Changes in equine endometrial oestrogen receptor alpha and progesterone receptor mRNAs during the oestrous cycle, early pregnancy and after treatment with exogenous steroids

Two experiments were performed to determine changes in the abundance of oestrogen and progesterone receptor (ER alpha and PR) mRNAs in equine endometrium during the oestrous cycle and early pregnancy, and under the influence of exogenous steroids. In Expt 1, endometrial biopsies were obtained from non-mated mares during oestrus and at days 5, 10 and 15 after ovulation, and from pregnant mares at days 10, 15 and 20 after ovulation. There were overall effects of day on the abundance of ER alpha (P = 0.0001) and PR (P = 0.0014) mRNAs. The amount of ER alpha mRNA decreased at day 10 of pregnancy, and PR mRNA was reduced at day 5 in non-mated mares and at day 15 of pregnancy, compared with oestrous values. Experiment 2 was conducted to determine the effects of exogenous steroids on endometrial ER alpha and PR mRNAs. Endometrial biopsies were obtained from 19 anoestrous mares that had been treated with vehicle, oestradiol, progesterone, or oestradiol followed by progesterone for either a short or a long duration. The steroid treatment affected the abundance of ER alpha mRNA (P = 0.0420), which was higher (P < 0.05) in the oestradiol group than in the group treated with oestradiol followed by long duration progesterone. The steroid treatment did not affect the abundance of PR mRNA. These results demonstrate that the amount of steroid receptor mRNA changes with the fluctuating steroid environment in the uterine endometrium of cyclic and early pregnant mares, and that the duration of progesterone dominance may affect ER alpha gene expression. In addition, factors other than steroids may regulate ER alpha and PR gene expression in equine uterine endometrium.     

Effect of administration of estradiol and progesterone,and bacterial contamination,on endometrial morphology of acyclic mares

Acyclic mares (free of uterine infection and with typical acyclic endometria on biopsy) received daily intramuscular injections in oil of either 1.5 mg estradiol benzoate (n - 4) or progesterone (n = 5). Estradiol and progesterone treatment induced biopsy changes consistent with estrus or diestrus respectively (Kenney, 1978). Subsequently, seven mares with typical acyclic endometria were given ten daily intra-uterine infusions of from 400 to 10 000 pg estradiol-17β. All mares developed Streptococcus zooepidemicus infections which masked any endometrial changes which might have been induced by estradiol infusion.     

Expression of progesterone receptor membrane component (PGRMC) 1 and 2, serpine mRNA binding protein 1 (SERBP1) and nuclear progesterone receptor (PGR) in the bovine endometrium during the estrous cycle and the first trimester of pregnancy

Progesterone (P4) is involved in the regulation of essential reproductive functions affecting the target cells through both nuclear progesterone receptors (PGRs) and membrane progesterone receptors. The aim of this study was to determine the mRNA and protein expression for PGRMC1, PGRMC2, SERBP1 and PGR within the bovine endometrium during the estrous cycle and the first trimester of pregnancy. There were no changes in PGRMC1 and PGRMC2 mRNA and protein expression during the estrous cycle, however, mRNA levels of PGRMC1 and PGRMC2 were increased (P < 0.001) in pregnant animals. SERBP1 mRNA expression was increased (P < 0.05), while the level of this protein was decreased (P < 0.05) on days 11–16 of the estrous cycle. The expression of PGR mRNA was higher (P < 0.01) on days 17–20 compared to days 6–10 and 11–16 of the estrous cycle and pregnancy. PGR-A and PGR-B protein levels were elevated on days 1–5 and 17–20 of the estrous cycle as compared to other stages of the cycle and during pregnancy. In conclusion, our results indicate that P4 may influence endometrial cells through both genomic and nongenomic way. This mechanism may contribute to the regulation of the estrous cycle and provide protection during pregnancy.     

Gene profiling of inflammatory genes in day 18 endometria from pregnant and non‐pregnant mares

