Hormone-dependent changes in A and B forms of progesterone receptor

The influence of different estrogen and/or progesterone treatments on concentrations of A and B forms of progesterone receptor (PR-A and PR-B) in the different cell types of chick oviduct was studied. A semiquantitative immunohistochemical assay for cellular PR concentrations was developed using a computer-assisted image analysis system. The staining intensity of nuclear PR in the basal layer of epithelial cells, glandular, smooth muscle and mesothelial cells was analysed separately using two monoclonal antibodies, PR6 and PR22. The measured concentrations of PR varied between different cell types and from cell to cell. A significant decrease in PR concentration, as noted by a decrease in staining intensity, was observed in all cell types studied 2 or 6 h after a single injection of progesterone with or without simultaneous estrogen administration. The decrease was also verified with immunoblotting and an immunoenzymometric assay (IEMA) for chicken PR. After down-regulation the concentration of PR recovered to the control level within 48 h after progesterone or estrogen administration. Estrogen administration alone was observed to cause changes in the concentration of PR-A only, having little or no effect on PR-B concentration depending on the cell type studied.

These findings indicate that estrogen and progesterone cause cell-specific changes not only to the total concentration of PR but also to the cellular ratio of PR-A and PR-B.     

Immunoelectron microscopic localization of progesterone receptor in the chick oviduct

A peroxidase-anti-peroxidase (PAP) method using polyclonal anti-PR antibodies was used to localize progesterone receptor (PR) electron microscopically in the chick oviduct. The immunoreaction precipitate indicating PR was localized inside the nuclei of epithelial, glandular and stromal cells. In the estrogen withdrawn oviduct cytoplasmic immunoreaction precipitate was not seen. Inside the nucleus unoccupied PR was localized mainly like the heterochromatin. As visualized by the PAP technique, the localization of PR was not systematically changed after progesterone administration. In conclusion, we suggest that progesterone receptor in the chick oviduct is an intranuclear protein.     

Cell-specific localization of progesterone receptors in the bovine ovary at different stages of the oestrous cycle

This immunohistochemical study describes the localization of progesterone receptors (PR) in the bovine ovary of 23 cows at different stages of the oestrous cycle. In primordial, primary and secondary follicles the score for PR in the follicle cells increased progressively with the maturation of the follicle. In vital tertiary follicles and cystic atretic follicles a moderate score for PR was found, while in obliterative atretic follicles the score was much lower. Scores were high in corpora hemorrhagica, low in corpora lutea and still lower in corpora albicantia. Low PR scores were also found in the tunica albuginea and surface epithelium. Cyclic variations of PR immunoreactivity were manifest in most ovarian tissues. Follicular scores for PR were high in oestrus and decreased during the following stages, whereas scores in corpora lutea cells varied according to a characteristic pattern with high levels during oestrus and metoestrus. The variations in the scores for PR in the different ovarian cell types suggest a cell-specific and cycle-dependent influence of progesterone. A negative correlation was found between the PR scores and the plasma progesterone concentration.     

一种新的荧光孕酮探测鸡输卵管孕酮受体

我们用化学合成的方法,制备了6S(α-氨基丙酸)-异硫氰酸荧光素-孕酮(简称:6NHPF),对鸡的输卵管孕激素受体(PR)进行了观察。发现PR存在于腔上皮细胞核,在平滑肌肌细胞及输卵管近泄殖腔端不存在PR。在输卵管相邻的组织切片上用孕酮或6NHPF的中间体化合物抑制剂,发现对合成的荧光孕酮都能够竞争性抑制,证实了这种新的,亲水性的小分子荧光孕酮能与PR特异性地结合。     

Different immunoelectron microscopic locations of progesterone receptor and HSP90 in chick oviduct epithelial cells.

The intracellular locations of the components of the heterooligomeric progesterone receptor (PR), heat-shock protein (hsp90), and the ligand-binding component were studied by immunoelectron microscopy in the chick oviduct, using immunogold double labeling and peroxidase techniques with monoclonal antibodies (MAb) against hsp90 (7D alpha and 4F3) and against PR (PR6 and PR13). PR was located in the nuclei of epithelial cells independently of the presence or absence of ligand. Cells with apically located nuclei were often PR negative. Ten minutes after progesterone administration no apparent change was seen in PR immunoreactivity, but chromatin underwent extensive rearrangement and PR was seen at the margins of the hetero- and euchromatin. The nucleoli did not contain PR. Hsp90 was located in the cytoplasm as aggregates, often inside small vesicles. In the apical part of the cell, hsp90 was located at the Golgi complex. The nuclei contained no detectable amounts of hsp90 except for that in the nucleoli. Ten minutes after progesterone administration the location or immunoreactivity of hsp90 did not alter. Thus, there seems to be a clear difference in the intracellular distribution of PR and hsp90. The epithelium also exhibited some cells with high levels of hsp90 and no or low levels of PR. These results raise the question of whether PR is associated with hsp90 in intact cells.     

