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PubMed1978

The possible mode of action of prostaglandins: XIV. Evidence of an involvement of progesterone in the initiation of prostaglandin F2a-induced premature labor in rats.

Prostaglandin F2a (PGF2a) at a dose of 2 mg/kg (sc) on day 18 of pregnancy induced premature emptying of gravid uteri by day 21 in the rat. Bilateral spaying or luteectomy on day 18 of pregnancy induced a refractoriness to respond to the abortifacient action of PGF2a. Injection of progesterone in the spayed or luteectomized pregnant rats, however, restored the sensitivity of the surgically manipulated animals to PGF2a. Premature parturition resulted in all of the animals so far tested. The importance of progesterone in terms of the abortifacient action of PGF2a is discussed.

Animals↗

PubMed1994

Ultrasound assessment of cervical dynamics during the first stage of labor.

OBJECTIVE: Assessment of cervical dynamics during the first stage of labor by a combination of ultrasound cervimetry and intrauterine tocography. METHODS: Sixty-two parturients were divided into four groups: nulliparous women in spontaneous (n = 9) or oxytocin-induced labor (n = 26), parous women in spontaneous (n = 11) or oxytocin-induced labor (n = 16). Intrauterine pressure and cervical dilatation were continuously recorded and assessed by off-line computer analysis. RESULTS: All women with spontaneous labor showed cervical responses to uterine contractions at the beginning of the recording. The first cervical response to a uterine contraction occurred at a significantly smaller dilatation in parous than in nulliparous women with induced labor (2.9 and 3.6 cm, respectively). Also, acceleration of cervical dilatation occurred at less dilatation in parous than in nulliparous women (3.4 cm and 4.8 cm, respectively), and myometrial work per cm of cervical dilatation was less in parous than in nulliparous parturients. CONCLUSIONS: The results indicate significant differences between cervical dilatation patterns in nulliparous and parous women, which may be due to structural cervical changes caused by labor and parturition. The labor patterns found were different from those originally described by Friedman (Friedman EA. Graphic analysis of labor. Am J Obstet Gynecol 1954; 68: 1568-1575), as no deceleration phases were detected. Ultrasound cervimetry is a valuable technique for the study of cervical dynamics during labor.

Adolescent↗

PubMed1995

Electromyographic activity in cervices with very low Bishop score during labor.

OBJECTIVES: To investigate the activity of the smooth muscles in the cervix at the onset of induced labor and to further elucidate this activity in relation to uterine contractions and to the duration of the latent phase of labor, taking cervical ripeness into account. METHODS: Cervical electromyographic (EMG) activity was studied at the onset of labor induced with amniotomy and oxytocin. Bipolar measurement of cervical electrical activity was performed. The root mean square of the cervical EMG activity and the intensity of intrauterine pressure in two groups of parturients with different cervical ripeness were compared. RESULTS: The EMG activity was higher in the group with lower Bishop scores. We found a significant positive correlation between EMG activity and duration of the latent phase of labor. CONCLUSION: Smooth muscles in the human cervix are active during labor and act to some extent independently of the uterine corpus.

Amnion↗

PubMed2005

Elective induction vs. spontaneous labor associations and outcomes.

OBJECTIVE: To determine factors and outcomes associated with elective medical induction of labor as compared with spontaneous labor in low-risk women. STUDY DESIGN: Using a birth certificate database including 11,849 low-risk, laboring women, univariate and multiple logistic regression was used to evaluate demographic and obstetric factors associated with elective labor induction. Low risk was defined as singleton, vertex, 37-41 weeks' gestation, no prior cesarean section, and no presenting medical/obstetric diagnoses considered indications for cesarean or induction. Adverse neonatal outcome was defined as 1- or 5-minute Apgar score < 7, neonatal intensive care unit admission or respiratory distress. Spontaneously laboring women (n = 10,608) were compared with women who underwent induced labor for no apparent medical/obstetric reason (n = 1,241). Interventions and outcomes during and after labor induction were adjusted for relevant associated variables. RESULTS: Odds ratios for epidural anesthesia, cesarean delivery and diagnoses of nonreassuring fetal heart rate patterns were independently increased following elective induction; odds ratios for cephalopelvic disproportion, instrumental delivery and adverse neonatal outcome were not. Maternal length of stay was 0.34 days longer with induction than with spontaneous labor (p < 0.0001). Slightly more induced labors ended before midnight. CONCLUSION: As compared with spontaneous labor, elective labor induction is independently associated with more intrapartum interventions, more cesarean deliveries and longer maternal length of stay. Neonatal outcome is unaffected.

