Pregnancy-induced decrease in the relaxant effect of terbutaline in the late-pregnant rat myometrium: role of G-protein activation and progesterone

Comparison of Placental HSD17B1 Expression and Its Regulation in Various Mammalian Species

During mammalian gestation, large amounts of progesterone are produced by the placenta and circulate for the maintenance of pregnancy. In contrast, primary plasma estrogens are different between species. To account for this difference, we compared the expression of ovarian and placental steroidogenic genes in various mammalian species (mouse, guinea pig, porcine, ovine, bovine, and human). Consistent with the ability to synthesize progesterone, CYP11A1/Cyp11a1, and bi-functional HSD3B/Hsd3b genes were expressed in all species. CYP17A1/Cyp17a1 was expressed in the placenta of all species, excluding humans. CYP19A/Cyp19a1 was expressed in all placental estrogen-producing species, whereas estradiol-producing HSD17B1 was only strongly expressed in the human placenta. The promoter region of HSD17B1 in various species possesses a well-conserved SP1 site that was activated in human placental cell line JEG-3 cells. However, DNA methylation analyses in the ovine placenta showed that the SP1-site in the promoter region of HSD17B1 was completely methylated. These results indicate that epigenetic regulation of HSD17B1 expression is important for species-specific placental sex steroid production. Because human HSD17B1 showed strong activity for the conversion of androstenedione into testosterone, similar to HSD17B1/Hsd17b1 in other species, we also discuss the biological significance of human placental HSD17B1 based on the symptoms of aromatase-deficient patients.

Progesterone - Effective for Tocolysis and Maintenance Treatment After Arrested Preterm Labour?: Critical Analysis of the Evidence

Numerous experimental studies indicate that natural progesterone, through various mechanisms, exerts an inhibitory effect on uterine contractility and sensitises the myometrium for tocolytics. It was therefore appropriate to investigate the possible benefits of oral/vaginal progesterone and the synthetic progesterone derivative 17-α-hydroxyprogesterone caproate, applied intramuscularly, in clinical studies on primary tocolysis, additively to established tocolytics ("adjunctive tocolysis") and as maintenance treatment after successful tocolysis in cases of threatened preterm birth. Three studies with a small number of cases do not yield any sufficient evidence for recommending progesterone/17-α-hydroxyprogesterone caproate as primary tocolysis in women with preterm labour. There is also no evidence that progesterone or 17-α-hydroxyprogesterone caproate combined with commonly used tocolytics leads to a prolongation of pregnancy and a significant decrease in the rate of preterm birth. The data on the use of progesterone as maintenance treatment is controversial. While randomised, controlled studies with low quality showed promising results, studies with high quality did not reveal any significant differences with regard to the rate of preterm birth < 37 weeks of gestation, the latency period until delivery and in the neonatal outcome between progesterone/17-α-hydroxyprogesterone caproate and placebo or no treatment. Significant differences in the methodology, the inclusion and outcome criteria, the mode of application and the dosages of the substances as well as the inadequate statistical power as a result of low numbers of cases make interpretation and comparability of the studies difficult. Therefore, well-designed randomised, placebo-controlled, double-blind studies with uniform primary outcome criteria are needed in order to clarify whether progesterone and via which route of administration and at which dosage is of clinical benefit for patients with manifest preterm contractions and as maintenance treatment after arrested preterm labour.

Progesterone as a tocolytic agent for preterm labor: a systematic review

PURPOSE OF REVIEW

Tocolytic agents have been used for over 60 years in the fight against preterm labor, which ultimately can lead to preterm birth. Currently, clinicians can choose from a variety of drug classes to achieve the primary goal of delaying delivery by 48 h, thereby allowing time for administration of corticosteroids for fetal lung maturity, and if appropriate, starting magnesium sulfate for fetal neuroprotection. However, there are currently no known therapies to maintain the tocolytic effect beyond those initial 48 h.

RECENT FINDINGS

Progesterone, which has been used in the prevention of preterm birth for over 10 years, has long been known to have the effect of uterine quiescence. It was first studied as a tocolytic agent in the 1960s. In the last several years, more studies have been done that suggest a potential use for maintenance tocolysis after the successful arrest of preterm labor. Although the studies are conflicting, the meta-analyses on progesterone show some promise in different outcomes of delayed delivery, reduced incidence of preterm birth, and reduced neonatal morbidity.

