant rats were administered varying Castor oil doses of low (12.4ml/kg), medium (18.6ml/kg) and high (24.8ml/kg), which were compared with misoprostol group as well as a control group. All animals were euthanized on gestational day 15 and day 20 respectively for the two phases and blood samples collected via cardiac puncture from the apex of the heart for hormonal assay, electrolyte and kidney function tests. The uterus was also removed for histological processing. Results: The abortifacient effect of castor oil is dose dependent with high dose castor oil group seen to have significantly reduced serum progesterone level (32.8±4.25 and 40.8±0.70 compared with 51.0±2.00 of controls), resulted in weight loss and interference with kidney function (increase in serum potassium while decrease in sodium electrolytes). Castor oil also exhibited labor inducing properties. Conclusion: Castor oil has the potential to induce abortion. This study has demonstrated a possible usage of castor oil in medical induction of labor in rats as it exerted uterotonic principle on the uterus.

Effect of neonatal exposure to endosulfan on myometrial adaptation during early pregnancy and labor in rats

Effect of neonatal exposure to endosulfan on myometrial adaptation during early pregnancy and labor in rats

Effect of neonatal exposure to endosulfan on myometrial adaptation during early pregnancy and labor in rats

Proper myometrial adaptation during gestation is crucial for embryo implantation, pregnancy maintenance and parturition. Previously, we reported that neonatal exposure to endosulfan alters uterine development and induces implantation failures. The present work investigates the effects of endosulfan exposure on myometrial differentiation at the pre-implantation period, and myometrial activation during labor. Newborn female rats were s.c. injected with corn oil (vehicle) or 600 μg/kg/day of endosulfan (Endo600) on postnatal days (PND) 1, 3, 5 and 7. On PND90, the rats were mated to evaluate: i) the myometrial differentiation on gestational day 5 (GD5, pre-implantation period), by assessment myometrial histomorphology, smooth muscle cells (SMCs) proliferation, and expression of proteins involved in myometrial adaptation for embryo implantation (steroid receptors, Wnt7a and Hoxa10); ii) the timing of parturition and myometrial activation during labor by determining the uterine expression of contraction-associated genes (oxytocin receptor, OTXR; prostaglandin F2α receptor, PTGFR and connexin-43, Cx-43). Endosulfan decreased the thickness of both myometrial layers, with a concomitant decrease in the collagen remodeling. Blood vessels relative area in the interstitial connective tissue between muscle layers was also decreased. Endo600 group showed lower myometrial proliferation in association with a downregulation of Wnt7a and Hoxa10. Although in all females labor occurred on GD23, the exposure to endosulfan altered the timing of parturition, by inducing advancement in the initiation of labor. This alteration was associated with an increased uterine expression of OTXR, PTGFR and Cx-43. In conclusion, neonatal exposure to endosulfan produced long-term effects affecting myometrial adaptation during early pregnancy and labor. These alterations could be associated with the aberrant effects of endosulfan on the implantation process and the timing of parturition.

Динамика активности лизоцима в крови интактных и подвергнутых алгогенному воздействию беременных самок крыс до и после родов

Labor pain can be the cause of the innate immunity factor, for example activity of lysozyme. It is the purpose of this research.Normative term labor in rats and labor with preceding electrical painful stimulation were accompanied with increase of lysozyme activity in the blood. The level of lysozyme activity was increased earlier and persisted longer in rats with painful irritation.

321: Cervical ripening with hyaluronidase: effect on myometrial contractility in vivo and in vitro

