The role of diacylglycerol as a modulator of oxytocin-stimulated phasic contractions in myometrium from pregnant and nonpregnant rats

Effectiveness of atosiban in women with previous single implantation failure undergoing frozen-thawed blastocyst transfer: study protocol for a randomised controlled trial

BACKGROUND

Uterine contractions may interfere with embryo implantation in assisted reproductive technology. To reduce these contractions and improve success rates, the oxytocin antagonist atosiban has been suggested for administration during embryo transfer. The aim of this study is to evaluate the effectiveness of atosiban in increasing live birth rates among women who have previously experienced a single implantation failure and are scheduled for single blastocyst transfer.

METHODS AND ANALYSIS

We conduct a single-centre randomised controlled study comparing atosiban and placebo in women undergoing a single blastocyst transfer with a previous failed blastocyst transfer. Women with endocrine or systemic illnesses, recurrent miscarriages, uterine malformations or fibroids, untreated hydrosalpinx, endometriosis (stage III or IV) or uterine fibroids, as well as women undergoing preimplantation genetic testing, are ineligible. The primary outcome is live birth resulting from the frozen-thawed embryo transfer. Secondary outcomes include biochemical/clinical pregnancy, miscarriage, ectopic pregnancy, multiple pregnancies as well as maternal and perinatal outcomes. We plan to recruit 1100 women (550 women per group). This will allow us to demonstrate or refute an increase in live birth rate from 40% to 50%. Data analysis will follow the intention-to-treat principle. We will measure patterns of uterine peristalsis which will allow subgroup analysis for women with or without uterine peristalsis.

ETHICS AND DISSEMINATION

This study has been approved by the Institutional Review Board of Northwest Women's and Children's Hospital (No. SZ2019001). Written informed consent will be obtained from each participant before randomisation. The results of the trial will be presented at scientific meetings and reported in publications.

TRIAL REGISTRATION NUMBER

ChiCTR1900022333.

Phorbol ester treatment of human myometrial cells suppresses expression of oxytocin receptor through a mechanism that does not involve activator protein-1

Oxytocin (OT) is a potent uterine agonist. Its receptor (OTR) is a G protein-coupled receptor that is downregulated by prolonged exposure to OT. We hypothesized that activation of PKC mediated this OT-induced decrease in OTR expression. Diminished PKC activity in late pregnancy could underlie the increased expression of uterine OTR preceding labor onset. Using cell cultures of transformed human uterine myocytes, we determined the effects of PKC agonists and antagonists on the expression of OTR. We also explored the effects of overexpression of activator protein-1 (AP-1, a mediator of many PKC- and phorbol ester-induced effects) using adenoviral expression vectors for the AP-1 subunits c-Jun and c-Fos. Stimulation of PKC using the phorbol ester 12-O-tetradecanoylphorbol 13-acetate caused a rapid, significant (P < or = 0.05) increase in c-Jun and c-Fos concentrations but a significant decrease in mRNA for OTR within 6 h followed by a significant decrease in OT binding by 24 h. Adenoviral infection of the cells with expression vectors for c-Jun and c-Fos increased the AP-1 subunits but had no effect on OTR expression. Furthermore, there were no changes in c-Fos or c-Jun levels in human intrauterine tissues around the time of labor onset, as measured by Western analyses. We conclude that phorbol ester treatment decreases OTR expression, likely through a mechanism that does not involve AP-1.

Stimulation of intracellular Ca2+ oscillations by diacylglycerol in human myometrial cells

