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Effect of LH on prostaglandin F₂ and prostaglandin E₂ secretion by cultured porcine endometrial cells

Division of Reproductive Endocrinology and Pathophysiology, Institute of Animal Reproduction and Food Research, Polish Academy of Sciences, Tuwima 10, Olsztyn 10-747, Poland

Correspondence should be addressed to A Blitek; Email: agas{at}pan.olsztyn.pl

	Abstract

Top Abstract Introduction Materials and Methods Results Discussion Acknowledgements References

 
LH appears to be a potent stimulator of the release of endometrial prostaglandins (PGs) in the pig. The aim of the present studies was to examine the effect of LH on PGF₂ and PGE₂ secretion by cultured porcine endometrial cells on days 10–12 and 14–16 of the oestrous cycle and to compare its action with oxytocin. A time-dependent effect of LH (10 ng/ml) on PGF₂ release from luminal epithelial and stromal cells on days 10–12 was observed (experiment 1). The highest increase in PGF₂ secretion in response to LH was detected in stromal cells after 6 h of incubation (P < 0.001). Epithelial cells responded to LH after a longer exposure time (P < 0.01). A concentration-dependent effect of LH (0.1–100 ng/ml) on PGF₂ release from stromal cells was examined after 6 h and from epithelial cells after 12 h (experiment 2). Effective concentrations of LH were 10 and 100 ng/ml. LH (10 ng/ml) and oxytocin (100 nmol/l) affected PGF₂ and PGE₂ secretion from endometrial cells on days 10–12 and 14–16 of the oestrous cycle (experiment 3). LH stimulated PGF₂ secretion from both cell types and its action was more potent on days 10–12. LH induced PGE₂ release, especially in epithelial cells on days 14–16. A stimulatory effect of oxytocin on PGF₂ was confirmed in stromal cells, but this hormone was also shown to enhance PGE₂ output. These results indicated that LH, like oxytocin, a very effective stimulator of PGF₂ release, could play an important role in the induction of luteolysis.

	Introduction

Top Abstract Introduction Materials and Methods Results Discussion Acknowledgements References

 
Pulsatile release of prostaglandin (PG) F₂ from the uterus in the late luteal phase of the oestrous cycle induces corpus luteum regression in many species, including pigs (for review see McCracken et al. 1999). Oxytocin (OT) is the major known stimulus for increased PGF₂ secretion at the time of luteolysis in pigs (Kieborz et al. 1991, Carnahan et al. 1996, Uzumcu et al. 1998). On the other hand, agreement between OT and 13,14-dihydro-15-keto-PGF₂ (PGFM) peaks in the blood is only about 30% and blocking of OT receptors neither prevented luteolysis nor changed the duration of the oestrous cycle in gilts (Kotwica et al. 1999). This may indicate that OT is not mandatory to induce endometrial release of PGF₂ at the time of luteolysis. Therefore, the induction and course of luteolysis is regulated not only by OT but apparently also by one or more other factors.

Porcine endometrium possesses functional luteinizing hormone (LH) receptors (Stepien & Ziecik 2002) and the incubation of endometrial strips with LH resulted in an increased PGFM accumulation in medium. The strongest effect was observed at the time of luteolysis when the numbers of LH receptors were also at their highest (Stepien et al. 1999). LH was shown to stimulate cyclooxygenase expression in the endometrium (Stepien et al. 1999) and increased PGF₂ release (Ziecik et al. 2000) on days 14–16 of the oestrous cycle in pigs. Moreover, both systemic infusion (Ziecik et al. 2001) as well as intramuscular injection (Guthrie & Bolt 1983) of human chorionic gonadotrophin induced PGF₂ secretion in vivo. This indicates that the endogenous LH pulses may provoke PG output from porcine endometrium and that LH participates in the process of luteolysis in this species.

The proper ratio between PGF₂ and PGE₂ seems to be responsible for the maintenance of corpora lutea and successful implantation (for review see Ziecik 2002). Despite many studies on the secretory properties of cultured porcine stromal and epithelial cells at different reproductive states (Zhang et al. 1991, Davis & Blair 1993) as well as cellular responsiveness to OT (Uzumcu et al. 1998, 2000) and steroids (Carnahan et al. 2002, Hu et al. 2003), little is known about the modulation of PGE₂ output from endometrial cells in vitro. Our recent results revealed that secretion of both PGs depends on the day of the oestrous cycle and the type of cells as well as the time of incubation (Blitek & Ziecik 2004).

