Expression of ER-α and ER-β during peri-implantation period in uterus is essential for implantation and decidualization in golden hamster

AIMS

The role of estrogen in embryo implantation in golden hamster (Mesocricetus auratus) is still ambiguous. In order to clarify it, we investigated the spatial distribution and expression of estrogen receptors, ER-α and ER-β in the uterus of pregnant hamster during peri-implantation period and identified the effect of estrogen receptor antagonist ICI-182,780 on the embryo implantation.

MAIN METHODS

We performed in vivo experiments on early pregnant hamsters involving treatment with ICI-182,780, an estrogen receptor antagonist. Immunohistochemistry, western blot analysis and quantitative PCR were employed to evaluate the spatio-temporal distribution and expression of ER-α and ER-β in the uterus of normal early pregnant and treated hamsters.

KEY FINDINGS

Results showed that embryo implantation was completely absent in ICI-182,780 treated uterine horn while, normal implantation occurred in control and vehicle treated horns. Both the receptors were differentially expressed in the uterus of hamster from day 1 (D1) to day7 (D7). In contrast, treated horns without any implantation site showed no trace of any receptors. Protein and mRNA expression of both the receptors were high around the day of implantation while, ER-β expression was up-regulated on D7 of embryo implantation. P value˂0.05 is considered significant.

SIGNIFICANCE

Spatio-temporal expression of ERs in the uterus during peri-implantation period have crucial role for endometrium receptivity and implantation in hamster. Recurrent implantation failure is the devastating problem among the desirable couple and is mainly due to defect in endometrium receptivity. This study may provide a new insight to manage the problem of idiopathic infertility.

Cyclooxygenase-2 derived PGE2 and PGI2 play an important role via EP2 and PPARdelta receptors in early steps of oil induced decidualization in mice

Differentiation of endometrial stromal cells into decidual cells (decidualization) is prerequisite for blastocyst implantation. Different prostanoids are shown to be involved in the cascade of events found in implantation and decidualization. Previous reports described that cyclooxygenase-2 (COX2) derived prostacyclin (PGI2) plays an important role via peroxisome proliferator activated receptor (PPARdelta) nuclear receptor in implantation and decidualization. Herein, we investigated the role of COX2 derived PGE2 and PGI2 and examined the protein expression and regulation of COX1, COX2, membrane-bound prostaglandin E synthase (mPGES-1), prostaglandin I synthase (PGIS), PGE2 receptor (EP2) and PPARdelta in hormone primed oil infused uterine horn as well as in non-infused uterine horn (control horn). Our results show that selective COX2 inhibitor (Nimesulide) inhibits decidualization while COX1 inhibitor (SC560) does not affect decidualization. COX2, mPGES-1, PGIS, EP2 and PPARdelta immunostaining are strongly observed at 24 h and 48 h in oil-induced horn and than significantly reduced at 72 h and 120 h and absent in non-infused horn. However COX1 immunostaining is observed in infused as well as in non-infused horn. Our immunohistochemical studies corroborated well with follow up western blotting of the same proteins. PGE2 and PGI2 products were also elevated at 24h and 48 h after oil induction in infused horn in comparison to control horn. Our data suggest that COX2 derived both PGE2 and PGI2 mediate its function via EP2 and PPARdelta receptors in early steps of decidualization in mice.

Induction of ovulation by clomiphene citrate in the Indian vespertilionid bat, Scotophilus heathi

The ovulation induction property of clomiphene citrate (CC) and human chorionic gonadotropin (hCG) was studied in Scotophilius heathi, an Indian tropical vespertilionid bat, during the period of delayed ovulation between December to early January. The results of the study showed that 10 microg of CC alone was ineffective to induce ovulation, whereas 100 microg CC and 10 IU hCG alone induced ovulation. A significant (P < 0.01) increase in the ovulation rate was observed when 10 microg CC followed by 10 IU hCG, compared to 10 IU hCG and 100 microg CC alone groups. Finally, CC at a 100 microg dose, followed by 10 IU hCG, produced superovulation (14.00 +/- 0. 70), which is significantly different in comparison to all other groups. This is the first report of ovulation induced by CC in the Indian tropical bat as well as in any animal model that exhibits temporary anovulation similar to polycystic ovary syndrome (PCOD) during the normal physiology of reproduction.