SUMMARY

Progesterone is currently the most promising agent for maintenance tocolysis. Although further trials are certainly needed, this is an exciting advancement in the realm of tocolysis.

Obesity in pregnancy: a novel concept on the roles of adipokines in uterine contractility

Obesity is a global health problem even among pregnant women. Obesity alters quality of labor, such as preterm labor, prolonged labor, and higher oxytocin requirements in pregnant women. The most important factors to play a role in the altered gestational period and serve as drug targets to treat the consequences are female sexual hormones, calcium channels, adrenergic system, oxytocin, and prostaglandins. However, we have limited information about the impact of obesity on the pregnant uterine contractility and gestation time. Adipose tissue, which is the largest endocrine and paracrine organ, especially in obesity, is responsible for the production of adipokines and various cytokines and chemokines, and there are no reliable data available describing the relation between body mass index, glucose intolerance, and adipokines during pregnancy. Recent data suggest that the dysregulation of leptin, adiponectin, and kisspeptin during pregnancy contributes to gestational diabetes mellitus and pre-eclampsia. A preclinical method for obese pregnancy should be developed to clarify the action of adipokines and assess their impact in obesity. The deeper understanding of the adipokines-induced processes in obese pregnancy may be a step closer to the prevention and therapy of preterm delivery or prolonged pregnancy. Gestational weight gain is one of the factors that could influence the prenatal development, birth weight, and adiposity of newborn.

The effects of estrogen on the α2-adrenergic receptor subtypes in rat uterine function in late pregnancy in vitro

AIM

To assess the effect of 17β-estradiol pretreatment on the function and expression of α2- adrenergic receptors (ARs) subtypes in late pregnancy in rats.

METHODS

Sprague-Dawley rats (n=37) were treated with 17β-estradiol for 4 days starting from the 18th day of pregnancy. The myometrial expression of the α2-AR subtypes was determined by real time polymerase chain reaction and Western blot analysis. In vitro contractions were stimulated with (-)-noradrenaline, and its effect was modified with the selective antagonists BRL 44408 (α2A), ARC 239 (α2B/C), and spiroxatrine (α2A). The cyclic adenosine monophosphate (cAMP) accumulation was also measured. The activated G-protein level was investigated by guanosine 5'-O-[gamma-thio]triphosphate (GTPγS) binding assay.

RESULTS

17β-estradiol pretreatment decreased the contractile effect of (-)-noradrenaline via the α2-ARs, and abolished the contractile effect via the α2B-ARs. All the α2-AR subtypes' mRNA was significantly decreased. 17β-estradiol pretreatment significantly increased the myometrial cAMP level in the presence of BRL 44408 (P=0.001), ARC 239 (P=0.007), and spiroxatrine (P=0.045), but did not modify it in the presence of spiroxatrine + BRL 44408 combination (P=0.073). It also inhibited the G-protein-activating effect of (-)-noradrenaline by 25% in the presence of BRL 44408 + spiroxatrine combination.

CONCLUSIONS

The expression of the α2-AR subtypes is sensitive to 17β-estradiol, which decreases the contractile response of (-)-noradrenaline via the α2B-AR subtype, and might cause changes in G-protein signaling pathway. Estrogen dysregulation may be responsible for preterm labor or uterine inertia via the α2-ARs.

The effects of progesterone on the alpha2-adrenergic receptor subtypes in late-pregnant uterine contractions in vitro

BACKGROUND

The adrenergic system and progesterone play major roles in the control of the uterine function. Our aims were to clarify the changes in function and expression of the α2-adrenergic receptor (AR) subtypes after progesterone pretreatment in late pregnancy.

METHODS

Sprague Dawley rats from pregnancy day 15 were treated with progesterone for 7 days. The myometrial expressions of the α2-AR subtypes were determined by RT-PCR and Western blot analysis. In vitro contractions were stimulated with (-)-noradrenaline, and its effect was modified with the selective antagonists BRL 44408 (α2A), ARC 239 (α2B/C) and spiroxatrine (α2A). The accumulation of myometrial cAMP was also measured. The activated G-protein level was investigated via GTPγS binding assays.

