Distribution of mast cells in vaginal, cervical and uterine tissue of non-pregnant mares: investigations on correlations with ovarian steroids

Mast cells constitute part of the cellular immune system of the genital tract. They play a potential role in cervical remodelling during parturition and are subject to the influence of ovarian steroids. In this study, the influence of oestradiol‐17β and progesterone on the distribution of mast cells in equine vaginal, cervical and uterine tissue was evaluated. Genital tracts were retrieved from healthy mares at a local slaughterhouse. The cervix was divided along the longitudinal axis into five equivalent regions from cranial to caudal (R1 to R5). Toluidine blue staining was used for the detection of mast cells. Hormone values were determined via radioimmunoassay. In cervical tissue, mast cells were present at higher frequency and higher density than in vaginal and uterine tissue. Statistically significant differences were obtained between cervical R1 (cranial) and uterus as well as cervical R2 and uterus (p < 0.05). In cervical tissue, an association between the presence of mast cells and peripheral oestrogen concentrations was observed, whereas such correlation could not be established for vaginal and uterine tissue. With increasing oestradiol‐17β concentrations, the density of mast cells in cervical tissue increased to a statistically significant degree in the cranial (r = 0.46; p = 0.05) and caudal (r = 0.5; p = 0.03) regions. We propose that mast cells play a role in the cyclic remodelling of the equine cervix during the course of the oestrous cycle. Elucidation of mechanisms controlling cervical remodelling could contribute to development of therapies for mares showing a lack in cervical opening during oestrus.     

Characterisation of lymphocyte subsets in the equine oviduct

REASONS FOR PERFORMING STUDY: The equine oviduct is the site of fertilisation and location of embryonic development during the first 5 or 6 days. It therefore has an important influence on mare fertility. Although histopathological changes have been described previously, there is limited information regarding lymphocyte subtypes present in the mucosa of the normal equine oviduct. OBJECTIVES: To characterise the distribution of CD3+, CD4+, CD8+ and B lymphocytes in the equine oviduct from inseminated mares during oestrus and dioestrus, and from noninseminated mares during the immediate post ovulatory period. METHODS: Oviductal tissues were collected from noninseminated mares at oestrus (> 30 mm follicle, n = 4), at Day 1 post ovulation (n = 3) and at dioestrus (Day 7 post ovulation; n = 4). Oviducts were also collected from inseminated mares at Days 1, 2, and 3 post ovulation (n = 4 for each period). Cross-sections of tissues from the ampullar-isthmic junction from each oviduct were snap frozen and cryostat sections stained by the immunoperoxidase technique with monoclonal antibodies directed against equine lymphocyte surface markers for B cells as well as CD3+, CD4+ and CD8+ cells. RESULTS: In all oviductal sections examined, B cells were rare whereas T cells were relatively abundant. The predominant cell type found was the CD8+ phenotype, with a lesser number of CD4+ cells. Among mares, individual variation was large; therefore, although breeding status and stage of oestrous cycle appeared to alter lymphocyte populations, these differences were not significant. CONCLUSIONS AND POTENTIAL RELEVANCE: A population of CD3+, CD4+ and CD8+ cells exists within the mucosal region of the equine oviduct. The density of these cells is similar to that described in the human oviduct. Their function is not currently known, but they may be involved with modulation of the maternal response to the presence of spermatozoa or the early conceptus within the equine oviduct. As our capacity to differentiate these cell types improves, along with the ability to identify the specific cytokines they produce, their functional significance will become more apparent.     

MHC Class II+ (HLA-DP-like) Cells in the Cow Reproductive Tract: II. Immunolocalization of MHC Class II+ Cells in Oviduct and Vagina

The aim of this study was to determine and examine the distribution of major frequency MHC II+ cells in the oviduct and vagina of cows during the oestrous and dioestrus phases. Right oviduct (ampulla, isthmus) and vaginal samples taken from a total of twenty seven multiparous cows were used. Tissue samples were processed to obtain both cryostat and paraffin sections. Sections were stained immunocytochemically using StreptABC method using a specific monoclonal antibody to MHC II+ cell population. Intra-epithelial and subepithelial areas along with lamina propria, muscularis mucosae and serosa of both ampulla and isthmus and intra-epithelial/subepithelial areas and mucosae of vagina were examined for the presence of MHC II+ cells. The density of immune positive cells was determined using a subjective scoring system. MHC II+ cells were demonstrated in all areas examined in both oestrus and dioestrus. In oestrus, the density of MHC II+ cells decreased in subepithelial areas (in between the epithelial cells and the basal membrane) of isthmus, whereas the density of immune positive cells was increased in muscularis mucosae of isthmus ( P  < 0.05), lamina propria and muscularis mucosae of ampulla ( P  < 0.05) as well as in the mucosae of vagina ( P  ≤ 0.005). This study indicates that the density of MHC II+ cells observed in the oviduct and vagina increases in the majority of areas examined due to the effect of oestrogen.     

