External calcium dependence of the uterine contraction induced by prostaglandins E2 and F2 alpha and its antagonism with natural progestins

Gestation age-associated dynamics of mitochondrial calcium uniporter subunits expression in feto-maternal complex at term and preterm delivery

Calcium plays a role of universal cellular regulator in the living cell and one of the crucial regulators of proper fetal development during gestation. Mitochondria are important for intracellular calcium handling and signaling. Mitochondrial calcium uniporter (mtCU) is a multiprotein complex of the mitochondrial inner membrane responsible for the transport of calcium to the mitochondrial matrix. In the present study, we analyzed the expression level of mtCU components in two parts of the feto-maternal system – placenta and myometrium at full-term delivery and at preterm birth (PTB) on different stages: 22–27, 28–32, 33–36 weeks of gestation (n = 50). A gradual increase of mRNA expression and changes in protein content of MCU and MICU1 subunits were revealed in the placenta during gestation. We also observed slower depolarization rate of isolated placental mitochondria induced by Ca2+ titration at PTB. In myometrium at PTB relative gene expression level of MCU, MCUb and SMDT1 increased as compared to full-term pregnancy, but the tendency to gradual increase of MCU protein simultaneous with MCUb increase and MICU1 decline was shown in gestational dynamics. Changes observed in the present study might be considered both natural dynamics as well as possible pathological mechanisms underlying preterm birth.

First-trimester maternal serum vitamin D and mode of delivery

Low maternal vitamin D levels have been associated with adverse pregnancy outcome. A recent study has suggested that low maternal vitamin D levels at the time of delivery are also associated with an almost fourfold increase in caesarean section risk. The aim of the present study was to investigate whether there is a difference in maternal serum 25-hydroxyvitamin D (25(OH)D) levels at 11-13 weeks' gestation according to the mode of delivery. Maternal serum 25(OH)D levels were measured at 11-13 weeks' gestation in 995 singleton pregnancies resulting in the birth of phenotypically normal neonates at term. The measured 25(OH)D levels were adjusted for maternal age, BMI, racial origin, smoking, method of conception and season of blood testing, and the adjusted levels (multiple of the median; MoM) were compared between those who subsequently delivered vaginally and those that delivered by caesarean section. Delivery was vaginal in 79·6 % of cases, by emergency caesarean section in 11·6 % and by elective caesarean section in 8·8 %. The median 25(OH)D level in our population was 46·82 (interquartile range (IQR) 27·75-70·13) nmol/l. The adjusted maternal median 25(OH)D levels in the emergency and elective caesarean section groups (0·99, IQR 0·71-1·46 MoM and 0·96, IQR 0·73-1·27 MoM, respectively) were not significantly different from the vaginal delivery group (0·99, IQR 0·71-1·33 MoM; P = 0·53 and P = 0·81, respectively). First-trimester maternal serum 25(OH)D levels are similar between women who subsequently have a vaginal delivery and those who deliver by elective or emergency caesarean section.

Uterine relaxant effects of Curcuma aeruginosa Roxb. rhizome extracts

The effects and plausible mechanism of action of Curcuma aeruginosa Roxb. (Zingiberaceae) rhizome chloroform and methanol extracts on the uterine contraction were investigated using isolated uterus strips from estrogen primed rats. The contractile responses were recorded isometrically with a Grass FT03 force transducer connected to a MacLab system. The experiments were carried out on both nonstimulated, agonist- and KCl-stimulated uteri. In the nonstimulated uterus, the two extracts (10-400 microg/ml) had no significant effect. In contrast, in the stimulated uterus, the chloroform and methanol extracts exerted concentration-dependent inhibition of the contractions induced by oxytocin (1 mU/ml), prostaglandin F2alpha (PGF2alpha, 0.5 microg/ml), ACh (3x10(-6) M) and KCl (40 mM) with the IC50 (inhibition of force) of 31.4, 58.59, 56.21 and 29.28 microg/ml; and 57.79, 69.3, 223.8 and 69.19 microg/ml, respectively. Verapamil, the reference L-type calcium channel blocker, exhibited a similar pattern of inhibition with the IC50 of 0.03, 0.25, 0.35 and 0.04 microg/ml. The IC50 of diclofenac against a PGF2alpha-induced contraction was 31.36 microg/ml. It is known that the contraction induced by agonists and KCl is mainly due to calcium influx through the voltage-gated L-type calcium channels opened indirectly or directly by agonist-receptor activation and KCl. Thus, it is speculated that the two plant extracts might inhibit uterine contraction by interrupting the influx of Ca2+ probably through voltage-gated L-type calcium channels. This possibility was further substantiated by the ability of the extracts to shift the CaCl2-contraction curves to the right. As the methanol extract also reduced the contraction of oxytocin in Ca2+-free EDTA solution; thus, it is suggested that part of its action may be involved with an intracellular mechanism. The effect of the two extracts did not involve the activation of beta2-adrenoceptors since their effects were unaffected by propranolol. Based on the inhibitory effect of the extracts on the oxytocin-induced contraction, it is concluded that the extracts might be useful as tocolytic agents for the prevention of preterm labor. Their effects on the inhibition of PGF2alpha-induced contractions also seem useful for the treatment of dysmenorrhea. There are reports by others that the plant rhizome contains beta-pinene and sesquiterpenes. In addition, there is evidence that these compounds possess spasmolytic effects in the rat intestine and uterus. Therefore, the uterine relaxant effect of the plant extracts could be due to beta-pinene and some sesquiterpene lactones contents. The methanol extract is less potent than the chloroform extract, and this might be due to the lower amount of terpene compounds or different compounds may involve in this action.