RESULTS

Progesterone pretreatment decreased the contractile effect of (-)-noradrenaline through the α2-ARs. The most significant reduction was found through the α2B-ARs. The mRNA of all of the α2-AR subtypes was increased. Progesterone pretreatment increased the myometrial cAMP level in the presence of BRL 44408 (p < 0.001), spiroxatrine (p < 0.001) or the spiroxatrine + BRL 44408 combination (p < 0.05). Progesterone pretreatment increased the G-protein-activating effect of (-)-noradrenaline in the presence of the spiroxatrine + BRL 44408 combination.

CONCLUSIONS

The expression of the α2-AR subtypes is progesterone-sensitive. It decreases the contractile response of (-)-noradrenaline through the α2B-AR subtype, blocks the function of α2A-AR subtype and alters the G protein coupling of these receptors, promoting a Gs-dependent pathway. A combination of α2C-AR agonists and α2B-AR antagonists with progesterone could be considered for the treatment or prevention of preterm birth.

The effects of female sexual hormones on the expression and function of α1A- and α1D-adrenoceptor subtypes in the late-pregnant rat myometrium

The aim of the study was to investigate the roles of α1-adrenoceptor subtypes in the last-day pregnant rat uterus in vitro by the administration of subtype-specific antagonists (the α1A-adrenoceptor antagonist WB 4101 and the α1D-adrenoceptor antagonist BMY 7378) after 17β-estradiol or progesterone pretreatment. In isolated organ bath studies, contractions were elicited with (-)-noradrenaline (10(-8)-10(-5)M) in the presence of propranolol (10(-5)M) and yohimbine (10(-6)M) in order to avoid β-, and α2-adrenergic action. The myometrial expressions of the α1-adrenoceptor subtypes were determined by means of the real time reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting techniques. The activated G protein levels were investigated through radiolabelled GTP binding assays. Both 17β-estradiol and progesterone pretreatment changed the myometrial contracting effect of (-)-noradrenaline. In the presence of WB 4101, progesterone pretreatment decreased the (-)-noradrenaline-induced myometrial contraction. In the presence of BMY 7378, both the 17β-estradiol and the progesterone pretreatment reduced the effect of (-)-noradrenaline. The mRNA and protein expressions of the α1A-adrenoceptors were decreased after 17β-estradiol pretreatment. (-)-Noradrenaline increased the [(35)S]GTPγS binding of the α1-adrenoceptors, which was most markedly elevated by progesterone. Pertussis toxin inhibited the [(35)S]GTPγS binding-stimulating effect of (-)-noradrenaline, indicating the role of Gi proteins in the signal mechanisms. 17β-estradiol pretreatment blocks the expression of the α1A-adrenoceptors, whereas it does not influence the expression of the α1D-adrenoceptors. Progesterone pretreatment does not have any effect on the myometrial mRNA and protein expressions of the α1-adrenoceptors, but it alters the G protein coupling of these receptors, promoting a Gi-dependent pathway.

ATP-sensitive potassium channels modulate in vitro tocolytic effects of β₂-adrenergic receptor agonists on uterine muscle rings in rats in early but not in late pregnancy

Aim

To investigate whether ATP-sensitive potassium (K_ATP) channels modulate the tocolytic effect of β₂-AR agonists (ritodrine and salmeterol) in early-pregnant (day 6) and late-pregnant (day 22) rat uterus in vitro, in order to examine the relation between the K_ATP channel sulphonylurea-binding regulatory subunit (SUR) expression and pharmacological reactivity of β₂-AR agonists.

Methods

The tocolytic effects of ritodrine and salmeterol (10^-10-10^-5 M) on spontaneous rhythmic contractions were investigated cumulatively, alone, or in the presence of the K_ATP channel blocker glibenclamide (10^-6 M) and the K_ATP channel opener pinacidil (10^-9-10^-7 M) after 5-min preincubation.

Results

β₂-AR agonist induced myometrial relaxation was inhibited by glibenclamide and enhanced by pinacidil on day 6, when SUR1 expression levels were high. Neither glibenclamide nor pinacidil mediated tocolytic effect was measured on day 22.

Conclusion

Low expression of the K_ATP channels at the end of gestation may facilitate enhanced excitability and contractility in the rat myometrium. The combination of a betamimetic and a K_ATP channel opener will therefore not be of therapeutic relevance in the treatment of preterm delivery.

