Uterine oxytocin gene expression. II. Induction by exogenous steroid administration

Impact of Magnesium on Oxytocin Receptor Function

BACKGROUND AND PURPOSE

The intranasal administration of oxytocin (OT) reduces migraine headaches through activation of the oxytocin receptor (OTR). Magnesium ion (Mg2+) concentration is critical to the activation of the OTR, and a low serum Mg2+ concentration is predictive of a migraine headache. We, therefore, examined the functional impact of Mg2+ concentration on OT-OTR binding efficacy using two complimentary bioassays.

EXPERIMENTAL APPROACH

Current clamp recordings of rat trigeminal ganglia (TG) neurons measured the impact of Mg2+ on an OT-induced reduction in excitability. In addition, we assessed the impact of Mg2+ on intranasal OT-induced craniofacial analgesia in rats.

KEY RESULTS

While OT alone dose-dependently hyperpolarized TG neurons, decreasing their excitability, the addition of 1.75 mM Mg2+ significantly enhanced this effect. Similarly, while the intranasal application of OT produced dose-dependent craniofacial analgesia, Mg2+ significantly enhanced these effects.

CONCLUSIONS AND IMPLICATIONS

OT efficacy may be limited by low ambient Mg2+ levels. The addition of Mg2+ to OT formulations may improve its efficacy in reducing headache pain as well as for other OT-dependent processes.

Oxytocin Signaling in the Early Life of Mammals: Link to Neurodevelopmental Disorders Associated with ASD

Oxytocin plays a role in various functions including endocrine and immune functions but also parent-infant bonding and social interactions. It might be considered as a main neuropeptide involved in mediating the regulation of adaptive interactions between an individual and his/her environment. Recently, a critical role of oxytocin in early life has been revealed in sensory processing and multi-modal integration that are essential for normal postnatal neurodevelopment. An early alteration in the oxytocin-system may disturb its maturation and may have short-term and long-term pathological consequences such as autism spectrum disorders. Here, we will synthesize the existing literature on the development of the oxytocin system and its role in the early postnatal life of mammals (from birth to weaning) in a normal or pathological context. Oxytocin is required in critical windows of time that play a pivotal role and that should be considered for therapeutical interventions.

Administration of atosiban in patients with endometriosis undergoing frozen-thawed embryo transfer: a prospective, randomized study

OBJECTIVE

To examine the effects of atosiban, given before transfer of frozen-thawed embryo to women with endometriosis (EMs).

DESIGN

A randomized, controlled clinical trial.

SETTING

University hospital and IVF center.

PATIENT(S)

One hundred twenty women with endometriosis undergoing frozen-thawed embryo transfer were randomly allocated into the atosiban treatment and the control groups. Another 120 women with infertility due to tubal factor were enrolled into a tubal factor group, to compare serum oxytocin (OT) and prostaglandin (PG)F2α levels and uterine contractions with the endometriosis group.

INTERVENTION(S)

In the endometriosis treatment group, a single bolus (6.75 mg, 0.9 mL per vial) of atosiban was administrated before ET.

MAIN OUTCOME MEASURE(S)

Implantation rate and pregnancy rate.

RESULT(S)

Serum OT level (1.89 ± 0.33 vs. 1.66 ± 0.32 ng/L), PGF2α (2.83 ± 0.34 vs. 2.36 ± 0.35 ng/L) level, and uterine contractions (2.5 ± 1.2 vs. 1.8 ± 1.0 waves per minute) in the endometriosis group were all significantly higher than in the tubal factor group. The clinical pregnancy rate per cycle and implantation rate per transfer were 58.3% and 41.0%, respectively, in the atosiban treatment group, significantly higher than in the control group (38.3% and 23.4%, respectively).

CONCLUSION(S)

Women with endometriosis showed higher serum OT level, PGF2α level, and uterine contractions. Atosiban treatment before ET in endometriosis is effective in the priming of the uterus, suitable for embryo implantation. This is the first study to evaluate the effect of atosiban treatment in patients with endometriosis.

CLINICAL TRIAL REGISTRATION NUMBER

ChiCTR-IOQ-14005715.

Fluorescent visualization of oxytocin in the hypothalamo-neurohypophysial system

Oxytocin (OXT) is well known for its ability to the milk ejection reflex and uterine contraction. It is also involved in several other behaviors, such as anti-nociception, anxiety, feeding, social recognition, and stress responses. OXT is synthesized in the magnocellular neurosecretory cells (MNCs) in the hypothalamic paraventricular (PVN) and the supraoptic nuclei (SON) that terminate their axons in the posterior pituitary (PP). We generated transgenic rats that express the OXT and fluorescent protein fusion gene in order to visualize OXT in the hypothalamo-neurohypophysial system (HNS). In these transgenic rats, fluorescent proteins were observed in the MNCs and axon terminals in the PP. This transgenic rat is a new tool to study the physiological role of OXT in the HNS.

