Hormonal and local regulation of uterine activity during parturition: Part II--The prostaglandin and adrenergic systems

Sperm migration, selection, survival, and fertilizing ability in the mammalian oviduct†

In vitro fertilization (IVF) gives rise to embryos in a number of mammalian species and is currently widely used for assisted reproduction in humans and for genetic purposes in cattle. However, the rate of polyspermy is generally higher in vitro than in vivo and IVF remains ineffective in some domestic species like pigs and horses, highlighting the importance of the female reproductive tract for gamete quality and fertilization. In this review, the way the female environment modulates sperm selective migration, survival, and acquisition of fertilizing ability in the oviduct is being considered under six aspects: (1) the utero-tubal junction that selects a sperm sub-population entering the oviduct; (2) the presence of sperm binding sites on luminal epithelial cells in the oviduct, which prolong sperm viability and plays a role in limiting polyspermic fertilization; (3) the contractions of the oviduct, which promote sperm migration toward the site of fertilization in the ampulla; (4) the regions of the oviduct, which play different roles in regulating sperm physiology and interactions with oviduct epithelial cells; (5) the time of ovulation, and (6) the steroid hormonal environment which regulates sperm release from the luminal epithelial cells and facilitates capacitation in a finely orchestrated manner.

Calcium Channels, Rho-Kinase, Protein Kinase-C, and Phospholipase-C Pathways Mediate Mercury Chloride-Induced Myometrial Contractions in Rats

Adverse effects of mercury on female reproduction are reported; however, its effect on myogenic activity of uterus and mechanism thereof is obscure. Present study was undertaken to unravel the mechanistic pathways of mercuric chloride (HgCl₂)-induced myometrial contraction in rats. Isometric tension in myometrial strips of rats following in vitro exposure to HgCl₂ was recorded using data acquisition system-based physiograph. HgCl₂ produced concentration-dependent (10 nM-100 μM) uterotonic effect which was significantly (p < 0.05) reduced in Ca²⁺-free solution and inhibited in the presence of nifedipine (1 μM), a L-type Ca²⁺ channel blocker, thus suggesting the importance of extracellular Ca²⁺ and its entry through L-type calcium channels in HgCl₂-induced myometrial contractions in rats. Cumulative concentration-response curve of HgCl₂ was significantly (p < 0.05) shifted towards right in the presence of Y-27632 (10 μM), a Rho-kinase inhibitor, suggesting the involvement of Ca²⁺-sensitization pathway in mediating HgCl₂-induced myometrial contraction. HgCl₂-induced myometrial contraction was also significantly (p < 0.05) inhibited in the presence of methoctramine or para-fluoro-hexahydro-siladifenidol, a selective M₂ and M₃ receptor antagonists, respectively, which evidently suggest that mercury also interacts with M₂ and M₃ muscarinic receptors to produce myometrial contractions. U-73122 and GF-109203X, the respective inhibitors of PLC and PKC-dependent pathways, downstream to the receptor activation, also significantly (p < 0.05) attenuated the uterotonic effect of HgCl₂ on rat uterus. Taken together, present study evidently reveals that HgCl₂ interacts with muscarinic receptors and activates calcium signaling cascades involving calcium channels, Rho-kinase, protein kinase-C, and phospholipase-C pathways to exert uterotonic effect in rats. Graphical Abstract Graphical abstract depicting the mechanism of mercury-induced myometrial contraction in rats. M receptor: Muscarinic receptor; PIP2: phospho-inositol bisphosphate; PLC: phospholipase-C; DAG: diacyl glycerol; IP3: inositol triphosphate; IP3R: inositol triphosphate receptor; PKC; protein kinase-C; MLCP: myosin light chain phosphatise; MYPT: myosin phosphatase; SR: sarco-endoplasmic reticulum.

Physiology of Upward Transport in the Human Female Genital Tract

The uterus and fallopian tubes represent a functionally united peristaltic pump under the endocrine control of ipsilateral ovary. We have examined this function by using hysterosalpingoscintigraphy (HSS), recording of intrauterine pressure, electrohysterography, and Doppler sonography of the fallopian tubes. An uptake of labeled particles into the uterus was observed during the follicular and luteal phases of the cycle after application into the vagina. Transport into the oviducts, however, could only be demonstrated during the follicular phase. Furthermore, the predominant transport was into the tube ipsilateral to the ovary containing the dominant follicle. The pregnancy rate following spontaneous intercourse or insemination was higher in those women in whom ipsilateral transport could be demonstrated. The amount of material transported to the ipsilateral tube was increased after oxytocin administration, as demonstrated by radionuclide imaging and by Doppler sonography following instillation of ultrasound contrast medium. An increase in the basal tone and amplitude of contractions was observed after oxytocin administration. These results support the idea that the uterus and fallopian tubes act as a peristaltic pump, which increases transport of sperm into the oviduct ipsilateral to the ovary bearing the dominant follicle. Oxytocin appears to play a critical role in this peristaltic pump. A failure of the peristaltic mechanism is possibly responsible for infertility. We propose the term tubal transport disorder (TTD) as a nosological entity. Results from HSS could be a useful adjunct for choosing treatment modalities in patients with patent fallopian tubes suffering from infertility. These patients may be better served with in vitro fertilization (IVF).