LH was shown to selectively affect the secretion of PGs from endometrial explants on days 14–16 of the oestrous cycle and early pregnancy, but it is not known which endometrial cell types are responsive to LH action around the time of luteolysis. The present studies were undertaken to examine the effect of LH on PGF₂ and PGE₂ secretion by cultured porcine stromal and luminal epithelial cells on days 10–12 and 14–16 of the oestrous cycle and to compare this with the action of OT.

	Materials and Methods

Top Abstract Introduction Materials and Methods Results Discussion Acknowledgements References

 
Tissue
Uteri of 12 crossbred gilts (Large White x Polish Landrace) were obtained from a local abattoir within 20 min after exsanguination and transported in ice-cold phosphate-buffered saline (PBS) buffer (137 mmol/l NaCl, 27 mmol/l KCl, 10 mmol/l Na₂HPO₄ and 2 mmol/lKH₂PO₄, pH 7.4) to the laboratory within 1 h. The stages of the oestrous cycle were determined by macroscopic observation of the ovaries and uterus as previously described (Akins & Morissette 1968, Leiser et al. 1988). Endometrial tissue obtained on days 10–12 and 14–16 of the oestrous cycle was used. These two periods were selected because during days 10–12 luteolytic release of PGF₂ is not yet observed but on days 14–16 the process of luteolysis is already initiated in cyclic gilts.

Isolation of endometrial cells
Porcine endometrial cells were isolated aseptically under a laminar flow hood using a procedure described recently (Blitek & Ziecik 2004). Briefly, a randomly selected uterine horn was washed with sterile PBS supplemented with 100 IU/ml penicillin and 100 µg/ml streptomycin (Sigma Chemical Co., St Louis, MO, USA) and cut longitudinally to expose the endometrium. Endometrial tissue was separated from the myometrium and digested with 0.48% (w/v) dispase (Gibco-BRL Life Technologies, Paisley, Strathclyde, UK) in Hanks’ balanced salt solution (HBSS), Ca-, Mg- and phenol red-free, pH 7.4; Sigma) at room temperature for 50 min with gentle shaking. Luminal epithelial cells released after this digestion were pelleted by centrifugation at 200 g for 10 min, washed once with Medium 199 (Sigma) containing 4% (w/v) bovine serum albumin (BSA; ICN Biomedicals, Inc., Costa Mesa, CA, USA), 100 IU/ml penicillin and 100 µg/ml streptomycin. Red blood cells were removed using red blood cell lysing buffer (Sigma). The luminal epithelial cells obtained were then washed three more times with fresh Medium 199 containing 4% BSA, resuspended in 3 ml culture medium (Medium 199 containing 2% BSA, 10% newborn calf serum (v/v; Sigma), and 100 IU/ml penicillin and 100 µg/ml streptomycin) and counted in a haemocytometer. The cell viability was higher than 90% as assessed by 0.5% (w/v) trypan blue dye exclusion

The remaining endometrial tissue was minced with scissors, placed in 0.25% trypsin solution (Biomed, Lublin, Poland) and digested for 1 h at 37 °C. The cell suspension was filtered to remove undigested tissue fragments, pelleted by centrifugation and washed with fresh medium. The remainder was further treated with 0.06% collagenase (w/v; Sigma) in Medium 199 containing 2% BSA for 1.5 h at 37 °C. The cell suspensions obtained after trypsin and collagenase digestions were pooled together, washed three times with fresh medium and counted in a haemocytometer. They were assessed as stromal cells and the cell viability was higher than 95%. The homogeneity of cells was evaluated by the immunofluorescent staining of cultured cells for cytokeratin and vimentin as described previously (Blitek & Ziecik 2004). The purity of stromal cells was 95–98% and luminal epithelial cells 85–90%.

Cells were cultured at 37 °C in a humidified atmosphere of 95% air:5% CO₂. Stromal cells were washed 24 h after plating to remove contaminating epithelial cells before continuing culture. Cells were cultured for 64–88 h to allow them to adhere to the plates before initiation of experiments when monolayers were estimated to be approximately 90–95% confluent.