Maternal recognition of pregnancy is a physiological process that primarily describes endometrial responses to a conceptus. Recognition of a conceptus prevents the release of prostaglandin F_2α, thereby ensuring survival of the corpus luteum and continued progesterone production. Exactly how this occurs in the mare is poorly understood. Because prostaglandin F_2α is a pro‐inflammatory hormone, we hypothesized that differential gene expression in the endometrium at the time of maternal recognition reflects an anti‐inflammatory event leading to decreased prostaglandin F_2α secretion. Mares were inseminated, and endometrial biopsies were recovered from pregnant mares on Day 18 post‐ovulation. In subsequent estrous cycles, mares were not inseminated and Day 18 post‐ovulation endometrial biopsies were collected (non‐pregnant control, matched per individual). Endometrial gene expression profiles were examined by screening an Affymetrix equine GeneChip containing probes specific for genes related to inflammatory processes. Microarray analysis revealed 118 genes that were up‐regulated and 93 genes that were down‐regulated (P < 0.001) at least 1.5‐fold in the endometrium of pregnant versus non‐pregnant mares. Quantitative, real‐time RT‐PCR confirmed the microarray results for three up‐regulated genes homologous to TSC22D3, PPAPDC2, and KLF6, and three down‐regulated genes homologous to ESR1, MARCKSL1, and EPSTI1 (P < 0.05). It is concluded that the presence of the equine embryo induces differential gene expression in the endometrium of Day 18 pregnant mares, and that these genes are associated with inflammatory processes and pathways involving cellular growth and proliferation. The results from this study provide important new insights into endometrial gene expression in response to early equine pregnancy. Mol. Reprod. Dev. 79: 777–784, 2012. © 2012 Wiley Periodicals, Inc.     

Progesterone and estrogen receptor distribution in the endometrium of the mare

An immunoperoxidase staining technique was used to localize receptors for progesterone and estrogen in the uterus of the mare. Specific staining for receptors was limited to cell nuclei. During estrus, stromal cells tended to stain more intensely for both receptor types than myometrial cells or luminal and glandular epithelial cells. During diestrus, staining intensities in stromal and myometrial cells tended to decrease. Staining intensities of epithelial cells were not affected by the cycle stage. Early pregnancy did not markedly affect the staining intensities of pregnant mares compared with the nonpregnant mares on Day 14 of diestrus. In mares susceptible to endometritis from which samples were taken during diestrus, stromal and myometrial staining for estrogen receptors was more intense than in endometrium from genitally-normal mares.     

Immunohistochemical localisation of progesterone and oestrogen receptors at the placental interface in mares during early pregnancy

Previous reports documenting progesterone receptors (PR) and oestrogen receptors (ER) in the endometrium of early pregnant mares included specimens only up to Day 20 post ovulation. This study aimed to localise PR and ERα on equine feto-maternal tissues between Days 20 and 68 to encompass the period around fixation of the conceptus, development of the endometrial cups and attachment and initial interdigitation of the allantochorion. During early pregnancy mares had the same pattern of PR in the endometrium as that reported for other mammals; namely, a loss of PR from the endometrial epithelia but continued localisation in stromal cells. The spatial arrangement of ERα over the same time period showed cytoplasmic staining of endometrial epithelia and in the nuclei of occasional stromal cells. In the fetal tissues, no cells had PR although ERα was evident in some tissue compartments. No major change in localisation of either receptor was noted throughout the time period examined despite important changes occurring at the placental interface. Nevertheless, these steroid receptor molecules probably play important roles in the production of histotroph and growth factors by the endometrium which go on to stimulate differentiation and growth of the feto-maternal tissues.     

Expression and localization of progesterone receptor membrane component 1 and 2 and serpine mRNA binding protein 1 in the bovine corpus luteum during the estrous cycle and the first trimester of pregnancy

The aim of this study was to evaluate the mRNA and protein expression and the localization of progesterone receptor membrane component 1 (PGRMC1), PGRMC2, and the PGRMC1 partner serpine mRNA binding protein 1 (SERBP1) in the bovine CL on Days 2 to 5, 6 to 10, 11 to 16, and 17 to 20 of the estrous cycle as well as during Weeks 3 to 5, 6 to 8, and 9 to 12 of pregnancy (n = 5–6 per each period). The highest levels of PGRMC1 and PGRMC2 mRNA expression were found on Days 6 to 16 (P < 0.05) and 11 to 16, respectively, of the estrous cycle and during pregnancy (P < 0.001). The level of PGRMC1 protein was the highest (P < 0.05) on Days 11 to 16 of the estrous cycle compared with the other stages of the estrous cycle and pregnancy, whereas PGRMC2 protein expression (P < 0.001) was the highest on Days 17 to 20 and also during pregnancy. The mRNA expression of SERBP1 was increased (P < 0.05) on Days 11 to 16, whereas the level of its protein product was decreased (P < 0.05) on Days 6 to 10 of the estrous cycle and was at its lowest (P < 0.001) on Days 17 to 20. In pregnant cows, the patterns of SERBP1 mRNA and protein expression remained constant and were comparable with those observed during the estrous cycle. Progesterone receptor membrane component 1 and PGRMC2 localized to both large and small luteal cells, whereas SERBP1 was observed mainly in small luteal cells and much less frequently in large luteal cells. All proteins were also localized in the endothelial cells of blood vessels. The data obtained indicate the variable expression of PGRMC1, PGRMC2, and SERBP1 mRNA and protein in the bovine CL and suggest that progesterone may regulate CL function via its membrane receptors during both the estrous cycle and pregnancy.     