Adult↗

PubMed2005

Emergency cesarean delivery in induction of labor: an evaluation of risk factors.

BACKGROUND: Induction of labor has been associated with an increased risk of emergency cesarean delivery. Knowledge of factors that influence the risk of cesarean delivery in women with induced labor is limited. METHODS: We performed a case-control study, nested within a population-based cohort of women with induced labor at term during 1991-1996 in Uppsala County, Sweden. Cases were women delivered with emergency cesarean delivery, and controls were women vaginally delivered (n = 193, respectively). Using logistic regression, analyses were performed. Odds ratio (OR) with 95% confidence intervals (CI) was used as a measure of relative risk. RESULTS: Women with a previous cesarean delivery had high risks of cesarean delivery (adjusted OR = 10.10, 95% CI = 3.30-30.92). The risk of cesarean delivery was also increased among nulliparous (adjusted OR = 4.92, 95% CI = 2.81-8.61), short (adjusted OR = 2.20, 95% CI = 1.06-4.59), and obese women (adjusted OR = 2.03, 95% CI = 1.07-3.84). A cervix dilatation less than 1.5 cm doubled the risk of cesarean delivery (adjusted OR = 2.26, 95% CI = 1.09-4.66). Mother's age, epidural analgesia, oxytocin augmentation, gestational age, and birthweight were not significantly associated with risks of cesarean delivery. CONCLUSIONS: Women with a previous cesarean delivery, nulliparous, short, and obese women with induced labor are at high risk of a cesarean delivery. When there is a need to deliver a woman with a previous cesarean section or a nulliparous woman with other risk factors for cesarean delivery, it may be prudent to consider an elective cesarean section.

Adult↗

PubMed1996

Postterm pregnancy: putting the merits of a policy of induction of labor into perspective.

BACKGROUND: Several randomized, controlled trials compared the policies of induction of labor and expectant management for women who reach 41 weeks' gestation, and although they suggest a better outcome for mothers and infants with such a policy in place, controversy continues as to which is the better form of care. The Canadian Multicenter Postterm Pregnancy Trial (CMPPT) enrolled 3407 women, of whom 1701 were randomized to a policy of induction of labor (induced group) and 1706 were randomized to a policy of expectant management (expectant group). Secondary analyses of data from the CMPPT were undertaken to explore a number of controversial issues. METHODS: We used data from the CMPPT to explore further the timing of delivery for women enrolled between 41 0/7 and 41 6/7 weeks' gestation, the potential impact of more liberal use of prostaglandins on cesarean section rates, and the relative merits of induced versus spontaneous labor in the two groups. RESULTS: Most women in the CMPPT (89%) were enrolled at 41 0/7 to 41 6/7 weeks' gestation, of whom 86.2 percent in the induced group and 63.6 percent in the expectant group gave birth before 42 weeks' gestation. Assuming that administration of prostaglandins would reduce the likelihood of cesarean section by 12 to 15 percent, cesarean section rates were reduced in the induction group from 21.2 percent to 20.8 to 20.9 percent, and in the expectant group from 24.5 percent 23.3 to 24.2 percent. If labor was induced as part of a policy of expectant management, the cesarean section rate was much higher (33.5%) than if labor was either spontaneous or induced as part of a policy of induction (18.5%, 22.4%). CONCLUSIONS: Women should be informed of the benefits and risks associated with the policies of induction of labor and expectant management, and their preferences regarding these policies should be respected.