Experiment 1
To determine the time-course for PGF₂ secretion in response to LH (pLH B-1; USDA Hormone Program, Bethesda, MD, USA) stromal and luminal epithelial cells obtained from six gilts at days 10–12 of the oestrous cycle were used. Cells were incubated with 0 or 10 ng/ml LH in Medium 199 (serum free) for 1, 3, 6, 12 or 24 h. At the end of each treatment period, media were collected and stored at –40 °C until PGF₂ concentrations were estimated by enzyme immunoassay (EIA). Cells were lysed with 100 mmol/l NaOH and total cellular protein was measured (Bradford 1976).

Experiment 2
To study the dose-dependent PGF₂ secretion in response to LH, stromal and luminal epithelial cells collected from six gilts (the same as in experiment 1) were treated with the following doses of LH: 0, 0.1, 1, 10 or 100 ng/ml. The time of incubation was chosen based on the results of experiment 1 and was 6 h for stromal cells and 12 h for epithelial cells. Cells were then lysed with 100 mmol/l NaOH and total cellular protein was measured (Bradford 1976).

Experiment 3
To study the effect of LH on PGF₂ and PGE₂ release, endometrial cells collected before (days 10–12) and at the time (days 14–16) of luteolysis were used. Time of incubation (6 h for stromal and 12 h for luminal epithelial cells) and the effective dose of LH (10 ng/ml) were chosen based on the results of experiments 1 and 2. Additionally, OT (Sigma) at the dose of 100 nmol/l (Uzumcu et al. 1998) was used as a positive control to study LH action on PGF₂ release, but OT action on PGE₂ secretion was examined for the first time and also compared with LH.

EIA of PGF₂ and PGE₂
Concentrations of PGF₂ in incubation medium were determined by direct EIA test as described earlier (Uenoyama et al. 1997). Cross-reactivities of the anti-PGF₂ serum (Sigma) were as follows: PGF₁ 60%, PGE₁ and PGE₂ <0.1% and PGA₁, PGA₂, PGB₁ and PGB₂ < 0.01%. The PGF₂ standard curve ranged from 0.11 to 30 ng/ml, and the median effective dose (ID₅₀) was 2.59 ng/ml. The intra- and interassay coefficients of variation were 7.6 and 12.3% respectively.

Concentrations of PGE₂ in incubation medium were determined by a direct EIA test as described earlier (Skarzynski & Okuda 2000). The anti-PGE₂ serum was donated by Dr S Ito, Kansai Medical University, Osaka, Japan. Cross-reactivities of the anti-PGE₂ serum were as follows: PGE₁ 18%, PGA₁ 10%, PGA₂ 4.6%, PGB₂ 6.7%, PGD₂ 0.13%, PGF₂ 2.8%, PGJ₂ 1.4% and 15-keto PGE₂ 0.05%. The PGE₂ standard curve ranged from 1.56 to 100 ng/ml and the ID₅₀ of the assay was 11.2 ng/ml. The intra- and interassay coefficients of variation were 5.8 and 9.2% respectively.

Statistical analysis
The data are shown as the mean ±S.E.M. of values obtained in four to six separate experiments (pigs), each performed in duplicate. Levels of PGF₂ and PGE₂ production were standardized on protein concentrations per well (ng/mg protein). The statistical significance of differences between controls and treated groups was assessed by one-way ANOVA followed by Bonferroni multiple comparison tests (GraphPad PRISM version 4; GraphPad Software, Inc., San Diego, CA, USA).

	Results

Top Abstract Introduction Materials and Methods Results Discussion Acknowledgements References

 
Experiment 1
LH stimulated PGF₂ output (ng/mg protein) from both endometrial cell types in a time-dependent manner (Fig. 1). Basal and LH-stimulated secretion of luteolytic PG was tenfold higher for luminal epithelial than for stromal cells. However, the effect of LH was more visible in stromal than in epithelial cells. LH-stimulated increase of PGF₂ secretion from stromal cells was observed during all time-periods studied (1–24 h). The most effective action of LH was detected after 6 h of incubation, when the amount of PGF₂ released into medium increased almost twofold (36.2 ± 3.3 vs 69.7 ± 3.0; P < 0.001). Epithelial cells needed more time of LH treatment (12 and 24 h) to significantly increase PGF₂ output (772.3 ± 21.2 vs 1452.9 ± 123.9 after 12 h and 3220.8 ± 187.0 vs 4326.9 ± 192.9 after 24 h; P < 0.01). No effect of LH on luminal epithelial cells was detected during the shorter periods of incubation (1–6 h).