We have shown that intracervical injection of hyaluronidase can induce cervical ripening and accelerate parturition after induction of labor in rats. Hyaluronidase also affects the biophysical properties of the rat cervix consistent with augmented ripening. A common issue using cervical ripening agents is their concomitant effect on uterine activity. The objective of this study was to determine whether hyaluronidase causes an increase in uterine contractility. Timed pregnant Sprague-Dawley rats were injected intracervically with 100 I.U. of hyaluronidase or saline on day 18 of pregnancy (n=7 or 8 per group). All rats were euthanized at term. Uterine rings were isolated for isometric tension experiments. Cumulative dose response curves to oxytocin and hyaluronidase, as well as the maximum contractile response to KCl (60 mM) were obtained and compared between the two groups. There was no difference in the contractile response of rat myometrium to oxytocin between hyaluronidase treated animals and controls (figure). Similarly, exposure of the myometrium to increasing doses of hyaluronidase did not cause uterine contractions in either of the study groups (figure). There was no signifiacnt variation in the maximal myometrial response to KCl between groups. Despite its effect on cervical maturation, the use of hyaluronidase is not associated with an increase in uterine contractions or myometrial sensitivity to oxytocin. This makes hyaluronidase a potentially superior agent for pre-induction cervical ripening as compared to currently available agents. It may be a safer alternative in women with a history of a previous cesarean delivery, or a candidate for use in outpatient settings.

Assessment of Behavior during Labor in Rats and Effect of Intrathecal Morphine

Efficacy of analgesics varies with the type of pain. Little is known in this regard concerning labor pain, given the ethical barriers to study in humans and the lack of surrogate animal models. To address this, the authors classified and quantified spontaneous behaviors during labor and delivery in rats and examined the effects of a known analgesic, intrathecal morphine. Pregnant rats were video recorded for 72 h surrounding the time of anticipated labor and delivery. Specific behaviors were identified and classified into general activities, phasic stretching behaviors, and maternal attention activities. Rats received intrathecal infusion of saline or morphine, 0.035-3.5 microg/h, beginning approximately 1 day before delivery, and effects on behaviors and response to noxious heating of the paw were quantified. Phasic stretching behaviors occurred with high frequency before delivery of the first pup and were rare after delivery of the last pup. Intrathecal morphine at infusion rates greater than 0.035 microg/h abolished these behaviors without affecting general or maternal behaviors or the timing or duration of labor and delivery. Morphine was also antinociceptive to noxious heat, but only at infusion rates of 1.0 microg/h or higher. Phasic stretching behaviors are observed after distension or inflammation of pelvic viscera in rats, and similar behaviors occur during labor and delivery. Selective and dose-related blockade by intrathecal morphine of only these behaviors suggests that they reflect nociception and that this simple monitoring method can be used to study therapies for the pain of labor and delivery.

Identification of term and preterm labor in rats using artificial neural networks on uterine electromyography signals

This study was undertaken to use artificial neural networks on uterine electromyography data to identify term and preterm labor in rats. Controls (group 1: n = 4) and preterm labor models (group 2: n = 4, treated with onapristone) were used. Uterine electromyography and intrauterine pressure (IUP) variables were measured by implanted telemetric devices. For each timepoint assessed, either a "labor event" or "nonlabor event" was first assigned by using visual and other means. 112 total labor and nonlabor events were observed. Artificial neural networks were then used with electromyography and intrauterine pressure parameters to attempt algorithmic, objective identification for time of labor in each group. For group 1, all 8 (100%) labor events and all 44 (100%) nonlabor events were correctly identified by the artificial neural networks. For group 2, 22 of 24 (92%) labor events and 31 of 36 (86%) nonlabor events were correctly determined by the artificial neural networks. Artificial neural networks can effectively predict term and preterm labor during pregnancy with the use of uterine electromyography and intrauterine pressure variables.

Arrest of preterm labor in rat and mouse by an oral and selective nonprostanoid antagonist of the prostaglandin F2α receptor (FP)

The purpose of this study was to assess the tocolytic effect of AS604872, an orally active, potent, and selective prostanoid prostaglandin F2alpha receptor (FP) antagonist. Compound AS604872 was characterized and tested for its ability to block uterine contraction and delay preterm parturition in rodent models. AS604872 inhibited spontaneous uterine contractions in pregnant rat near term. In pregnant mouse, AS604872 delayed parturition induced by either the antiprogesterone RU-486 or the endotoxin lipopolysaccharide. Pups from treated mothers were delivered alive. The efficacy of AS604872 was superior to the beta-mimetic drug ritodrine. Combination of AS604872 and ritodrine showed an additive inhibitory effect on spontaneous uterine contractions in rat. A selective antagonist of the FP receptor suppresses uterine contractility and delays labor. Our findings identify a new potential modality for the pharmacological management of preterm labor.