Prostaglandins and ovum implantation in mice

The possible involvement of prostaglandins (PGs) in events of ovum implantation is investigated. The levels of PGF and PGE-A were measured by radioimmunoassay in the implantation and interimplantation sites on days 4, 5, 6, and 7 of pregnancy. The concentration of prostaglandins was determined in morulae and blastocysts also. The levels of PGE-A were higher in implantation sites in comparison to PGF. PGE-A level showed a peak on d5 and remained significantly higher on d6 and d7, in comparison to d4. The concentration of PGF was found to be very low in both interimplantation sites and implantation sites before implantation. The concentration of PGF showed a significant increase on d6 in the interimplantation sites which peaked up to 32.61 +/- 2.01 ng on d7. The embryos showed an increase in PGE-A concentration along with development. However, PGF could not be found in the embryos. The present result shows that in mice PGE is the main prostaglandin involved in ovum implantation and PGF is associated with maintaining the embryos in the uterus. It is also predicted that in mice, blastocysts differentially stimulate PG synthesis in the uterus between implantation sites and interimplantation sites.

Effect of unilateral ovariectomy and subsequent ovum implantation in mice

Unilateral ovariectomy (ULO) was done on any stage of the cycle and the animals were mated within day 1 to day 21 to observe the acute and long term effect of ULO on ovum implantation. Implantation reduced in proportion to single ovary if the animals were mated within 24 hr of ULO. Increase in ovarian weight along with an increase in implantation number continued in mated mice and reached at peak on day 19-21 of ULO (sacrificed after 6 days i.e., 25-27 days of ULO). After ULO the remaining ovary compensated within day 5-6 of ULO even during pregnancy. Ovarian histology showed stimulation of small antral follicles in mice mated on day 3 of ULO (sacrificed after 6 days i.e., day 9 of ULO) along with a decrease of large antral follicles and pre-antral follicles. Preantral follicles were at peak on day 12-14. Large antral follicles attained a peak on day 4 which slowly decreased. The occurrence of implantation in such ULO conditions are discussed.

Pre-implantation embryo development in BALB/C ByJ mice

Problem of failure of ovum implantation in BALB/C ByJ strain in comparison to Swiss inbred mouse was studied. The results were compared with those of BALB outbred mice thereafter. BALB/C ByJ strain showed a poor responsiveness to superovulatory stimuli and their embryo development was not uniform. The embryo were delayed in attaining blastocyst stage on day 4. The delay was not significant in Swiss inbred embryos and was prevented by in vitro cultures. By direct embryo transfer it was shown that the uterus was not receptive for successful implantation. However, when these blastocysts were transferred to F1 hybrid (CBA x BALB outbred) recipients demonstrated normal acceptances. This may be a manifestation of inbreeding depression.

Estrogens with reduced catechol-forming capacity fail to induce implantation in the rat

Catechol estradiol can induce implantation of the embryo in a progesterone-primed uterus, but we do not know whether conversion of estrogen to a catechol is essential for implantation. The present study examined the ability of fluorinated estradiols that have a reduced capability of catechol formation to induce implantation. Delayed implantation in rats that were hypophysectomized on the third day postcoitum was maintained by daily injection of progesterone. On the fifth day of progesterone treatment they were injected intravenously with estradiol-17 beta (E2), or various doses of 2-fluoroestradiol-17 beta (2-F1-E2) or 4-fluoroestradiol-17 beta (4-F1-E2) and examined 24 hr later for evidence of initiation of implantation. All animals treated with 25 ng of E2 showed normal numbers of implantation sites, as did those receiving 60 ng of 4-F1-E2. In contrast, 2-F1-E2 failed to initiate implantation with doses as high as 300 ng per animal; there were only single sites in two of eight rats treated with 500 ng. Initiation of implantation was not correlated with lack of uterotropic estrogenicity. The results suggest that formation of catechol estrogen may be an important step in mediating estrogen function for implantation of the embryo.

Evidence for pituitary regulation of placental lactogen in the rat

The present studies examined whether the pituitary hormones, particularly prolactin, have any role in the regulation of rat placental lactogen (rPL) secretion. Total rPL was measured using a lymphoma cell bioassay. Hypophysectomy on day 13 of pregnancy increased total serum rPL levels above those of intact control rats and delayed for 3 days the decline in rPL usually seen by day 14. To test the effect of early hypophysectomy on rPL secretion, a delayed implantation model was used. Hypophysectomy was carried out on day 3, progesterone (2 mg) was given daily until day 8 and oestrone (1.0 micrograms) was given on day 8. This initiated implantation on day 9, which is 4 days later than normal. Rats hypophysectomized on day 3 had high serum levels of rPL (10-13 mg/l) 7 days after initiation of implantation compared with control values of 2-3 mg/l, and these levels remained raised for the duration of the experiment. Termination of maintenance injections of steroids did not affect the high levels of rPL for several days, even though there was fetal and placental resorption. When a pair of anterior pituitaries was transplanted under the kidney capsule on day 13 (day 9 of development) of rats hypophysectomized on day 3, serum rPL levels still increased for the next 3 days. However, unlike similarly treated rats not receiving transplants, rPL levels fell rapidly thereafter and were only 5% of those in control animals 1 week later.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for an inverse relationship between cyclooxygenase and lipoxygenase pathways in the pregnant rabbit endometrium