View larger version (23K): [in this window] [in a new window]   Figure 1 Time-dependent effect of LH (10 ng/ml) on PGF2 output by cultured porcine (A) stromal and (B) luminal epithelial cells obtained at days 10–12 of the oestrous cycle. Data are presented as means ±S.E.M. *P < 0.05, **P < 0.01, ***P < 0.001.

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View larger version (53K): [in this window] [in a new window]   Figure 2 Dose-dependent effect of LH on PGF2 output by cultured porcine (A) stromal and (B) epithelial cells obtained at days 10–12 of the oestrous cycle. LH (0.1–100 ng/ml) was added for 6 h in stromal and 12 h in luminal epithelial cell cultures. Data are presented as means ±S.E.M. **P < 0.01, ***P < 0.001 when compared with control value.

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View larger version (34K): [in this window] [in a new window]   Figure 3 Effect of LH (10 ng/ml) and OT (100 nmol/l) on PGF2 and PGE2 secretion by cultured porcine stromal cells obtained on days 10–12 and 14–16 of the oestrous cycle. Cells were incubated with hormones for 6 h. Data are presented as means ±S.E.M. *P < 0.05, ***P < 0.001 when compared with control value.

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View larger version (32K): [in this window] [in a new window]   Figure 4 Effect of LH (10 ng/ml) and OT (100 nmol/l) on PGF2 and PGE2 secretion by cultured porcine luminal epithelial cells obtained on days 10–12 and 14–16 of the oestrous cycle. Cells were incubated with hormones for 12 h. Data are presented as means ±S.E.M. *P < 0.05, **P < 0.01, ***P < 0.001 when compared with control value.

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion Acknowledgements References

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In our studies OT served as a positive control for studying stimulated PGF₂ secretion (Uzumcu et al. 1998, 2000), but its effect on PGE₂ release from cultured porcine endometrial cells has been here examined for the first time. The present study demonstrated that, in pigs, LH stimulated PGF₂ secretion from cultured endometrial stromal and luminal epithelial cells. The action of LH depended on the cell type and the day of the oestrous cycle as well as the duration of incubation with the hormone. The results of our experiments also revealed a different cellular response to LH. Stromal cells were more sensitive to LH, and LH-stimulated increase in PGF₂ secretion was observed after all periods of incubation studied (1–24 h). Luminal epithelial cells responded with elevated PG output after longer (12 and 24 h) hormone treatment periods. The present results were not expected since LH receptor mRNA and protein expression were present mainly in the epithelium of porcine endometrium (B Gawronska, A Stepien & A J Ziecik, unpublished observations). Our previous studies (Stepien & Ziecik 2002) showed that endometrial LH receptors are functional because treatment of isolated cells (a mixture of luminal epithelial cells with some stromal and glandular epithelial cells) resulted in higher cAMP output and increased accumulation of inositol phosphates in medium. In addition to PG production, LH could be also responsible for other activities, such as protein secretion in these cells. Nevertheless, further studies on the number of LH receptors and second messenger systems in separated and cultured porcine stromal and epithelial cells are needed to clarify the different cellular response to this hormone.

Similar responsiveness of cultured porcine endometrial cells was previously observed during OT treatment. Stromal cells were the most responsive and luminal epithelial cells the least responsive to this hormone (Uzumcu et al. 1998), even though OT receptor expression appeared to be greater within the epithelium than stroma of the porcine endometrium (Boulton et al. 1995). Further studies on polarized luminal epithelial cells revealed that these cells were completely unresponsive to a 3-h long treatment with exogenous OT (Braileanu et al. 2000). The authors of those studies concluded that epithelial cells may not contribute to OT-stimulated pulses of PGF₂. However, the results of Uzumcu et al.(1998) indicated that after longer incubation (12 h), OT showed a tendency (no statistical differences) to increase PG secretion. These data are in agreement with our results since longer incubation resulted in elevated PGF₂ release in response to both OT and LH. On the other hand, OT is a peptide with a very short half-life, and the stimulatory effect of this hormone observed after 12 h may not be due to its direct effect on PG synthesis. However, cultured bovine endometrial epithelial cells, which are the main target of OT action (Asselin et al. 1996), responded in increased PGF₂ production after 12 and 24 h (Parent et al. 2003).

