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The regulation of estrogen and progesterone receptor (ER, PR) expression by estradiol (E2) and progesterone (P4) in the oviduct, uterus and cervix of female lambs was studied. The animals received three intramuscular injections of E2, P4 or vehicle with an interval of 24 h and they were slaugthered 24 h after the third injection. Determinations of ER and PR were performed by binding assays and mRNAs of ERα and PR by solution hybridization. High levels of ER and PR in both cervix and oviduct were found in the female lamb, differing from other mammalian species. No significant effects by either E2 or P4 treatment on ER and PR levels in the cervix and oviduct could be observed. E2 treatment increased the mRNA levels of ERa and PR more than 3-fold in the cervix, while P4 treatment increased the mRNA levels of ERa and PR in the uterus. The results show differential effects of gonadal steroids on sex steroid receptor expression along the reproductive tract in female lambs, suggesting that steroid target tissues can modulate responses to the same circulating levels of steroid hormones.

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Contents The aim of the study was to localize oxytocin receptors ( OTR) and measure mRNA expression of OTR in the canine uterus with and without the influence of progesterone. Uterine samples were taken from nine anoestrous and eight dioestrous bitches during ovariohysterectomy. Histological changes were evaluated in haematoxylin and eosin ( HE)-stained samples. Purified polyclonal antibody for OTR was used in immunohistochemistry to localize receptors in uterine layers. Relative mRNA concentration of OTR was evaluated with real-time PCR from full-thickness uterine samples taken from the middle horn and the body. Myometrial smooth muscle cells, endometrial luminal epithelium ( LE) and deep and superficial glandular epithelium were positively stained for oxytocin receptors in non-pregnant animals. No significant difference in staining intensity was detected between uterine middle horn and body. However, the staining intensity of LE was significantly higher in dioestrous than in anoestrous uteri ( p < .05). Leucocytes and endothelium of blood vessels were also positively stained for OTR. Real-time PCR showed no significant differences in OTR mRNA expression between the middle horn and the body of the uterus, or between anoestrous and dioestrous uterus. No correlation was noted between OTR mRNA expression and blood progesterone concentration. In conclusion, despite the apparent inactivity, the uterus of the non-pregnant bitch expresses OTR. The distribution or relative expression of OTR does not differ between uterine horn and body in dioestrus or anoestrus except in LE. LE may have more oxytocin-dependent activity during dioestrus than anoestrus. [ABSTRACT FROM AUTHOR]

Contents [ABSTRACT FROM AUTHOR]

Objectives To analyze the expression of the androgen receptor(AR) and syndecan-1 in breast tissue during long-term hormonal treatment in cynomolgus monkeys. Methods Sixty oophorectomized macaques were randomized to receive either tibolone, conjugated equine estrogens (CEE), CEE + medroxyprogesterone acetate (MPA) or no hormonal treatment. Breast tissue was collected at necropsy after 2 years and stained for AR and syndecan-1. Results Apparent differences were seen between treatment groups as compared to untreated animals. AR expression was markedly increased by tibolone and suppressed by combined CEE/MPA. Both treatments increased syndecan-1 in stromal tissue, whereas CEE alone had no significant effect. Conclusions We found alternative regimens for hormonal therapy to differ in their influence on two markers of importance for the development of breast cancer. The results may be relevant for the ongoing clinical discussion on the long-term safety of different hormonal treatments. [ABSTRACT FROM AUTHOR]

Objective: To analyze the expression of Syndecan-1 in dense and non-dense human breast tissue. Methods: Specimens of histologically normal tissue were obtained from postmenopausal women undergoing surgery for breast cancer. Each tissue block was subject to radiological examination and pair-wise samples of dense and non-dense tissue were collected. Semi-quantitative assessment of immunohistochemical staining intensity for Syndecan-1 and estrogen receptor subtypes was performed. Results: The expression of Syndecan-1 in all tissue compartments was significantly higher in dense than in non-dense specimens. The strongest staining was recorded in stromal tissue. There was a strong correlation between epithelial estrogen receptor alpha and stromal cell Syndecan-1 expression in dense tissue (rs = 0.7; p = 0.02). This association was absent in non-dense tissue. Conclusion: An increase of Syndecan-1 in all tissue compartments and a redistribution from epithelium to stroma may be a characteristic feature for dense breast tissue. [ABSTRACT FROM AUTHOR]