Expression of progesterone and oestrogen receptors by early intrauterine equine conceptuses

Progesterone and oestrogen play essential roles in the maintenance of pregnancy in eutherian mammals and are thought to exert their effects on the developing conceptus indirectly, via the endometrium. In some species, early embryos have themselves been shown to express steroid receptors, thereby suggesting that reproductive steroids may also influence embryonic development directly. The aim of this study was to determine whether early intrauterine equine conceptuses express either the classical intracellular progesterone (PR) and oestrogen receptors (ERalpha and ERbeta) or the more recently characterised membrane-bound progesterone receptors (PGRMC1 and mPR). Horse conceptuses recovered on days 7, 10 and 14 after ovulation (n=8 at each stage) were examined for steroid receptor mRNA expression using quantitative rtPCR. Where commercial antibodies were available (PR, ERbeta), receptor localisation was examined immunohistochemically in day 10, 12, 14, 15 and 16 conceptuses (n=2 at each stage). mRNA for PR, PGRMC1 and mPR was detected at all stages examined, but while PGRMC1 and mPR expression increased during the day 7-14 period, PR expression decreased. ERalpha mRNA was not detected at any stage examined, whereas ERbeta mRNA was detected in all day 14, some day 10 and no day 7 conceptuses. Immunoreactive ERbeta receptors were localised to the trophectoderm of day 14-16 conceptuses; PR were not detected immunohistochemically in conceptus tissue. In summary, this study demonstrates that equine conceptuses express mRNA and, in the case of ERbeta, protein for steroid hormone receptors during the period encompassing rapid conceptus growth, differentiation and maternal pregnancy recognition.     

Factors controlling epidermal growth factor (EGF) gene expression in the endometrium of the mare

Previous studies showed a dramatic increase in EGF gene expression in the endometrial glands of pregnant mares around day 40 after ovulation. To investigate how the steroid hormones of pregnancy might regulate this expression, in situ hybridization was used to monitor the levels of EGF mRNA in endometrial biopsies obtained from seasonally anoestrous or ovariectomised mares given exogenous progesterone and oestrogen, alone or in combination, for up to 46 days. Biopsies were also taken from mares during the non‐pregnant cycle, during normal pregnancies and pregnancies compromised by endometrial pathology (endometrosis) or because of incompatible extraspecific embryo transfers (donkey‐in‐horse pregnancies). Only a few samples showed weak EGF expression during the late luteal phase of the oestrous cycle. During normal pregnancy, the previously observed dramatic increase of expression after day 40 of gestation was confirmed. Although aged mares suffering from endometrosis and mares carrying an extraspecific donkey conceptus showed the same increase of EGF mRNA in normal glands, this was virtually absent from gland cross‐sections compromised due to inflammatory or fibrotic changes. Administration of various doses and combinations of progesterone and oestrogen for <35 days yielded negative or only weakly positive hybridization results, whereas progesterone alone for ≥40 days upregulated EGF expression strongly irrespective of additional treatment with oestrogen. This is the first experimental evidence that EGF expression in the endometrium can be induced by progesterone alone. The requirement for prolonged progesterone priming is of considerable interest in the context of the unusually late stage of gestation at which placental attachment commences in equids. Mol. Reprod. Dev. 53:255–265, 1999. © 1999 Wiley‐Liss, Inc.     