Calcium levels during the initiation of labor

OBJECTIVE

To investigate the physiological role of calcium in the labor process.

STUDY DESIGN

Eighty-eight term healthy pregnant women who gave birth to normal healthy neonates participated in our study. We compared calcium levels between pregnant women who had normal delivery and those who underwent scheduled cesarean section. The control group consisted of pregnant women with gestation > or =37 weeks without contractions. The groups were compared with respect to calcium levels: (a) in maternal blood serum; (b) in blood serum of the neonates and mothers; and (c) in blood serum between neonates.

RESULTS

Significantly higher calcium levels were found in the group of pregnant women who delivered vaginally compared to those who delivered by scheduled cesarean section and those of the control group.

CONCLUSION

We assume that the increased calcium levels during the first stage of labor are involved with a possible role of calcium in the mechanism of initiation of labor.

Intracellular calcium stores and agonist-induced contractions in isolated human myometrium

OBJECTIVE

We hypothesized that the release of calcium from intracellular stores contributes to the contractions produced by the agonists oxytocin, carbachol, and prostaglandin F(2 )(alpha ) in human myometrium.

STUDY DESIGN

Strips of myometrium were obtained at cesarean section and hysterectomy. The strips were loaded with the calcium-sensitive dye Indo-1 to enable simultaneous measurement of tension and intracellular calcium levels. Agonist-induced responses in the presence and absence of extracellular calcium were studied.

RESULTS

Strips of myometrium were obtained from 48 women not in labor undergoing cesarean section and 6 women not pregnant undergoing hysterectomy. An increase in intracellular calcium level after agonist stimulation invariably preceded an increase in tension. Intracellular calcium level returned to baseline before myometrial relaxation. Oxytocin, carbachol, and prostaglandin F(2)(alpha) all gave both force and intracellular calcium responses in the absence of extracellular calcium, although both these responses were only 26% to 40% of the maximal response when extracellular calcium was present.

CONCLUSIONS

Release of calcium from internal stores induced by oxytocin, carbachol, and prostaglandin F(2)(alpha) may contribute to agonist-induced myometrial force production.

Possible role of Ca2+ channels in the vasodilating effect of 5beta-dihydrotestosterone in rat aorta

It has previously been shown that the androgen, 5beta-dihydrotestosterone (17beta-hydroxy-5beta-androstan-3-one, 5beta-DHT), is able to produce an endothelium-independent vasodilating effect in rat aorta. The present study analyzed the mechanisms underlying the above vasodilator effect of 5beta-dihydrotestosterone, with particular emphasis on verifying a possible interaction with GABA(A) receptors, beta-adrenoceptors and Ca2+ channels. Rat aortic rings without endothelium were isometrically recorded. 5Beta-dihydrotestosterone produced a concentration-dependent relaxation on the contractions induced by noradrenaline (NA; 0.3 microM) or K+ (KCl; 60 mM), with the latter being more sensitive to 5beta-dihydrotestosterone-induced relaxation than the former; the concentration-response curves showed that 5beta-dihydrotestosterone is significantly more potent than 17beta-estradiol(1,3,5(10)-estratrien-3,17beta-diol) to induce vasodilatation. The vasodilating effect of 5beta-dihydrotestosterone on noradrenaline-induced contraction was resistant to blockade by the GABA(A) receptor antagonists, picrotoxin or bicuculline, and the beta-adrenoceptor antagonist, propranolol, a finding that excludes an interaction of the steroid with GABA(A) receptors and beta-adrenoceptors. Interestingly, the contractions evoked by calcium in depolarized tissues were substantially inhibited by 5beta-dihydrotestosterone, implying that this steroid could be an endogenous calcium channel blocker; consistent with this finding, 5beta-dihydrotestosterone was able to relax tissues precontracted with the calcium channel opener, Bay K 8644. Moreover, although the rings precontracted with noradrenaline and potassium were almost equipotently relaxed by 5beta-dihydrotestosterone. Nifedipine was more potent than 5beta-dihydrotestosterone to block the potassium-induced contraction, but the steroid was more effective than nifedipine to prevent noradrenaline-induced contraction. The above results suggest that 5beta-dihydrotestosterone causes relaxation of rat aorta by acting directly on the membrane of smooth muscle cells; this non-genomic action may be explained in terms of a blockade of voltage- and receptor-dependent calcium channels, a mechanism that restricts the availability of extracellular calcium in the contractile machinery.

