Up-regulation of oxytocin receptor messenger ribonucleic acid and protein by estradiol in the cervix of ovariectomized rat

Contractile function of the cervix plays a role in normal and pathological pregnancy and parturition

The cervix plays an integral part in ensuring the proper timing of pregnancy and parturition. It maintains the fetus within the uterus and protects it from pathogens present in the vaginal canal. The cervix undergoes extensive remodeling during pregnancy and parturition. This process is associated with collagen degradation, an increase in immune cell response and inflammation in the cervix. However, our understanding of the role of cervical smooth muscles and their contribution to cervical remodeling is still lacking. In this paper, we propose that the active contractile function of the cervix influences cervical remodeling during pregnancy and parturition. Contraction of the cervical smooth muscles helps the cervix to remain firm and closed during early pregnancy, while relaxation of the cervical smooth muscles help facilitate cervical dilatation during labor. This contractile function of the cervix can be influenced by endocrine signals, such as estrogen, progesterone, and oxytocin; local paracrine signals, such as inflammatory chemokines and cytokines, as well as extracellular vesicles, such as exosomes and ectosomes; and by pharmacological agents used for cervical ripening and the induction of labor. A deeper understanding of the role of smooth muscles in cervical remodeling can help us elucidate the cellular processes in the cervix during pregnancy and parturition. This can also help in finding critical signaling pathways and therapeutic targets in the cervix that may decrease the rates of premature cervical ripening and preterm birth.

Direct stimulatory effects of oxytocin in female rat gonadotrophs and somatotrophs in vitro: comparison with lactotrophs

The peptide oxytocin (OT) is secreted by hypothalamic neurons and exerts numerous actions related to reproduction. OT stimulation of prolactin secretion in female rats is important during the estrous cycle, pregnancy, and lactation. Here we report that OT also stimulates transients of intracellular Ca(2+) concentration in somatotrophs and gonadotrophs as well as the release of GH and LH in a dose-dependent manner with EC50 values that closely correspond to the ligand affinity of the OT receptor (OTR). Remarkably, the hormone-releasing effect of OT in these two cell types is 2 orders of magnitude more sensitive than that in lactotrophs. The specific OTR agonist [Thr(4),Gly(7)]-oxytocin acutely stimulated the release of LH, GH, and prolactin from female rat pituitary cells in primary culture and increased intracellular Ca(2+) concentration in gonadotrophs, somatotrophs, and lactotrophs. In these three cell types, the effects on hormone release and intracellular Ca(2+) of both OT and [Thr(4),Gly(7)]oxytocin were abolished by the specific OT receptor antagonist desGly-NH2-d(CH2)5[D-Tyr(2),Thr(4)]OVT but not by the highly selective vasopressin V1a receptor antagonist, d(CH2)5[Tyr(Me)(2),Dab(5)]AVP. Furthermore, 10 nM arginine vasopressin stimulated LH and GH release comparably with a dose of OT that was at least 10 times lower. Finally, the presence of the OTR-like immunoreactivity could be observed in all three cell types. Taken together, these results show that OT directly stimulates gonadotrophs, somatotrophs, and lactotrophs through OT receptors and suggest that OT signaling may serve to coordinate the release of different pituitary hormones during specific physiological conditions.

The effect of estradiol on COX-2, EP2, and EP4 mRNA expression and the extracellular matrix in the cervix of the hypogonadotrophic, ovariectomized ewe

