The effect of progesterone and human interferon alpha-2 on the release of PGF2 alpha and PGE from epithelial cells of human proliferative endometrium.

Progesterone and interferon-like trophoblastic proteins modulate prostaglandin (PG) synthesis from endometrium in early ovine and bovine pregnancy. Enriched epithelial cells were prepared from human endometrium removed in the proliferative phase of menstrual cycle (n = 8). Progesterone at a concentration of 1 microM suppressed PGE release from the cells during the first 24 hours in culture. After 48 hours in culture progesterone at a dose of 100 nM and 1 microM suppressed both the release of PGF2 alpha and PGE from the cells and this suppression was maintained for a further two days. Addition of exogenous 30 microM arachidonic acid (AA) abolished this effect of progesterone on both PGF2 alpha and PGE release. Interferon alpha-2 did not suppress the basal release of PGF2 alpha nor PGE. In the presence of progesterone, interferon alpha-2 attenuated the progesterone mediated suppression of PGF2 alpha but not PGE release from endometrial cells. These findings suggest that progesterone suppresses the basal release of PGs from human endometrium, but unlike the sheep, interferon alpha-2 does not exert this action on human endometrium.     

Progesterone reduces erectile dysfunction in sleep-deprived spontaneously hypertensive rats

Background

The rate-limiting step in prostaglandin (PG) biosynthesis is catalyzed by phospholipase A2 (PLA2) enzymes which hydrolyze arachidonic acid from membrane phospholipids. Despite their importance in uterine PG production, little is known concerning the specific PLA2 enzymes that regulate arachidonic acid liberation in the uterine endometrium. The objectives of this study were to evaluate the expression and activities of calcium-independent Group VI and Group IVC PLA2 (PLA2G6 and PLA2G4C) and calcium-dependent Group IVA PLA2 (PLA2G4A) enzymes in the regulation of bovine uterine endometrial epithelial cell PG production.

Methods

Bovine endometrial epithelial cells in culture were treated with oxytocin, interferon-tau and the PLA2G6 inhibitor bromoenol lactone, alone and in combination. Concentrations of PGF2alpha and PGE2 released into the medium were analyzed. Western blot analysis was performed on cellular protein to determine the effects of treatments on expression of PLA2G4A, PLA2G6 and PLA2G4C. Group-specific PLA2 activity assays were performed on cell lysates following treatment with oxytocin, interferon-tau or vehicle (control), alone and in combination. To further evaluate the role of specific PLA2 enzymes in uterine cell PG biosynthesis, cells were transfected with cDNAs encoding human PLA2G6 and PLA24C, treated as described above and PG assays performed.

Results

Constitutive cell production of PGF2alpha was about two-fold higher than PGE2. Oxytocin stimulated production of both PGs but the increase of PGF2alpha was significantly greater. Interferon-tau diminished oxytocin stimulation of both PGs. The PLA2G6 inhibitor, bromoenol lactone, abolished oxytocin-stimulated production of PGF2alpha. Treatments had little effect on PLA2G4A protein expression. In contrast, oxytocin enhanced expression of PLA2G6 and this effect was diminished in the presence of interferon-tau. Expression of PLA2G4C was barely detectable in control and oxytocin treated cells but it was enhanced in cells treated with interferon-tau. Oxytocin stimulated PLA2 activity in assays designed to evaluate PLA2G6 activity and interferon-tau inhibited this response. In assays designed to measure PLA2G4C activity, only interferon-tau was stimulatory. Cells overexpressing PLA2G6 produced similar quantities of the two PGs and these values were significantly higher than PG production by non-transfected cells. Oxytocin stimulated production of both PGs and this response was inhibited by interferon-tau. Bromoenol lactone inhibited oxtocin stimulation of PGF2alpha production but stimulated PGE2 production, both in the absence and presence of oxytocin. Cells over-expressing PLA2G4C produced more PGE2 than PGF2alpha and interferon-tau stimulated PGE2 production.

Conclusion

Results from these studies indicate that oxytocin stimulation of uterine PGF2alpha production is mediated, at least in part, by up-regulation of PLA2G6 expression and activity. In addition to its known inhibitory effect on oxytocin receptor expression, interferon-tau represses oxytocin-stimulated PLA2G6 expression and activity and this contributes to diminished PGF2alpha production. Furthermore, endometrial cell PGE2 biosynthesis was associated with PLA2G4C expression and activity and interferon-tau was stimulatory to this process.     