Female sex steroids are implied in breast cancer development. The estrogen (ER) and progesterone (PR) receptor subtypes may have different roles to modulate the cellular response. Paired samples of cancer and adjacent normal tissue were collected from postmenopausal women at surgery for ductal breast cancer. The expression of ERa, ERss, PRA and PRB was quantified by immunostaining and digitized image analysis. We found ERss to be significantly reduced in breast cancer tissue (35% vs 50%; p=0.001) and there was also a decrease of the ERss/ERa ratio. Among women using hormones at the time of diagnosis tumor tissue showed higher values for both PRB and PRA, as compared to women without such treatment. The results extend previous animal data to be valid also in women. There is evidence that loss of ERss expression may relate to estrogen dependent tumor progression. Increased PR expression could possibly relate to breast cancer risk during combined estrogen/progestogen treatment. [ABSTRACT FROM AUTHOR]

The concept of a blockade of progesterone during human pregnancy and withdrawal of this blockade at parturition remains controversial There is no sharp fall in serum progesterone before parturition, but treatment with an antiprogestin is successful for labor induction at term pregnancy. The human progesterone receptor (PR) exists in two isoforms (PR-A and PR-B), mediating different biological responses. Here, the hypothesis of a progesterone withdrawal at parturition in terms of a change in PR isoforms was tested. Cervical biopsies were obtained at term before the onset of labor, immediately after parturition and from non-pregnant women. Solution hybridization showed a tendency for the PR mRNA level to be decreased at parturition. Immunohistochemistry displayed decreased PR(A+B) and PR-B levels (p < 0.05) immediately after parturition. The relative importance of PR-A seemed higher immediately after parturition as compared to its importance in non-pregnant and term pregnant women. Our results are consistent with the concept of a functional progesterone blockade at the receptor level at term pregnancy, and withdrawal of this blockade at parturition. These observations may have important clinical and therapeutic implications. [ABSTRACT FROM AUTHOR]

Examines the presence of glutaredoxin mRNA in the human cervix and its expression during cervical remodelling in term pregnancy and immediately post-partum as compared to non-pregnant state. Glutaredoxin mRNA expression in the human cervix; Level of cervical glutaredoxin mRNA on prostaglandin-treated women vis-a-vis spontaneous ripening and delivery; Involvement of glutaredoxin in the regulation of cervical ripening.

Thioredoxin is a small multifunctional protein which acts as a dithiol hydrogen donor for ribonucleotide reductase in DNA synthesis. Thioredoxin participates in the regulation of different metabolic processes, such as changes in the activity of different enzymes, receptors or transcription factors. The aim of the present study was to determine possible differences in the expression of thioredoxin between myometrium and fibroids in women during different periods of life. Thioredoxin mRNA concentrations were determined in myometrial and fibroid tissues obtained from women during the menstrual cycle, during treatment with an analogue of gonadotrophin releasing hormone (GnRH agonist), in the postmenopausal period (PMP) and during pregnancy. The concentration of thioredoxin mRNA was measured by a solution hybridization method. The localization of thioredoxin protein was examined by immunohistochemistry. There were significantly lower levels of thioredoxin expression in both fibroids and myometrium from GnRH agonist treated and PMP women in comparison with the pregnant women. No difference in thioredoxin expression was found between myometrium and fibroids from the same woman or between myometria from uteri with or without fibroids in the same patient group. Thioredoxin expression in uterine fibroids does not seem to be up-regulated, but changes in response to the endocrine conditions in a similar way to that observed in the myometrium. [ABSTRACT FROM AUTHOR]