In the present investigation, experiments were undertaken to determine whether a relationship does exist between cyclooxygenase and 5-lipoxygenase pathways in rabbit endometrial cells on day 6 of pregnancy. Endometrial single-cell suspensions were incubated in RPM1-1640 for 1 h under a gas phase of 95% O2 + 5% CO2 at 37 degrees C for 1 h in the presence and absence of indomethacin, a known inhibitor of cyclooxygenase or nordihydroguaiaretic acid (NDGA), a preferential inhibitor of 5-lipoxygenase. Prostaglandins (PGF2 alpha, PGE2 and 6-keto-PGF1 alpha) and 5 (S)-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) were measured in the media by radioimmunoassay. Indomethacin or NDGA at all concentrations used suppressed the release of PGs or 5-HETE, respectively. However, NDGA at the lowest dose (15 microM) stimulated, but at higher doses (30-60 microM) suppressed the release of PGs. On the other hand, indomethacin at both the concentrations (55 microM and 110 microM) used stimulated the release of 5-HETE. The results suggest the existence of an inverse relationship between the two pathways in the preimplantation rabbit endometrial cells.

Cyclooxygenase and lipoxygenase pathways in the preimplantation rabbit uterus and blastocyst

We have measured by radioimmunoassay the concentration and production of 5(S)-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE), a metabolite in the lipoxygenase pathway, and PGs in different uterine compartments, and blastocysts during the preimplantation period in the rabbit. The production is defined as the synthesis minus the metabolism for a defined period of time. The pattern of uterine PGF production on days 5-6.5 was quite similar for the whole uterus and the myometrium showing a peak production on Day 6. The concentration and production of PGF were always higher in the endometrium. While significant production of PGE was noticed in the whole uterus on days 5-6 and in the myometrium on Day 6, the endometrium showed some production on these days. On the contrary, absolutely no production of this PG was observed in the endometrium on Day 6.5. The concentration and production of 6-keto-PGF1 alpha were always lower in the endometrium than those observed in the myometrium or the whole uterus. While highest production of this PG was found to be on Day 6.5 in the whole uterus and on Day 5 in the endometrium, the production in the myometrium remained constant on all days examined. The production of 5-HETE in the endometrium was noticeable on Days 5-6.5, in the whole uterus on Days 5 and 6.5, and in the myometrium only on Day 6.5. However, the concentrations of 5-HETE showed a tendency to be higher at 2 h than at 0 h in these compartments on Days 5-6.5. Furthermore, a linear increase in 5-HETE levels both at 0 h and 2 h was observed in the endometrium on Days 5-6.5; no such difference in mean 5-HETE level was noted in the whole uterus or myometrium on any of these days. The production of 5-HETE in the blastocyst was noted only on Day 5. The results not only demonstrate the presence of both the cyclooxygenase and the lipoxygenase pathways in the preimplantation rabbit uterus and blastocyst, their differential operation in various compartments of the uterus on various days of early pregnancy suggests an integrated role for these mediators in embryo-uterine interaction during implantation.

Role of calmodulin in blastocyst formation in the mouse

Preimplantation mouse embryos were recovered by flushing the oviducts on Day 3 at 09:30-10:00 h, 15:30-16:00 h and 21:30-22:00 h: When placed in culture for 48 h, 79% of the 4-8 cell embryos recovered at 09:30-10:00 h developed into blastocysts, but a large number of these embryos failed to form blastocysts when exposed to trifluoperazine, a calmodulin antagonist, at 0.5 or 0.6 microM in culture. About 45% of the embryos recovered at 15:30-16:00 h were compacted and blastocyst formation was again markedly depressed in the presence of the drug. Advanced compacted embryos recovered at 21:30-22:00 h showed normal development into blastocysts in the presence of 0.6 microM-trifluoperazine. Trifluoperazine sulphoxide (the inactive form of trifluoperazine) at 0.6 or 1.2 microM concentration had no effect on blastocyst formation of uncompacted embryos recovered at 09:30-10:00 h. These embryos and those recovered at 21:30-22:00 h and developed into blastocysts in the presence of trifluoperazine were transferred to Day-4 pseudopregnant mice and healthy young were born. When exposed to calcium-free medium or medium containing trifluoperazine all compacted embryos recovered at 18:30 h became decompacted; development to the blastocyst stage was normal in medium alone but reduced when trifluoperazine was added. Compacted embryos recovered at 23:00 h showed 100% decompaction in the calcium-free medium but completely failed to decompact in the presence of 0.6 microM-trifluoperazine. We suggest that extracellular calcium is essential for the continuance of compaction, while intracellular calcium is required only during the initial phase of this process.