Role of ERK1/2 in uterine contractility and preterm labor in rats.

The present study tested the hypothesis that ERK activation is an essential step in the onset of labor in a rat model of preterm labor. The administration of RU-486, an antiprogesterone agent, to rats induced preterm delivery 22.2 +/- 0.24 h after treatment. Changes in basal signaling events were studied in myometrial tissue from CO(2)-euthanized rats. Rats treated with RU-486 displayed a dramatically increased in vitro uterine contractility compared with gestational stage-matched, sham-treated rats. In vitro contractility was not significantly different from that during spontaneous labor. During RU-486-induced preterm labor, as previously described for spontaneous labor, ERK phosphorylation levels increased, as did phosphorylation of caldesmon at Ser(789), an ERK phosphorylation site. Also, a small but significant increase in 20-kDa myosin light chain phosphorylation was seen at a constant intracellular pCa of 7. When rats were chronically treated with an agent that prevents ERK activation, U-0126, the onset of RU-486-induced preterm labor was delayed in a statistically significant manner. Chronic in vivo treatment with U-0126 also significantly inhibited the RU-486-induced increase in in vitro contractility and ERK and caldesmon phosphorylation but did not alter the RU-486-induced increase in 20-kDa myosin light chain phosphorylation. These data indicate that ERK activation is a component of the multiple events leading to the development of labor in this rat model. We suggest that the ERK pathway could possibly be used to identify targets for the development of a novel class of tocolytic agents.

Role of oxytocin in the initiation of term and preterm labor in rats: Changes in oxytocin receptor density and plasma oxytocin concentration and the effect of an oxytocin antagonist, L-366,509

Objective: Our purpose was to compare the functional roles of oxytocin in term and preterm labor in rats by both biochemical and pharmacologic means. Study Design: We determined the myometrial oxytocin receptor density and the maternal plasma concentrations of oxytocin and progesterone on gestational days 18, 20, and 22 (morning) and at the onset of delivery (day 22 afternoon) in rats with labor at term and at the onset of delivery (day 20 afternoon) in rats in preterm labor induced by the combined use of bilateral ovariectomy and estradiol injection. We also evaluated the effects of an oxytocin antagonist, L-366,509, on the initiation of both term and preterm labor. Results: The number of tritiated oxytocin binding sites in myometrial membranes rapidly increased on gestational day 22 (morning) in rats with term labor. Plasma progesterone level decreased in an inverse fashion. A rapid increase in circulating oxytocin concentration was observed at the onset of delivery in rats in labor at term. Both the plasma oxytocin concentration and the receptor density had the same values in rats with preterm labor as in rats with term labor. L-366,509 delayed the initiation of labor in rats with term and preterm labor in a dose-dependent manner. Conclusion: It is confirmed biochemically and pharmacologically that oxytocin plays an important role in the initiation of both term and preterm labor in rats. The oxytocin antagonist examined was able to delay term and preterm labor, so it might prove useful in clinical practice for the treatment of preterm labor. (Am J Obstet Gynecol 1999;180:621-7.)

Uterine relaxation responses to calcitonin gene–related peptide and calcitonin gene–related peptide receptors decreased during labor in rats