Progesterone in Peri- and Postmenopause: A Review

Around 14.5 million peri- and postmenopausal women currently live in Germany. Moreover, approximately 450 000 women, each with a life expectancy of around 85 years, reach menopause every year in Germany. The challenge is therefore to find a therapy with few side effects which could improve the quality of life of women with menopausal symptoms. The aim of hormone therapy (HT) is to remedy hormone deficiencies using substances that offer the best trade-off between benefits and risks. This is where progesterone has a new and important role to play. Progesterone is one of the most important gestagens. Biologically effective progesterone formulations created with micronization techniques have been used in clinical practice since 1996. Nevertheless, up until 2003 preference was given to synthetic gestagens rather than progesterone. The increased breast cancer hazard ratio of 1.23 reported in the WHI study and of 2 given in the Million Women Study has been associated with the use of synthetic gestagens. In a comparison between synthetic gestagens and progesterone, the E3N Study showed that the transdermal administration of estrogen and progesterone did not lead to an increase in breast cancer rates (RR: 1.08). The administration of progesterone does not change the HDL/LDL cholesterol ratio. Because of its anti-mineralocorticoid effect, progesterone has no impact on carbohydrate metabolism, hemostasis, blood pressure, thrombogenicity and body weight. The administration of 200 mg/day progesterone over 12 days of a menstrual cycle or a daily administration of 100 mg combined with an estrogen are a safe and well-tolerated option to treat menopausal symptoms, with a better benefit risk profile compared to synthetic gestagens.

Tocopherol inhibits the relaxing effect of terbutaline in the respiratory and reproductive tracts of the rat: the role of the oxidative stress index

AIMS

Reactive oxygen species play a role in the signal transduction of beta-adrenergic receptors. We investigated whether an antioxidant (tocopherol) can reduce the effect of terbutaline in beta-2-adrenergic receptor (β2-AR)-regulated smooth muscles.

MAIN METHODS

Contractility of the tissues from nonpregnant (trachea) and 22-day-pregnant (myometrium and cervix) rats was investigated in an isolated organ bath. The tracheal and uterine β2-AR expressions were increased by 17-beta-estradiol valerate (E2) and progesterone (P4), respectively. The accumulation of cyclic-AMP (cAMP), and the total oxidant (TOS) and total antioxidant status (TAS) were also measured. The oxidative stress index (OSI) was defined as the ratio of TOS and TAS.

KEY FINDINGS

Terbutaline (10(-10)-10(-5)M) decreased the contractions in the nontreated and the P4-pretreated myometria, but tocopherol (10(-7)M) did not alter these actions. Terbutaline (10(-6)M) increased the cervical resistance both in the nontreated and in the P4-treated samples, while tocopherol reduced this action only in the P4-treated cervices. Terbutaline (10(-9)-10(-4)M) reduced the tracheal tones both in the nontreated and in the E2-treated tissues, while tocopherol reduced these effects. The changes in the intracellular cAMP levels of the tissues were in harmony with the isolated organ results. The OSI was highest in the trachea and lowest in the pregnant myometrium.

SIGNIFICANCE

A higher OSI is linked to a higher tocopherol sensitivity of beta-mimetic-induced relaxation. Our results suggest that the antiasthmatic effect of beta-mimetics may worsen, while their tocolytic effect may remain unchanged during parallel tocopherol administration.

Uterus-relaxing effect of β2-agonists in combination with phosphodiesterase inhibitors: studies on pregnant rat in vivo and on pregnant human myometrium in vitro

AIMS

Our aims were to examine the effects of a simultaneous stimulation of β(2) -adrenergic receptors and inhibition of uterine phosphodiesterases (PDE), in the pregnant rat uterus in vivo and on human uterine tissue in vitro. We also set out to measure cAMP levels and detect the expressions of the isoenzymes PDE4B and PDE4D in human uterine tissue samples.

MATERIAL AND METHODS

Preterm birth was induced in Sprague-Dawley rats with bacterial lipopolysaccharide. The uterine effects of terbutaline alone or in combination with rolipram were tested in vivo. Human myometrial strips from cesarean sections at full-term pregnancy and at preterm labor were stimulated with oxytocin, and the inhibitory effects of theophylline, rolipram and terbutaline were studied. The myometrial accumulation of cAMP in the presence of rolipram and terbutaline was determined by enzyme immunoassay. The expressions of PDE4B and PDE4D proteins were detected by Western blotting.