There is a degree of cervical relaxation in the ewe at estrus that is regulated by changes in prostaglandin synthesis, prostaglandin receptor expression, and changes in the cervical extracellular matrix. It is likely that these are regulated by changes in periovulatory hormones, particularly estradiol. This study determined the effect of estradiol benzoate on the mRNA expression of cyclooxygenase-2 (COX-2) and the prostaglandin E receptors EP(2) and EP(4), the concentration of cervical hyaluronan, and the proportion of smooth muscle and collagen in the cervix of the hypogonadotrophic ovariectomized ewe (Ovis aries). Ovariectomized hypogonadotrophic ewes were given 100 microg estradiol benzoate, and their cervices were collected 0, 24, and 48 h thereafter to determine the expression of cervical COX-2, EP(2), and EP(4) mRNA by in situ hybridization, the concentration of hyaluronan by ELISA, and the proportion of smooth muscle and collagen by Masson's trichrome staining. Estradiol benzoate increased the mRNA expression of COX-2 and EP(4) within 24h after treatment (P<0.05), whereas EP(2) mRNA, hyaluronan, and the ratio of smooth muscle to collagen did not change within 48 h after treatment. The COX-2, EP(2), and EP(4) mRNA expression were greatest in the smooth muscle layers (P<0.05) and least in the luminal epithelium (P<0.05). In conclusion, we inferred that estradiol regulates cervical COX-2 and EP(4) mRNA expression and may regulate cervical relaxation via the synthesis of prostaglandin E(2) and activation of the PGE(2) receptors EP(2) and EP(4).

The roles of alpha2-adrenoceptor subtypes in the control of cervical resistance in the late-pregnant rat

The roles of the alpha(2)-adrenoceptor subtypes in the regulation of cervical resistance have previously not been investigated. The aim of the present study was to identify these receptors in the late-pregnant cervix and determine their functions in vitro in the rat. The expressions of the alpha(2)-adrenoceptor subtypes were determined by means of RT-PCR and Western blotting techniques. The changes in cervical resistance due to subtype-selective antagonists were investigated in stretching tests. The cyclic AMP immunoassay technique was used to detect the level of cyclic AMP following stimulation of the alpha(2)-adrenoceptors with or without pertussis toxin. On pregnancy days 18, 20, 21 and 22, the RT-PCR and Western blotting studies revealed the expressions of all three alpha(2)-adrenoceptor subtype mRNAs and proteins. On days 18 and 20, noradrenaline increased and decreased the resistance, respectively. Its effect was blocked by each of the antagonists used, except ARC 239 on both days. On day 21, noradrenaline again increased the resistance, this effect being maintained only in the presence of spiroxatrine. Noradrenaline was ineffective on day 22. These results were supported by the changes in cyclic AMP levels. Pertussis toxin pretreatment eliminated the changes in the cyclic AMP level on days 18 and 21. We presume that the alpha(2A)- and alpha(2C)-adrenoceptors play predominant roles in the regulation of cervical resistance on days 18-21. Depending on the day of pregnancy, stimulation of these alpha(2)-adrenoceptors could even result in opposite effects. This fluctuation can be explained by the changes in the G(i)/G(s)-coupling of the alpha(2A)- and alpha(2C)-adrenoceptors.

Antagonism of oxytocin prevents suckling- and estradiol-induced, but not progesterone-induced, secretion of prolactin

In female rats, estradiol (E(2)) and suckling induce prolactin (PRL) secretion. This involves inhibition of hypothalamic dopaminergic tone and stimulation by a PRL-releasing hormone, possibly oxytocin (OT). Infusing an OT antagonist (OTA) i.v., we evaluated the role of OT on suckling- and E(2)-induced PRL secretion. Three days after parturition at 0900 h, lactating dams were fitted with 24-h osmotic minipumps filled with saline or OTA. On d 5 of lactation, pups were separated from their dams for 6 h. Immediately or 20 min after the resumption of suckling, dam trunk blood was collected. Also, ovariectomized (OVX) rats were treated with E(2) (OVE) and OTA at 1000 h on d 1. Blood samples were obtained from 1300 to 2100 h on d 2 for PRL measurements. Additionally, OVX rats were evaluated on d 2 after receiving progesterone (P(4)). OTA blocked suckling and E(2)-induced release of PRL but not that induced by E(2)+P(4). Pups from treated dams failed to gain weight when allowed to nurse for 20 min on d 5 but gained more than 7 g when nursed on d 7 of lactation, indicating that the OTA was active 48 h later. Western blot analysis showed that E(2) treatment increased OT receptors in the anterior pituitary when compared with OVX animals. No further increase was observed in response to the P(4), suggesting that the enhancing effect of P(4) on E(2)-induced PRL release may act through mechanisms independent of OT. These data demonstrate the role of OT in the control of suckling and steroid-induced PRL secretion.