Studies on the temporal pattern of prostaglandin synthesis in the uterus of the delayed implanting rat with or without implantation inducing stimuli

The model of delayed implantation produced by injection of progesterone (P4) following hypophysectomy on day 3 of pregnancy, was used to study the temporal relationship between phospholipase A2 (PLA2) activity and endogenous concentrations and/or in vitro production of prostaglandins (PGs) in the rat uterus during the early phase of implantation. No definitive correlation between the endogenous concentration of uterine PGs and their in vitro production, or PLA2 activity, was found following various treatments. However, an interesting interaction between various treatments and PLA2 activity, as well as PG production, was evident within 0.5 h-4 h. The unaltered PLA2 activity and PG production in the uterus at 0.5 h and 4 h after the last injection of P4 only suggest that PLA2 is probably the limiting step in PG synthesis in the P4 dominated uterus. On the other hand, the depressed uterine PG production at 0.5 h, in the face of unaltered PLA2 activity, in P4-primed rats injected with an optimal dose of estradiol-17 beta (E2: 20 ng/rat, i.v.) suggests a reduction in PG synthetase activity with estrogen. Because PLA2 activity remained unchanged, the stimulation in PGE, and to some extent PGF, production at 0.5 h following superimposition of histamine on the E2 treatment appears to be mediated via stimulation of PG synthetase. The increase in PGE and PGF production at 4 h as compared to 0.5 h following E2 injection was accompanied by increased PLA2 activity. However, PGF production did not exceed that obtained with only P4. Addition of histamine to the P4 and E2 treatment potentiated the stimulation of PG production at 4 h without further elevation in PLA2 activity. A suboptimal dose of E2 (10 ng/rat, i.v.) failed to increase PLA2 activity and PG production, compared to those obtained with 20 ng/rat of E2. However, coadministration of histamine with the low dose of E2 increased PG production to the level found with the optimal dose of E2; this was achieved without a significant change in PLA2 activity. On the other hand, histamine did not reverse the inhibitory effect of dexamethasone on E2 stimulation of PLA2 activity and PG production. Taken together these results suggest that histamine induced potentiation of PG production in P4 and E2 treated rats is probably mediated via activation of PG synthetase activity. PLA2 activity was increased significantly at 8 h after the last injection of P4. However, this increase in activity was reflected in increased PGE, but not PGF production.(ABSTRACT TRUNCATED AT 400 WORDS)

Prostaglandins in the uterus: modulation by steroid hormones

Phospholipase A2 (PLA2), one of the enzymes considered to be rate-limiting in generating free arachidonic acid for prostaglandin (PG) synthesis, endogenous concentrations and in vitro production of PGs in the rat uterus were studied under various experimental conditions. Uterine PLA2 activity showed a 167-fold increase in ovariectomized rats bearing estradiol-17 beta (E2)-implants as compared to those treated with vehicle only. On the other hand, dexamethasone treatment reduced the E2-stimulable PLA2 activity by about 24-fold. The uterine PLA2 activity in the ovariectomized rat uterus was low and not altered by instillation of progesterone (P4) implants or by administration of dexamethasone. On the contrary, simultaneous placement of E2- and P4-implants prevented significantly the rise in PLA2 activity as observed under unopposed E2 exposure. Dexamethasone treatment further reduced the activity. The endogenous concentration of uterine PGF was several fold higher in the E2-implanted ovariectomized rats as compared to those without the E2-implants or carrying only P4-implants. The simultaneous treatment of the E2-implanted rats with P4 and/or dexamethasone reduced the uterine PGF concentrations considerably. The uterine PGF concentration was always lower in the ovariectomized rats under any condition if they were not treated with E2. Uterine PGE-A concentration did not change significantly between the ovariectomized rats and the ovariectomized rats carrying E2-implants. The treatment with P4 and/or dexamethasone, however, tended to decrease the PGE-A concentration. The production of PGF by the uterine homogenate increased by several fold in ovariectomized rats implanted with E2-silastic capsules as compared to those without the E2 implants. The treatments of the E2-implanted rats with P4 or dexamethasone did not alter this production. However, simultaneous exposure of E2-implanted rats to P4 and dexamethasone lowered the production rate of PGF in the uterus. The treatment of the ovariectomized rats with dexamethasone of P4 tended to elevate the uterine PGF production. The uterine PGE-A production followed more or less the same pattern. The analysis of our present data suggests that although a relationship exists between uterine PLA2 activity and PGF concentration, the role of PG synthetase could also be important in regulating PGF synthesis. Our study with dexamethasone, which showed inhibition of uterine PLA2 activity and decline in endogenous but not in vitro production of PGs, indicate that cellular integrity is essential for PLA2 to function as a rate-limiting step in PG synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Catechol estrogens stimulate synthesis of prostaglandins in the preimplantation rabbit blastocyst and endometrium