Effects of oestradiol, progesterone, hydrocortisone and oxytocin on prostaglandin output from the guinea-pig endometrium maintained in tissue culture

The effects of oestradiol, oxytocin, progesterone and hydrocortisone in vitro on prostaglandin (PG) output from guinea-pig endometrium, removed on days 7 and 15 of the oestrous cycle and maintained in tissue culture for 3 days, have been investigated. Oestradiol (3.7 to 3700 nM) and oxytocin (2 to 200 pM) did not stimulate endometrial PGF2 alpha output, thus not confirming the findings of a previous report (Leaver & Seawright, 1982), nor did they stimulate the outputs of PGE2 and 6-keto-PGF1 alpha. In fact, oestradiol (3700 nM) inhibited the outputs of PGF2 alpha, PGE2 and, to a lesser extent, 6-keto-PGF1 alpha. Progesterone (3.2 to 3200 nM) inhibited the outputs of PGF2 alpha and PGE2; hydrocortisone (2.8 to 2800 nM) had no effect on endometrial PG output. These findings indicate that the inhibitory effect of progesterone on endometrial PG synthesis and release in the guinea-pig is not due to progesterone having a glucocorticoid-like action. Furthermore, progesterone had no effect on 6-keto-PGF1 alpha output, suggesting that the mechanisms controlling endometrial PGI2 synthesis (as reflected by measuring 6-keto-PGF1 alpha) are different from those controlling endometrial PGF2 alpha and PGE2 synthesis.     

Prostaglandin E and E2 alpha secretion by glandular and stromal cells of the pig endometrium in vitro: effects of estradiol-17 beta, progesterone, and day of pregnancy.

Prostaglandins (PGs) are believed to play important roles in the establishment of pregnancy. Glandular and stromal cells were isolated from pig endometrium on days 11 through 19 of pregnancy and cultured in the presence of estradiol-17 beta (E2) and progesterone (P4) to determine the effect of day of pregnancy and steroids on the secretion of PGE and PGF2 alpha. Estradiol at concentrations between .01 and 1 microM did not affect PGE and PGF2 alpha secretion into the medium by glandular and stromal cells. Progesterone (.1 microM) suppressed (P less than .001) PGE and PGF2 alpha production from both cell types. Glandular cells secreted more (P less than .01) PGF2 alpha than PGE, whereas stromal cells collected on days 11, 12, 13, and 19 secreted more (P less than .05) PGE than PGF2 alpha. Stromal cells isolated from tissues collected on day 13 of pregnancy produced PGs with higher (P less than .01) PGE:PGF2 alpha ratio than those from tissues harvested on other days of pregnancy. Glandular cells isolated from tissues collected on days 13 and 19 and stromal cells isolated from tissue collected on day 13 of pregnancy secreted more (P less than .05) PGE and PGF2 alpha than cells isolated on other days of pregnancy. We conclude that: 1) P4 has a suppressing effect on PG secretion; 2) endometrial glandular and stromal cells each produce a unique profile of PGs; and 3) endometrial cells harvested on different days of pregnancy secrete different amounts of PGE and PGF2 alpha.     

Effects of conjugated linoleic acid on prostaglandins produced by cells isolated from maternal intercotyledonary endometrium, fetal allantochorion and amnion in late pregnant ewes

The anticarcinogenic properties of conjugated linoleic acid (CLA) are, at least partially, attributed to its ability to interrupt the n-6 polyunsaturated fatty acid (PUFA) metabolic pathway for the biosynthesis of eicosanoids, including prostaglandins (PG). Both PGE(2) and PGF(2alpha) play key roles in parturition. In the present study, we compared the effects of CLA (a mixture of cis- and trans-9, 11- and -10, 12-octadecadienoic acid) and linoleic acid (LA) on PG production by cells isolated from maternal intercotyledonary endometrium, fetal allantochorion and amnion from late pregnant ewes. The results demonstrated that supplementation of LA and CLA significantly affected both the proportions and the amounts of PGs produced by all three tissue types. The ability of the uterus and placenta to respond to oxytocin (OT, endometrium only) and lipopolysaccharide (LPS) was also affected. LA inhibited PGE(2) and PGF(2alpha) production in the absence or presence of either oxytocin or LPS. In endometrial cells with or without oxytocin or LPS, CLA dose-dependently suppressed PGF(2alpha) generation, whereas low doses of CLA (20 microM) increased PGE(2) generation. Supplementation with CLA therefore increased the PGE(2)/PGF(2alpha) ratio in the endometrial cells. These results suggest that dietary supplementation of LA or CLA may affect both the initiation and progression of parturition.     