Effects of nomegestrol acetate on spontaneous and sulprostone-induced uterine contractions in pregnant cynomolgus monkeys monitored by telemetry

OBJECTIVE

Our purpose was to study the effects of the progestomimetic compound nomegestrol acetate on spontaneous and sulprostone-induced uterine contractility in pregnant cynomolgus monkeys.

STUDY DESIGN

Intrauterine pressure was continuously monitored with use of an implanted intraamniotic catheter and a telemetric pressure transmitter from day 115 to 135 of gestation (term = 165 days). After surgery the animals received either nomegestrol acetate (5 mg per day orally, n = 3) or vehicle only (controls, n = 3). The intramuscular prostaglandin E2 analog sulprostone (25 micrograms) was administered as a single injection 10 days after amniotic catheter implantation. Spontaneous and sulprostone-induced uterine contractions were compared between nomegestrol acetate- and vehicle-treated animals.

RESULTS

The frequency of spontaneous uterine contractions in control animals demonstrated a 24-hour pattern with a minimum at 12 hours and a maximum at 0 hours. The frequency of spontaneous contractions did not differ between nomegestrol acetate- and vehicle-treated animals. Sulprostone induced an increase in both the frequency and amplitude of contractions, reaching a maximum 12 hours after injection and fading out after 24 hours in vehicle-treated animals. In animals receiving nomegestrol acetate, the frequency of contractions increased moderately and transiently for a total duration of 6 hours only and returned to control levels thereafter.

CONCLUSION

Nomegestrol acetate significantly decreases the contractile response of the pregnant uterus induced by the prostaglandin E2 analog sulprostone.

Inhibitory effect of sex steroids on guinea-pig airway smooth muscle contractions

We assessed the possible inhibition of airway smooth muscle contraction by progesterone and pregnanolones (5 alpha and 5 beta-reduced). Progesterone and 5 beta-pregnanolone prevented histamine- or carbachol-induced contraction in isolated guinea-pig trachea and potency was related to their respective chemical structure; progesterone was the most potent inhibitor in a concentration-dependent manner. The steroids also exhibited calcium antagonist activities in this tissue as assessed by their action on calcium entry in depolarized preparations; this event involved the immediate blockade of the extracellular calcium influx in the muscle cell membrane, indicating a nongenomic action. Classical GABAA antagonists did not block the progesterone response, implying no involvement of the GABAA-receptor complex. Our results suggest a bronchodilating effect induced by sex steroids, and probably by other related compounds, before the genomic mechanisms take place. This nongenomic action of steroids could have potential therapeutic usefulness in the treatment of asthma.

The relaxant effect of sex steroids in rat myometrium is independent of the gamma-amino butyric acid system

The mechanism of action on the uterine-relaxant effect of sex steroids has been suggested to involve an interaction with gamma-amino butyric acid (GABA) receptors. However, other lines of evidence do not seem to support this suggestion. In view of this controversy, this study was designed to investigate the potential relaxant effect of GABA, muscimol (a GABA(A) receptor agonist), testosterone, progesterone and their 5-reduced metabolites in rat uterus at different endocrine stages (pregnant, nonpregnant and estrogenized), with particular emphasis on verifying if the relaxant effect of steroids involves an interaction with GABA(A) receptors. Contractions from uterine rings were recorded by isometric method, the sequential addition of either GABA (at different concentrations) on the spontaneous and KCl-induced contraction or muscimol (also at different concentrations) on the contraction induced by KCl was devoid of any significant effect. In contrast, the sequential addition of progesterone relaxed the tonic KCl-induced contraction in a concentration-dependent manner. This effect of progesterone was mimicked by its 5-reduced metabolites. The 5(beta)-configured isomers were more potent than progesterone and the 5(alpha)-configured ones. Interestingly, the relaxation produced by the above steroids was not blocked by the GABA(A) receptor antagonists, picrotoxin or bicuculline, but was reversed by calcium. Taken together, the above findings suggest that the relaxant action of the sex steroids analyzed in this study is not mediated by an interaction with GABA(A) receptors, instead a blockade of calcium influx appears to be responsible.