The acute effects of oestradiol-17 β on the expression of the oestrogen receptor (ER) and insulinlike growth factor I (IGF-I) in the endometrium of ovariectomized pigs were examined. The steroid receptor level was assayed by hormone binding techniques and specific mRNAs analyzed by solution hybridization using 35S-labelled RNA probes complementary to the ligand-binding domain of the ER receptor gene and a 160bp Panl-Pvul fragment of the IGF-I gene. One hour after a single injection of oestradiol (1 μg/kg BW), the nuclear oestrogen receptor (ERn) mean level was increased 3-fold whereas the ER mRNA content had not changed significantly. After 3 hours the ERn mean concentration was still high; the mean ER mRNA level had decreased by 15% and the mean IGF-I mRNA had increased 3-fold above that in the samples collected prior to treatment from these ovariectomized animals. Six hours after the injection the ERn content had returned to the basal level and stayed there during the following six hours. The ER mRNA concentration continued to decline, reached its lowest value after six hours and had increased slightly by twelve hours. The IGF-I mRNA level increased steadily during the course of the experiment. At twelve hours after the injection it had increased 3-fold. From these data we conclude that in the pig uterus oestradiol down-regulates its own receptor and acts as a potent stimulator of endometrial growth by inducing IGF-I expression. [ABSTRACT FROM AUTHOR]

Abstract Background Prostaglandins are important for female reproduction. Prostaglandin-E2 acts via four different receptor subtypes, EP1, EP2, EP3 and EP4 whereas prostaglandin-F2alpha acts through FP. The functions of prostaglandins depend on the expression of their receptors in different uterine cell types. Our aim was to investigate the expression of EPs and FP in rat uterus and to identify the regulation by estradiol, progesterone and estrogen receptor (ER) selective agonists. Methods We performed four different rat experiments involving treatments with estradiol, progesterone and ER agonists. Real-time PCR and immunohistochemistry were employed to evaluate receptor expression. Results Our results showed that all mRNAs and proteins of EPs and FP are expressed in the rat uterus. The expression pattern and intensity of immunostaining vary between different cell types and treatments. The mRNA expression of all EPs and FP are downregulated by estradiol and the ERalpha specific agonist PPT, whereas the ERbeta specific agonist DPN downregulates only EP2 and EP4. The protein expression however, showed an increase in EP2 and EP3 after estradiol treatment. When treated with estradiol and progesterone in combination, the expressions of EP1 and EP3 are upregulated. Conclusions Regulation of EPs and FP expression by estradiol appears to be mainly modulated via ERalpha for EP1, EP3 and FP, while EP2 and EP4 also are affected by the ERbeta selective ligand. Our immunohistochemical data shows a cell specific regulation of prostaglandin receptors under the influence of ovarian steroids, where EP2 is estrogen regulated in all uterine tissues examined. EP1 and EP3 are upregulated by the combination of estradiol and progesterone. Thus, our observations indicate that estradiol and progesterone regulate the mRNA and protein expression of EPs and FP in a receptor and tissue specific way.

Abstract Treatment with prostaglandin(PG)-E2 is clinically efficient for cervical priming. The aim of this study was to evaluate the impact of PG-E2 on the expression of the progesterone (PR), androgen (AR) and glucocorticoid (GR) receptors in human uterine cervix in prolonged pregnancy. The study groups were postterm nulliparous women with unripe cervices undergoing cervical priming with PG-E2 before labor induction. Responders (n = 12) who delivered vaginally were compared with non-responders (n = 10), who underwent cesarean section due to failure to progress to the active phase of labor. Controls (n = 18) with vaginal partus at a normal gestational age served as a reference group. Cervical levels of PR-A and PR- B isoforms, AR and GR, serum levels of their ligands and sex hormone-binding globulin (SHBG) were quantified. The responder group displayed lower total PR-AB and AR protein levels as compared to non-responders, and lower PR-B and AR protein levels as compared to controls. In addition, the PR mRNA level was lower in responders as compared to non-responders. The GR protein level did not differ between the groups. We conclude that successful PG-E2 priming was followed by a progesterone and androgen withdrawal at the receptor level in the uterine cervix.