RESULTS

The selective PDE4 inhibitor rolipram was more effective than the non-selective PDE inhibitor theophylline in inhibiting the oxytocin-induced contractions in the human uterus. The uterus-relaxing effects of low doses of terbutaline were markedly potentiated by rolipram, both in rats and in human tissues. The changes in uterine cAMP levels correlated with these results. At preterm labor, PDE4B was the predominant form of PDE4 expressed; at full term, PDE4D was expressed more strongly.

CONCLUSIONS

A combination of selective PDE4 inhibitors and β(2) -agonists should be considered for the treatment of preterm contractions.

β(2)-Adrenergic activity of 6-methoxykaempferol-3-O-glucoside on rat uterus: in vitro and in silico studies

6-Methoxykaempferol-3-O-glucoside (6-MKG) was isolated from a Sudanese herb (El-hazha). The pharmacological effects of 6-MKG were tested on isolated non-pregnant or late-pregnant rat uteri in vitro, whilst docking studies were carried out modelling of the binding of 6-MKG to the rat β(2)-adrenoceptor in silico. In vitro studies revealed that 6-MKG was able to relax both the non-pregnant and the late-pregnant uterine contractility with 50% of the E(max) of terbutaline, whilst the EC(50) for 6-MKG was at least half than that of terbutaline. The β(2)-adrenoceptors antagonist 3-(isopropylamino)-1-[(7-methyl-4-indanyl)oxy]butan-2-ol(ICI118,551) competitively antagonised the relaxing effect of 6-MKG. Radioligand binding and cAMP studies confirmed the β(2)-adrenoceptors agonistic property of the compound. In in silico docking studies, 6-MKG bound to rat β(2)-adrenoceptors with low ∆G(bind) value (-11.53±0.06 kcal/mol) and it interacted with four residues of the active site (Asp(113), Asn(312), Cys(191)and Tyr(316)). It is concluded that 6-MKG exerts weak β(2)-adrenoceptor agonistic activity and can be considered a natural compound with potential therapeutic significance in the field of premature pregnant uterine contractions and asthmatic problems.

Improving the relaxing effect of terbutaline with phosphodiesterase inhibitors: studies on pregnant rat uteri in vitro

AIMS

Previous results by our group showed that the in vitro uterus-relaxing potency of β(2)-adrenergic receptor (β(2)-AR) agonists and uterine cAMP accumulation are enhanced in case of visceral inflammation. Our aim was to study the effects of the non-selective phosphodiesterase (PDE) inhibitor theophylline and the selective PDE4 inhibitor rolipram on the uteri of intact late-pregnant female rats (on days 20 and 22 of pregnancy) and of pregnant rats treated with lipopolysaccharide (LPS) to evoke preterm labor (on day 20).

MAIN METHODS

The effects of theophylline and rolipram alone and of rolipram with terbutaline were investigated in isolated organ system. Contractions were evoked with KCl. The forskolin- and terbutaline-stimulated cAMP accumulations were determined by enzyme immunoassay, with or without rolipram.

KEY FINDINGS

The maximum uterus-relaxing effects of theophylline and rolipram decreased significantly (p<0.05) with the progression of pregnancy in intact rats. The most pronounced effect of rolipram was detected in rats challenged with LPS on day 20. Rolipram increased the in vitro effect of terbutaline both in intact and in LPS-treated rats. In the presence of rolipram, the forskolin- and terbutaline-stimulated cAMP accumulations were higher in LPS-treated than in intact rats.

SIGNIFICANCE

The previous findings led us to conclude that the combined administration of PDE4 inhibitors with β(2)-agonists is of therapeutic value for the inhibition for uterine contractions, especially in the case of genital inflammation, which often triggers preterm birth. Combination therapy in general is associated with lesser side-effects, as a consequence of lower effective doses of each drug.