In the present study, LH action on PGF₂ secretion was more effective in cells collected before the onset of luteolysis. An almost twofold increase in PGF₂ concentration in the medium was observed in stromal and luminal epithelial cells obtained on days 10–12 of the oestrous cycle. These findings support our observations on the possible participation of LH in the PG surge at luteolysis. LH is released in a pulsatile manner during the luteal phase of the oestrous cycle (Parvizi et al. 1976, Van de Wiel et al. 1981). The porcine uterus could be exposed in vivo to the dose of LH used in our experiment (10 ng/ml), since the highest pulses of LH occurring in the mid-luteal phase of the oestrous cycle and at the time of luteolysis (days 13–16) vary from 5 to 10 ng/ml (Van de Wiel et al. 1981, Ziecik et al. 2001). Moreover, much greater agreement was found between LH and PGFM (79.2%; Ziecik et al. 2001) than between OT and PGFM peaks (30%; Kotwica et al. 1999). However, in the present study, the influence of OT on PGF₂ output was highly effective especially in stromal cells, which were more sensitive to OT than to LH action. Such a result could be caused by a combined effect of exogenous and endogenous OT. It was shown that OT is produced by porcine stromal and epithelial cells and may act in an auto- and/or paracrine manner to increase PGF₂ output (Hu et al. 2001). Additionally, in our studies, OT like LH, was more effective before luteolysis (days 10–12). These findings are in agreement with earlier data (Uzumcu et al. 2000), in which stromal cells collected on day 12 responded to OT to a higher degree than on day 16 of the oestrous cycle. Since stromal cells are present in the uterus in much greater number than luminal epithelial cells (Blackwell et al. 2003) they are expected to contribute the major portion to endocrine secretions of PGF₂. Moreover, their proximity to the uterine vasculature also predestines them to be the main source of luteolytic levels of PGF₂. Consequently, OT as well as LH could be important stimulators for PGF₂ release from the uterus at the time of luteolysis.

In the present studies, basal secretion of PGE₂ was comparable on days 10–12 and 14–16 in stromal as well as in epithelial cells. PGE₂ release from the endometrium was increased by both LH and OT on all the days of the oestrous cycle studied, especially in epithelial cells. On days 14–16, PGF₂ secretion was only slightly increased after treatment of these cells with LH but in the same period the output of PGE₂ was substantially increased. LH preferentially stimulated PGF₂ compared with PGE₂ in epithelial cells obtained on days 10–12, whereas OT highly increased PGE₂ output. Bovine endometrial epithelial cells treated with OT for 24 h also responded with elevated PGF₂ (14-fold) and PGE₂ (fourfold) concentrations in the incubation medium (Parent et al. 2003). PGF₂ and PGE₂ are synthesized directly from endoperoxide H₂ by PGF synthase (PGFS) and PGE synthase (PGES) respectively. The basal and stimulated PG secretion by endometrial cells in vitro is dependent on different patterns of PGFS and PGES expression on mRNA and protein levels (Waclawik et al. 2004). Another source of PGF₂ is PGE₂, which could be converted into PGF₂ by PGE₂ 9-keto reductase. Despite the great significance of PGE₂ 9-keto reductase as a regulator the of PGE₂/PGF₂ ratio, little is known about the modulation of this enzyme expression. The activity of PGE₂ 9-keto reductase was inhibited by oestradiol and progesterone but stimulated by OT and calcium ions in human decidua vera (Schlegel et al. 1984). Moreover, oestradiol strongly inhibited PGE₂ 9-keto reductase in the bovine placenta (Kankofer & Wiercinski 1999). Thus, during the maternal recognition of pregnancy in pigs, oestrogen of conceptus origin can increase the PGE₂/PGF₂ ratio which is essential for luteal maintenance. On the other hand, the LH-stimulated release of PGE₂ in cyclic gilts found in our studies would not prevent luteolysis, since PGE₂ could be converted to PGF₂ (Okrasa et al. 1985) and the number of PGE₂ receptors on porcine luteal cells is decreased on days 12–14 of the oestrous cycle (Feng & Almond 1999).