Cell-type specific responses in prostaglandin secretion by glandular and stromal cells from pig endometrium treated with catecholestrogens, methoxyestrogens and progesterone.

The pig conceptus and endometrium possess the ability to convert estrogens into catecholestrogens and catecholestrogens into methoxyestrogens. Experiments were carried out to evaluate the effect of catecholestrogens, methoxyestrogens and progesterone on the secretion of prostaglandin (PG) E and F2 alpha by porcine endometrial glandular and stromal cells in vitro. Both 2-hydroxyestradiol (2-OH-E2, 0-20 microM) and 4-hydroxyestradiol (4-OH-E2, 0-20 microM) increased (P less than .05) PGE and PGF2 alpha secretion by stromal cells in a dose response manner. Two-hydroxyestradiol tended (P less than .1) to decrease PGF2 alpha production by glandular cells. Two-methoxyestradiol (20 microM) suppressed (P less than .05) PGF2 alpha secretion by glandular and stromal cells. Four-methoxyestradiol (20 microM) stimulated (P less than .05) PGE production and PGE:PGF2 alpha ratio. Progesterone (.1 microM) suppressed (P less than .05) PG secretion in both cell types. We conclude that catecholestrogens, methoxyestrogens, and progesterone may participate in the establishment of pregnancy by modulating PG production in the endometrium.     

Differential effects of progesterone treatment on the oxytocin-induced prostaglandin F2 alpha response and the levels of endometrial oxytocin receptors in ovariectomized ewes.

The oxytocin-induced uterine prostaglandin (PG) F2 alpha response and the levels of endometrial oxytocin receptors were measured in ovariectomized ewes after they had been given steroid pretreatment (SP) with progesterone and estrogen to induce estrus (day of expected estrus = Day 0) and had subsequently been treated with progesterone over Days 1-12 and/or PGF2 alpha over Days 10-12 postestrus. The uterine PGF2 alpha response was measured after an i.v. injection of 10 IU oxytocin on Days 13 and 14, using the PGF2 alpha metabolite, 13,14-dihydro-15-keto-PGF2 alpha (PGFM), as an indicator for PGF2 alpha release. The levels of oxytocin receptors in the endometrium were measured on Day 14. During the treatment with progesterone, the peripheral progesterone concentrations were elevated and remained above 1.8 ng/ml until the morning of Day 14. The PGFM responses to oxytocin in untreated controls and SP controls were low on both Days 13 and 14 whereas the levels of endometrial oxytocin receptors in the same ewes were high. Treatment with progesterone either alone or in combination with PGF2 alpha significantly (p less than 0.04) increased the PGFM response on Day 14 and reduced the levels of endometrial oxytocin receptors; treatment with PGF2 alpha alone had no effect. It is concluded that progesterone promotes the PGFM response to oxytocin while simultaneously suppressing the levels of endometrial oxytocin receptors. PGF2 alpha treatment had no effect on either the uterine secretory response to oxytocin or the levels of oxytocin receptors in the endometrium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hormonal effects of PGF2 alpha output by cultures of epithelial and stromal cells in human endometrium

Estradiol stimulation and progesterone inhibition of human uterine PGF2 alpha production were studied using in vitro preparations of endometrial tissue and cells. Measurement of PGF2 alpha levels in media from primary cultures of glandular epithelia and stoma revealed that basal outputs were similar in both cell types but could be increased by estradiol only in epithelial cells. Tamoxifen (Tam) and trans-4-hydroxy tamoxifen (OHTam) did not affect basal PGF2 alpha outputs by secretory endometrium in organ culture and by monolayer cultures of epithelial cells, but counteracted the stimulatory effects of estradiol in both systems. The almost pure antiestrogenic activity exhibited by OHTam was at least 10 times greater than that of Tam, suggesting that the estrogen-stimulated increases in uterine PGF2 alpha output are mediated by specific estrogen receptors. Fragments of endometrium also released lipocortin, a phospholipase A2-inhibiting protein believed to mediate inhibitory effects of glucocorticoids on prostaglandin production in several types of cells. Although dexamethasone increased lipocortin and decreased PGF2 alpha output in secretory endometria in vitro, progesterone inhibited both lipocortin and PGF2 alpha output. The mechanisms by which P inhibits PGF2 alpha production remain to be elucidated.     