Effect of estrogen on muscarinic acetylcholine receptor expression in rat myometrium

We report the effect of acute estrogen treatment in the expression of muscarinic acetylcholine receptors (mAChRs) in myometrium. Strips were obtained from rats in estrus (control) and treated with estrogen, 24h before the experiments. Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed and m2, m3 and m5 mAChR mRNA subtypes were detected in myometrium from both groups. [(3)H]Quinuclidinyl benzilate [(3)HQNB] binding studies indicated that estrogen treatment did not change the affinity and density of mAChRs in myometrial membranes. Displacement curves of [(3)HQNB] with different mAChRs antagonists indicated a one-site fit for all antagonists tested. Comparison of pK(i) values indicated a significant correlation to M(2)-mAChR subtype. Functional studies, however, showed that estrogen treatment increased myometrium sensitivity to carbachol and the calculated apparent affinity values were significantly correlated to M(3)-mAChR. Furthermore, the pharmacological profile of the two populations of mAChR was not affected by estrogen. In conclusion, these results provide evidence for the presence of M(2)- and M(3)-mAChR, at the mRNA and protein level, in the rat myometrium and indicate that estrogen induces an increase in myometrial responsiveness to mAChR agonists.

Sphingosine 1-phosphate in amniotic fluid modulates cyclooxygenase-2 expression in human amnion-derived WISH cells

The metabolism of arachidonic acid, in particular the generation of prostaglandins (PGs), has been proposed to play a key role in the regulation of labor. Moreover, several extracellular proteins have been reported to modulate PG synthesis in amnion cells. In this study, we found that lipid components dissolved in the amniotic fluid modulate PG synthesis in WISH human amnion cells and identified one of these components as a sphingosine 1-phosphate (S1P). WISH cells express several S1P receptors including S1P1, S1P2, and S1P3. When WISH cells were stimulated with S1P, PGE2 synthesis increased in a concentration-dependent manner, showing maximal activity at around 100 nM. S1P treatment also caused the up-regulation of cyclooxygenase-2 (COX-2) mRNA and protein, which was apparent within 3-12 h of stimulation. In terms of the intracellular signaling pathway of S1P-induced WISH cell activation, we found that S1P stimulated two kinds of MAPK, ERK, and p38 kinase. We examined the roles of these two MAPKs in S1P-induced COX-2 expression. S1P-induced COX-2 expression was blocked completely by PD-98059 but not by SB-203580, suggesting that ERK has a critical role in the process. Transfection of S1P1 or S1P3 but not of S1P2 antisense oligonucleotide inhibited S1P-induced COX-2 expression and PGE2 production in WISH cells, indicating the involvements of S1P1 and S1P3 in the processes. This study demonstrates the physiological role of S1P in amniotic fluid and its effect on the modulation of COX-2 expression and PGs synthesis in WISH cells.

FGL2 prothrombinase messenger RNA expression in gravid and nongravid human myometrium

OBJECTIVE

Thrombin is a potent uterotonic agent that may play an important role in human parturition. FGL2 is a prothrombinase that cleaves prothrombin to thrombin. The purpose of this study was to determine FGL2 messenger RNA expression in human myometrium and to assess its relationship to the expression of EP3-6 prostaglandin receptor and inducible nitric oxide synthase.

STUDY DESIGN

Myometrium was obtained from gravid women who underwent cesarean delivery (n = 19), from premenopausal (n = 10) and menopausal (n = 10) women who underwent hysterectomy, and from nonpregnant women who received 200 mg of misoprostol vaginally 12 hours before hysterectomy (n = 8). FGL2 messenger RNA expression was determined with the use of semiquantitative polymerase chain reaction and was compared with previously determined messenger RNA expression levels for EP3-6 and inducible nitric oxide synthase for the same samples. Statistical analysis was performed with the use of independent t test, Fisher exact test, analysis of variance, and linear regression, where appropriate.

RESULTS

All samples that were analyzed contained demonstrable quantities of FGL2 messenger RNA. The highest FGL2 expression was found in gravid women, followed by women who were treated with misoprostol, by premenopausal nonpregnant women, and by menopausal women (P <.0001, analysis of variance). Significantly higher levels of FGL2 expression were found in the gravid women compared with the women who were treated with misoprostol (P <.001), the premenopausal nonpregnant women (P <.001), and the menopausal women (P <.0001). FGL2 messenger RNA expression correlated with EP3-6 and inducible nitric oxide synthase expression in all samples combined (r = 0.55, P <.0001; and r = 0.67, P <.001, respectively).