Progesterone decreases the relaxing effect of the beta3-adrenergic receptor agonist BRL 37344 in the pregnant rat myometrium

Although the published results regarding the function of the beta(3)-adrenergic receptors (beta(3)-ARs) in the regulation of smooth muscle activity are very promising, the question of the mechanism of beta(3)-ARs' action in the pregnant myometrium cannot be fully answered by human investigations. To assess whether it possesses an essential role in the regulation of uterine contractility in pregnant rats, as in humans, we performed functional, western blotting and molecular biology experiments on the late-pregnant rat myometrium. The influence of progesterone on the function of the beta(3)-ARs was also investigated. We demonstrated the presence and the functional activity of the beta(3)-ARs in the late-pregnant rat myometrium. The maximum dose-dependent uterus-relaxing effect of the selective beta(3)-agonist BRL 37344 was recorded at the end of pregnancy in rats, similarly as in humans. The extent of its relaxing action was regarded as moderate. The expression of beta(3)-AR protein and mRNA remained unchanged during the investigated period. The administration of progesterone had no effect on the beta(3)-AR mRNA and protein expression or the maximum relaxation effect of BRL 37344, but shifted the dose-response curve to the right and decreased the synthesis of the second messenger, cAMP. It can be concluded that the beta(3)-ARs play an additional role in the regulation of the contractile activity of the pregnant rat uterus. The inhibitory effect of progesterone on the functional activity of the beta(3)-ARs may have important consequences in the case of human application if this effect is also demonstrated in pregnant human myometrial tissue.

Effects of experimentally induced diabetes mellitus on pharmacologically and electrically elicited myometrial contractility

1. Diabetes is one of the most frequent complications of gestation, affecting approximately 7% of pregnancies. However, little is known about its effects on electrically and pharmacologically stimulated myometrial contractility. The aim of the present study was to investigate the consequences of streptozotocin (STZ)-induced diabetes on: (i) electrical field stimulation (EFS)-evoked contraction of isolated uterine rings as a function of gestational age; and (ii) the uterotonic and tocolytic actions of α- and β-adrenoceptor stimulation, respectively. The effects of oxytocin in late pregnancy were also investigated. 2. During pregnancy, EFS-evoked contractions of isolated uterine rings from intact rats declined, whereas isolated uterine rings from diabetic rats exhibited continuously low sensitivity to EFS. 3. In non-pregnant rats, diabetes resulted in increased noradrenaline-mediated contractility and a decreased relaxation response to terbutaline. At the mRNA level, diabetes enhanced the expression of α1B-adrenoceptors in non-pregnant rats from 14.65 to 18.39 μg/mL (P < 0.05), whereas the expression of α1D-adrenoceptors decreased (from 42.87 to 35.67 μg/mL; P < 0.05). During pregnancy, the responses to these sympathomimetics did not differ between diabetic and intact rats. 4. In late pregnancy (on Days 15 and 21), oxytocin caused greater maximum contractility of uterine rings from diabetic rats without affecting the EC(50). In addition, on Day 15 of pregnancy, the expression of oxytocin receptors in the myometrium of diabetic rats was higher than that in intact rats. 5. The results of the present study indicate that experimental diabetes facilitates gestation-induced denervation and increases myometrial sensitivity to oxytocin in late pregnancy. If similar mechanisms operate in humans, this could contribute to a tendency to premature uterine contractions in diabetes-complicated pregnancies.

Inflammatory processes enhance cAMP-mediated uterus relaxation in the pregnant rat: the role of TNF-alpha

The objective of this study was to assess the in vitro uterus relaxing potency of beta(2)-adrenergic receptor (beta(2)-AR) agonists in pregnant rats after in utero administration of the bacterial lipopolysaccharide, Escherichia coli endotoxin (LPS). The LPS (100 microg/kg) was injected into the uterine lumen on day 16 of pregnancy. The effects of beta(2)-AR agonist terbutaline was tested in vitro, in isolated uterine rings precontracted by electric field stimulation. Uterine beta(2)-AR densities were detected by radioligand binding assay, the activated G-protein levels were investigated by a radiolabelled GTP binding assay. Uterine cAMP accumulation and the serum tumor necrosis factor-alpha (TNF-alpha) levels were measured by enzyme immunoassay. The endotoxin-evoked preterm delivery occurred on day 21. Higher pD(2) values of terbutaline (p < 0.001) were detected in endotoxin-treated rats: 9.14 +/- 0.36 vs. 7.71 +/- 0.12 compared with sham-operated rats. The densities or the equilibrium dissociation constants of beta(2)-ARs were not different (p > 0.05) in LPS-treated vs. control animals. Serum TNF-alpha level rose threefold after LPS treatment, but this rise was abolished by thalidomide. In LPS + thalidomide-treated rats, the effect of terbutaline became similar to that in sham-operated controls. By the measurement of myometrial cAMP levels, we documented that the concentration-response curve of terbutaline on cAMP accumulation was shifted to the left in the LPS-treated rats, with a significant rise in the pD(2). We concluded that in the case of uterine inflammation, the in vitro uterus-relaxing potency of beta(2)-agonists enhances, which is possibly mediated by TNF-alpha and uterine cAMP levels and that may serve as a rationale for the use of beta(2)-AR agonists in the attenuation of preterm uterine contractions on an inflammatory basis.