Endometrial prostaglandin E2 binding: characterization in rats sensitized for the decidual cell reaction and changes during pseudopregnancy

As an initial step in testing the hypothesis that uterine receptivity for blastocyst implantation and sensitivity for decidualization are controlled in part by the presence of functional receptors for prostaglandin E2 (PGE2) in the endometrium, we have characterized the high-affinity binding of [3H]PGE2 to an endometrial membrane preparation from ovariectomized rats treated with progesterone and estradiol so that their uteri were sensitized for the decidual cell reaction. As determined by Scatchard analysis, a single class of [3H]PGE2 binding sites with an apparent Kd ranging from 2 to 6 nM and a capacity of approximately 100 fmol/mg protein was found. Prostaglandins E1 and E2 competed equally for binding while relative cross-reactivity of other prostanoids and compounds tested was less than 3%. Binding was temperature-dependent and reversible. Under the assay conditions used, no metabolism of [3H]PGE2 was detectable. Pretreatment of the membrane preparation with proteolytic enzymes, or by heating, reduced subsequent specific [3H]PGE2 binding. These data are consistent with the presence of endometrial PGE receptors in the sensitized endometrium. The binding of [3H]PGE2 to endometrial membrane preparations from rats on Days 2 to 7 pseudopregnancy was determined. No specific binding could be detected on Day 2. A low binding capacity was found on Days 3 and 4; this increased markedly on Day 5 and reached a maximum on Day 6. These data indicate that the onset of uterine receptivity/sensitivity is temporally correlated with the appearance of endometrial PGE binding sites.     

Non-genomic effect of steroids on oxytocin-stimulated intracellular mobilization of calcium and on prostaglandin F2alpha and E2 secretion from bovine endometrial cells

Progesterone (P4) was found to interfere directly with the interaction of oxytocin (OT) with its own receptor in bovine endometrium. The aim of these studies was to investigate whether other steroids have a similar effect. Endometrial slices and epithelial endometrial cells from days 14 to 18 of the estrous cycle were used. Progesterone (P4), pregnenolone (P5), 17beta-hydroxyprogesterone (17-OHP4), the P4 receptor antagonist (aP4), and testosterone (T4) did not affect (P > 0.01) basal secretion of PGE2 and PGF 2alpha during 4h of incubation but all steroids inhibited (P < 0.05) OT-stimulated PGF2alpha secretion both from endometrial slices and from dispersed cells. None of the steroids used affected OT-stimulated PGE2 secretion from the cells (P > 0.01). In the next experiment it was studied whether P5, 17-OHP4 and P4 pretreatment for 30min modifies intracellular mobilization of Ca(2+) in response to OT. Oxytocin induced a rapid increase in intracellular Ca(2+)concentrations within 15s, while cells pretreated with steroids this increase occurred later. The total amount of intracellular Ca(2+)concentrations was lower (P < 0.05) in cells preincubated with steroids compared to controls. We conclude that steroids and aP4 are able to suppress OT-stimulated endometrial PGE2 and PGF2alpha secretion via a non-genomic pathway.     

Progesterone inhibits activation of latent matrix metalloproteinase (MMP)-2 by membrane-type 1 MMP: enzymes coordinately expressed in human endometrium