OBJECTIVES: Our purpose was to investigate (1) whether uterine relaxation responses to calcitonin gene–related peptide are differentially regulated during pregnancy and labor, (2) the involvement of nitric oxide in smooth muscle relaxant action of calcitonin gene–related peptide in the rat uterus, (3) whether receptors for calcitonin gene–related peptide are expressed in rat uterus, and if so (4) whether the concentrations of these receptors are differently regulated during pregnancy and labor. STUDY DESIGN: Rats were killed on day 18 of gestation, at the time of spontaneous labor, or postpartum day 2. The uteri were removed for in vitro contractility measurements, nitric oxide production, and calcitonin gene–related peptide receptor binding assay. RESULTS: (1) Calcitonin gene–related peptide induced a dose-dependent relaxation in spontaneously contracting uterine strips from pregnant rats on day 18 of gestation; (2) the relaxation effects of calcitonin gene–related peptide on the uterus were decreased during spontaneous delivery at term and post partum compared with that during pregnancy; (3) calcitonin gene–related peptide–induced relaxation was inhibited by pretreatment of the uterine tissue with a calcitonin gene–related peptide receptor antagonist, calcitonin gene–related peptide 8-37; (4) nitric oxide synthesis inhibitor ( N G-nitro- l-arginine methyl ester) and soluble guanylate cyclase inhibitor (LY83583) significantly decreased calcitonin gene–related peptide–induced relaxation of the rat uterus during pregnancy; (5) calcitonin gene–related peptide increased the uterine nitric oxide production in pregnant rats, and this increase was obliterated in the presence of calcitonin gene–related peptide 8-37; and (6) calcitonin gene–related peptide receptors are present in rat uterus, and the concentration of these receptors dramatically increases during pregnancy and decreases during labor at term. CONCLUSIONS: Calcitonin gene–related peptide inhibits uterine spontaneous contractions in rats during pregnancy but not during labor and post partum. The inhibitory effects of calcitonin gene–related peptide on uterine contractility appear to be modulated, at least in part, by the activation of nitric oxide generation in the rat uterus. Changes in calcitonin gene–related peptide receptors could contribute to the changes in calcitonin gene–related peptide–mediated uterine relaxation during pregnancy and labor. (Am J Obstet Gynecol 1998;179:497-506.)

In vivo effects of corticotropin-releasing factor in pregnant rats

OBJECTIVE: Our purpose was to study the effects of corticotropin-releasing factor on (1) maternal blood pressure, (2) uterine vasculature, and (3) parturition in pregnant rats. STUDY DESIGN: Infusion minipumps containing vehicle, corticotropin-releasing factor, or α-helical corticotropin-releasing factor 9-41 (corticotropin-releasing factor receptor antagonist) were inserted subcutaneously in timed pregnant rats on day 16 of gestation. Systolic blood pressure was measured daily by the tail-cuff method. The time of onset of labor was determined and the newborn pups were weighed. Circulating levels of corticotropin-releasing factor were measured in untreated controls by radioimmunoassay. Relaxant responses to corticotropin-releasing factor were studied in isolated segments of uterine artery from late (day 18) and term (day 22) pregnant rats mounted in a wire myograph. RESULTS: The blood pressure was decreased by corticotropin-releasing factor and increased by α-helical corticotropin-releasing factor 9-41 ( p < 0.05). The time of onset of labor was not affected by either treatment. Pup weight was decreased by corticotropin-releasing factor ( p < 0.05). Circulating levels of corticotropin-releasing factor (immunoreactive) were not changed in pregnancy. In vitro, corticotropin-releasing factor caused relaxation of the uterine artery in a concentration-dependent manner and the relaxation was decreased at term compared with late pregnancy ( p < 0.05). CONCLUSIONS: Endogenously produced corticotropin-releasing factor lowers blood pressure during pregnancy in rats. It is a relaxant of uterine vasculature and this effect is decreased at term. It does not play an essential role in the initiation of labor in rats. (Am J Obstet Gynecol 1998;178:186-91.)