Gestagen treatment enhances the tocolytic effect of salmeterol in hormone-induced preterm labor in the rat in vivo

OBJECTIVE

The purpose of this study was to determine whether gestagen treatment enhances the effects of beta2-mimetics in hormone-induced preterm delivery in pregnant rats in vivo.

STUDY DESIGN

Preterm birth was induced with a combination of mifepristone and prostaglandin E2 on day 19 of pregnancy. The animals were treated with salmeterol or gestagens (progesterone or 17alpha-hydroxyprogesterone) or their combination. The treatments were launched on different days (15-18) of pregnancy. The efficacy of treatment was determined in terms of the delivery time counted from the mifepristone injection.

RESULTS

Salmeterol treatment delayed premature labor by 2.4 hours, whereas the delay because of the gestagen-salmeterol combinations was more than 5 hours. Progesterone had no effect on the delivery time.

CONCLUSION

Parallel treatment with salmeterol and gestagens can be more than twice as effective as salmeterol therapy alone. These results open up a possibility for human trials of combined beta2-agonist-gestagen therapy in threatening preterm delivery.

Inhibitory effect of alprostadil against sevoflurane-induced myometrial relaxation in rats

PURPOSE

For anesthetic management of cesarean sections, regardless of the use of regional or general anesthesia, it is crucial to achieve sufficient uterine contraction immediately following the delivery of an infant in order to reduce excessive bleeding. No previous study has investigated the ability of alprostadil, a synthesized prostaglandin, to inhibit myometrial relaxation induced by volatile anesthetics. The aim of the present study was to investigate the inhibitory effects of alprostadil on sevoflurane-induced myometrial relaxation using myometrial strips isolated from pregnant rats.

METHODS

Myometrial strips were isolated from Sprague-Dawley rats (300-400 g) in the late stage of gestation (19-21 days). The time course of changes in spontaneous myometrium contraction was studied in the presence and absence of sevoflurane. Additionally, alprostadil was titrated at three different concentrations during continuous introduction of sevoflurane 2%, and myometrium contraction was studied. As an index of contraction, the area under the contraction curve was used, and data were analyzed by repeated measure one-way analysis of variance.

RESULTS

We have shown a significant decrease in myometrium contraction as a result of the use of sevoflurane (2%). Additionally, alprostadil has been shown to inhibit myometrial relaxation induced by sevoflurane in a dose-dependent manner. The areas under the contraction curve were 87%, 87%, 129%, and 172% of the baseline value for the control and at low, medium, and high concentrations of alprostadil, respectively.

CONCLUSION

The ability of alprostadil to inhibit myometrial relaxation induced by sevoflurane suggests that the use of alprostadil during general anesthesia for cesarean section may be advantageous for the reduction of postpartum bleeding.

Mechanisms of progesterone action in inhibiting prematurity

Progesterone is a steroid hormone that plays an integral role in each step of human pregnancy. In early pregnancy, progesterone produced by the corpus luteum is critical to the maintenance of early pregnancy until the placenta takes over this function at 7 to 9 weeks of gestation, hence its name (pro-gestational steroid hormone). The role of progesterone in later pregnancy, however, is less clear. It has been proposed that progesterone may be important in maintaining uterine quiescence in the latter half of pregnancy by limiting the production of stimulatory prostaglandins and inhabiting the expression of contraction-associated protein genes within the myometrium. Although systemic progesterone withdrawl may not correlate directly with the onset of labour in humans, there is increasing evidence to suggest that progesterone exerts its influence indirectly via a 'functional' withdrawl at the level of the uterus. The molecular mechanisms by which progesterone is able to maintain uterine quiescence and prevent preterm birth in some high-risk women are not clear. Six putative mechanisms have been proposed in the literature by both US and other investigators and are explored in this review.