A comparison of the uterine proteome of mares in oestrus and dioestrus

Proteomic analysis of mare uterine flush fluid provides a minimally invasive technique for studying protein changes associated with the oestrous cycle. The aim of this study was to identify differentially abundant proteins in the uterine flush fluid of mares in oestrus and dioestrus. In this study, uterine flush fluid samples were collected from eight reproductively healthy mares in either oestrus (n = 5) or dioestrus (n = 3). Proteomic analysis was performed using liquid chromatography‐tandem mass spectrometry. Of 172 proteins identified, six proteins (immunoglobulin lambda‐like polypeptide 1, haemoglobin subunit alpha, alpha‐1B‐glycoprotein, serotransferrin, apolipoprotein A‐1, and haemoglobin subunit beta) were significantly more abundant in oestrus. These proteins may contribute to the endometrial defence system through roles in inflammation, immunity or antimicrobial activity. In other species, some of these proteins have been described as immunoglobulins, negative acute phase proteins or defence agents against micro‐organisms. During dioestrus, immunoglobulin alpha‐1 chain C region‐related, complement factor I, CD 109 antigen and uterocalin, were significantly more abundant. Research in other species suggests that these four proteins contribute to the immune response through proposed immunoregulatory characteristics, complement system involvement or roles in B cell–T cell interactions. In conclusion, ten differentially abundant proteins were identified in the uterine flush fluid of mares in oestrus and dioestrus. Targeted studies on these proteins could elucidate their role in uterine defence mechanisms during the oestrous cycle in the mare.     

Histomorphology of the equine cervix

The cervix provides an effective, morphological barrier between the uterus and the outside world. The aim of this study was to characterize the epithelial morphology and the vascular structures of the equine cervix along the longitudinal and horizontal axis in more detail by light microscopy. For this purpose, cervical tissue specimens that had been removed from five different regions along the caudocranial axis of 10 genitally healthy mares were available. The histological staining was carried out with haematoxylin-eosin, azan according to Heidenhain, periodic acid-Schiff reaction and resorcinfuchsin. An average epithelial cell height of 17.5 +/- 1.7 microm is measured, there being differences in the various areas of the mucosal folds and along the longitudinal axis of the cervix. Three types of cells can be differentiated morphologically. Contrary to the data in the literature, in a large number of cells the free cell membrane shows a clearly discernible border of kinocilia along the total cervical canal. The deep layers of the lamina propria mucosae show pronounced vascularization (46.3 +/- 25.1 vessels/mm2) that mainly consists of veins and venules. Support of the occlusive function of the cervical canal in the form of a cavernous body is assumed to be the function of this vascular plexus.     

Qualitative analysis and functional classification of the uterine proteome of mares in oestrus and dioestrus

Quantitative analysis of the uterine flush fluid proteome of mares in oestrus and dioestrus has been previously reported. The objectives of this study were to: a) evaluate qualitative differences in the uterine flush fluid proteome between mares in oestrus and mares in dioestrus and b) perform a functional classification of proteins either unique to each stage or common between the two stages. Uterine flush fluid samples were collected from 8 light breed mares in either oestrus (n = 5) or dioestrus (n = 3). Proteomic analysis of the samples was conducted using liquid chromatography–tandem mass spectrometry. Proteins exclusively detected in oestrus or dioestrus and those common to both stages were identified using the Scaffold software (version 4.4.8, Proteome Software Inc., Portland, OR). The identified proteins were classified into gene ontology (GO) categories (cellular component [CC], molecular function [MF] and biological process [BP]) using the PANTHER ( www.pantherdb.org ) classification system version 14.0. Of 172 proteins identified, 51 and 28 were exclusively detected in mares in oestrus and dioestrus, respectively, and 93 proteins were common to both stages. The most represented terms in various GO categories were similar among the three subsets of proteins. The most represented CC terms were extracellular region and cell, the most represented MF terms were catalytic activity and binding, and the most represented BP terms were metabolic process and cellular process. In conclusion, proteomic analysis of the uterine flush fluid enabled the identification of subsets of proteins unique to oestrus or dioestrus, or common to both stages. The results of this study can serve as a baseline for future research focused on finding stage-specific protein markers or evaluating differences in the uterine flush fluid proteome between normal mares and those with uterine disease.     