Matrix metalloproteinases (MMP) have specific spatial and temporal expression patterns in human endometrium and are critical for menstruation. Expression and activation mechanisms for proMMP-2 differ from other MMPs; in many cells proMMP-2 is specifically activated by membrane-type (MT)-MMPs. We examined the expression and localization of proMMP-2, MT1-MMP, and MT2-MMP in human endometrium across the menstrual cycle; and we examined the expression of MT1-MMP and activation of proMMP-2 in cultured endometrial stromal cells and their regulation by progesterone. MMP-2 was immunolocalized in 25 of 32 endometrial samples in all cellular compartments but with greatest intensity in degrading menstrual tissue. MT1-MMP mRNA was present throughout the cycle, and immunoreactive protein was detected in 24 of 32 samples, with the strongest staining in subsets of macrophages, neutrophils, and granular lymphocytes (but not mast cells or eosinophils) during the menstrual, mid-proliferative and mid-secretory phases. Patchy epithelial staining and staining of decidual cells, often periglandular in menstrual tissue, were also seen. MT2-MMP was more widespread than MT1-MMP without apparent cyclical variation and with maximal intensity in glandular epithelium. Cultured endometrial stromal cells released proMMP-2, and progesterone treatment significantly reduced the percentage level of its active (62 kDa) form (22.5 +/- 1.8% vs. 3.0 +/- 1.3%, without and with treatment, respectively, mean +/- SEM, P < 0.0001). This activation was blocked by a specific MMP inhibitor and restored following inhibitor removal. Progesterone also attenuated cell expression of MT1-MMP mRNA. We postulate that MT1-MMP activates proMMP-2 in endometrium, this activity being increased at the end of the cycle when progesterone levels fall, thus contributing to menstruation.     

Regulation of prostaglandin secretion from epithelial and stromal cells of the bovine endometrium by interleukin-1 beta, interleukin-2, granulocyte-macrophage colony stimulating factor and tumor necrosis factor-alpha.

Bovine endometrium was obtained on day 16 of pregnancy (estrus = 0) and separated into epithelial and stromal cell populations. When confluent, the two cell populations were treated for 24 h with cytokines at 1, 10 and 100 ng/ml. Prostaglandin (PG) E2 was the major prostaglandin produced by both cell types. For control cultures, more PGE2 was secreted into medium by stromal cells than by epithelial cells, whereas secretion of PGF was similar for epithelial and stromal cells. Interleukin-1 beta had no effect on prostaglandin production by stromal cell cultures but increased epithelial production of PGE2 and, to a lesser extent, PGF. Conversely, granulocyte-macrophage colony stimulating factor had no effect on epithelial cells but reduced secretion of PGE2 and PGF from stromal cells. There were no effects of interleukin-2 or tumor necrosis factor-alpha on prostaglandin secretion. Results indicate that certain cytokines can regulate endometrial prostaglandin secretion in a cell type-restricted manner.     

17beta-estradiol suppresses TLR3-induced cytokine and chemokine production in endometrial epithelial cells

Background  

The human endometrium is an important site for contact between the host and pathogens ascending the reproductive tract, and thus plays an important role in female reproductive tract immunity. Previous work in our laboratory has suggested that Toll-like receptors (TLRs) are involved in endometrial epithelial recognition of pathogens and that ligation of endometrial TLRs results in the production of cytokines and chemokines important for both immune and reproductive functions of the endometrium. We have also demonstrated cyclic regulation of TLR3 mRNA and protein expression in human endometrium, suggesting that steroid hormones might play a role in the expression and function of TLR3. In this study, the effects of 17beta-estradiol (E2) and progesterone (P) on TLR3 expression and function in endometrial cell lines were investigated.     

Control of endometrial oxytocin receptor and uterine response to oxytocin by progesterone and oestradiol in the ewe