In-VITRo effect of Ficus deltoidea on the contraction of isolated rat's uteri is mediated via multiple receptors binding and is dependent on extracellular calcium

BACKGROUND

Ficus deltoidea, is a perennial herb that is used to assist labor, firm the uterus post-delivery and to prevent postpartum bleeding. In view of its claimed uterotonic action, the mechanisms underlying plant's effect on uterine contraction were investigated.

METHODS

Adult female SD rats were injected with 2 mg/kg 17β-oestradiol (E2) to synchronize their oestrous cycle. A day after injection, uteri were removed for in-vitro contraction studies. The dose dependent effect of Ficus deltoidea aqeous extract (FDA) on the tension produced by the isolated rat's uteri was determined. The effects of atropine (2×10(-8) M), atosiban (0.5 IU), THG113.31 (10 μM), oxodipine (0.25 mM), EDTA (1 mM), 2-amino-ethoxy-diphenylborate (2-APB) (40 mM) and thapsigargin (1 mM) on the maximum force of contraction (Emax) achieved following 2 mg/ml FDA administration were also investigated.

RESULTS

FDA induced in-vitro contraction of the isolated rat's uteri in a dose-dependent manner. Administration of atropine, atosiban and THG113.31 reduced the Emax with atosiban having the greatest effect. The Emax was also reduced following oxodipine and EDTA administration. There was no significant change observed following 2-APB administration. Thapsigargin, however, augmented Emax.

CONCLUSIONS

FDA-induced contraction of the isolated rat's uteri is mediated via multiple uterotonin receptors (muscarinic, oxytocin and prostaglandin F2α) and was dependent on the extracellular Ca2+. Contraction, however, was not dependent on the Ca2+ release from the internal stores. This in-vitro study provides the first scientific evidence on the claimed effect of Ficus Deltoidea on uterine contraction.

The effect of continuous morphine administration on maternal plasma oxytocin concentration and uterine contractions after open fetal surgery

OBJECTIVE

A major complication of open fetal surgery is prematurity. We propose that fetal and maternal stress/pain after surgery may affect the concentration of circulating oxytocin and the frequency of uterine contractions, thus increasing the risk of preterm delivery. The objective of this study was to test whether continuous morphine sulfate administration after open fetal surgery has an effect on maternal plasma oxytocin concentration and the frequency of uterine contractions.

METHODS

An established time-pregnant primate model for open fetal surgery was used. From the time of surgery until the end of the three-day study period, three animals received prophylactic antibiotics, a bolus of indomethacin, and a bolus of morphine sulfate (group I). Three other animals received the same prophylactic antibiotics and an i.v. bolus of indomethacin, as well as a continuous i.v. infusion of morphine sulfate throughout the entire study period (group II). Maternal blood samples were collected to determine oxytocin plasma concentrations. Oxytocin was measured by radioimmunoassay. Uterine activity was continuously recorded through an amniotic fluid catheter and quantified as number of contractions (10 mmHg increase from base line in intrauterine pressure) per hour (UCs/h).

RESULTS

The mean maternal plasma oxytocin concentration was higher (p < 0.01) and the number of uterine contractions more frequent (p < 0.05) in the group of animals with intermittent doses of morphine than in the group that received morphine continuously.

CONCLUSIONS

These data suggest that maternal plasma oxytocin concentration and uterine activity after open fetal surgery may be related to inadequate maternal/fetal analgesia/sedation.

Relationship between gene expression and function of uterotonic systems in the rat during gestation, uterine activation and both term and preterm labour

We have documented gestation- and labour- (preterm and term) dependent changes in expression of genes encoding contraction associated proteins in the rat uterus and correlated these changes with various parameters of uterine contractility. The data demonstrate increased expression of contractile agonist systems concurrent with decreased expression of relaxant systems after gestational day 20. Significant increases in expression of oxytocin (OT), its receptor (OTR), prostaglandin (PG) H synthase isoform 1 (PGHS-1) and PGF(2alpha) receptor (FP) occurred first, followed by increases in PGHS-2, connexin-43, endothelin-1 (ET-1) and the ET-1 receptor isoform ET(A). Expression of OTR and FP was significantly reduced during mid-gestation compared to non-pregnant animals. Expression of inducible nitric oxide synthase (iNOS) increased significantly during pregnancy then decreased concurrently with the increase in OTR and FP. Functional changes in uterine contractility accompany changes in gene expression. OT was the most potent contractile stimulant. Sensitivity of uterine strips to OT was reduced in early and mid-pregnancy then increased at uterine activation. Progesterone antagonist-induced preterm labour caused changes similar to those at normal term. Comparison of mRNA transcripts in separated endometrium and myometrium suggested that the endometrium is an important regulator of myometrial contractility, analogous to the relationship between endothelium and vascular smooth muscle. This novel combination of functional and genetic expression analyses provides new insight into the physiology of parturition.