Effects of Exogenous Insulin on Luteolysis and Reproductive Cyclicity in the Mare

Insulin is a pancreatic hormone that classically regulates carbohydrate and fat metabolism, but also appears to play a role in various reproductive processes. A preliminary study suggested insulin production by day 10 to 18 equine conceptuses. The aim of the present study was to examine the hypothesis that insulin is the conceptus signal responsible for maternal recognition of pregnancy (MRP) in the mare, or otherwise influences reproductive cyclicity during the MRP period. Six Warmblood mares were treated daily during days 7 to 17 after ovulation of two successive oestrous cycles with either (short and intermediate acting) insulin or control saline. Mares were assigned randomly to treatment, and crossed over during the subsequent cycle. Time of ovulation and corpus luteum surface area were determined by serial transrectal ultrasonographic examination of the mares' ovaries, and daily jugular vein blood samples were analysed for progesterone and luteinizing hormone (LH) concentrations. On day 14 of dioestrus, the luteolytic drive was examined by measuring systemic 15-ketodihydroprostaglandin F_{2 α} (PG-metabolite) release in response to oxytocin challenge. In addition, yolk sac fluid recovered from 32 day 10 to 14 equine conceptuses was analysed for insulin concentrations. Insulin administration did not affect luteal size, dioestrus length, the interovulatory interval, or circulating LH concentrations. Insulin administration also failed to suppress oxytocin-induced PGF_{2 α} release, and tended to depress systemic progesterone concentrations. Finally, insulin could not be detected in the yolk sac fluid of day 10 to 14 equine conceptuses by radio-immunoassay. It is concluded that insulin administered daily during days 7 to 17 of dioestrus has little or no effect on reproductive cyclicity in the mare, and is unlikely to be the MRP signal.     

Characterization and clinical application of mesenchymal stem cells from equine umbilical cord blood

Tendinitis of the superficial digital flexor tendon (SDFT) is a significant cause of lameness in horses; however, recent studies have shown that stem cells could be useful in veterinary regenerative medicine. Therefore, we isolated and characterized equine umbilical cord blood mesenchymal stem cells (eUCB-MSCs) from equine umbilical cord blood obtained from thoroughbred mares during the foaling period. Horses that had tendinitis of the SDFT were treated with eUCB-MSCs to confirm the therapeutic effect. After eUCB-MSCs transplantation, the core lesion in the SDFT was found to decrease. These results suggest that transplantation using eUCB-MSCs could be another source of cell treatment.     

Cyclical endometrial steroid hormone receptor expression and proliferation intensity in the mare

The aims of this study were to investigate the steroid hormone receptor expression and the proliferation intensity during the equine endometrial cycle by immunohistological methods, established for routine examination of formalin-fixed, paraplast-embedded specimens. Endometrial biopsy specimens were obtained during one cycle from 7 mares. In comparison with the blood steroid hormone levels the quantity and distribution of oestrogen (ER) and progesterone receptors (PR) and the proliferation marker Ki-67 antigen expression were investigated. Rising 17beta-oestradiol concentrations in preoestrus induce a synchronous expression of ER, PR and Ki-67 antigen in stromal cells. In the early dioestrus 17beta-oestradiol levels decrease and progesterone levels reach their maxima. This correlates with an intense proliferation activity and the highest hormone receptor expression in epithelial cells. In accordance to the morphological features of asynchronous glandular differentiation in fibrotic areas (endometrosis) their epithelial hormone receptor expression is out of phase.     

Measurement of the cytotoxic effects of different strains of Mycoplasma equigenitalium on the equine uterine tube using a calmodulin assay.