Sexual maturation-associated and estrogen-induced progesterone receptor expression in the bursa of Fabricius

The expression of the progesterone receptor (PR) was studied in the chicken bursa of Fabricius (BF) in both sexes from the time of hatching until the bursal involution. Steroid binding studies, immunohistochemistry, and autoradiography were used to characterize and localize the receptor. Three different polyclonal antibodies (IgG-RB, IgG-G3, and IgG-RB2) directed against the chick oviduct progesterone receptor were used for the studies. With immunohistochemistry, no receptor-positive cells were detected in the bursae of young chicks. The first receptor-positive cells were occasionally seen at the age of 10 wk in the frozen sections, not in the paraffin sections. In older female chicks, the staining became more abundant. In males, the PR was expressed only after estradiol treatment. The staining was located in the nuclei of the subepithelial and the interfollicular cells, which were probably mesenchymal in origin. The bursal epithelium and the lymphocytes were not stained. By using a combined technique of autoradiography and immunohistochemistry, we were able to demonstrate that the same cells also concentrated tritiated ORG 2058 (a specific synthetic progestin) in their nuclei. In steroid binding studies with tritiated ORG 2058, the receptor concentration after the age of 10 wk was 50 to 120 fmol/mg protein. Low-level ORG 2058 binding was also detected in young chicks of both sexes before the age of 10 wk. The progestin-binding molecule resembled the progesterone receptor of the chick oviduct in molecular size (studied with HPLC) and binding properties. The PR expression in the BF was preceded by the expression of PR in the oviduct stromal cells and by an increase in oviduct epithelial proliferation, indicating the BF is affected by factors associated with sexual maturation. It is concluded that the subepithelial and the interfollicular stromal cells in the BF, but not the epithelial or follicular cells, are estradiol-sensitive in both sexes immediately after hatching. The endogenous estrogens, however, are not able to induce PR until after the onset of sexual maturation, and only in females. This implies that estrogen and progesterone may affect the structural organization of the BF through the stromal cells, but probably not before the onset of puberty.     

Augmentation of progesterone receptor concentration by progesterone and estrogen treatments in the chick oviduct

Cytosol receptors for progesterone in the chick oviduct were measured by charcoal-adsorbtion assay by using ORG 2058 as a ligand after long-term administration of progesterone and diethylstilbestrol (DES). Steroid administration was carried out by using daily injections or silastic capsules. DES treatment increased the progesterone receptor concentration (from 11500 to 21500 sites per cell, day 14). Progesterone also augmented the concentration of its own receptors (from 11500 to 29000 sites per cell, day 14). In the experiments with capsule administration the same trend was seen. This indicates that both diethylstilbestrol and progesterone are able to increase the concentration of progesterone specific cytosol receptors in the non-differentiated chick oviduct.     

Sex-steroid-sensitive stromal cells and oviduct differentiation

The chick oviduct differentiates during sexual maturation before the age of 20 weeks. In the present work we used immunohistochemistry to study sexual maturation associated progesterone receptor (PR) expression in the chick oviduct as an indication of progesterone sensitivity. Since the PR is estrogen inducible protein, its expression also reflects the effects of endogenous estrogens. Thus PR expression can be used as a marker for action and sensitivity of cells to these sex steroids. In the luminal epithelium and mesothelium (peritoneal epithelium) the PR was expressed in high concentrations from the time before hatching (the constitutive PR). The PR was not detectable in stromal cells of immature chicks. At the age of 7-10 weeks the PR was detected in submucosal but not in mucosal stromal cells (the inductive PR). The appearance of these PR-expressing cells was associated with an increase in luminal epithelial cell proliferation. At the age of 14-16 weeks the mucosal plicae increased in height and the PR-expressing stromal cells were seen in the center of these mucosal plicae. There were also areas in the mucosal plicae where a large number of stromal cells expressing the PR were seen in the mucosal layer. Thereafter the size of the oviduct increased rapidly and the gland formation commenced. In the fully matured oviduct (over 18 weeks of age) virtually all stromal cells both in mucosa and submucosa expressed the PR. It is concluded that the PR expression in the luminal epithelium and mesothelium was constitutive (independent of sexual maturation). In stromal cells this was expressed during sexual maturation (probably induced by endogenous estrogen) and was associated with histological changes in the oviduct. We propose that direct effects of estrogen and progesterone in the oviduct growth and glandular formation are mediated through these stromal cells.     