In the present studies, basal PGF₂ release from stromal cells was increased on days 14–16 in comparison with days 10–12, but decreased about twofold in epithelial cells on comparable days. The same pattern of non-stimulated PGF₂ secretion from cultured porcine endometrial cells on days 12 and 16 has been demonstrated previously (Uzumcu et al. 2000). It has been well documented that porcine stromal cells principally produce PGE₂ and epithelial cells produce more PGF₂ (Zhang et al. 1991, Blitek & Ziecik 2004). However, our previous results (Blitek & Ziecik 2004) revealed that, in stromal cells, the ratio between PGF₂ and PGE₂ depends on the time of incubation. Long incubation (24 h) resulted in balanced production of both PGs or even a tendency for the release of PGF₂ to dominate. Basal PGF₂ secretion from epithelial cells was approximately tenfold greater than from stromal cells. This may be caused by the higher expression of cyclooxygenase COX-2 (a key enzyme in PG synthesis), but also by a greater availability of the substrate, arachidonic acid, in epithelial cells. However, this suggestion needs detailed investigations.

In summary, these results revealed that stromal cells were more sensitive to LH than epithelial cells. Furthermore, LH action was more effective in stimulating PGF₂ secretion from cells collected before luteolysis. However, PGE₂ release was also increased in the presence of LH, especially in epithelial cells obtained during luteolysis. Additionally, our studies confirmed the stimulatory effect of OT on PGF₂ secretion from stromal cells of the porcine endometrium, but this hormone was also shown to enhance PGE₂ output. Moreover, OT seems to be a more potent modulator of PG secretion from the endometrium of the pig in in vitro conditions. The overall results indicate that LH and OT could play an important role in the induction of luteolysis, since they are very effective stimulators of PGF₂ release from endometrial cells obtained on days 10–12 of the oestrous cycle. The results of the present and earlier studies (Uzumcu et al. 1998, 2000, Stepien et al. 1999, Ziecik et al. 2000, 2001, Carnahan et al. 2002, Stepien & Ziecik 2002, Hu et al. 2003) on endometrial cells indicate that, in pigs, PG production at the time of luteolysis is regulated by at least two factors (i.e. OT and LH). Until now it is still not clear which of them dominates.

	Acknowledgements

Top Abstract Introduction Materials and Methods Results Discussion Acknowledgements References

 
We thank Dr S Ito of Kansai Medical University for the PGE₂ antiserum. The authors are grateful to Ms K Gromadzka-Hliwa and Mr J Klos for technical help with the PG EIAs. This research was supported by the State Committee for Scientific Research as a solicited project PBZ-KBN-084/P06/2002 from 2003 to 2005. The authors declare that there is no conflict of interest that would prejudice the impartiality of this scientific work.

	Footnotes

 
Received 20 December 2004
First decision 3 March 2005
Revised manuscript received 4 April 2005
Accepted 5 May 2005

	References

Top Abstract Introduction Materials and Methods Results Discussion Acknowledgements References

 

Akins EL & Morissette MC 1968 Gross ovarian changes during estrous cycle of swine. American Journal of Veterinary Research 29 1953–1957.[Web of Science][Medline]

Asselin E, Goff AK, Bergeron HR & Fortier MA 1996 Influence of sex steroids on the production of prostaglandin F₂ and E₂ and response to oxytocin in cultured epithelial and stromal cells of the bovine endometrium. Biology of Reproduction 54 371–379.[Abstract]

Blackwell DM, Speth RC & Mirando MA 2003 Morphometric analysis of the uterine endometrium of swine on days 12 and 16 postestrus. Anatomical Record 270 59–66.[CrossRef]

Blitek A & Ziecik AJ 2004 Prostaglandins F₂ and E₂ secretion by porcine epithelial and stromal endometrial cells on different days of the estrous cycle. Reproduction in Domestic Animals 39 340–346.[CrossRef][Web of Science][Medline]

Boulton MI, McGrath TJ & Gilbert CL 1995 Oxytocin receptor mRNA expression in the porcine uterus during the oestrous cycle, and pregnancy. Journal of Reproduction and Fertility 16 (Abstract Series) 21.