The cytopathic effects induced by five strains of Mycoplasma equigenitalium for cells of equine uterine tube explants were tested by measuring changes in cellular and extracellular concentrations of calmodulin (CaM). Calmodulin concentrations in samples of total homogenate (TH) and total homogenate supernates (THS) of the infected equine uterine tube explants were significantly lower than respective measurements on noninfected controls. In tissue culture medium fractions (TCM) of some infected explants, CaM concentrations were significantly higher than noninfected controls (p > 0.95). The results suggest that M. equigenitalium colonization on ciliated cells of the equine uterine tube can affect the permeability of the cell membrane leading to leakage or release of CaM during cell breakdown. Measurement of CaM concentrations in samples of TH revealed significant differences in the cytotoxic effects induced by different strains of M. equigenitalium on the equine uterine tube (EUT). The data suggests that some strains of M. equigenitalium may have a role in reproductive failure in the mare. In addition comparisons of the means of the concentrations of CaM in samples of TH or THS in EUT explants from four mares in the follicular and four in the luteal phase of the estrous cycle were found to be not significantly different.     

Videoendoscopic evaluation of the mare's uterus: I. Findings in normal fertile mares.

The new generation of videoendoscopes uses an electronic, instead of an optical, system for image transmission. Advantages over conventional fibre-optic endoscopes include increased image quality, handling robustness and direct display of the image on a TV monitor for multiple simultaneous viewing. In the present study, hysteroscopy was performed on 14 normal fertile Welsh Pony and Thoroughbred mares at various times during the annual and ovarian breeding cycles. Oestrus was characterised by an oedematous, relaxed cervix lying on the floor of the vagina, diffuse oedema of the endometrium and the occasional accumulation of small amounts of clear secretions in the uterine lumen. In dioestrus, the cervix appeared tight and pale and was located in the centre of the vaginal fornix. The endometrium appeared thinner due to the reduction in interstitial fluid, which allowed the underlying blood vessels to become visible, but it still had a glistening surface as a result of endometrial gland secretions. The appearance of the uterotubal papillae reflected the changes in the cervix, being relaxed, pinkish and oedematous during oestrus but remaining pale, tight and erect in dioestrus (between Days 7 and 12 after ovulation). A flexible polythene cannula was passed into the uterine lumen through the working channel of the endoscope for directed collection of uterine fluid for cytological and bacteriological examinations. Site-directed biopsies of the endometrium were taken, with flexible forceps inserted through the working channel of the endoscope, or with rigid forceps passed through the cervix alongside the endoscope. Both methods enabled accurate visual selection of the sampling area but the rigid forceps were preferred due to the larger size of the piece of endometrium recovered.     

Influence of breed and oestrous cycle on endometrial gland surface density in the mare

REASON FOR PERFORMING STUDY: The diffuse noninvasive epitheliochorial equine placenta develops an intimate and complex interdigitation with the maternal endometrium throughout gestation to maximise surface contact and, consequently, optimise nutritional and gaseous maternofetal exchanges. A significant reduction occurs in the surface density of microcotyledons on the placentae of Welsh Pony vs. Thoroughbred mares that may relate to a difference in either the number or density of endometrial glands between these breeds. OBJECTIVES: To examine this hypothesis and to determine the influence of the oestrous cycle upon the development and surface density of endometrial glands. METHODS: Endometrial biopsies were taken under videoendoscopic visual control from the base of a uterine horn from young, fertile, Welsh Pony and Thoroughbred mares at defined stages of the oestrous cycle. Computer-assisted morphometric analysis then permitted the surface density of endometrial glands within the stratum spongiosum to be assessed. CONCLUSIONS: There was a statistically significant reduction in endometrial gland surface density in the Welsh Pony vs. Thoroughbred mares during both oestrus and dioestrus. POTENTIAL RELEVANCE: A substantial upregulation of epidermal growth factor (EGF) mRNA in the epithelial cells lining the apical portions of endometrial glands has been demonstrated in pregnant mares between Days 35 and 40 after ovulation, coincident with the onset of interdigitation between the allantochorion and endometrium to form the microcotyledonary placenta. The increased surface density of endometrial glands noted in the uteri of Thoroughbred mares might account for the greater surface density of placental microcotyledons in this breed.     