The effects of administration of progesterone and oestradiol on ovine endometrial oxytocin receptor concentrations and plasma concentrations of 13,14-dihydro-15-keto prostaglandin F-2 alpha (PGFM) after oxytocin treatment were determined in ovariectomized ewes. Ewes received progestagen pre-treatment, progesterone and/or oestradiol in 11 different treatment schedules. Progestagen pre-treatment decreased oxytocin receptor concentrations in endometrium from ewes treated subsequently with either progesterone for 5 days or progesterone for 5 days plus oestradiol on Days 4 and 5 of progesterone treatment. Oestradiol increased endometrial oxytocin receptor concentrations when administered on Days 4 and 5 of 5 days progesterone treatment. Progestagen pre-treatment followed by progesterone treatment for 12 days caused a large increase in oxytocin receptors and no further increase occurred when ewes were given oestradiol on Days 11 and 12, or when progesterone was withdrawn on Days 11 and 12, or these two treatments were combined. Oxytocin administration caused an increase in plasma PGFM concentrations in ewes which did not receive progestagen pre-treatment, and subsequently received progesterone treatment for 5 days and oestradiol treatment on Days 4 and 5 of progesterone treatment. Similarly treated ewes which received progestagen pre-treatment did not respond to oxytocin. Oxytocin administration also increased plasma PGFM concentrations in ewes which received progestagen pre-treatment followed by progesterone treatment for 12 days, progesterone treatment for 12 days plus oestradiol on Day 11 and 12 of progesterone treatment, progesterone withdrawal on Day 11 and 12, or progesterone withdrawal and oestradiol treatment combined. The results indicate that (1) progesterone pre-treatment affects oxytocin receptor concentrations in the endometrium and uterine responsiveness to oxytocin and (2) progesterone treatment alone for 12 days after a treatment which mimics a previous luteal phase and oestrus is sufficient to induce oxytocin receptors and increase oxytocin-induced PGF release. These results emphasize the importance of progesterone and provide information which can be used to form an hypothesis for control of luteolysis and oestrous cycle length in the ewe.     

Possible involvement of oxytocin and its receptor in the local regulation of prostaglandin secretion in the cat endometrium

Ovarian originated oxytocin (OT) is involved in several reproductive process, amongst them its role in the regulation/modulation of the estrous cycle in several species has been demonstrated. Although the systemic role of endometrial originated prostaglandins (PGs), especially prostaglandin F(2α) (PGF(2α)), is equivocal in cats, their possible involvement in the local regulation of uterine events during the estrous cycle is uncertain. We examined the spontaneous and LH-stimulated OT production in cultured luteal cells, the spatial and temporal arrangement of OT receptors (OTR) in a cat endometrium and, finally the effects of OT on PG secretion and prostaglandin-endoperoxide synthase (PTGS2) expression in the feline cultured endometrial cells. Uteri together with ovaries were collected from adult domestic cats (n=27) at different stages of the estrous cycle, after routine ovariohysterectomy procedures. The endometrial and luteal cells were separated enzymatically. Luteinizing hormone (LH) augmented OT secretion in cultured luteal cells 2-fold compared with control (P<0.05). Oxytocin receptor was abundantly expressed in different ovarian structure, as well as in uterine tissues collected at early/developing and mid-luteal phase. The secretion of PGF(2α) by endometrial epithelial cells was increased by OT at a dose 10(-7)M (P<0.001). Atosiban (specific OTR blocker) alone did not affect PG secretion but atosiban in combination with OT abolished the stimulating effect of OT on PGF(2α) secretion. Oxytocin augmented PGE(2) secretion at a dose 10(-7)M and 10(-6)M in the endometrial stromal cells (P<0.001). The treatment with atosiban did not abrogated positive effect of OT on PGE(2) production in the stromal cells. Effect of OT on PTGS2 mRNA expression, the rate-limiting enzyme in PG production, was examined by Real Time-PCR and PTGS2 mRNA expression was significantly affected by OT in both epithelial and stromal cell cultures (P<0.01). The present observations have shown that OT is locally produced by the early/developing corpora lutea and that corpora lutea delivered OT may regulate PG secretion in a cat endometrium especially at early- and mid-diestrus, by affecting PTGS2 mRNA expression.     

A light microscopic and ultrastructural study on the presence and location of oxytocin in the equine endometrium

It has been reported that oxytocin is produced not only in the hypothalamus and posterior pituitary but also in outside the classical hypothalamo-neurohypophyseal axis such as the ovary, testis, placenta and in some nonreproductive sites. In the mare, oxytocin-mRNA has been identified in the endometrium, and oxytocin and its neurophysin have been identified in the uterus. In the present study, oxytocin was localised in the endometrium of the mare at the light microscopic and ultrastructural level by immunostaining and immunogold labelling of endometrial biopsy specimens collected during estrus.Strong positive immunostaining for oxytocin was found in the secretory vesicles of the secretory (nonciliated) epithelial cells of the uterine lumen and of the superficial glands. Using immunogold labelling, oxytocin was detected in the secretory vesicles of secretory epithelial cells. The vesicles containing immunoreactive oxytocin were present on the luminal surface suggesting that oxytocin is secreted into the uterine lumen by apical exocytosis. There was no positive immunostaining in ciliated epithelial cells of the uterine lumen and endometrial glands, in the stromal cells, or in the basal endometrial glands. To our knowledge, this is the first report of the location of oxytocin in specific secretory cells in the endometrium of any domestic species. This locally synthesised uterine oxytocin may have an important role in the autocrine/paracrine control of uterine contractility and luteolysis in the mare.     