CONCLUSION

The expression of FGL2 messenger RNA is increased in gravid myometrium compared with nonpregnant samples. Its expression significantly correlates to EP3-6 and inducible nitric oxide synthase expression. FGL2 prothrombinase expression may mediate the role of thrombin in human parturition.

The expression of EP3-6 and inducible nitric oxide synthase messenger RNA are correlated in pregnant and misoprostol-treated but not in nongravid or menopausal myometrium

OBJECTIVE

Our purpose was to investigate the expression level of inducible nitric oxide synthase (iNOS) in nongravid and gravid human myometrium and assess its relation to the expression of EP3 prostaglandin receptor isoforms.

STUDY DESIGN

Myometrial tissue from a cohort of gravid, nongravid, and menopausal subjects and from nongravid subjects exposed to misoprostol was obtained and analyzed for iNOS messenger RNA (mRNA) expression and compared with previously determined mRNA levels for the EP3-6 prostaglandin receptor from the same samples by means of semiquantitative polymerase chain reaction.

RESULTS

Significantly higher levels of iNOS mRNA expression were found in the gravid compared with premenopausal nongravid (P <.02) and menopausal (P <.05,) samples. Linear regression analysis of iNOS versus EP3-6 expression showed a positive correlation between all studied samples (n = 47, P <.0001, r = 0.815). Among individual groups, a significant linear correlation was found only in pregnant (n = 10, P <.0001, r = 0.785) and misoprostol-exposed (n = 7, P =.0256, r = 0.815) subjects. No correlation between iNOS and EP3-6 mRNA levels was noted in the nongravid premenopausal groups (n = 10, P =.205, r = 0.350), although a nonsignificant trend was found for the menopausal group (n = 10, P =.0535, r = 0.624). When the data from pregnant patients were stratified, both laboring and nonlaboring women displayed the observed correlation (n = 6, P <.0001, r = 0.993; and n = 13, P =.008, r = 0.697, respectively).

CONCLUSION

iNOS and EP3-6 expression are strongly correlated in gravid and misoprostol-treated, nongravid myometrium.

Regulation of cyclooxygenase-2 expression by phospholipase D in human amnion-derived WISH cells

Prostaglandins (PGs) are known to play a key role in the initiation of labor, but the mechanisms regulating their synthesis in amnion are largely unknown. In this study, the regulatory mechanisms for PGE(2) production during phospholipase D (PLD) and p38-dependent activation of WISH cells were investigated. We found that the stimulation of WISH cells with interleukin (IL)-1 beta elicited dose-dependent synthesis of cyclooxygenase-2 (COX-2) mRNA, protein, and their products, PGE(2). Moreover, the treatment of [(3)H]myristate-labeled cells in the presence of 1-butanol caused the dose-dependent formation of [(3)H]phosphatidylbutanol (PBt), a product specific to PLD activity. Pretreating the cells with 1-butanol and Ro 31-8220 inhibited the IL-1 beta-induced COX-2 expression, but 3-butanol did not affect this response. In addition, evidence that PLD was involved in the stimulation of COX-2 expression was provided by the observations that COX-2 expression was stimulated by the dioctanoyl phosphatidic acid (PA) and that the prevention of PA dephosphorylation by 1-propranolol potentiated COX-2 expression by IL-1 beta. Moreover, IL-1 beta stimulation of the cells caused the phosphorylation of p38 and extracellular signal-regulated kinase (ERK), and IL-1 beta-induced COX-2 expression was inhibited by the pretreatment of WISH cells with a p38 inhibitor, in contrast ERK upstream inhibitor had no effect. Furthermore, Ro 31-8220 inhibited IL-1 beta-induced p38 phosphorylation but not ERK phosphorylation. The results of this study indicate that in human amnion cells, IL-1 beta might activate PLD through an upstream protein kinase C to elicit p38 and finally induce COX-2 expression.

Epidermal growth factor (EGF) in the goat uterus: immunohistochemical localization of EGF and EGF receptor and effect of EGF on uterine activity in vivo

This study examined the distribution of immunoreactive epidermal growth factor (EGF) and EGF receptor (EGF-R) in the uterus and the effects of EGF on uterine activity in goats. Immunohistochemistry of EGF and EGF-R in the uteri showed distinct staining in the luminal and glandular epithelium and slight to moderate staining in the stromal and myometrial cells. To examine possible roles of the EGF system in the regulation of uterine activity, pressure changes in the intrauterine balloon were determined after intraluminal infusion of EGF into the uterine horn. Either at estrus or diestrus (9 to 14 days after the first day of estrus), treatment with 1 or 5 microg of EGF gradually reduced uterine activity, whereas infusion of the vehicle alone had no effect. The maximum reduction in uterine activity was seen 4 h after the treatment with 1 microg of EGF (40% to 45% reduction in the area surrounded by the contraction curve and its baseline), and the activity slowly returned thereafter. These results suggest that EGF in the uterus may play a role in regulating uterine activity in goats.