Adult↗

PubMed2006

Controlled-release misoprostol vaginal insert in parous women for labor induction: a randomized controlled trial.

OBJECTIVE: To assess the ability of a controlled-release misoprostol vaginal insert to induce labor using dose reservoirs of 25, 50, 100, and 200 microg. METHODS: This double-blind, dose ranging, randomized study was carried out in parous women requiring induction of labor at term. Each woman was randomly assigned to receive a single misoprostol vaginal insert that could remain in place for up to 24 hours and was removed for onset of active labor, an adverse event, or having reached 24 hours in situ. The primary outcome measure was time from insertion of the misoprostol vaginal insert to vaginal delivery of the neonate. RESULTS: A total of 124 women participated in the study. The median time to vaginal delivery was 27.5, 19.1, 13.1, and 10.6 hours for the 25-, 50-, 100-, and 200-microg doses, respectively. The percentage of women who delivered vaginally within 12 hours was 9%, 14%, 47%, and 53% (P<.001 using the 25-microg group as the comparator) and within 24 hours was 42%, 79%, 81%, and 70% (P=.003). Uterine hyperstimulation syndrome occurred in one woman who received the 25-mug, two women who received the 100-microg, and three women who received the 200-microg dose reservoirs. CONCLUSION: Misoprostol vaginal inserts effectively induced labor in pregnant parous women at term. LEVEL OF EVIDENCE: I.

Administration, Intravaginal↗

PubMed2004

Urinary nitric oxide metabolite changes in spontaneous and induced onset active labor.

BACKGROUND: The aim of this prospective, randomized study was to investigate the changes in urinary nitric oxide (NO) metabolite between the latent and the active phases of spontaneous and either prostaglandin E(1) (PGE(1)) or prostaglandin E(2) (PGE(2))-induced labors. METHODS: Eighty-eight singleton pregnant women at 36-41(+) weeks' gestation without signs of fetal distress were enrolled. The first group consisted of 29 pregnant women in whom labor was induced by PGE(1) applied intravaginally. The second group consisted of 29 pregnant women with labor induced by PGE(2) applied intracervically. The third group consisted of 30 women, who had spontaneous active labor. Clinical data of the three groups were assessed as labor progressed. RESULTS: Urinary nitric oxide/creatinine (U NO/Cr) decreased significantly after the onset of active labor in all three groups (p < 0.005), with the percentage decline of 42.2%, 28.6% and 10.1%, respectively. The magnitude of the difference in decline in U NO/Cr after active labor between the PGE(1)-induced and the spontaneous labor group was significantly reduced (p = 0.0047) after adjustment for potential confounders using the generalized estimating equations test (GEE). The duration of the latent phase was significantly shortened in the PGE(1)-induced group as compared with the spontaneous labor group (p < 0.01). CONCLUSIONS: Decreased U NO/Cr may facilitate transition from the latent to the active phase either in spontaneous or induced labors. Our results indicate that U NO/Cr can serve as an easily obtained marker for use in controlling myometrial contractility and cervical ripening at the onset of active labor. The nitric oxide system is present in the human uterus and may contribute to uterine quiescence during pregnancy and show down-regulation in U NO/Cr at the initiation of active labor.

Administration, Intravaginal↗

PubMed2003

Prediction of successful induction of labor at term: role of clinical history, digital examination, ultrasound assessment of the cervix, and fetal fibronectin assay.

