Uterine oxytocin gene expression. I. Induction during pseudopregnancy and the estrous cycle

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.

Termination of pseudopregnancy in the rat alters the response to progesterone, chlordiazepoxide, and MK-801 in the elevated plus-maze

RATIONALE

Allopregnanolone, a neurosteroid-reduced metabolite of progesterone, is a well-documented positive modulator of the gamma-aminobutyric type A (GABA(A)) receptor. As has been reported for other positive modulators of the GABA(A) receptor, chronic exposure to neurosteroids is hypothesized to decrease GABA(A) receptor function. Drawing from the literature on chronic exposure to benzodiazepines or alcohol, putative changes in N-methyl-D-aspartate (NMDA) receptor function are also expected after chronic neurosteroid exposure.

OBJECTIVES

To assess the sensitivity of the GABA(A) and NMDA receptors after chronic elevation of neurosteroid produced by termination of pseudopregnancy in behavioral tests of anxiety and sensorimotor coordination.

METHODS

Female rats ovariectomized on day 10 of pseudopregnancy were tested in the elevated plus-maze and on the rotor rod after an acute injection of progesterone (4 mg/0.2 ml, s.c.), chlordiazepoxide (5 or 15 mg/kg, i.p.), or MK-801 (0.025, 0.05, or 0.1 mg/kg, i.p.).

RESULTS

Pseudopregnancy termination produced an anxiogenic-like response in the plus-maze; an acute injection of progesterone restored baseline levels of behavior in this test. Pseudopregnancy termination eliminated the anxiolytic-like, sedative, and ataxic effects of chlordiazepoxide. In contrast, pseudopregnancy termination produced an increased sensitivity to the anxiolytic-like and ataxic effects of MK-801.

CONCLUSIONS

The effects of pseudopregnancy termination on the behavioral response to positive modulators of the GABA(A) receptor are consistent with results from studies in which chronic exposure to neurosteroids decreases the response to acute neurosteroid and benzodiazepine administration. However, unlike the enhanced glutamatergic tone resulting from discontinuation of chronic benzodiazepine or alcohol exposure, the termination of pseudopregnancy apparently decreases NMDA receptor function.

Uterine motor alterations and estrous cycle disturbances associated with colonic inflammation in the rat

The impact of colitis on uterine contractility and estrous cycle was investigated after intracolonic administration of 2,4,6-trinitrobenzenesulfonic acid (TNBS) in rats. Colitis severity was assessed by macroscopic damage scoring (MDS) 4 days after TNBS, and myeloperoxidase (MPO) activity was measured in both colon and uterus of control and colitic rats. Estrous cycle stages were determined by vaginal smears and histology, and uterine contractility was assessed in vitro on longitudinal and circular strips. In control rats, uterine MPO activity varied markedly during the cycle and peaked around estrus. In rats with moderate colitis [MDS < 5, 3.1 ± 0.2 (mean ± SE)], uterine MPO decreased by 61% compared with estrus control, without disruption of the cycle. Frequency of spontaneous contractions was reduced by 32% in circular muscle. Contractile responses to KCl and carbachol were not affected, whereas maximal response to oxytocin decreased by 47% in the longitudinal muscle. In rats with severe colitis (MDS > 5, 6.0 ± 0.2), uterine MPO was reduced by 96% and estrous cycle was disrupted. Spontaneous contractility was impaired in circular strips, and a 39% decrease in the contraction frequency occurred in the longitudinal strips. Circular strips did not contract to KCl or carbachol; however, longitudinal strips had maximal responses to KCl, carbachol, and oxytocin reduced by 36%, 27%, and 46%, respectively. Estrogen replacement protected the uterine responses to carbachol in colitic rats, whereas oxytocin responses remained depressed. These data indicate that colonic inflammation can influence both spontaneous and evoked uterine contractility, in relation to estrous cycle disturbances, impaired estradiol production, and functional alterations of myometrial cells.

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.

Oxytocin and its receptors are synthesized in the rat vasculature

Produced and released by the heart, oxytocin (OT) acts on its cardiac receptors to decrease the cardiac rate and force of contraction. We hypothesized that it might also be produced in the vasculature and regulate vascular tone. Consequently, we prepared acid extracts of the pulmonary artery and vena cava of female rats. OT concentrations in dog and sheep aortae were equivalent to those of rat aorta (2745 +/- 180 pg/mg protein), indicating that it is present in the vasculature of several mammalian species. Reverse-phase HPLC of aorta and vena cava extracts revealed a single peak corresponding to the amidated OT nonapeptide. Reverse-transcribed PCR confirmed OT synthesis in these tissues. Using the selective OT receptor ligand compound VI, we detected a high number of OT-binding sites in the rat vena cava and aorta. Furthermore, OT receptor (OTR) mRNA was found in the vena cava, pulmonary vein, and pulmonary artery with lower levels in the aorta, suggesting vessel-specific OTR distribution. The abundance of OTR mRNA in the vena cava and pulmonary vein was associated with high atrial natriuretic peptide mRNA. In addition, we have demonstrated that diethylstilbestrol treatment of immature female rats increased OT significantly in the vena cava but not in the aorta and augmented OTR mRNA in both the aorta (4-fold) and vena cava (2-fold), implying regulation by estrogen. Altogether, these data suggest that the vasculature contains an intrinsic OT system, which may be involved in the regulation of vascular tone as well as vascular regrowth and remodeling.