Abstract Background Prolonged pregnancies are associated with increased rate of maternal and fetal complications. Post term women could be divided into at least two subgroups, one where parturition is possible to induce by prostaglandins and one where it is not. Our aim was to study parameters in cervical biopsies in women with spontaneous delivery at term (controls) and compare to those that are successfully induced post term (responders), and those that are not induced (non-responders), by local prostaglandin treatment. Methods Stromal parameters examined in this study were the accumulation of leukocytes (CD45, CD68), mRNAs and/or proteins for the extracellular matrix degrading enzymes (matrix metalloproteinase (MMP)-2, MMP-8 and MMP-9), their inhibitors (tissue inhibitor of MMP (TIMP)-1 and TIMP-2), interleukin-8 (IL-8), the platelet activating factor-receptor (PAF-R), syndecan-1 and estrogen binding receptors (estrogen receptor (ER)α, ERβ and G-coupled protein receptor (GPR) 30) as well as the proliferation marker Ki-67. Results The influx of leukocytes as assessed by CD45 was strongest in the responders, thereafter in the controls and significantly lower in the non-responders. IL-8, PAF-R and MMP-9, all predominantly expressed in leukocytes, showed significantly reduced immunostaining in the group of non-responders, while ERα and GPR30 were more abundant in the non-responders, as compared to the controls. Conclusion The impaired leukocyte influx, as reflected by the reduced number of CD45 positive cells as well as decreased immunostaining of IL-8, PAF-R and MMP-9 in the non-responders, could be one explanation of the failed ripening of the cervix in post term women. If the decreased leukocyte influx is a primary explanation to absent ripening or secondary, as a result of other factors, is yet to be established.

Abstract Background Estradiol (E2) and progesterone (P) are well known regulators of progesterone receptor (PR) expression in the rat uterus. However, it is not known which receptor subtypes are involved. Little knowledge exist about possible differences in PR regulation through ERalpha or ERbeta, and whether the PR subtypes are differently regulated depending on ER type bound. Thus, in the present study PR immunostaining has been examined in uteri of ovariectomized (ovx) rats after different treatments of estrogen and P, in comparison with that in immature, cycling, and pregnant animals. Methods The uteri were collected from 1) ovx rats treated with E2 and/or P; 2) immature rats, intact cycling rats and animals pregnant day 8 and 18; 3) ovx rats treated with E2 or an estrogen receptor (ER)alpha agonist or an ERbeta agonist. Two antibodies were used, one detecting PRA+B and another one specific for PRB. Real-time PCR was used to determine mRNA levels for PRAB and PRB in experiment 3. Results In stroma and myometrium faint staining was detected in ovx controls (OvxC), whereas E2 treatment resulted in strong staining. In contrast to this, in luminal epithelium (LE) the staining was strong in the OvxC group, whereas E2 treatment during the last 24 hrs before sacrifice caused a decrease. Similar to OvxC the LE of the immature animals was strongly stained. In the pregnant rats LE was negative, well in agreement with the results seen after E2 treatment. In the pregnant animals the stroma and decidua was strongly stained for PRAB, but only faint for PRB, indicating that PRA is the most expressed isoform in this state. The increase in stromal and myometrial immunostaining after E2 treatment was also found after treatment with the ERalpha agonist PPT. The ERbeta agonist DPN caused a decrease of the PR mRNA levels, which was also found for PRAB and PRB immunostaining in the GE. Conclusion Stromal and myometrial PRAB levels are increased via ERalpha, as shown by treatment with E2 and the ERalpha agonist PPT, while the levels in LE are decreased. The uterine stroma of pregnant rats strongly expressed PRAB, but very little PRB, which is different to E2 treated ovx animals where both PRAB and PRB are strongly expressed. The ERbeta agonist DPN decreased the mRNA levels of PRAB and PRB, as well as the PRAB protein level in GE. These results suggest that ERbeta signals mainly down-regulate PR levels in the epithelial cells. ERalpha, on the other hand, up-regulates PR levels in the stroma and myometrium while it decreased them in LE. Thus, the effects from E2 and PPT on the mRNA levels, as determined by PCR, could be annihilated since they are increased and decreased depending on cell type. The distribution and amount of PR isoforms strongly depend on the hormonal milieu and cell type within the rat uterus.