Role of progesterone and oestradiol in the regulation of uterine oxytocin receptors in ewes.

The interaction between oestrogen and progesterone in the regulation of the uterine oxytocin receptor in sheep was evaluated by measuring the binding of oxytocin to membrane preparations of caruncular and intercaruncular endometrium and myometrium. Ovariectomized ewes were assigned in groups of five to each cell of a 4 x 2 factorial design. The four treatments were (a) vehicle (maize oil) for 12 days, (b) progesterone (10 mg day-1) for 9 days, (c) progesterone for 9 days followed by maize oil until day 12 and (d) progesterone for 12 days. The two oestradiol treatments consisted of the administration of implants in the presence or absence of oestradiol. The ewes were killed on day 10 (group b) or day 13 (groups a, c and d) for collection of uterine tissues. The response of the caruncular and intercaruncular endometrium to the treatments was similar. In the absence of oestradiol, treatment with progesterone continuously for either 9 or 12 days reduced the concentration of the oxytocin receptor in comparison with both the control and the progesterone withdrawal group (in which values were similar). The presence of oestradiol reduced the receptor concentrations in control and both 9- and 12-day continuous progesterone treatment groups, but enhanced the concentration in the progesterone withdrawal group. The myometrial oxytocin receptors responded in a similar way to those in the endometrium to progesterone treatment alone, but the addition of oestradiol produced no further effect. In conclusion, progesterone and oestradiol caused downregulation of the endometrial oxytocin receptor. On the other hand, progesterone withdrawal, similar to that which occurs during luteolysis, increased receptor density in the presence of oestradiol. Progesterone may influence the response of the myometrium to oxytocin by causing a reduction in receptor density.     

Oxytocin-stimulated production of prostaglandin F2alpha by isolated endometrium of rabbit: modulation by ovarian steroids

To test the hypothesis that ovarian steroid hormones modulate oxytocin-induced release of prostaglandin F2alpha (PGF2alpha) from uterine endometrium, 2 ovariectomized rabbits were pretreated with progesterone (5 mg/day for 10 days), 2 with estradiol-17 beta (25 microgram/day for 10 days), 2 with both steroids, and one with sesame oil only. On the last day of treatment, endometrial fragments were excised and incubated in vitro with or without oxytocin (100 muU/ml). Although endometrium from rabbits pretreated with combined steroids released more PGF2alpha immediately after excision than did tissue from animals pretreated with either steroid by itself, endometrium from animals pretreated with estradiol-17 beta alone released the most PGF2alpha during sustained incubation in vitro. Moreover, only this tissue exhibited significant oxytocin-dependent release of PGF2alpha. At the dosages used, progesterone completely antagonized both of these effects of estradiol-17 beta. The results support the hypothesis that ovarian steroid hormones regulate oxytocin-dependent release of PGF2alpha from endometrial cells. A posible mechanism of action is suggested.     

Stimulation of progesterone production by adrenocorticotropic hormone and prostaglandin E2 in rat luteal cells

The effects of adrenocorticotropic hormone (ACTH), human chorionic gonadotropin (hCG) and prostaglandin E2 (PGE2) on the progesterone secretion of luteal cells from rats were studied. Corpora lutea were harvested on Day 6 of pseudopregnancy and digested by trypsin. Homogeneous suspensions of luteal cells were used for short-term incubation. ACTH, PGE2, and hCG were added to the medium and the changes in progesterone production were measured by radioimmunoassay (RIA). Furthermore, specific ACTH-binding sites of the luteal cell membrane were studied by Scatchard analysis. ACTH, PGE2 and hCG increased synthesis of progesterone, and the combination of hCG with ACTH or PGE2 further increased production of the hormone. The effect of ACTH could be prevented by indomethacin. These effect of ACTH seem to be connected with specific ACTH-binding sites of the luteal cell membrane and with increased production of PGE2.