Regulation of epididymal contractility during semen emission, the first part of the ejaculatory process: a role for estrogen

INTRODUCTION

Ejaculation is an important step of the male sexual response, and consists of three separate phases: emission, ejection, and orgasm. In contrast to the erectile process, whose neurological and vascular mechanisms have been well elucidated, the pathophysiology of the ejaculatory process remains yet to be completely investigated. In humans, the emission and the ejection phases are regulated by an integrated and time-coordinated activity of the parasympathetic and sympathetic systems, which finally leads to sperm propulsion from the urethra. The first step in the ejaculatory process involves the epididymis, where a series of contractile waves begins, allowing sperm progression throughout the duct and toward the vas deferens. Interestingly, along with the complex neurological pathways, some non-neuronal factors (oxytocin [OT] and endothelin-1 [ET-1]) and sex hormones (estrogen) have been demonstrated to take part in the peripheral regulation of epididymal contractility.

AIM

This article reviews some of the physiological non-neuronal mechanisms underlying the epididymal contractility, and reports evidences of an estrogenic regulation.

METHODS

We reviewed here our and other groups' publications on the role of ET-1/OT and estrogens in modulating the epididymal contractility.

MAIN OUTCOME MEASURE

Data were obtained by an extensive examination of the published peer-reviewed literature on this topic.

RESULTS

Evidences support that, although the epididymis has a rich innervation, other local, non-neuronal factors participate in the nerve-independent epididymal contractility. ET-1 and OT, along with their cognate receptors, have been demonstrated to act, in an estrogen-dependent autocrine and paracrine loop, to regulate epididymal contractile activity in rabbit, and at least partially, in humans.

CONCLUSION

Ejaculation is the result of the complex, and today still not fully elucidated, interplay between neuronal and non-neuronal, sex-steroid-dependent factors.

Expression and regulation of functional oxytocin receptors in bovine T lymphocytes

The corpus luteum (CL) produces oxytocin (OXT), which has been proposed to regulate the pulsatile release of prostaglandin F2alpha during luteolysis in ruminants. This action of OXT is mediated via oxytocin receptors (OXTRs) present on uterine epithelial cells. It is hypothesized that luteal OXT acts as a paracrine regulator of resident immune cells. In the present study, OXTR mRNA expression in bovine lymphocytes was analyzed, as well as its regulation during the estrous cycle. OXTR transcripts were observed in freshly purified bovine peripheral blood mononuclear cells and T lymphocytes. OXTR mRNA in bovine lymphocytes on Day 3 was numerically greater than but not significantly different from that of Day 19 of the estrous cycle (P=0.091). In cultured T cells, estradiol (E2) treatment significantly increased the steady-state concentrations of OXTR mRNA, but the stimulatory effect of E2 was inhibited by the addition of progesterone (P4). Each of the major T cell subsets (CD4+, CD8+, and gamma delta+) expressed OXTR mRNA, with no significant difference in expression among them. Western blot analyses demonstrated the presence of the bovine OXTR protein at about 45 kDa in lymphocytes, as well as expression of the 14-kDa precursor of OXT. When lymphocytes were treated with OXT, intracellular concentrations of calcium ([Ca2+]i) were rapidly and dramatically increased. This study demonstrated that bovine lymphocytes express OXTRs and that this expression can be regulated in a steroid-dependent manner. Furthermore, OXT elicited a functional [Ca2+]i response in T lymphocytes, supporting the possibility that OXT within the CL could act as a paracrine or autocrine regulator of resident T lymphocytes.