Effect of estrogen on intracellular signaling pathways linked to activation of M(2)- and M(3)-muscarinic acetylcholine receptors in the rat myometrium

The estrogen treatment of adult female rats induces an increase in myometrium sensitivity to cholinergic agonists and in this tissue the presence of M(2)- and M(3)-muscarinic acetylcholine (mACh) receptor was shown. We now report the effect of estrogen on intracellular signaling pathways linked to activation of M(2)- and M(3)-mACh receptor subtypes. The intracellular cyclic AMP accumulation and [3H]-inositol phosphates content were measured in myometrium strips from rats in estrus (control) and estradiol-treated rats (12.5 microg/100 g body weight, sc, 24 h before experiments) (the plasma estradiol level was 30.9+/-3.5 pg/ml and 119.3+/-14.1 pg/ml from control and estrogen-treated rats, respectively). Estrogen treatment increased 2.5-fold the intracellular cyclic AMP accumulation induced by 10 microM forskolin. The effects of muscarinic agonist and antagonists on cyclic AMP accumulation were tested. Carbachol reduced the forskolin-induced intracellular cyclic AMP content, 3.0 and 10.5-fold, in myometrium from control and estradiol-treated rats, respectively. This inhibitory effect failed to occur when carbachol was incubated in the presence of methoctramine. Carbachol also induced increase on total [3H]-inositol phosphates accumulation in myometrium from estradiol-treated rats when compared with control rats. This effect was reversed by pfHHSiD. These studies suggest the modulation by estrogen of intracellular signaling pathways linked to activation of M(2)- and M(3)-mACh receptors in the rat myometrium.

Regulation of cyclooxygenase-2 expression by phosphatidate phosphohydrolase in human amnionic WISH cells

Prostaglandins are known to play a key role in the initiation of labor in humans, but the mechanisms governing their synthesis in amnion are largely unknown. In this study, we have examined the regulatory pathways for prostaglandin E(2) (PGE(2)) production during protein kinase C-dependent activation of human WISH cells. In these cells, PGE(2) synthesis appears to be limited not by free arachidonic acid availability but by the expression levels of cyclooxygenase-2 (COX-2). Concomitant with the cells being able to synthesize and secrete PGE(2), we detected significant elevations of both COX-2 protein and mRNA levels. Specific inhibition of COX-2 by NS-398 totally ablated PGE(2) synthesis. All of these responses were found to be strikingly dependent on an active phosphatidate phosphohydrolase 1 (PAP-1). Inhibition of PAP-1 activity by three different strategies (i.e. use of bromoenol lactone, propranolol, and ethanol) resulted in inhibition of COX-2 expression and hence of PGE(2) production. These data unveil a novel signaling mechanism for the regulation of PGE(2) production via regulation of COX-2 expression and implicate phosphatidate phosphohydrolase 1 as a key regulatory component of eicosanoid metabolic pathways in the amnion.

Different proliferative responses of Gi/o-protein-coupled receptors in human myometrial smooth muscle cells. A possible role of calcium

The majority of studies investigating the proliferative effect of Gi/o-protein-coupled receptor agonists are performed in recombinant receptor systems or cell lines. In these systems the relative stoichiometry of receptors compared to other cell components might be changed, which may lead to anomalies in cellular responses in contrast to natural occurring systems. In the present study, we have used primary cultures of smooth muscle cells (SMCs) isolated from human myometrium to characterize the proliferative effects of agonists binding to two different G protein-coupled receptors. Treatment of quiescent SMCs with lysophosphatidic acid (LPA) and noradrenaline resulted in significant increases in [3H]thymidine incorporation. However, LPA was almost four times more effective than noradrenaline in this respect. The proliferative effects of the agonists could be completely blocked by pertussis toxin, indicating that the response are mediated through Gi/o-proteins. The selective alpha 2-adrenergic receptor (alpha 2-AR) antagonist yohimbine dose-dependently reduced the effect of noradrenaline suggesting that the proliferative response was mediated through alpha 2-ARs. The proliferative effects induced by LPA and noradrenaline was markedly reduced in SMCs treated with the tyrosine kinase inhibitor genistein and the cAMP elevating compound forskolin. However, LPA but not noradrenaline induced rapid rises in the cytosolic free Ca2+ concentration [Ca2+]i. The ability to increase Ca2+ might be one explanation why LPA produce a more pronounced proliferative response than noradrenaline in primary cultures of human myometrial SMCs.