Involvement of nitric oxide pathway in prostaglandin F 2 α–induced preterm labor in rats

OBJECTIVE: Our purpose was to investigate the roles of nitric oxide and prostaglandins in controlling parturition. STUDY DESIGN: Pregnant rats on day 18 of gestation were injected intraperitoneally with prostaglandin F 2α, prostaglandin F 2α plus diethylenetriamine–nitric oxide (a donor of nitric oxide), prostaglandin F 2α plus diethylenetriamine without nitric oxide, or vehicle. Uterine nitrite production, nitric oxide synthase messenger ribonucleic acid and contractile response in vitro, and serum progesterone levels were measured. The labor and delivery of the rats also were monitored. RESULTS: Exogenously administered prostaglandin F 2α significantly inhibited nitric oxide production by the uterus in a time-dependent manner with maximal effects observed 48 hours after prostaglandin F 2α treatment. Messenger ribonucleic acid for inducible nitric oxide synthase but not endothelial nitric oxide synthase messenger ribonucleic acid in the uterus was significantly inhibited by prostaglandin F 2α with maximal inhibition at 48 hours after prostaglandin F 2α injection. The serum progesterone concentration was substantially reduced by prostaglandin F 2α, and this reduction was partially reversed by administration of diethylenetriamine–nitric oxide but not diethylenetriamine without nitric oxide. Prostaglandin F 2α caused increases in contractile activity of the uterus in a dose-dependent manner. Diethylenetriamine–nitric oxide (10 –4 mol/L) blocked prostaglandin F 2α–induced contractions. Premature parturition was induced within 48 hours after prostaglandin F 2α injection in 100% of the animals. Coadministration of diethylenetriamine–nitric oxide completely prevented the preterm labor induced by prostaglandin F 2α. CONCLUSION: Prostaglandin F 2α inhibited inducible nitric oxide synthase messenger ribonucleic acid and subsequent nitric oxide generation in the rat uterus. Nitric oxide can prevent prostaglandin F 2α–induced preterm labor, possibly by attenuating the fall in serum progesterone and blocking uterine contractions induced by prostaglandin F 2α administration. (Am J Obstet Gynecol 1997;177:907-17)

Connexin-26 and connexin-43 are differentially expressed and regulated in the rat myometrium throughout late pregnancy and with the onset of labor.

Gap junctions are characteristically increased in the myometrium during term and preterm delivery and are thought to be essential for the development of labor contractions. The expression of connexin-43 (Cx-43), the major myometrial gap junction protein, is increased during delivery (associated with an increase in the plasma estradiol/progesterone ratio) and after estradiol treatment of ovariectomized nonpregnant rats. However, Cx-43 is only 1 member of at least 16 proteins encoded by this family of gap junction genes. Using a RT-PCR method, we identified the presence of another member of this family, Cx-26, in laboring rat myometrium. The temporal expression pattern of Cx-26 was assessed using Northern and Western analyses. In contrast to Cx-43, whose expression is low throughout the pregnancy but increases immediately before the onset of labor (day 23), the expression of Cx-26 increased on day 17, reached maximal levels between days 19-21, and fell to low levels before the onset of labor. Treatment of pregnant rats with progesterone beginning on day 20 (which blocks both the increase in Cx-43 expression and the onset of labor) maintained the elevated expression of Cx-26. Induction of preterm labor in rats after ovariectomy on day 17 inhibited the normal preterm increase in Cx-26 transcripts. Progesterone treatment of these animals reversed the effects of ovariectomy. Immunofluorescence data identified Cx-26 antigen in the cell membranes of myometrial cells and in the luminal and glandular epithelium of the endometrium in the late pregnant (day 21) uterus. These data suggest that the role of gap junction formation in the myometrium in relation to the maintenance of pregnancy and the onset of labor is much more complex than previously recognized. Myometrial cell-cell communication is afforded by at least two different gap junction proteins, Cx-43 and Cx-26, that not only exhibit temporally distinct patterns of expression but are also subject to differential regulation.

Nitric oxide prevents prostaglandin F2$alpha;-induced preterm labor in rats

Nitric oxide prevents prostaglandin F2$alpha;-induced preterm labor in rats

Steroid hormone regulation of rat myometrial gap junction formation: effects on cx43 levels and trafficking.