Uterine estrogen receptor alpha and progesterone receptor during the follicular and luteal phase in llamas

Estrogen receptor-alpha (ERalpha) and progesterone receptor (PR) were characterized in different endometrial cell types as luminal and glandular epithelium and stroma during the follicular (FP) and the luteal phase (LP) in llamas. Animals were examined daily by transrectal ultrasonography for the determination of the presence of an ovulatory follicle and ovulation was immediately induced by a GnRH injection (Day 0). Endometrial samples were obtained by transcervical biopsies from the left uterine horn on Day 0 (FP) and 9 days after the GnRH injection (Day 9, LP). Blood samples were collected on these days for estradiol 17beta and progesterone determination by RIA. An immunohistochemical technique was used to visualize ERalpha and PR immunostaining which was then analyzed by two independent observers. Total positive area and average staining for ERalpha were affected by the phase of the ovarian activity: in the three cell types there was more positive area and intense staining during the FP than during the LP. Similar findings were observed for PR, more positive stained areas were found during the FP than during the LP in the epithelia. In addition, the three cell types had more intense staining during the FP than during the LP. An effect of the cell type for ERalpha and PR was observed; epithelia (luminal and glandular) had more positive stained areas and greater intensity than stromal cells. In conclusion, the results of the present study suggest that in llamas, like in other ruminants, estradiol has a stimulatory effect while progesterone downregulates the ERalpha and PR and that the receptor is cell type specific.     

Antibodies against highly purified B-subunit of the chick oviduct progesterone receptor

A rabbit was immunized with the highly purified B-subunit (110kDa) (20 to 50 micrograms per injection) of the chick oviduct progesterone receptor (PR). Specific antibodies (IgG-RB) were observed 2 weeks after the first booster injection and high antibody titers in the serum were found after the second and third booster injections (with Kdeq of interaction integral of 2 nM). IgG-RB were tested by immunoprecipitation, immunoblotting, density gradient ultracentrifugation and protein A-sepharose assay methods. They recognized not only the B-subunit but also the A-subunit (79K), the nuclear PR, the mero-receptor (proteolytic cleavage product) and the "non-activated" molybdate-stabilized "8S" PR. However, IgG-RB did not interact with the 90K non hormone-binding component of this 8S-PR. IgG-RB did not affect the binding of the hormone to PR, whether incubated with the receptor before or after labelling with tritiated progesterone. They did not cross-react with glucocorticosteroid receptor of the chick oviduct. Weak interaction was observed with estrogen receptor of the chick oviduct and with KC1 activated "4S" forms of the rabbit and human uterus PR.     

Progesterone receptor does not form oligomeric (8S), non-DNA-binding complex in intact cell nuclei

We raised a polyclonal antibody, αD, against a synthetic peptide (amino acids 522–535) of chichen progesterone receptor (PR). The Sequence is located between the DNA-binding domain and the hormone-binding domain in the refion within the sequences required for stability of the oligomeric form of PR. In the immunoblot, αD reacted with both A and B forms of PR. in the sucrose gradient and dot-blot the antibody did bot recognize the so-called 8S form of PR, which is an oligomeric complex of PR and other proteins, When the oligomeric complex was dissociated by salt treatment, the antibody recognized the resulting 4S form of PR. This would suggest that the epitope is masked in the 8S form of PR and exposed in the 45 form. To study whether a similar Complex exists in vivo, we used the antibody for immunohistochemistry. Two different fixation techniques were employed, Freeze-drying-vapor fixation and liquid fixation. In the animals not treated with progesterone, intensive nuclear Staining was Detected independent of the fixation technique. when receptor from similarly treated animals was analyzed by sucrose gradient, all of the receptor molecules were in the oligomeric complex (85). Ligand binding is known to promote a dissociation of this complex. Thus progesterone treatment should lead to an incerased immunodetection of the epitope; however, progesterone treatment decreased the intensity of PR immunostaining. These Results Suggest that the oligomeric complex (85), Present in tissue extracts, does not exist in intact cell nuclei. They also Call into question the propesed role of hsp90 in regulating progesterone receptor function. © Wiley-Liss, Inc.     