Effects of Topical Application of Misoprostol on Cervical Relaxation in Mares

Mares who have not delivered a foal early in life may experience limitations in cervical relaxation, primarily during oestrus. A closed cervix prevents intrauterine deposition of semen during natural breeding, may delay uterine clearance after insemination leading to intrauterine fluid accumulation in, and subsequent infertility. Therefore, a reliable pharmacological method of dilating the equine cervix would have practical application in veterinary medicine. The goal of this study was to investigate the effectiveness of topically applied, synthetic prostaglandin E₁ analogue (PGE₁) for stimulating dilation of the equine cervix. Ten mares in dioestrus were randomly assigned to one of two treatments in a single‐blind crossover study: (treatment) PGE₁ gel (1000 mcg compounded misoprostol cream) applied topically to the external cervical os (n = 5), and (control) a vehicle cream applied topically to the external cervical os (n = 5). Transrectal palpation and ultrasonographic measurements of the cervix were performed prior to, six and 24 h post‐treatment. Digital measurements were taken, per vagina, at six and 24 h post‐treatment. Mares were monitored through the subsequent oestrous cycle for ovulation. Mares were assigned to the opposite treatment group such that each mare served as her own control (crossover). Data were analysed using parametric (split‐plot anova ), as well as nonparametric (Kruskal–Wallis anova , Wilcoxon's rank‐sum test) methods. At six and 24 h there were no significant differences for tone, length, height, degree of relaxation or echotexture between control and PGE₁ treated groups at the measured time points (p > 0.05). Topical cervical application of PGE₁ did not induce a measurable degree of cervical relaxation under the conditions of this experiment.     

Isolation and cryopreservation of functionally competent equine leucocytes

Sufficient numbers of functionally competent polymorphonuclear neutrophil granulocytes (PMN) seem to be of major importance during the course of equine endometritis. In this study, we wanted to establish a method for cryopreservation of functionally competent neutrophils for an intended local endometritis therapy in mares. The separation of leucocytes by hypotonic lysis of whole blood from clinically healthy mares was superior to the separation by dextrose sedimentation. After suspension of the cells in the cryoprotective solution [equine plasma with 5% (v/v) dimethyl sulphoxide (DMSO)], the leucocytes were frozen in liquid nitrogen. A temperature gradient with low cooling velocity (1 degree C/min between 4 and -70 degrees C) resulted in highest numbers of viable cells after thawing. Thawed PMN had a high phagocytic capacity for opsonized streptococci. Their ability to generate reactive oxygen species (ROS) after stimulation with a phorbol ester was even higher than that of freshly isolated PMN and was preserved up to 6 h after thawing. The results of this study indicate that cryopreservation of PMN may provide viable and functionally competent neutrophils for therapeutic use in mares susceptible to endometritis.     

Contagious equine metritis: distribution of organisms in experimental infection of mares

After contagious equine metritis bacteria were inoculated into the uterus of mares, genital tract tissues were examined for presence of the organism by bacteriologic cultural technique and an indirect immunofluorescent staining technique. Up to 14 days after mares were inoculated, the organism was frequently in the lumen of the uterus and in the cervix and, less frequently, in the vagina, vestibule, clitoral fossa, clitoral sinus, and uterine tubes. After 21 to 116 days, the organism was occasionally found on the ovarian surface, in the uterine tubes, uterus, cervix, and vagina and more frequently in the clitoral sinus and clitoral fossa. The distribution of organisms in the remainder of the genital tract was not different in mares that had been clitorectomized.     

Serologic responses of pregnant thoroughbred mares to vaccination with an inactivated equine herpesvirus 1 vaccine

The immunogenic potency and safety of a chemically inactivated equine herpesvirus 1 vaccine with added adjuvant was evaluated by testing serum-neutralizing and complement-fixation antibody responses of pregnant Thoroughbred mares. The vaccinated population comprised 321 pregnant mares on 7 farms; 3 in Normandy, France; 1 in Kildare, Ireland; and 3 in central Kentucky. The pattern of antibody response to vaccination was found qualitatively and quantitatively similar to that of pregnant mares previously vaccinated and determined by challenge exposure to be immune to abortigenic infection under experimentally controlled conditions. The safety of the vaccine was demonstrated by the occurrence of only 2 local untoward reactions to the administration of 941 IM injections.     