Effects of steroids on oxytocin secretion by the human prostate in vitro

Oxytocin (OT) concentrations are elevated in prostate tissue of patients with benign prostatic hyperplasia (BPH). Oxytocin specifically increases growth, 5 alpha-reductase activity and contractility in the prostate. In the rat prostatic OT concentrations are regulated by gonadal steroids, with androgens reducing but oestrogens increasing OT concentrations. The regulation of prostatic oxytocin in man is not understood. This study investigates the effects of gonadal steroids on oxytocin production by the human prostate. Primary explants (approx. 1 mm3) of prostate tissue from patients with BPH were incubated in Dulbecco's modified Eagle's media in the absence or presence of 10 nmol/L testosterone (T), 10 nmol/L dihydrotestosterone (DHT), T or DHT plus 100 nmol/L of the anti-androgen cyproterone acetate (CPA), 55 pmol/L diethylstilbestrol (DES), or DES plus DHT. The amount of oxytocin secreted into the media after 3 days was measured by radioimmunoassay. Testosterone and DHT significantly increased oxytocin concentrations secreted into the media from 0.86 +/- 0.11 ng/g of tissue (control) to 1.51 +/- 0.14 ng/g (p < 0.01) and 1.54 +/- 0.13 ng/g (p < 0.05), respectively. Incubation of tissue samples with CPA resulted in oxytocin concentrations similar to control levels. Treatment with DES caused a significant increase from 1.99 +/- 0.71 to 3.98 +/- 1.36 ng/g (p < 0.05). A similar increase was measured in media of tissue incubated in DES plus DHT (p < 0.001). The results demonstrate that, unlike the rat where androgens decrease oxytocin, in hyperplastic human prostate tissue both androgens and oestrogens increase oxytocin. This imbalance in the regulation of oxytocin may result in promoting prostatic overgrowth in the pathogenesis of BPH.

Determination of velocity of tubar transport with dynamic hysterosalpingoscintigraphy

Transport of 99mTc labelled albumin macroaggregates (MAA) can be used as a substitute for assessing transport of spermatozoa within the female genital tract. As yet, the velocity of tubar MAA transport has not been systematically studied in a large group. Dynamic hysterosalpingoscintigraphy (HSS) was performed after intrauterine instillation of 10-20 MBq 99mTc-MAA in 88 pre-ovulatory women suffering from infertility. They had to have anatomical patency of both tubes and at least one enlarged follicle. The direction and the latency of transport were evaluated. Forty-four per cent of patients exhibited MAA transport only to the dominant follicle, 31% to both ovaries and 16% to the contralateral ovary. In 9% no transport was visible. Fifty per cent of all patients studied exhibited MAA transport to the dominant follicle within 30 s, 75% within 20 min. Transport velocity in women having bilateral or ipsilateral transport did not differ significantly. There was no significant correlation between the size of the follicle and transport velocity. We conclude that in the majority of cases MAA transport occurs within 30 s after instillation. The variation in transport time between 30 s and 20 min suggests that dynamic scintigraphy is, in principle, better suited to a refined analysis of tubar function than static HSS.

The affinity and activity of the multiple hormone response element in the proximal promoter of the human oxytocin gene

In vivo there appears to be a marked association between oestrogen levels and the expression of the oxytocin (OT) gene in most tissues. Transfection and DNA-protein binding experiments using high levels of either oestrogen receptor (ER)alpha or ERbeta imply a direct interaction of these transcription factors with the multiple hormone response element (HRE) at approximately -160 from the transcription start site of the OT gene in most species. In an extensive set of experiments, we show, using both transfection and protein-DNA binding, that low to moderate amounts of either oestrogen receptor, while being able to interact directly with a classic oestrogen response element (ERE) fail to interact with the human OT -160 HRE. Instead, this element, similar to its bovine counterpart, has a high affinity for the orphan receptors steroidogenic factor 1 and chicken ovalbumin upstream promoter transcription factor. Second, the human and bovine OT promoter can be made artificially responsive towards oestrogen in a cotransfection system over-expressing ERalpha or ERbeta, but not in cells expressing natural levels of these steroid receptors. Interestingly, nuclear extracts from both ERalpha-positive MCF7 cells and ERalpha-negative MDA-MB231 cells both contain a transcription factor which binds specifically to both the hOT-HRE element and to a classic ERE, and which has orphan receptor-like binding properties rather than those of an oestrogen receptor. Together, these and other results suggest that oestrogen action in vivo on the OT gene in all species is more likely to involve a DNA-independent mechanism than classic direct interactions with dimeric oestrogen receptors.