The Expression of Prostaglandin Endoperoxide Synthase 2 Messenger RNA and the Proportion of Smooth Muscle and Collagen in the Sheep Cervix During the Estrous Cycle

The use of transcervical artificial insemination in sheep is limited because of the anatomy of the cervix, which restricts the passage of an inseminating pipette into the uterine lumen. There is a degree of natural cervical relaxation at estrus that enables greater penetration with an inseminating pipette. We hypothesize that this relaxation may be regulated by cervical prostaglandin synthesis and remodeling of the cervical extracellular matrix. The present study investigated the changes in prostaglandin endoperoxide synthase 2 (PTGS2) mRNA expression and the proportion of smooth muscle and collagen in the sheep cervix during the estrous cycle. Sheep cervices were collected at four stages of the estrous cycle: prior to the LH surge, during the LH surge, after the LH surge, and during the luteal phase. The expression of cervical PTGS2 mRNA was determined by in situ hybridization, and the proportion of smooth muscle and collagen in the cervix was investigated by Masson trichrome staining. The expression of PTGS2 mRNA in the sheep cervix was greatest prior to the LH surge, when estradiol concentrations were also greatest. The increase in PTGS2 mRNA expression was associated with an increase in the proportion of collagen in the sheep cervix. We propose that prior to the LH surge, estradiol may stimulate PTGS2 mRNA expression and hence prostaglandin E2 synthesis in the sheep cervix to regulate cervical relaxation, most likely through the rearrangement of collagen bundles within the cervical extracellular matrix.

The inhibitory effects of oxytocin on distal colonic contractile activity in rabbits are enhanced by ovarian steroids

AIMS

To study the effects of oxytocin on isolated rabbit distal colon and the regulation of ovarian steroids by its action.

METHODS

Muscle strips parallel to either the circular or the longitudinal fibres were excised and suspended in tissue chambers containing 5 mL Krebs solution (37 degrees C) and bubbled continuously with 95% O(2) and 5% CO(2). The effects of oxytocin on isometric spontaneous contractile responses were recorded. The effects of atosiban, tetrodotoxin, Mg(2+), progesterone and oestradiol on the oxytocin-induced response were also examined.

RESULTS

Oxytocin (1, 10 and 100 nmol L(-1)) dose dependently decreased the area under the contraction curve of distal colonic smooth muscle strips. The oxytocin receptor antagonist atosiban blocked the oxytocin (10 nmol L(-1))-caused responses in a dose-dependent manner. Tetrodotoxin (10 micromol L(-1)) had no effect on the oxytocin-induced response. Mg(2+)-free Krebs solution attenuated the oxytocin-induced response, but oestradiol (0.1 micromol L(-1)) or progesterone (0.1 micromol L(-1)) increased the oxytocin-induced response.

CONCLUSION

These results suggest that oxytocin inhibits the contractile motility of the distal colon, which is regulated by Mg(2+) and ovarian steroids.

The anatomy of the sheep cervix and its influence on the transcervical passage of an inseminating pipette into the uterine lumen

The anatomy of the sheep cervix is highly variable between animals and may explain the differing success of transcervical AI between individuals. This study aims to quantify the variation in cervical morphology between ewes and investigate the relationship between cervical anatomy and cervical penetration. Two series of reproductive tracts were collected. Series A: 132 adult anoestrous ewes, and series B: 165 cycling adult ewes and ewe lambs which were identified as luteal or non-luteal based on the presence of a corpus luteum. The morphology of the cervical external os was classified as slit, papilla, duckbill, flap or rose. An inseminating pipette was inserted into the lumen and the depth of penetration recorded. The cervix was opened longitudinally, its length recorded, the number of cervical rings counted and the arrangement of those rings graded. The maximum depth of cervical penetration was affected by cervical grade (series A: P=0.021; series B: P=0.037) and the stage of the oestrous cycle (P=0.008). Grade 1 cervices were more penetrable than grade 2, with grade 3 the least penetrable and non-luteal cervices could be penetrated further than luteal cervices. The distribution of os types differed with age, with rose types more common in adult ewes, and papilla os types more common in ewe lambs. These results indicate that the depth of cervical penetration is affected by the anatomy of the cervical lumen. Cervices with a less convoluted lumen (grade 1) were more penetrable. Non-luteal cervices are likely to have higher oestradiol concentrations than luteal, stimulating cervical relaxation and enabling deeper penetration. The difference in os types with age may be contributable to a morphological alteration at parturition.