OBJECTIVE: The purpose of this study was to evaluate whether biochemical (fetal fibronectin assay) or biophysical (cervical assessment by transvaginal ultrasound) tests may have more value than digital examination in predicting successful induction of labor at term. STUDY DESIGN: The study enrolled prospectively 134 women undergoing labor induction at term caused by several obstetric conditions. All participants submitted to digital examination, fetal fibronectin assay, and transvaginal ultrasound for measurement of the cervical length and detection of funneling. The performance of each test in predicting delivery within 24 hours of labor induction was evaluated. Cox multiple regression analysis was performed to identify, among clinical and laboratory tests, which variables were independently associated with the duration of the latent phase and with the total duration of induced labor. RESULTS: The likelihood ratios for positive results (predicting that delivery would occur within 24 hours) were 6.61 (95% CI, 1.7-25.8) for a positive obstetric history (previous vaginal delivery), 2.61 (95% CI, 1.6-4.3) for a "favorable" digital examination, 1.41 (95% CI, 0.9-2.2) for a positive fetal fibronectin test, 1.61 (95% CI, 0.9-3.0) for cervical length, and 2.20 (95% CI, 1.1-4.4) for the presence of funneling at transvaginal ultrasound. The likelihood ratios for negative results were 1.81 (1.3-2.5) for obstetric history, 4.34 (2.5-7.7) for digital examination, 1.41 (0.9-2.1) for fetal fibronectin, 1.29 (1.0-1.7) for cervical length, and 1.48 (1.1-2.0) for funneling. On multiple regression, the only variables independently associated with the duration of the latent phase and with the total duration of induced labor were obstetric history and digital examination. CONCLUSION: Only obstetric history and digital examination predicted accurately vaginal delivery within 24 hours and were independently associated with labor duration. Fetal fibronectin and ultrasound measurements failed to predict accurately the outcome of induced labor.

Adult↗

PubMed2005

Uterine electromyography characteristics for early diagnosis of mifepristone-induced preterm labor.

OBJECTIVE: Differentiating uterine contractions leading to preterm birth from ineffective uterine activity is difficult with current tools. Uterine electromyographic activity is recordable and consists of bursts (group of action potentials) characterized by characteristics that are different during pregnancy and labor. Our aim was to identify the chronology of the changes in uterine pressure and electromyographic characteristics during mifepristone-induced preterm labor in pregnant rats and to determine the earliest characteristic to change. METHODS: On day 17 of gestation, intrauterine catheter and electromyography electrodes were implanted in the uterus. On day 18, rats were allocated for treatment with mifepristone or placebo. Intrauterine pressure and electromyography integral activities and electromyography mean were calculated before treatment and 6, 12, 18, 20, 22, and 24 hours after treatment. After mathematical transformation, burst analysis was performed by using power density spectrum energy, peak amplitude, and frequency. RESULTS: As expected, delivery rate within 24 hours was higher in the mifepristone-treated group. Changes in electromyography integral activity and mean, power density spectrum energy, and intrauterine pressure integral activity occurred late during preterm labor, in a range of 2-4 hours before delivery. Electromyography peak frequency of the power density spectrum exhibited early changes, with a shift from low to high frequencies starting at 12 hours before delivery. CONCLUSION: Electromyography peak frequency of the power density spectrum from individual bursts was the first characteristic to change after antiprogestin treatment, preceding any change in intrauterine pressure, making it a potentially useful marker for the early diagnosis of preterm labor.

Abortifacient Agents, Steroidal↗

PubMed2001

Increased risk of cesarean delivery with advancing maternal age: indications and associated factors in nulliparous women.

OBJECTIVE: To investigate factors that contribute to the increased risk of cesarean delivery with advancing maternal age. STUDY DESIGN: We reviewed demographic and ante- and intrapartum variables from a data set of term, nulliparous women who delivered at Brigham and Women's Hospital in 1998 (n = 3715). RESULTS: Cesarean delivery rates increased with advancing maternal age (< 25 years, 11.6%; > or = 40 years, 43.1%). Older women were more likely to have cesarean delivery without labor (< 25 years, 3.6%; > or = 40 years, 21.1%). Malpresentation and prior myomectomy were the indications for cesarean delivery without labor that were more prevalent in our older population as compared to our younger population. Even among women with spontaneous or induced labor, cesarean delivery rates increased with maternal age (< 25 years, 8.3%; > or = 40 years, 30.6%). Cesarean delivery rates were higher with induced labor, and rates of induction rose directly and continuously with maternal age, especially the rate of elective induction. Cesarean delivery for failure to progress or fetal distress was more common among older parturients, regardless of whether labor was spontaneous or induced. Among women who underwent cesarean delivery because of failure to progress, use of oxytocin and length of labor did not vary with age. CONCLUSIONS: Older women are at higher risk for cesarean delivery in part because they are more likely to have cesarean delivery without labor. However, even among those women who labor, older women are more likely to undergo cesarean delivery, regardless of whether labor is spontaneous or induced. Part of the higher rate among older women who labor is explained by a higher rate of induction, particularly elective induction. Among women in both spontaneous and induced labor, cesarean delivery for the diagnoses of failure to progress and fetal distress was more frequent in older patients, although management of labor dystocia for these patients was similar to that for younger patients.