Abstract Insulin-like growth factor-I (IGF-I) and thioredoxin are regulated by gonadal steroids in the female reproductive tract of many species. Oestradiol regulates IGF-I and thioredoxin mRNA levels in the reproductive tract of prepubertal lambs. The physiological status (different endocrine environment) may affect the sensitivity of the reproductive tract to oestradiol and progesterone. We studied the effects of different endocrine milieus (late-follicular and luteal phases of the oestrous cycle, and ovariectomy before or after puberty) on the expression of IGF-I, thioredoxin, oestrogen receptor α (ERα) and progesterone receptor (PR) in sheep. The mRNA levels were determined by a solution hybridisation technique. In the uterus the levels of ERα, PR and thioredoxin mRNA were higher in the late-follicular phase group than in the other three groups, and IGF-I mRNA was high during both the late-follicular and the luteal phases. In the cervix only PR mRNA was significantly higher in the ewes in the late-follicular phase than in the other groups. In the oviducts the levels of thioredoxin and ERα mRNA were highest in the ovariectomised adult ewes, and thioredoxin mRNA was higher than the levels found in the ewes in the late-follicular phase. The IGF-I mRNA levels in the oviduct did not differ between any of the groups. The transcripts of IGF-I, thioredoxin, ERα and PR, varied according to the physiological status and also along the female reproductive tract, suggesting that the regulation of the mRNA levels of these factors by the steroid environment is tissue specific. Koncentrationen av insulin-like growth factor-I (IGF-I) och thioredoxin regleras hos många arter i honors reproduktionsorgan av könssteroider. Sålunda reglerar östradiol IGF-I och thioredoxin mRNA i reproduktionsorganen hos prepubertala lamm. Djurets fysiologiska status (dvs den endokrina miljön) kan påverka känsligheten hos reproduktionsorganen för östradiol och progesteron. Vi studerade effekterna av olika endokrina miljöer (sen follikelfas och lutealfas i östruscykeln, samt ovariektomi före och efter puberteten) på uttrycket av IGF-I, thioredoxin, östrogenreceptor α (ERα) och progesteronreceptorn (PR) hos får. Lösningshybridisering användes för att bestämma mRNA nivåerna. I livmodern var mRNA koncentrationen för ERα, PR och thioredoxin högre i sen follikelfas än i de andra tre grupperna och IGF-I mRNA nivån var hög både under sen follikelfas och i lutealfas. PR mRNA i cervix var signifikant högre hos tackorna under sen follikelfas än i de andra grupperna. I äggledarna var mRNA nivåerna av thioredoxin och ERα högst i de djur som ovariektomerats som vuxna, och thioredoxin mRNA var högre än hos tackorna under sen follikelfas. Det förelåg ingen skillnad vad gäller IGF-I mRNA nivåerna i äggledaren mellan någon av grupperna. IGF-I, thioredoxin, ERα och PR mRNA nivåerna varierade beroende på fysiologisk status och morfologisk lokalisation i reproduktionsorganen. Detta tyder på att steroidhormonernas reglering av dessa faktorers mRNA uttryck också är vävnadsspecifik.