The oxytocin receptor system: structure, function, and regulation

The neurohypophysial peptide oxytocin (OT) and OT-like hormones facilitate reproduction in all vertebrates at several levels. The major site of OT gene expression is the magnocellular neurons of the hypothalamic paraventricular and supraoptic nuclei. In response to a variety of stimuli such as suckling, parturition, or certain kinds of stress, the processed OT peptide is released from the posterior pituitary into the systemic circulation. Such stimuli also lead to an intranuclear release of OT. Moreover, oxytocinergic neurons display widespread projections throughout the central nervous system. However, OT is also synthesized in peripheral tissues, e.g., uterus, placenta, amnion, corpus luteum, testis, and heart. The OT receptor is a typical class I G protein-coupled receptor that is primarily coupled via G(q) proteins to phospholipase C-beta. The high-affinity receptor state requires both Mg(2+) and cholesterol, which probably function as allosteric modulators. The agonist-binding region of the receptor has been characterized by mutagenesis and molecular modeling and is different from the antagonist binding site. The function and physiological regulation of the OT system is strongly steroid dependent. However, this is, unexpectedly, only partially reflected by the promoter sequences in the OT receptor gene. The classical actions of OT are stimulation of uterine smooth muscle contraction during labor and milk ejection during lactation. While the essential role of OT for the milk let-down reflex has been confirmed in OT-deficient mice, OT's role in parturition is obviously more complex. Before the onset of labor, uterine sensitivity to OT markedly increases concomitant with a strong upregulation of OT receptors in the myometrium and, to a lesser extent, in the decidua where OT stimulates the release of PGF(2 alpha). Experiments with transgenic mice suggest that OT acts as a luteotrophic hormone opposing the luteolytic action of PGF(2 alpha). Thus, to initiate labor, it might be essential to generate sufficient PGF(2 alpha) to overcome the luteotrophic action of OT in late gestation. OT also plays an important role in many other reproduction-related functions, such as control of the estrous cycle length, follicle luteinization in the ovary, and ovarian steroidogenesis. In the male, OT is a potent stimulator of spontaneous erections in rats and is involved in ejaculation. OT receptors have also been identified in other tissues, including the kidney, heart, thymus, pancreas, and adipocytes. For example, in the rat, OT is a cardiovascular hormone acting in concert with atrial natriuretic peptide to induce natriuresis and kaliuresis. The central actions of OT range from the modulation of the neuroendocrine reflexes to the establishment of complex social and bonding behaviors related to the reproduction and care of the offspring. OT exerts potent antistress effects that may facilitate pair bonds. Overall, the regulation by gonadal and adrenal steroids is one of the most remarkable features of the OT system and is, unfortunately, the least understood. One has to conclude that the physiological regulation of the OT system will remain puzzling as long as the molecular mechanisms of genomic and nongenomic actions of steroids have not been clarified.

Effect of progesterone on intracellular Ca2+ homeostasis in human myometrial smooth muscle cells

Although it is well known that progesterone alters uterine contractility and plays an important role in maintenance of pregnancy, the biochemical mechanisms by which progesterone alters uterine contractility in human gestation are less clear. In this investigation we sought to identify progesterone-induced adaptations in human myometrial smooth muscle cells that may alter Ca2+ signaling in response to contractile agents. Cells were treated with vehicle or the progesterone analog medroxyprogesterone acetate (MPA) for 5 days, and intracellular free Ca2+ concentration ([Ca2+]i) was quantified after treatment with oxytocin (OX) or endothelin (ET)-1. OX- and ET-1-induced increases in [Ca2+]i were significantly attenuated in cells pretreated with MPA in a dose-dependent manner. Progesterone receptor antagonists prevented the attenuated Ca2+ transients induced by MPA. ETA and ETB receptor subtypes were expressed in myometrial cells, and treatment with MPA resulted in significant downregulation of ETA and ETB receptor binding. MPA did not alter ionomycin-stimulated increases in [Ca2+]i and had no effect on inositol trisphosphate-dependent or -independent release of Ca2+ from internal Ca2+ stores. We conclude that adaptations of Ca2+ homeostasis in myometrial cells during pregnancy may include progesterone-induced modification of receptor-mediated increases in [Ca2+]i.