Bradford MM 1976 A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Analytical Biochemistry 72 248–254.[CrossRef][Web of Science][Medline]

Braileanu GT, Hu J & Mirando MA 2000 Directional secretion of prostaglandin F(2alpha) by polarized luminal epithelial cells from pig endometrium. Prostaglandins and Other Lipid Mediators 60 167–174.

Carnahan KG, Prince BC & Mirando MA 1996 Exogenous oxytocin stimulates uterine secretion of prostaglandin F_2ß in cyclic and early pregnant swine. Biology of Reproduction 55 838–843.[Abstract]

Carnahan KG, Uzumcu M, Hu J, Sample GL, Braileanu GT & Mirando MA 2002 Oxytocin stimulates secretion of prostaglandin F₂ from endometrial cells of swine in the presence of progesterone. Domestic Animal Endocrinology 23 435–445.[CrossRef][Web of Science][Medline]

Davis DL & Blair RM 1993 Studies of uterine secretions and products of primary cultures of endometrial cell in pigs. Journal of Reproduction and Fertility 48 (Suppl) 143–155.

Feng SM & Almond GW 1999 PGE receptor characteristics on porcine luteal cells during the estrous cycle and early pregnancy. Prostaglandins and Other Lipid Mediators 57 13–22.[CrossRef]

Gleeson AR, Thorburn GD & Cox RJ 1974 Prostaglandin F concentrations in the utero-ovarian venous plasma of the sow during the late luteal phase of the oestrous cycle. Prostaglandins 5 521–529.[CrossRef][Web of Science][Medline]

Guthrie HD & Bolt DJ 1983 Changes in plasma estrogen, luteinizing hormone, follicle stimulating hormone and 13,14-dihydro-15-keto-prostaglandin F₂ during blockade of luteolysis in pigs after human chorionic gonadotropin treatment. Journal of Animal Science 52 993–1000.

Hu J, Ludwig TE, Salli U, Stormshak F & Mirando MA 2001 Autocrine/paracrine action of oxytocin in pig endometrium. Biology of Reproduction 64 1682–1688.[Abstract/Free Full Text]

Hu J, Braileanu GT & Mirando MA 2003 Effect of ovarian steroids an basal and oxytocin-induced prostaglandin F₂ secretion from pig endometrial cells. Reproduction, Fertility and Development 15 197–205.[CrossRef][Medline]

Kankofer M & Wiercinski J 1999 Prostaglandin E₂ 9-keto reductase from bovine term placenta. Prostaglandins, Leukotrienes and Essential Fatty Acids 61 29–32.[CrossRef][Web of Science][Medline]

Kieborz KR, Silvia WJ & Edgerton LA 1991 Changes in uterine secretion of prostaglandin F₂ and luteal secretion of progesterone in response to oxytocin during the porcine estrous cycle. Biology of Reproduction 45 950–954.[Abstract]

Kotwica G, Franczak A, Okrasa S & Kotwica J 1999 Effect of an oxytocin antagonist on prostaglandin F₂ secretion and the course of luteolysis in sows. Acta Veterinaria Hungarica 47 249–262.[Web of Science][Medline]

Leiser R, Zimmerman W, Sidler X & Christen A 1988 Normal-zyklische Erscheinungen im Endometrium und am Ovar des Schweines. Tierärztliche Praxis 16 261–280.[Medline]

McCracken JA, Custer EA & Lamsa JC 1999 Luteolysis: a neuroendocrine-mediated event. Physiological Reviews 79 263–323.[Abstract/Free Full Text]

Moeljono MPE, Thatcher WW, Bazer FW, Frank M, Owens LJ & Wilcox CJ 1977 A study of prostaglandin F₂ as the luteolysin in swine. II. Characterization and comparison of prostaglandin F, estrogen and progestin concentration in utero-ovarian vein plasma of non-pregnant and pregnant gilts. Prostaglandins 14 543–555.[CrossRef][Web of Science][Medline]

Okrasa SO, Tilton JE & Weigl RM 1985 Utero-ovarian venous concentrations of prostaglandin E₂ (PGE₂) and prostaglandin F₂ (PGF₂) following PGE₂ intrauterine infusions. Prostaglandins 30 851–856.[CrossRef][Web of Science][Medline]