Immunologic analysis of human breast cancer progesterone receptors. 2. Structure, phosphorylation, and processing

We have used a monoclonal antibody (MAb) directed against chick oviduct progesterone receptors (PR), that cross-reacts with human PR, to analyze PR structure and phosphorylation. This MAb, designated PR-6, interacts only with B receptors (Mr 120,000) of T47D human breast cancer cells; it has no affinity for A receptors (Mr 94,000) or for proteolytic fragments from either protein. The antibody immunoprecipitates native B receptors and was used to study the structure of native untransformed 8S and transformed 4S receptors, using sucrose density gradient analysis, photoaffinity labeling, and gel electrophoresis. On molybdate-containing low-salt gradients, PR-6 complexes with 8S B receptors, causing their shift to the bottom of the gradient while A receptors remain at 8 S. Therefore, A and B receptors form separate 8S complexes, and we conclude that A and B do not dimerize in the holoreceptor. Similar gradient studies using salt-containing, molybdate-free buffers show that there are two forms of salt-transformed 4S receptors, comprising either A proteins or B proteins, suggesting that A and B are also not linked to one another in transformed PR. The independence of A- and B-receptor complexes was confirmed by the finding that purified, transformed B receptors bind well to DNA-cellulose. Since PR-6 cross-reacts with nuclear PR, it was used to analyze nuclear PR processing--a down-regulation step associated with receptor loss as measured by hormone binding. Insoluble nuclear receptors and soluble cytosol receptors were measured by immunoblotting following treatment of T47D cells for 5 min to 48 h with either R5020 or progesterone. From 8 to 48 h after R5020 treatment, immunoassayable receptors decreased in nuclei and were not recovered in cytosols. Nuclear receptors also decreased after progesterone treatment but replenished in cytosols between 8 and 24 h after the start of treatment. Thus, processing involves a true loss of nuclear receptor protein, and not just loss of hormone binding activity, and occurs after progesterone or R5020 treatment. This loss is chronic, however, only in R5020-treated cells. Additional studies focused on the covalent modifications of receptors. We previously described shifts in apparent molecular weight of nuclear PR following R5020 treatment using in situ photoaffinity labeling. To show whether these shifts can be explained by receptor phosphorylation, untreated cells and hormone-treated cells were metabolically labeled with [32P]orthophosphate, and the B receptors were isolated by immunoprecipitation with PR-6 and analyzed by sodium dodecyl sulfate (SDS) gel electrophoresis.(ABSTRACT TRUNCATED AT 400 WORDS)     

Chick oviduct glucocorticosteroid receptor. Specific binding of the synthetic steroid RU 486 and immunological studies with antibodies to chick oviduct progesterone receptor

The glucocorticosteroid receptor (GR) has been studied in oviduct cytosol prepared from estrogen-primed, 4-week-withdrawn chicken. The equilibrium dissociation constant was 6 nM for dexamethasone, and 18 300 receptor sites/cell were measured assuming that all cells contain identical concentrations of GR. Dexamethasone, used in most studies investigating glucocorticosteroid action, was found not to be the best GR ligand. The affinities of several natural and synthetic glucocorticosteroids for GR increased in the following order: cortisol less than deoxycorticosterone less than dexamethasone less than corticosterone less than triamcinolone acetonide. The synthetic steroid RU 486 was the most specific ligand of GR (its affinity was approximately equal to 10-fold higher than that of triamcinolone acetonide), while it did not bind either to plasma transcortin (which binds dexamethasone nor, surprisingly, to progesterone receptor (PR), contrary to what occurs in mammalian species. The molybdate-stabilized, 8-S form of GR was prepared from withdrawn chick oviduct, whole chick embryo or cultured chick embryo fibroblasts (which do not contain PR), and was labeled with either [3H]dexamethasone or [3H]RU 486. The sedimentation coefficient of radioactive ligand--8-S GR complexes was shifted towards heavier forms after incubation with polyclonal (IgG-G3) or monoclonal (BF4) antibodies generated against the molybdate-stabilized, 8-S form of the chick oviduct PR. Since neither IgG-G3 nor BF4 interacted with the steroid binding 4-S form of GR, it is suggested that these antibodies recognized a non-steroid binding protein common to molybdate-stabilized, 8-S forms of GR and PR.     