Terbutaline increases the cervical resistance of the pregnant rat in vitro

Cervical ripening is a crucial process leading to delivery. Early dilation of the pregnant cervix can contribute to premature labour. The maturity of the cervix can be characterized by its resistance to mechanical stretching. Although a number of compounds are considered to increase cervical resistance (e.g., progesterone, nitric oxide synthase inhibitors and nonsteroidal anti-inflammatory drugs), none of them seem to be safe for clinical application. Other compounds, such as beta(2)-adrenergic receptor (beta(2)-AR) agonists, have been used for several decades to stop premature myometrium contractions, but their cervical action has never been investigated. The aim of this study was to detect the effects of the beta(2)-AR agonist terbutaline on nonpregnant and late-pregnant (day 18, 20, 21 or 22) cervices isolated from Sprague-Dawley rats. Cervical resistance was measured by means of a mechanical stretching test in vitro, the beta(2)-AR density was determined by Western blot analysis, the beta(2)-AR mRNA was determined by RT-PCR, while the G-protein activation following cervical beta(2)-AR stimulation with terbutaline was evaluated via a [(35)S]GTPgammaS binding assay. Terbutaline at 10(-6) M increased the cervical resistance of the late-pregnant samples in vitro from day 18 to day 22, but did not alter the resistance of the nonpregnant samples. This cervical resistance-increasing effect was concentration dependent and antagonized with propranolol on day 21. Terbutaline was ineffective on cervical samples when gradual stretching was omitted. RT-PCR and Western blot studies revealed increased beta(2)-AR mRNA and beta(2)-AR levels respectively on day 18 of pregnancy compared with the nonpregnant cervix, but no further changes were detected up to the end of pregnancy. The [(35)S]GTPgammaS binding assay demonstrated a decreased G-protein activation on the days of pregnancy investigated, but no activation was found in the nonpregnant samples. The degree of decrease in G-protein activation by terbutaline was in harmony with its cervical resistance-increasing action. On day 21, the G-protein activation-decreasing effect of terbutaline was antagonized with propranolol. We presume that the cervical resistance-increasing effect of terbutaline is a consequence of its G-protein activation-decreasing property via beta(2)-ARs, which finally leads to an increased muscle resistance against mechanical stretching. This action of terbutaline seems unique among the smooth muscles, and may open up a new perspective in the prevention of premature labour. Clinical experience indicates that beta(2)-AR agonists will not be sufficient to stop the overall process, but their combination with more potent inhibitors of uterine contractions may be of clinical benefit.

Anatomical differences in uterine sensitivity to prostaglandin F(2alpha) and serotonin in non-pregnant rats

The ovarian steroids regulate the sensitivity of a population of uterine receptors to prostaglandin F(2alpha), serotonin and oxytocin. However, the uterine sensitivity to prostaglandin F(2alpha) and oxytocin does not coincide with the estrogen-induced increase in the number of receptors. Anatomical differences affect the uterine sensitivity to agonists. We investigated whether anatomical differences between ovarian and cervical uterine regions modulate the hormone-regulated sensitivity to prostaglandin F(2alpha), serotonin and oxytocin. Non-cumulative concentration-response curves for these agonists were recorded for ovarian and cervical uterine segments from adult ovariectomized rats treated with 17beta-estradiol, 17beta-estradiol+progesterone, or vehicle. The ovarian segments displayed a higher maximal response (E(max)) to prostaglandin F(2alpha) and a lower E(max) to serotonin than the cervical segments. Both uterine segments displayed a similar sensitivity to oxytocin. The ovariectomized controls displayed the highest E(max) and the lowest effective concentration 50 (EC(50)) for oxytocin and prostaglandin F(2alpha). Anatomical differences between ovarian and cervical uterine regions modulate the hormonal regulation of uterine sensitivity to serotonin and prostaglandin F(2alpha) in the non-pregnant rat uterus.