Role of carboxy-extended forms of oxytocin in the rat uterus in the process of parturition

The hypothalamic synthetic pathway of oxytocin (OT) involves the synthesis of carboxy-extended forms that serve as intermediate prohormones. We hypothesized that extended forms of OT are synthesized in the late-gestational rat uterus and that they compete for OT receptor binding. Parturition occurs only when the ratio of OT to its extended forms reaches a critical level. We have measured OT and its extended forms using two antisera, one recognizing OT and its extended forms, the other recognizing only mature amidated OT. Uterine tissue concentrations of extended forms of OT were 5- to 30-fold greater than those of OT, and both increased progressively and significantly through late gestation. The ratio of OT to its extended forms did not change significantly. Antagonists of estrogen or progesterone receptors reduced concentrations of extended forms by > 90% and of OT by 50%, though the estrogen antagonist significantly prolonged gestation and the progesterone antagonist induced preterm delivery. Using a muscle bath preparation, extended forms of OT were weak uterine stimulants and did not alter the OT concentration-response curves. Extended forms of OT were two to three orders of magnitude less able than OT to displace radiolabeled OT from late-gestational uterine binding sites. We conclude that uterine carboxy-extended OT prohormones are regulated in part by estrogen and progesterone. However, these extended forms of OT have little direct biological activity and do not compete with OT for receptor binding. Their role in the process of parturition may be confined to acting as substrates for OT synthesis.

Local paracrine effects of estradiol are central to parturition in the rhesus monkey

The central biochemical mechanisms involved in primate parturition are still unclear. Studies in both humans and nonhuman primates such as the baboon and rhesus monkey indicate that many factors play a part in the cascade of interactive positive feedforward loops that progressively promote parturition: changes in maternal endocrinology, a nocturnal switch in myometrial activity from low amplitude, infrequent contractures to high amplitude, high frequency contractions (see Fig. 1), dilation of the cervix and biochemical changes in the fetal membranes that lead to rupture. Here we demonstrate that infusion of the aromatase inhibitor 4-hydroxyandrostenedione (4OHA) inhibits conversion of androgen to estrogen and prevents premature delivery caused by administration of androgen to pregnant rhesus monkeys at 0.8 of pregnancy term. 4OHA also inhibited the androstenedione induced maternal endocrine and fetal membrane biochemical changes, and alteration of myometrial activity patterns. Secondly, peripheral estrogen infusions increased myometrial activity but did not produce preterm delivery or fetal membrane changes. We conclude that paracrine functions of estrogen at its site of production play critical and central roles in delivery in the non-human primate.

Bovine oxytocin transgenes in mice. Hypothalamic expression, physiological regulation, and interactions with the vasopressin gene

To gain insights into the molecular mechanisms that restrict the expression of the oxytocin gene to anatomically defined groups of neurons in the hypothalamus, we generated transgenic mice bearing bovine oxytocin genomic fragments. Appropriate neuron-specific and physiological regulation was observed in mice bearing transgene bOT3.5, which consists of the oxytocin structural gene flanked by 0.6 kilobase pair (kbp) of upstream and 1.9 kbp of downstream sequences. bOT3.5 is expressed in oxytocin magnocellular neurons in the mouse supraoptic nucleus and paraventricular nucleus, but transgene RNAs are excluded from vasopressin neurons. Replacement of the drinking diet of the transgenic mice with 2% (w/v) NaCl for 7 days significantly increased the abundance of bovine oxytocin transcripts in the supraoptic nucleus, but not in the paraventricular nucleus, in parallel with the endogenous mouse oxytocin RNA. Surprisingly, mimicry of the endogenous oxytocin gene expression pattern was lost with larger transgenes. Addition of 0.7 kbp of contiguous downstream sequences (transgene bOT) or linkage to the bovine vasopressin gene (transgene VP-B/bOT3.5) repressed hypothalamic expression. No mice were derived bearing transgene bOT6.4, which consists of the oxytocin structural gene flanked by 3 kbp of upstream and 2.6 kbp of downstream sequences, suggesting that the presence of this DNA is detrimental to normal embryonic development. These data suggest that while bOT3.5 contains sufficient cis-acting sequences to mediate expression to particular subsets of hypothalamic neurons, the overall regulation of the oxytocin gene is governed by multiple interacting enhancers and repressors.