Role of endothelium in the vasodilating effect of progestins and androgens on the rat thoracic aorta

1. In the rat thoracic aorta, contractions induced by noradrenaline were inhibited by the steroids progesterone, pregnanolone, testosterone and 5 alpha- and 5 beta-dihydrotestosterone. 2. Removal of endothelium did not prevent relaxation to the steroids, suggesting that the vasodilating effect of steroids occurred on the smooth muscle cells. 3. gamma-Aminobutyric acid (GABA) did not modify noradrenaline-induced contraction. Thus, the vasodilation elicited by steroids is not apparently mediated by GABA receptors. 4. On the basis that noradrenaline opens receptor-operated calcium channels to induce contraction, we suggest that relaxation by steroids involves a blockade of this type of channels.

Fetal membranes inhibit prostaglandin but not oxytocin-induced uterine contractions

OBJECTIVE

Paracrine signaling in fetal membranes and uterus is hypothesized to play a role in the initiation of labor in women. Numerous fetal membrane signals that stimulate uterine contractions have been described. Recently, by means of the dual-chamber, fetal membrane, uterine muscle model we showed that fetal membranes inhibit spontaneous uterine contractions. This study was designed to test whether human fetal membranes can also inhibit agonist-induced uterine contractions.

STUDY DESIGN

A rat uterine muscle strip was mounted into the maternal side of a Plexiglas acrylic plastic chamber. Uterine contractions were recorded for 3 hours after the addition of either 50 nmol/L prostaglandin E2 or 0.1 nmol/L oxytocin to the maternal side of the chamber. During the first and third hours no fetal membranes were present (basal condition). At the beginning of the second hour fetal membranes were inserted into the chamber so that they divided the chamber into maternal and fetal compartments. The membranes were removed before the beginning of the third hour. The integrated force of uterine contractions during the second hour, when the muscle was exposed to fetal membranes, was compared with the basal condition (first and third hours) by repeated-measure analysis of variance.

RESULTS

Fetal membranes reversibly inhibited prostaglandin E2-induced uterine contractions by 22%. Fetal membranes did not inhibit oxytocin-induced uterine contractions.

CONCLUSION

Fetal membranes inhibit agonist-induced uterine contractions. The fetal membrane inhibitory system is agonist selective.

Progesterone-like relaxant effect of RU 486 in the rat myometrium

The antihormone RU 486 is characterized by its antiprogesterone and antiglucocorticoid activities. In this work the likelihood of a non-genomic effect for this compound was assessed. Thus, RU 486 was compared with progesterone and the 5 beta-progestin pregnanolone, for its ability to modify the uterine contractility of the rat. An outstanding relaxant effect elicited by RU 486 was observed, slightly higher than that produced by progesterone but lower than pregnanolone. Moreover, calcium promoted contractions were antagonized by RU 486, in the same way as the endogenous steroids. The data suggest the capability of RU 486 to block the calcium channels. It is concluded that a non-genomic effect of RU 486 is produced before its journey into the cell for its genomic action.

Rapid non-genomic actions of progesterone stimulate Ca2+ influx and the acrosome reaction in human sperm

This review summarizes some recent findings in human sperm which show that progesterone and 17 alpha hydroxyprogesterone are able rapidly (within seconds) to elevate [Ca2+]i and elicit the acrosome reaction (AR) via a non-genomic cell surface receptor. Progesterone promotes a transient elevation in [Ca2+]i which is blocked by extracellular La3+ and Ni2+ and removal of extracellular Ca2+ following chelation with EGTA. Some studies suggest that polyamines, trypsin-like proteases, and progesterone receptor aggregation are involved in progesterone-induced Ca2+ influx and AR. The receptor is not stimulated by the potent synthetic progestigins (e.g. promegestone, norethynodrel, megestrol acetate, cyproterone acetate) and is weakly antagonized by the genomic anti-progestins RU 486 and ZK 98.299. The sedative-hypnotic 3 alpha hydroxyl A-ring reduced pregnane steroids, which are powerful activators of the GABAA Cl- channel, are weak activators of Ca2+ influx and the AR. These data suggest that human sperm have a cell surface steroid receptor which is unlike the genomic progesterone receptor and the GABAA Cl- channel steroid receptor.