Use of a Low Dose of Equine Purified FSH to Induce Multiple Ovulations in Mares

The effects of a low dose of equine purified FSH (eFSH) on incidence of multiple ovulations and embryo recovery rate in mares were studied. During the physiological breeding season in Brazil (19°45′45′S), 14 Mangalarga Marchador donor mares were used in a crossover study and another 25 mares of the same breed, between 3 years and 12 years of age were used as recipients for the embryo transfers. Donors were monitored during two consecutive oestrus cycles, an untreated control cycle followed by a treated cycle, when eFSH was administered. In both cycles, after an embryo collection attempt on day 8 post‐ovulation all mares received 7.5 mg dinoprost and had their two largest follicles tracked daily by ultrasonography until the period of ovulation. Mares were inseminated every 48 h with extended fresh semen from a single stallion after the identification of a 35‐mm follicle until the period of ovulation. Ovulations were induced by intravenous administration of 2.500 IU of human chorionic gonadotropin, upon detection of a 35‐ to 40‐mm follicle. In the treated cycle, 5 mg eFSH was given intramuscularly once a day, from day 8 post previous ovulation until at least one follicle reached 35 mm in diameter. Embryo flushes were performed on day 8 of dioestrus (day 0 = ovulation). Treatment with eFSH resulted in higher (p < 0.05) ovulation rate and incidence of multiple ovulations compared to the control (1.6 vs 1.0 and 50% vs 0%, respectively – one mare had triple ovulation). However, embryo recovery rates in the control and treated cycles were similar (0.8 and 1.0, respectively; p > 0.05). Pregnancy rates in the recipient mares following embryo transfer were similar for the control and eFSH cycles (11/11 and 10/14, respectively). Additional studies are necessary in order to develop a low‐dose protocol for the use of eFSH that brings a more consistent contribution to the efficiency of commercial equine embryo transfer programs.     

Induction of ovulation and multiple ovulations in seasonally anovulatory and ovulatory mares with an equine pituitary extract

A crude equine pituitary ethanol extract (EE) was used to induce single and miltiple ovulations in seasonally anovulatory pony mares 3-15 years of age. 12 mares were injected daily for 14 days with EE; 6 of the EE-treated mares were also treated with human chorionic gonadotropin (HCG), and 6 control mares received saline vehicle only. In a 2nd experiment designed to determine if EE treatment could induce multiple ovulations in seasonally ovulatory mares, 7 mares were treated during diestrus, 7 mares were treated beginning on Day 1 of estrus, and 7 remained untreated. The results of experiment 1 confirmed that EE treatment can induce ovulation in mares during the anovulatory season, that the timing of ovulation can be improved with HCG, and that ova from induced ovulations are fertilizable. Results of experiment 2 demonstrated that EE treatment can induce follicular activity and multiple ovulations during the ovulatory season.     

Influence of age and parity on the distribution of cells expressing major histocompatibility complex class II, CD4, or CD8 molecules in the endometrium of mares during estrus

OBJECTIVE: To evaluate effect of age and parity on distribution and number of cells expressing major histocompatibility complex (MHC) class II, CD4, or CD8 molecules in the endometrium of mares during estrus. ANIMALS: 32 gynecologically healthy mares, categorized as young (3 to 8 years; n = 17) or old (9 to 16 years; 15) and nulliparous (n = 6), nulliparous embryo donors (16), or parous (10). PROCEDURES: Endometrial specimens collected from the uterine body and horns during estrus were stained by use of the avidin-biotin-peroxidase method, using monoclonal antibodies against equine MHC class II, CD4, and CD8 molecules. Labeled cells in the stratum compactum within 5 randomly selected fields at 400x magnification (total area = 0.31 mm2) were counted, and numbers were compared among groups and between locations. RESULTS: Age did not affect cell numbers within the 3 cell subsets examined. Numbers in each subset were higher in the uterine body than in the horns, although the difference was not significant for cells expressing MHC class II. Significantly more cells expressing MHC class II molecules were detected in the uterine body of nulliparous and parous mares than in embryo donors, whereas in the horns, these cells were significantly higher in number only in parous mares. Parity did not affect number of CD4+ or CD8+ cells. CONCLUSIONS AND CLINICAL RELEVANCE: The increased likelihood for endometritis to develop in mares as they age cannot be explained by a decrease in number of cells expressing MHC class II, CD4, or CD8 molecules within the endometrium. However, greater number of cells within these 3 subsets detected in the uterine body, compared with the horns, during estrus suggests a local readiness to act against microorganisms or semen introduced during mating or insemination.     

Macrophage clearance of 125I-labelled polyvinyl pyrrolidone in the horse: effect of ovarian steroids and persistent endometritis

The rate of clearance of 125I-labelled polyvinyl pyrrolidone (PVP) from blood was measured in mares as an indicator of macrophage function. In three out of four cycling mares, PVP clearance was slower during oestrus than dioestrus. Similarly, administration of oestrogen to four ovariectomised mares tended to depress PVP clearance compared with clearance from the same mares before they received oestrogen. However, the effect of oestrogen was not statistically significant. Mares susceptible to persistent endometritis had rates of PVP clearance which were similar to those of genitally normal mares.