Cell proliferation patterns during development of the equine placenta

Placentation involves considerable growth and reorganization of both maternal and fetal tissues. In this investigation, immunohistochemical localization of the proliferation marker Ki-67 antigen was used to monitor cell division during placentation in mares. Endometrial biopsies were obtained from eight mares between day 14 and day 26 of pregnancy and from eight anoestrous mares that had been treated with various combinations of progesterone and oestrogen. Samples of endometrium and fetal membranes were obtained from 19 mares carrying normal horse conceptuses between day 30 and day 250 of gestation and from three failing extraspecific donkey-in-horse pregnancies. Proliferation in the superficial strata of the endometrium was increased by day 18 of gestation and this effect could be mimicked by supplementing with oestradiol benzoate during the last 6 days of a prolonged period (18-36 days) of progesterone administration. Fetal chorionic girdle cells were proliferating vigorously at days 30-32 of gestation, but stopped dividing after they invaded the endometrium, while the trophoblast cells of the allantochorion showed an increase in mitotic activity after day 38. The luminal epithelium of the endometrium started to proliferate only after the primary villi of the true epitheliochorial placenta had been formed, and during days 58-70 this effect was seen only in the pregnant horn in which placentation was further advanced. During the second half of gestation, most of the mitotic activity was confined to the periphery of the microcotyledons which were still growing. In the donkey-in-horse pregnancies, proliferation rates of the maternal and fetal epithelial at day 70 of gestation were markedly reduced in areas of heavy endometrial lymphocyte infiltration and poor placentation. These results provide a basis for further studies on factors that influence invasive and non-invasive placentation.     

Prostaglandin H synthase Type 2 is differentially expressed in endometrium based on pregnancy status in pony mares and responds to oxytocin and conceptus secretions in explant culture

The equine embryo must signal its presence to the uterus for pregnancy to continue to term. Mobility of the conceptus throughout the uterus is crucial for its survival, and this action presumably permits the conceptus to transmit its antiluteolytic signal to the endometrium. Studies were completed to establish whether this unidentified antiluteolytic signal targets prostaglandin G/H synthase 2 (PGHS2), a rate limiting enzyme in converting arachidonic acid to prostaglandins (PGs). In the first study, quantitative RT-PCR was used to determine the relative abundance of PGHS2 mRNA in endometrium derived from estrous cyclic and pregnant mares on day 14 post-ovulation. PGHS2 mRNA abundance was substantially greater in endometrium from estrous cyclic mares. Additional studies were completed to better understand PGHS2 in equine endometrium. An estrogen and progesterone treatment regimen in ovariectomized mares was developed as a test model for detecting endometrial PGHS2 mRNA. Also, exposing endometrial explants to conceptus secretions (conditioned culture medium) decreased PGHS2 mRNA abundance whereas exposing explants to oxytocin increased PGHS2 mRNA abundance. Exposure to conceptus secretions also decreased PGF2α concentrations in explant-conditioned medium whereas oxytocin supplementation increased PGF2α concentrations in medium. These data support the hypothesis that PGHS2 is a target for the antiluteolytic signal produced by equine conceptuses during early pregnancy. Also, the endometrial explant culture system used for these studies can serve as a model for identifying and characterizing the maternal recognition of pregnancy factor in equids.     

Cell proliferation patterns in the equine endometrium throughout the non-pregnant reproductive cycle.

Immunohistochemical detection of the proliferation marker Ki-67 antigen was used to monitor mitotic activity in the endometrium of mares. The monoclonal antibody MIB1 was validated for use on equine tissues by demonstrating its reaction with activated peripheral blood lymphocytes, and endometrial biopsies were recovered from 26 non-pregnant mares at selected stages during the reproductive cycle. The proportion of positively stained nuclei was counted in five random areas on each histological section to determine the percentage and type of proliferating cells. Multiplication rates in the types of cell found in the superficial strata, comprising the luminal epithelium, the epithelium of the gland necks and the stromal cells of the stratum compactum, were greatest during oestrus, presumably under the influence of oestrogens secreted by the growing ovarian follicles. In contrast, the mitotic activity in the cells of the deeper secretory portions of the endometrial glands was restricted to a brief phase between day 3 and day 7 of dioestrus, most likely as a delayed response to the decreasing oestrogen concentrations after ovulation. Some of the degenerate glands in subfertile mares did not follow this pattern of increased epithelial proliferation at that stage. After day 7 of dioestrus, the proliferation rates of cells in the endometrium decreased to basal values and remained low for as long as progesterone concentrations remained evaluated, even during prolonged dioestrus. The technique enabled characterization of normal cell proliferation patterns in the endometrium of mares and it will be a useful tool in the future for monitoring the endometrial responses of reproductively healthy and subfertile mares.     

Estrogen and antagonist-induced changes in endometrial topography of immature and cycling rats

The topographical changes of the luminal surface of the endometrium of immature and ovariectomized rats treated with estrogen, antagonists to estrogen, and progesterone. and during various stages of the estrous cycle and in pregnancy were examined by scanning electron microscopy. Massive increases in numbers and length of endometrial cell microvilli were observed at estrus, after injection of estradiol-17beta, diethylstilbestrol, estrogen plus progesterone. or the inhibitor C1628 to immature and ovariectomized rats. Withdrawal of the estrogen stimulus results in diminution of microvilli, producing a state identical to diestrus, during pregnancy, and after injection of progesterone, The estrogen antagonist appears to have both estrogenic and progestogenic properties, stimulating endometrial cell hypertrophy, secretion of protein, and production of numerous apical microvilli.     