Parent J, Villeneuve C & Fortier MA 2003 Evaluation of the contribution of cyclooxygenase 1 and cyclooxygenase 2 to the production of PGE2 and PGF2 alpha in epithelial cells from bovine endometrium. Reproduction 126 539–547.[Abstract]

Parvizi N, Elsaesser F, Smidt D & Ellendorff F 1976 Plazma luteinizing hormone and progesterone in the adult female pig during the oestrous cycles, late pregnancy and lactation, and after ovariectomy and pentobarbitone treatment. Journal of Endocrinology 69 193–203.[Abstract/Free Full Text]

Schlegel W, Kruger S & Korte K 1984 Purification of prostaglandin E2-9-oxoreductase from human decidua vera. FEBS Letters 171 141–144.[CrossRef][Web of Science][Medline]

Skarzynski DJ & Okuda K 2000 Different actions of noradrenaline and nitric oxide on the output of prostaglandins and progesterone in cultured bovine luteal cells. Prostaglandins and Other Lipid Mediators 60 35–47.

Stepien A & Ziecik AJ 2002 Second messenger systems in the action of LH and oxytocin on porcine endometrial cells in vitro. Theriogenology 57 2217–2227.[CrossRef][Web of Science][Medline]

Stepien A, Shemesh M & Ziecik AJ 1999 Luteinizing hormone receptor kinetic and LH-induced prostaglandin production throughout the estrous cycle in porcine endometrium. Reproduction, Nutrition and Development 39 663–674.

Uenoyama Y, Hattori S-I, Miyake M & Okuda K 1997 Up-regulation of oxytocin receptors in porcine endometrium by adenosine 3' ,5'-monophosphate. Biology of Reproduction 57 723–728.[Abstract]

Uzumcu M, Braileanu GT, Carnahan KG, Ludwig TE & Mirando MA 1998 Oxytocin-stimulated phosphoinositide hydrolysis and prostaglandin F secretion by luminal epithelial, glandular epithelial and stromal cells from pig endometrium. I. Response of cyclic pig on day 16 postestrus. Biology of Reproduction 59 1259–1265.[Abstract/Free Full Text]

Uzumcu M, Carnahan KG, Braileanu GT & Mirando MA 2000 Oxytocin-stimulated phosphoinositide hydrolysis and prostaglandin F₂ secretion by luminal epithelial, glandular epithelial and stromal cells from pig endometrium. II. Responses of cyclic, pregnant and pseudopregnant pigs on Days 12 and 16 post oestrus. Reproduction, Fertility and Development 12 157–164.[CrossRef][Medline]

Van de Wiel DFM, Erkens J, Koops W, Elene V & van Landeghem AAJ 1981 Periestrous and midluteal time courses of circulating LH, FSH, prolactin, estradiol-17ß and progesterone in the domestic pigs. Biology of Reproduction 24 223–233.[Abstract]

Waclawik A, Rahman NA, Rivero-Muller A, Brokken LJS, Watanabe K, Blitek A & Ziecik AJ 2004 Novel functional characterization of expression of prostaglandin F₂ synthase (PGFS) and microsomal prostaglandin E₂ synthase (mPGES) in porcine oestrous cycle endometrium and in early pregnancy. Reproduction 31 13 (abstract O29).

Zhang Z, Paria BC & Davis DL 1991 Pig endometrial cells in primary culture: morphology, secretion of prostaglandins and proteins, and effects of pregnancy. Journal of Animal Science 69 3005–3015.[Abstract]

Ziecik AJ 2002 Old, new and the newest concepts of inhibition of luteolysis during early pregnancy in pig. Domestic Animal Endocrinology 23 265–275.[CrossRef][Web of Science][Medline]

Ziecik AJ, Stepien A & Gawronska B 2000 Importance of endometrial LH receptors in induction of luteolysis and maternal recognition of pregnancy in the pig. Reproduction in Domestic Animals 35 190–192.

Ziecik AJ, Bodek G, Ciereszko R, Stepien A & Kotwica G 2001 Involvement of gonadotropins in induction of luteolysis in pigs. Reproductive Biology 1 33–50.

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