Abstract Background Cervical ripening is an inflammatory reaction. The glucocorticoid receptor (GR) mediates glucocorticoid anti-inflammatory reactions, whereas nuclear factor (NF)kappaB is a key pro-inflammatory transcription factor. Prostaglandins as well as platelet activating factor (PAF) are inflammatory mediators. Inducible nitric oxide synthase (iNOS) regulates the level of nitric oxide (NO) in response to various inflammatory stimuli. We hypothesize that a changed biological response to glucocorticoids could be a mechanism regulating the inflammatory events resulting in cervical ripening. Methods We monitored GR and NFkappaB, prostaglandin synthases cyclooxygenase (COX)-1 and -2, iNOS, as well as the PAF-receptor (PAF-R) in the uterine cervix from term pregnant women (with unripe cervices) before the onset of labor (TP), immediately after parturition (PP), as compared to non-pregnant (NP), using immunohistochemistry and RT-PCR. Results The GR protein was detected by immunohistochemistry in the nuclei of stroma and squamous epithelium (SQ). Stromal GR staining was increased in TP as compared to the NP group and decreased again after parturition. GR staining in SQ was decreased after parturition as compared to term. NFkappaB was present in SQ and glandular epithelium (GE), stroma and vascular endothelium. Increased nuclear NFkappaB staining was observed postpartum as compared to term pregnancy in stroma and GE. Stromal immunostaining for COX-1 as well as COX-2 was increased in the TP and PP groups as compared to the NP, and GE displayed an intensely increased COX-2 immunostaining at term and postpartum. Stromal PAF-R immunostaining was highest at term, while it was greatly increased in GE postpartum. No difference in the immunostaining for iNOS was found between the groups. RT-PCR showed a predominance of GRalpha to GRbeta mRNA in cervical tissue. The COX-2 mRNA level was increased in the PP group as compared to the TP group. Conclusions There is a decrease in GR levels in human cervix at parturition. Concomitantly there is an increase of factors such as NFkappaB, PAF-R, COX-1 and COX-2, suggesting that they may participate in the sequence of events leading to the final cervical ripening.

Abstract Background Selective estrogen receptor modulators (SERMs) have been developed in order to create means to control estrogenic effects on different tissues. A major drawback in treatment of estrogen receptor (ER) positive breast cancer with the antagonist tamoxifen (TAM) is its agonistic effect in the endometrium. Raloxifene (RAL) is the next generation of SERMs where the agonistic effect on the endometrium has been reduced. Methods The aim of the present study was to determine the effect of SERM treatment on the uterus, as assessed by proliferation markers and several factors involved in uterine growth. Ovariectomized (ovx) rats were treated with estradiol (E2), tamoxifen (TAM), RAL, ICI182780 (ICI) or vehicle (OVX-controls). We studied the effects on mRNA levels of the growth hormone (GH) receptor, insulin-like growth factor-I (IGF-I), ERα and ERβ. In addition, by immunohistochemistry the proliferation markers PCNA and Ki-67, as well as ERα and ERβ, were detected. Results The uterine weight of the rats treated with E2 or TAM was increased as compared to OVX-controls. The uterine GH-receptor mRNA level was highest in the E2 treated animals. In ICI treated rats no GH-receptor mRNA could be detected. The IGF-I mRNA level increased 16-fold in uteri of the TAM treated group and 9-fold in the E2 treated rats as compared to OVX-controls. The ERα mRNA level was increased in the E2 treated rats, while the ERβ mRNA level was increased after TAM treatment. The proliferation, as assessed by PCNA, was lowest in ICI treated animals. Conclusions The uterine wet weight, the LE height and the GH-receptor mRNA levels showed similar patterns, indicating that GH is involved in the regulation of uterine weight. Tamoxifen, which has been related to increased incidence of endometrial carcinoma in women, dramatically increased IGF-I mRNA levels in rat uterus. Since proliferation was not higher in TAM and E2 treated rats than in OVX controls, this assay of simple, early proliferation does not give the full explanation of why TAM should enhance the risk of developing endometrial cancer.