The formation of myometrial gap junctions coincides with onset of labor in many mammalian species, including humans. The assembly of gap junction protein into functional gap junction plaques is a final step in a cascade that begins with estrogen-dependent expression of the connexin43 (cx43) gene and continues with synthesis of cx43 in the rough endoplasmic reticulum (RER) and transport to the Golgi, followed by its trafficking to the plasma membrane and its assembly into functional gap junctions. Moreover, in several models of preterm labor in rats, precocious synthesis, trafficking, and assembly of cx43 follow an increase in the estrogen:progesterone ratio. The actions of these steroids on cx43 expression, gap junction formation, and labor led us to consider whether or not the cascade of cx43 expression and gap junction assembly typical of preterm and term labor would be disrupted by manipulations that inhibit labor through experimental reduction of the estrogen:progesterone ratio. Ovariectomized and non-ovariectomized pregnant rats were treated with minimal doses of progesterone or the anti-estrogenic compound ICI 182780 over a time course sufficient to inhibit labor. We found that cx43-positive gap junction formation was prevented in all animals treated with ICI 182780 or progesterone but that the mechanism by which this disruption occurred was different in anti-estrogen- and progesterone-treated animals. We found that ICI 182780 significantly inhibited the typical rise in myometrial cx43 concentrations normally observed just before labor. In contrast, it was surprising to find that significant cx43 was synthesized in myometrium of progesterone-treated intact and ovariectomized animals even though labor was inhibited. However, we found that the trafficking of myometrial cx43 from the Golgi and assembly into gap junctions at the plasma membrane were suppressed in these progesterone-treated animals, providing further support for the hypothesis that it is not synthesis of cx43 per se but trafficking of cx43 to the plasma membrane and its assembly into gap junctions that are required for effective synchronized myometrial contractions typical of labor.

An immunochemical and immunocytologic study of the increase in myometrial gap junctions (and connexin 43) in rats and humans during pregnancy

Myometrial gap junctions are thought to play a necessary role in control of parturition. In this study we evaluated the presence of gap junctions in myometrial tissues with a specific antibody to the gap junction protein, connexin 43, with immunocytochemistry and immunoblots. Immunofluorescence of rat heart showed gap junctions were localized along the intercalated disks, but no change occurred during pregnancy. Fluorescent staining of rat myometria showed punctate staining of gap junctions between muscle cells during term and preterm birth, illustrating the tremendous increase in gap junctions during labor. Similarly, staining of human myometrial tissues was present in specimens from pregnant patients but absent in tissues from nonpregnant women. Immunoblots of myometrial tissues from rat and humans confirmed the existence of high levels of connexin 43 during term and preterm labor in rats and also during late pregnancy in humans.

Evaluation of 1-deamino-[D-Tyr(Oethyl)2, Thr4, Orn8] vasotocin, an oxytocin antagonist in animal models of uterine contractility and preterm labor: A new tocolytic agent

We attempted to characterize the ability of a new oxytocin derivative, 1-deamino[D-Tyr(Oethyl)2,Thr4,Orn8] vasotocin (ORF 22164), to antagonize the action of oxytocin in several in vitro and in vivo animal models of uterine hyperactivity. In these studies, the derivative was found to be a specific competitive inhibitor of oxytocin-induced contractions of pregnant guinea pig uterus in vitro. In addition, its intravenous administration induced a dose-dependent inhibition of oxytocin-induced uterine contractions in situ. Finally, like ritodrine, the drug induced a dose-dependent delay of ongoing labor in rats. These results suggest that 1-deamino-[D-Tyr(Oethyl)2,Thr4,Orn8] vasotocin, unlike ritodrine, is a potent and specific antagonist of oxytocin-induced uterine contractions and thus may have potential clinical utility in the treatment of preterm labor.

Influence of the antigestagens ZK 98.299 and ZK 98.734 on the production of prostaglandin F2α (PG F2α and prostaglandin E2 (PG E2) in human endometrium in vitro

Antigestagens prevent the implantation of blastocysts in guinea pigs [1] and induce premature labor in rats [2]. Both implantation and labor are prostaglandin-mediated events [3, 4]. The interaction of antigestagens and prostaglandins in human uterine tissue is poorly understood.