Sensitivity of myometrium to CGRP varies during mouse estrous cycle and in response to progesterone

Calcitonin gene-related peptide (CGRP) inhibits contractions of the myometrium. Isometric force measurements on myometrial strips were carried out to monitor the inhibitory capacity of CGRP in the myometrium during the estrous cycle and in response to estrogen and progesterone in ovariectomized mice. CGRP inhibition of KCl-induced contractions was lowest at estrus and significantly increased during metestrus and diestrus. Progesterone treatment of ovariectomized mice resulted in a significant increase in the responsiveness of the myometrium to CGRP. Expression of CGRP-receptor component protein (CGRP-RCP), a marker of CGRP-receptor expression, was quantitated by Western and Northern blot analyses. The levels of inhibition exerted by CGRP during the various stages of the estrous cycle and in response to steroid hormone treatment correlated with the protein levels of CGRP-RCP. The mRNA levels did not change significantly during the estrous cycle or in response to hormone treatment, indicating that the regulation of CGRP-RCP protein does not occur at the transcriptional level. CGRP had an inhibitory effect both when applied before the stimulus for contraction and when applied during a sustained contracture induced by KCl. This suggests that CGRP-induced generation of second messengers can influence late events in electro-/chemomechanical coupling and/or the contractile machinery directly.

Oxytocin-neurophysin I mRNA abundance in equine uterine endometrium

A positive-feedback loop between luteal oxytocin and uterine prostaglandin F2 alpha (PGF) is a major signal for luteolysis in ruminants. Likewise, uterine PGF causes luteolysis in mares, but the involvement of oxytocin in this process is unclear. We wanted: 1) to determine if the oxytocin-neurophysin I (OT-NP I) gene is transcribed into mRNA in the endometrium of mares; and, if so, 2) to analyze relative changes in abundance of endometrial OT-NP I mRNA throughout the estrous cycle and during early stages of pregnancy. Endometrial biopsies were obtained from nonbred mares during estrus, and 5, 10, and 15 d after ovulation (n = 3/d). Biopsies were also obtained from pregnant mares 10, 15, and 20 d after ovulation (n = 3/d). Relative amounts of OT-NP I and glyceraldehyde-3-phosphate dehydrogenase mRNA in endometrium were assessed by reverse transcription-polymerase chain reaction and Southern blotting. Endometrial OT-NP I mRNA abundance changed with day of the cycle or pregnancy, and levels at estrus were higher than at any other days examined. The OT-NP I mRNA levels were negatively correlated with serum progesterone across all days examined and positively correlated with serum estradiol in nonbred mares. The reverse transcription-polymerase chain reaction products for both OT-NP I and glyceraldehyde-3-phosphate dehydrogenase were cloned into vectors and sequenced. Each shared greater than 89% nucleotide and predicted amino acid identities with the respective human, bovine, ovine, and rat products. Uterine oxytocin may be involved in regulation of reproductive tract function during the estrous cycle and/or establishment of pregnancy in horses.

Oxytocin is required for nursing but is not essential for parturition or reproductive behavior

Oxytocin, a neurohypophyseal hormone, has been traditionally considered essential for mammalian reproduction. In addition to uterine contractions during labor and milk ejection during nursing, oxytocin has been implicated in anterior pituitary function, paracrine effects in the testis and ovary and the neural control of maternal and sexual behaviors. To determine the essential role(s) of oxytocin in mammalian reproductive function, mice deficient in oxytocin have been generated using embryonic stem cell technology. A deletion of exon 1 encoding the oxytocin peptide was generated in embryonic stem cells at a high frequency and was successfully transmitted in the germ line. Southern blot analysis of genomic DNA from homozygote offspring and in situ hybridization with an exonic probe 3' of the deletion failed to detect any oxytocin or neurophysin sequences, respectively, confirming that the mutation was a null mutation. Mice lacking oxytocin are both viable and fertile. Males do not have any reproductive behavioral or functional defects in the absence of oxytocin. Similarly, females lacking oxytocin have no obvious deficits in fertility or reproduction, including gestation and parturition. However, although oxytocin-deficient females demonstrate normal maternal behavior, all offspring die shortly after birth because of the dam's inability to nurse. Postpartum injections of oxytocin to the oxytocin deficient mothers restore milk ejection and rescue the offspring. Thus, despite the multiple reproductive activities that have been attributed to oxytocin, oxytocin plays an essential role only in milk ejection in the mouse.

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.