Adult↗

PubMed2006

Preterm labor is induced by intraamniotic infusions of interleukin-1beta and tumor necrosis factor-alpha but not by interleukin-6 or interleukin-8 in a nonhuman primate model.

OBJECTIVES: The purpose of this study was to determine the relative contributions of individual proinflammatory cytokines and chemokines to the triggering of preterm labor. STUDY DESIGN: Eighteen chronically instrumented pregnant rhesus monkeys at 135 +/- 3 days gestation (term = 167 days) received 1 of 5 intraamniotic infusions: (1) interleukin-1beta (IL-1beta) (10 microg; n = 5), (2) tumor necrosis factor-alpha (TNF-alpha) (10-100 microg; n = 5), (3) IL-6 (20 microg twice a day; n = 2), (4) IL-8 (20 microg twice a day; n = 2), and (5) saline control (n = 4). Primary study outcomes were the mean uterine hourly contraction area (mm Hg x s/h) in 24 hours during peak response to cytokine infusion (all groups) and the interval from cytokine infusion until labor onset (IL-1beta, IL-6, and IL-8 groups). Secondary outcomes were quantities of amniotic fluid cytokines and chemokines (IL-1beta, TNF-alpha, IL-6, and IL-8), prostaglandins E2 and F2alpha, leukocytes, and matrix metalloproteinase-9 (MMP-9). Histopathology of fetal lungs and placental membranes was assessed. RESULTS: IL-1beta stimulated the most intense contraction patterns, resulting in preterm labor in all cases. TNF-alpha induced a variable degree of uterine activity among individual animals stimulating either preterm labor (n = 2) or a uterine contraction pattern of moderate intensity (n = 3). Despite prolonged elevations in amniotic fluid levels, neither IL-6 nor IL-8 induced preterm labor or an increase in uterine activity until near term. The mean interval from the initiation of IL-6 and IL-8 infusion to the onset of labor was significantly longer than after IL-1beta (21.9 vs 1.1 days; P < .01), and did not differ from the saline control group (27.6 days; P = NS). Intraamniotic infusion of IL-1beta or TNF-alpha was associated with significant elevations in all tested amniotic fluid cytokines, IL-8, prostaglandins, MMP-9 and leukocytes compared with gestational age-matched saline controls. IL-6 and IL-8 infusions were not associated with increases in IL-1beta or TNF-alpha and only produced a moderate increase in amniotic fluid prostaglandins. All cytokine infusions induced histologic chorioamnionitis and an accumulation of neutrophils in fetal lungs. CONCLUSION: Preterm labor was induced by intraamniotic infusions of IL-1beta and TNF-alpha, but not by IL-6 or IL-8 although inflammatory changes in fetal membranes and lungs were uniformly present. Our results indicate a primary role for IL-1beta and TNF-alpha in the triggering of preterm labor associated with inflammation or infection.

Amniotic Fluid↗

PubMedDate not supplied

[13, 14-Dihydro-15-keto-PGF2 alpha (PGFM) and progesterone serum levels in labor].