The influence of estradiol-17 beta (E2) or catechol estradiols [4-hydroxyestradiol-17 beta (4-OH-E2) or 2-hydroxyestradiol-17 beta (2-OH-E2)] on prostaglandin (PG) production in the rabbit blastocyst and endometrial cell in vitro on Day 6 of pregnancy (144 h postcoitum) was studied. Blastocysts (4-6) were incubated in 1 ml of RPMI-1640 medium for a total period of 8 h. Media were changed every 2 h and stored at -80 degrees C. E2, 4-OH-E2 or 2-OH-E2 at various concentrations were added during the second and fourth periods, while the vehicle was added during the first and third periods. Single cell suspensions of endometrial tissues in 0.5 ml of RPMI-1640 were incubated for 2 h with and without estrogens. The media and cells were separated and stored at -80 degrees C. PGs were determined by radioimmunoassay. The results for blastocyst were expressed as the cumulative release of PGs over a period of two 2-h incubations of the same experimental conditions (pg/blastocyst per 4 h). The release of PGs from the blastocyst was not influenced by 8.8 microM of 4-OH-E2, whereas 44 microM of this steroid stimulated the release of PGE-A by about 25% and PGF by 59% (P less than 0.05) over the vehicle-treated controls. The release of PGE-A and PGF in the presence of 44 microM of 2-OH-E2 was stimulated by about 60% and 37%. On the other hand, E2 at any concentration, either showed none or inhibitory effects on the release of PGs from the blastocyst.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandins in swine blastocysts

The activity of phospholipase A2 (PLA2) and the content of prostaglandins (PGF and PGE-A) in swine blastocysts were determined on Days 7 through 14 of gestation by using radioenzymatic and radioimmunoassay techniques. Both PLA2 activity and PG content increased in the blastocyst with age. PLA2 activity on Day 14 and PG content on Day 12 were significantly higher than those on earlier stages of pregnancy. The content of PGE-A was always greater than that of PGF and the difference became significant on Days 11 and 12 of pregnancy. It is suggested that PGs of embryonic origin may be associated with blastocyts elongation and migration as well as early pregnancy recognition in the pig.

Blastocyst is the source of prostaglandins in the implantation site in the rabbit

The levels of prostaglandins (PGs) were measured by radioimmunoassay in the interimplantation and the implantation sites as well as in the implantation site without the blastocyst in the rabbit on day 7 of pregnancy (168 h post coitum). The concentrations of PGs were also determined in the blastocyst (PGF:101.59+/-4.33 and PGE-A:29.74+/-3.11 ng/blastocyst, n=6) and the blastocoel fluid (PGF:253.55+/-39.56 and PGE-A:83.29+/-6.60 ng/100 microliters, n=4) on day 7. The levels of both PGF and PGE-A were significantly higher in the implantation site as compared to interimplantation site (PGF:73.63+/-6.68 vs. 0.59+/-0.21 and PGE-A:25.52+/-3.30 vs. 1.22+/-0.18 ng/100 mg wet weight, n=8). The removal of the blastocyst from the implantation site drastically reduced the concentrations of PGs in this site (PGF:8.71+/-2.80 and PGE-A:1.64+/-0.12 ng/100 mg wet weight, n=8). The results provide evidence that the blastocyst is the major source of PGs which contribute to the high concentration in the implantation site in the rabbit.

Effect of p-coumaric acid on immature estrogen treated and cyclic female mice

Oral administration of p-coumaric acid to estrogen-primed immature female mice exerts neither estrogenic nor anti-estrogenic activity, but when it is administered to cyclic female mice in single dose at proestrus or in repeated doses, induces alteration in estrus cycle, ovarian and uterine weight and structure.