雌激素和孕激素对不同发情方式小鼠子宫内膜中孕激素受体分布的影响

目的探讨雌（Estrogen,E2）、孕激素（Progesterone,P4）对同期发情与自然发情小鼠子宫内膜中孕激素受体（Progesterone receptor,PR）分布的影响。方法45只同日龄雌鼠,根据处理方式的不同随机分为5组：自然发情组（对照组）、同期发情组、卵巢摘除组、P4处理组和E2处理组,5组小鼠在见栓后第4、6、8天分别取样后,采用免疫组织化学法观察小鼠子宫内膜中PR的分布变化情况。结果免疫组织化学染色结果显示,5个处理组小鼠子宫内膜的三种细胞中都有PR存在;同期发情组小鼠子宫内膜中三种类型细胞PR的表达与自然发情组差异有显著性（P〈0.05）;P4处理组小鼠子宫内膜中三种类型细胞PR的表达在见栓第4、6天显著低于卵巢摘除组（P〈0.05）;E2处理组小鼠子宫内膜腺上皮和间质中PR在第4、6、8天时都显著高于卵巢摘除组（P〈0.05）,而在腔上皮中则显著低于卵巢摘除组（P〈0.05）。结论同期发情处理与自然发情小鼠的子宫内膜上PR的分布,都受E2和P4的特异诱导而变化。     

Progestins, progesterone receptor modulators, and progesterone antagonists change VEGF release of endometrial cells in culture

The influences of the synthetic progestin, medroxyprogesterone acetate (MPA), the progesterone receptor modulator J867, and the antagonist ZK137316 were studied in vitro on isolated endometrial epithelial cells, as well as endometrial fibroblasts. We evaluated the expression of estrogen receptor alpha (ER) and the progesterone receptor (PR) by RT-PCR. ER and PR were strongly expressed in the fibroblasts and epithelial cells under treatment with 10(-8) M 17beta-estradiol (E(2)). Treatment with 10(-6) M J867 or ZK137316 upregulated the PR expression as did E(2), in contrast to treatment with 10(-6) M MPA, which caused a downregulation of PR in epithelial cells, but not in fibroblasts. In addition, the vascular endothelial growth factor (VEGF) release into the cell culture medium was analyzed by a VEGF-ELISA. VEGF which plays an important role in angiogenesis, is regulated by steroid hormones as well as hypoxia. E(2) stimulates VEGF release into the medium in both cell types. MPA reduces VEGF release significantly in the fibroblast cell culture, but increases it in the epithelial cell culture. ZK137316, in the presence or absence of E(2), reduces VEGF release in fibroblast cell culture. J867 increases the VEGF production in fibroblasts only in the presence of E(2). Both compounds show no significant effects, compared to E(2), in epithelial cell culture. The different results for the epithelial cells and fibroblasts indicate that the pharmacological effects of PR modulators (PRMs) and progesterone antagonists (PAs) may be cell specific and depend on the presence or absence of partial progestagenic agonistic activities. This observation opens up new perspectives for various clinical applications.     

Biochemical characterization of the progesterone receptor in the chick bursa of Fabricius

In a previous work we demonstrated estrogen-inducible progesterone binding sites in the bursa of Fabricius. In the present study these were characterized and compared to the progesterone receptor (PR) in the chick oviduct. When the size of the binding sites was analyzed with sucrose gradient centrifugation, 2 peaks of bound progesterone were obtained. The sedimentation coefficients of the peaks were 8-9 S and 3-4 S. In size exclusion HPLC only 1 peak was seen with a size corresponding to the 8-9 S in the sucrose gradient. The Stokes radius was 7.7 nm. When the ionic strength was elevated or CaCl2 was added, smaller steroid binding forms were detected. The sizes of these progesterone binding molecules at low and high ionic strength and in the presence of CaCl2 were equal in bursa and oviduct when analyzed with HPLC. The Stokes radii of these forms were 5.6 nm in high salt and 2.1 nm with CaCl2. The steroid binding components in the bursa cytosol eluated as 2 peaks from the DEAE column with KCl gradient. The peaks corresponded to the so-called A and B components in the chick oviduct. In the presence of molybdate, bound progesterone eluated as one peak from DEAE in both oviduct and bursa. The progesterone binding capacity was shown to be heat labile with equal half-lives in the bursa and the oviduct. Progesterone and ORG 2058 had a high affinity for the binding site and their binding was specific for progestins. It is concluded that the estrogen-inducible progesterone binding site in the bursa of Fabricius resembles the oviductal progesterone receptor in structural and binding properties.     