Progesterone and PGFM serum levels were estimated by RIA in patients with spontaneous and induced labor. Induction of labor was performed by amniotomy or by local application of prostaglandins. Mean progesterone serum levels were at 130 ng/ml at the time of admission into the labor-room, and declined to mean levels of some 50 ng/ml in all 3 groups of patients 30 minutes after placenta expulsion. Mean PGFM serum levels were 2,5 to 3,5 times higher in patients with spontaneous labor than in those in whom labor was induced. Parallel decline of progesterone and PGFM serum levels was noted in patients with spontaneous labor, whereas declining progesterone levels but increasing PGFM serum levels were observed in patients with induced labor. These data combine to suggest that an increase in PGFM serum levels may be the cause for the onset of labor. But, the question whether progesterone triggers these processes cannot be answered by the present observations.

Dinoprost↗

PubMed2002

Effect of labor induction on cesarean section rates in diabetic pregnancies.

OBJECTIVE: To determine if induced labor increases the incidence of cesarean delivery in pregnancies complicated by diabetes. STUDY DESIGN: This retrospective cohort study of pregnancies complicated with diabetes involved data from birth certificates reported to the New Mexico Department of Health between January 1996 and December 1999. RESULTS: There were 108,487 births, with 3,392 (3.1%) in women with diabetes. As compared to those without diabetes, this group had an almost twofold-increased risk of primary cesarean delivery (20.3% versus 11.3%; OR 2.00; 95% CI 1.83, 2.19). The risk of primary cesarean delivery in diabetic women was lower in the presence than in the absence of induced labor (17.7% versus 21.9%; OR .77; 95% CI .50, 0.89). This association continued after controlling for birth weight > or = 4,000 g, breech presentation, twins, maternal age > 35 and gestational age > 42 weeks. CONCLUSION: Induction of labor was not an independent risk factor that could explain the higher cesarean delivery rate in diabetic pregnancies.

Adult↗

PubMed2003

The effects of pre-B-cell colony-enhancing factor on the human fetal membranes by microarray analysis.

OBJECTIVE: Our purpose was to show the effects of pre-B-cell colony-enhancing factor on the genes that are expressed by the human fetal membranes. STUDY DESIGN: Explants of fetal membranes (amnion, chorion, and decidua) from three term patients were treated with 100 ng/mL recombinant human pre-B-cell colony-enhancing factor for 4 hours. RNAs were hybridized to gene chips that contained >18,000 known genes. One experiment was done in triplicate to assess replication. Data were analyzed to quantitate the signal intensities of each complementary DNA on the array. Confirmation of the results was carried out on tissues from nine other patients by the measurement of the proteins or quantitative real-time reverse transcriptase-polymerase chain reaction. RESULTS: Replication gave <92.6% identical results, which showed high method reproducibility. Pre-B-cell colony-enhancing factor treatment caused a significant increase in 103 genes and decrease in 139 genes. Only 8 genes were up-regulated consistently and significantly in all three patients (three key inflammatory cytokines [tumor necrosis factor-alpha, interleukin-6, and interleukin-1beta], four important chemokines [macrophage inflammatory protein-1alpha, macrophage inflammatory protein-1beta, macrophage inflammatory protein-3alpha, and growth-related oncogene-gamma], and prostaglandin-endoperoxide synthase 2). These data were confirmed by the measurement in the media with the use of specific enzyme-linked immunosorbent assays for tumor necrosis factor-alpha, interleukin-6, and interleukin-1beta, macrophage inflammatory protein-1alpha, macrophage inflammatory protein-1beta, and macrophage inflammatory protein-3alpha and by quantitative real-time reverse transcriptase-polymerase chain reaction for growth-related oncogene-gamma and prostaglandin-endoperoxide synthase 2. CONCLUSION: Pre-B-cell colony-enhancing factor appears to be at the proximal end of the pathway to labor initiation and may link sterile distention-induced labor with that of infection-induced labor.

Amnion↗

PubMed1976

Maternal and fetal plasma cortisol levels at parturition.