Stimulation of G-protein coupled membrane receptors linked to phospholipase C results in production of the second messengers diacylglycerol and inositol-1,4,5-trisphosphate (IP3). IP3 releases Ca2+ from the endoplasmic reticulum, which triggers increased Ca2+ influx across the plasma membrane, so-called capacitative calcium entry. DAG can also activate plasma membrane calcium-permeable channels but the mechanism is still not fully understood. In the pregnant human myometrial cell line PHM1 and in primary myometrial cells, 1-oleoyl-2-acetyl-sn-glycerol (OAG), a membrane-permeant analogue of diacylglycerol, induced variable oscillatory patterns of intracellular free Ca2+. Similar behavior was seen with Sr2+ entry. The Ca2+ oscillations were not blocked by a broad spectrum of protein kinase C inhibitors, including chelerytrine, bisindolylmaleimide I and calphostin C, and were enhanced and prolonged by RHC-80267, an inhibitor of diacylglycerol lipase. The OAG-induced oscillatory response was not dependent on Ca2+ release from the endoplasmic reticulum but required extracellular Ca2+. Our results indicate that diacylglycerol directly activates cation channels in PHM1 and primary myometrial cells and promotes intracellular Ca2+ oscillations by actions independent of intracellular Ca2+ -ATPase activity and protein kinase C involvement.

Magnesium sulfate induces translocation of protein kinase C isoenzymes alpha and delta in myometrial cells from pregnant women

OBJECTIVES

The purpose of this study was to determine the effect of magnesium sulfate on protein kinase C (PKC) translocation in myometrial cells from pregnant women.

STUDY DESIGN

Myometrium was obtained at the time of cesarean delivery from women at term before labor. Cultured myometrial cells were treated with magnesium sulfate (3, 5, and 10 mmol/L), oxytocin (0.1 micromol/L), or 12-O-tetradecanoylphorbol-13-acetate (TPA, 0.1 micromol/L). The translocation of PKC isozymes alpha (calcium dependent) and delta (calcium independent) from cytosol to membrane fractions was assessed with use of Western blot analysis.

RESULTS

In unexposed control cells, the majority of PKC alpha and delta was located in the cytosol fraction. Exposure to magnesium sulfate for 60 minutes induced translocation of both PKC alpha and delta at concentrations as low as 5 and 3 mmol/L, respectively. The magnitude of magnesium sulfate induced translocation for PKC delta is similar to that seen after oxytocin or TPA exposure but less for PKC alpha. Exposure to oxytocin for 30 minutes and 60 minutes induced translocation of PKC alpha and delta, respectively. Exposure to TPA for 5 and 30 minutes induced translocation of PKC alpha and PKC delta, respectively. In calcium-free media, only TPA induced translocation of these two isoenzymes.

CONCLUSION

Magnesium sulfate stimulates PKC translocation in cultured myometrial cells from pregnant women. Magnesium sulfate and oxytocin require extracellular calcium to induce translocation of both PKC alpha and delta.

Expression of capacitative calcium TrpC proteins in rat myometrium during pregnancy

External Ca2+ entry into myometrial smooth-muscle cells is important to uterine contraction and hence to labor progression and parturition. Proteins of the transient receptor potential (Trp) channel family are putative capacitative Ca2+ entry channels that respond to contractant-generated signals and intracellular Ca2+ store depletion. Quantitative reverse transcription-polymerase chain reaction was used to examine the relative expression of TrpC mRNAs in rat myometrium and determine their expression pattern during pregnancy and labor. rTrpC1, rTrpC2, rTrpC4, rTrpC5, rTrpC6, and rTrpC7 mRNAs, but not rTrpC3 mRNA, were expressed in nonpregnant rat myometrium. With the exception of rTrpC7, the resulting products were sequenced and found to be identical with published sequences; new rTrpC7 sequence exhibited >88% homology to mouse and human TrpC7 coding regions. Relative to beta-actin mRNA, rTrpC4 mRNA was expressed in the greatest abundance. rTrpC1, 5, and 6 mRNAs were expressed at lower levels, whereas rTrpC2 and 7 mRNAs were barely detectable. This relative expression pattern was also observed throughout the course of gestation. There were no major differences in expression of rTrpC1, 2, 4, or 7 mRNAs between Day 13 and Day 21 of gestation or labor. Rat TrpC5 and TrpC6 mRNA expression decreased in pregnancy but was not altered between Day 13 and Day 21 or in labor. Western blot analysis generally confirmed these observations with respect to protein expression. These data suggest that rTrpC4 may play a major role in regulated Ca2+ entry in myometrial cells and throughout pregnancy but do not rule out contributions from other Trp proteins.