Abstract The progesterone receptor (PR) and androgen receptor (AR) belong to the nuclear receptor superfamily. Two isoforms of PR (A and B) have been identified with different functions. The expression of AR, each isoform of PR and their involvement in long-term effects on the endometrium after hormonal replacement therapy (HRT) or tamoxifen (TAM) treatment is not known. The aims of this study were to determine PR(A+B), PRB and AR distribution by immunohistochemistry in the macaque (Macaca fascicularis) endometrium. Ovariectomized (OVX) animals were orally treated continuously for 35 months with either conjugated equine estrogens (CEE); medroxyprogesterone acetate (MPA); the combination of CEE/MPA; or TAM. Treatment with CEE/MPA tended to down-regulate PR in the superficial glands, but increased it in the stroma. TAM treatment increased both the PR and PRB levels in the stroma. Overall, less than 20% of the cells were positive for the PRB isoform and less variation was observed after steroid treatment. AR was found in the stroma, mainly distributed in the basal layer of the endometrium in the OVX and steroid treated groups, but was absent in the TAM treated group. No AR was found in the glandular epithelium. The present data show that long-term hormone treatment affects the PR level, and also the ratio between PRA and PRB in the endometrium.

Estrogen receptors have earlier been shown in the normal mouse, rat and human inner ear. If estrogens are important in normal hearing and development of presbyacusis in the normal population is not known. However it is known that patients with Turner syndrome, where a lack of estrogens is one of the main characteristics, commonly develop an early presbyacusis. A ‘Turner mouse’ has been developed, as a model for the ear problems in Turner syndrome, and it shows otitis media and a premature aging of the hearing. Estrogen receptors exist in an α and a β form. In this study inner ear tissue, from the Turner mouse and an estrogen receptor β knockout mouse (βERKO), was investigated regarding estrogen receptor α and β using immunohistochemistry. Results show that the Turner mouse has the same pattern of inner ear labeling, both concerning the estrogen receptor α and β, as that of a normal CBA/Ca mouse, with positive staining in the organ of Corti and spiral ganglion. The βERKO mice show close to normal inner ear morphology and positive estrogen receptor α immunostaining at the same locations as the CBA/Ca mouse. [Copyright &y& Elsevier]

Abstract: The aim of the present study was to investigate differences in the expression of mRNAs for ERα, ERβ and PR in the sow uterus at different stages of the estrous cycle as well as in inseminated sows at estrus and during early pregnancy by use of solution hybridization and in relation to plasma levels of estradiol and progesterone. Uterine samples were collected at different stages of the estrous cycle and after insemination/early pregnancy. In the endometrium, the expression of ERα mRNA and PR mRNA was similar for cyclic and early pregnant groups. Both were highest at early diestrus/70h after ovulation and ERα mRNA was lowest at late diestrus/d 19 while PR mRNA was lowest at diestrus and late diestrus/d 11 and d 19. The expression of endometrial ERβ was constantly low during the estrous cycle but higher expression was found in inseminated/early pregnant sows at estrus and 70h after ovulation. In the myometrium, high expression of ERα mRNA and PR mRNA was observed at proestrus and estrus in cyclic sows and at estrus in newly inseminated sows. Higher expression of myometrial ERβ mRNA was found in inseminated/early pregnant sows compared with cyclic sows, although significant only at estrus. In conclusion, the expression of mRNAs for ERα, ERβ and PR in the sow uterus differed between endometrium and myometrium as well as with stages of the estrous cycle and early pregnancy. In addition to plasma steroid levels, the differences between cyclic and inseminated/early pregnant sows suggest that other factors, e.g. insemination and/or the presence of embryos, influence the expression of these steroid receptor mRNAs in the sow uterus. [Copyright &y& Elsevier]