Fetal adrenal function during pregnancy has a probable role in parturition. Ninety-five mothers and fetuses were evaluated to ascertain maternal or fetal plasma cortisol interrelationships under various clinical situations. When mode of delivery was evaluated, maternal cortisol levels showed no differences. However, the fetuses from vaginal delivery (mean, 43.7 mug/100 ml) had higher levels than those from cesarean section (mean, 34.7 mug/100 ml). Induction of labor showed a rise in maternal cortisol from preinduction levels (mean, 40.2 mug/100 ml) to delivery (mean, 49.6 mug/100 ml), probably reflecting the maternal stress of labor. The fetal cortisol level after induced labor (mean, 35.2 mug/ml) supporting the adrenal contribution to the initiation of labor. Gestational age of the fetus was significant in the fetal cortisol levels: 36 weeks or less (mean, 34.1 mug/100 ml); 37 weeks or more (mean, 44.5 mug/100 ml). This again supports the development of adrenal maturity. Fetal weight, postdatism, acute and chronic fetal distress, hypertensive disease in pregnancy, and race were evaluated without revealing any significant intergroup differences. Two anencephalic pregnancies were also studied.

Adrenal Glands↗

PubMed2002

Tyrphostins inhibit lipopolysaccharide induced preterm labor in mice.

OBJECTIVE: We tested whether lipopolysaccharide (LPS)-induced murine preterm birth was delayed by tyrphostins (inhibitors of tyrosine kinases). STUDY DESIGN: The tyrphostins, AG126 or AG1288, or the prostaglandin endoperoxide H synthase-2 (PGHS-2) inhibitor, NS-398, were administered 2 h before LPS, with LPS, or 2 h after LPS and their effect on gestational length was measured. RESULTS: Only tyrphostins and NS-398 administered 2 h before LPS successfully delayed preterm birth (p < 0.05). CONCLUSIONS: Both tyrphostins AG126 and AG1288 as well as NS-398 inhibited LPS induced preterm birth to the time of normal birth.

Animals↗

PubMed1984

[The importance of oxytocin and prostaglandins to the mechanism of labor in humans].

In the present work an attempt is made to get a deeper insight into the mechanism of labor and the events leading to the onset of labor by means of radioimmunological measurements of OT, PGE, PGF, PGEM and PGFM and by determining the oxytocin sensitivity and the concentration of oxytocin receptors. Prostaglandins play a major role for the mechanism of labor in labor of spontaneous onset as well as in several forms of induced labor (intravenous infusion of OT, amniotomy, local application of PGE2). The reason for this seems to be the 3 fold action of prostaglandins: stimulation of myometrial contractions, cervical softening, induction of gap junctions. Moreover prostaglandins produced in the placenta play a major role in the mechanism of placental separation and expulsion. Oxytocin seems to be of importance for the initiation of labor and the final expulsion of the fetus. Immediately before the onset of regular contractions a marked increase of oxytocin sensitivity can be demonstrated which correlates very well with an increase of oxytocin receptor concentration in the myometrium and decidua. Due to this increase in oxytocin sensitivity no rise in oxytocin plasma levels is necessary to induce labor. Apart from the induction of myometrial contractions oxytocin leads via receptors in the decidua to a stimulation of prostaglandin synthesis which can also be demonstrated in vitro. In cases of premature contractions the same mechanisms seem to be operational as at term, oxytocin and prostaglandins again playing a major role. Inhibition of contractions with ethanol is based on the capacity of alcohol to inhibit oxytocin secretion. The contractions inhibiting effect of ritodrine is mediated through the cAMP induced relaxation of the myometrium although possibly a direct reduction of prostaglandin synthesis by ritodrine is possible. Increasing estrogen and decreasing progesterone activities at term lead to multiple subtile changes leading to an increased prostaglandin synthesis and mainly to a rise in oxytocin receptor concentration in the myometrium and the decidua. Oxytocin from the fetal and maternal side stimulates contractions in the myometrium and prostaglandin synthesis in the decidua leading to the onset of labor. With progressing cervical dilatation prostaglandin synthesis is further stimulated; these prostaglandins together with the increased oxytocin plasma levels in the second stage of labor lead to expulsion of the fetus. After delivery prostaglandin synthesis in the placenta leads to placental separation and expulsion.(ABSTRACT TRUNCATED AT 400 WORDS)

Administration, Topical↗