Reproductive function of mares given daily injections of prostaglandin F2alpha beginning at day 42 of pregnancy

Mares at Day 42 of pregnancy received daily intramuscular (i.m.) injection of 5 mg of prostaglandin F2alpha (PGF(2alpha)) until the beginning of the first (Group I, n = 3) or second estrous cycle (Group II, n = 2). All mares aborted 3 to 4 d after the first injection; they displayed estrus 2 to 6 d after this injection. As determined by palpation per rectum and serum progesterone levels, each estrus was accompanied by an ovulation. Endometrial cups did not regress after PGF(2alpha) treatment since serum samples from the mares contained pregnant mare serum gonadotropin (PMSG) for at least 30 d after first injection, as determined by mare immunopregnancy test. After the first estrus, two of three mares in Group I displayed a prolonged diestrus (> 25 d). In contrast, the first estrous cycle was short (8 to 12 d) for mares in Group II. Serum progesterone levels in the first 6 d postovulation were lower (P < 0.05) for Group II than for Group I, indicating that formation of the corpus luteum was impaired by daily injections of PGF(2). Results indicate that 1) daily injections of PGF(2alpha) can induce abortion in mares at Day 42 of pregnancy, 2) abortion is followed by estrus and ovulation, 3) the endometrial cups do not regress as a result of this treatment, and 4) daily injections of PGF(2) can impair early corpus luteum development.     

Epidermal growth factor, transforming growth factor-α, and epidermal growth factor receptor expression and localization in the canine endometrium during the estrous cycle and in bitches with pyometra

Gene expression and immunohistochemical localization of epidermal growth factor (EGF), transforming growth factor-α (TGF-α), and epidermal growth factor receptor (EGF-R) were compared between the endometrium of bitches (Canis familiaris) with pyometra accompanied by cystic endometrial hyperplasia (CEH) and that of healthy bitches at similar stages of the estrous cycle. In normal bitches, endometrial TGF-α mRNA levels were highest at proestrus and gradually decreased as the cycle progressed to anestrus. Epidermal growth factor receptor mRNA levels were not significantly affected by the stage of the estrous cycle. Epidermal growth factor mRNA levels were higher at Day 35 of diestrus than at other stages of the estrous cycle (P < 0.05). In bitches with pyometra, endometrial TGF-α and EGF-R mRNA levels did not differ significantly from those at diestrus in normal bitches, but EGF mRNA levels were lower than those at Day 35 of diestrus in normal bitches (P < 0.05). In normal bitches, positive immunohistochemical staining for TGF-α, EGF, and EGF-R was mainly present in the glandular and luminal epithelial cells of the endometrium. In contrast, in bitches with pyometra, immunoreactivity for EGF was clearly present in endometrial stromal cells. Inflammatory cells that had infiltrated the endometrial stroma stained strongly for TGF-α and EGF-R. Luminal and glandular epithelial cells also stained positive for EGF-R. In conclusion, expression of TGF-α by inflammatory cells and a low level of expression and differential localization of EGF may be involved in aberrant growth of endometrial glands and development of CEH.     

The effect of transcervical uterine manipulations on establishment of uterine infection in mares under the influence of progesterone

Four pony mares were used in a cross-over study to investigate the effect of different treatments on experimentally-induced endometritis. The mares were treated with progesterone to facilitate establishment of uterine infections. They received an intrauterine infusion of Streptococcus zooepidemicus 5 days after the start of progesterone therapy. Five days later, they were treated by intrauterine infusions of 2 g ampicillin in 50 ml sterile water or by sterile water without antibiotic for 3 consecutive days. Prior to infusion of Strep. zooepidemicus , no bacteria were cultured from the uteri of the mares. However, 5 days after infusion of Strep. zooepidemicus and prior to antibiotic therapy, mixed bacterial growths were cultured from endometrial swabbings. After antibiotic therapy, ampicillin-resistant organisms were cultured from endometrial swabbings. Two other progesterone-treated mares received an intrauterine infusion of sterile phosphate buffered saline instead of bacteria. Mixed bacterial cultures were recovered 5 days later from the endometrial swabbings of these mares. It was concluded that the high circulating concentrations of progesterone were probably responsible for the treatment failure and that in clinical situations, therapy involving transcervical manipulations should not be administered when mares are in diestrus.