Intracellular progesterone receptors are differentially regulated by sex steroid hormones in the hypothalamus and the cerebral cortex of the rabbit

The aim of this study was to examine the role of sex steroid hormones in the regulation of intracellular progesterone receptors (PR) in the rabbit central nervous system. We determined PR concentration in cytosol preparations from the hypothalamus, the frontal, tempo-parietal and occipital cortex, by using the specific binding of the synthetic progestin [³H]ORG 2058. PR concentration was higher in the hypothalamus of intact adult females than in that of adult males and prepubertal females, whereas no significant differences were observed in the cerebral cortex of these animals. PR concentration was similar in the three cortical regions analyzed, indicating a homogeneous distribution of PR in the cerebral cortex. The administration of estradiol to ovariectomized animals increased PR concentration in the hypothalamus but not in the cortex. The administration of progesterone to ovariectomized rabbits did not modify PR concentration in any region, however when progesterone was administered after estradiol, it induced a significant diminution in hypothalamic PR concentration without effects in the cortex. These findings suggest that in the rabbit, PR are estrogen regulated in the hypothalamus but not in the cerebral cortex. In the latter, PR are not regulated by progesterone, whereas in the former the estrogen-induced PR are down-regulated by progesterone. Interestingly, hypothalamic PR constitutively expressed in ovariectomized animals are progesterone-insensitive.     

Demonstration of steroid hormone receptors and steroid action in primary cultures of rat glial cells

Primary cultures of rat glial cells were established from newborn rat forebrains. A mixed population of oligodendrocytes and astrocytes was obtained, as confirmed by indirect immunofluorescence staining with specific markers for each cell type. Receptors were measured 3 weeks after primary culture in glial cells cultured in the presence or not of 50 nM estradiol and we have identified progesterone, glucocorticoid, estrogen, and androgen receptors (PR, GR, ER and AR), but only PR was inducible by the estrogen treatment. This estrogen-induction of PR was more dramatic in glial cells derived from female offsprings than from males, as measured by binding studies and by immunohistochemical techniques with the KC 146 anti-PR monoclonal antibody. The antiestrogen tamoxifen inhibited the estrogen induction, but had no effect by itself on PR concentration. Specific binding sites for PR, GR, ER and AR were measured by whole cell assays after labeling cells with, respectively, [³H]R5020, [³H]dexamethasone, [³H]OH-tamoxifen or [³H]R1881. PR and GR were also analyzed by ultracentrifugation and after exposure of cells to agonists, both receptors were recovered from cytosol as a 9S form, and from the nuclear high-salt, tungstate ions-containing fraction as a 4–6S form. In contrast, when the antiprogestin- and antiglucocorticosteroid RU486 was used as a ligand, a non-activated 8.5S receptor complex was found for both receptors in this nuclear fraction. The 8.5S complex of the GR was further analyzed in the presense of specific antibodies and, in addition to GR, the presence of the heat shock protein hsp90 and of a 59 kDa protein was found.

During primary culture, the effects of progesterone (P) and estradiol (E₂) were tested on glial cell multiplication, morphology and differentiation. Cell growth was inhibited by P and stimulated by E₂. Both hormones induced dramatic morphologic changes in oligodendrocytes and astrocytes and increased synthesis of the myelin basic protein in oligodendrocytes and of the glial fibrillary acidic protein in astrocytes.     

Effect of plane of nutrition on endometrial sex steroid receptor expression in ewes

The effect of plane of nutrition on progesterone receptor (PR) and estrogen receptor alpha (ERalpha) expression in ovine endometrium was investigated. Rasa Aragonesa ewes (n=26) were fed diets to provide either 1.5 (Group C) or 0.5 (Group L) times the daily maintenance requirement and were slaughtered at Days 5 or 10 of the estrous cycle (Day 0=estrus). PR and ERalpha immunoreactivity were analyzed in eight endometrial cell compartments, defined by cell type and location. Group L had less PR immunostaining on Day 5 (P<0.05), which is consistent with lesser endometrial content of progesterone found in such animals. Most cell types of Group C had down regulation of PR at Day 10, but in Group L, this pattern was observed only in three cell compartments. The lesser PR contents found at Day 5 in Group L ewes may explain the lack of inhibition of PR. No effect of treatment or day of the estrous cycle was observed in ERalpha. Results indicate that endometrial PR is affected in a cell type, in specific manner, by plane of nutrition.