{"paper_id":"4e8e5d2b-089a-40e4-955a-59dc66708386","body_text":"DOI 10.2478/pjvs-2014-0083\nReview\nEndometrosis – significance for horse\nreproduction, pathogenesis, diagnosis,\nand proposed therapeutic methods\nJ. Buczkowska1, R. Kozdrowski1, M. Nowak2, A. Raś3, J. Mrowiec1\n1 Department of Reproduction and Clinic for Farm Animals, Faculty of Veterinary Medicine,\nUniversity of Life and Environmental Science, Plac Grunwaldzki 49, 50-366 Wrocław, Poland\n2 Department of Pathology, Faculty of Veterinary Medicine, University of Life and Environmental Science,\nC.K. Norwida 31, 50-375 Wrocław, Poland\n3 Department of Animal Reproduction, Faculty of Veterinary Medicine,\nUniversity of Warmia and Mazury, Oczapowskiego 14, 10-719 Olsztyn, Poland\nAbstract\nEquine endometrosis is a multifactorial disease considered to be a one of the most important\ncauses of equine infertility, especially in older mares. This article reviews the current knowledge of\nequine endometrosis: pathogenesis, diagnosis, and optional treatment. Also describes the histomor-\nphological and immunohistochemical characterization of endometrosis as well as potential etiological\nfactors which may influence disease progression. Unfortunately, the etiology and pathogenesis of\nendometrosis still remains unclear, and consequently no effective treatment has been proposed so far.\nTherefore future studies are needed for explanation of this disease.\nKey words: mare, endometrium, biopsy, endometrosis\nIntroduction\nAccording to the scheme proposed by Troedsson\n(1999), endometritis in mares is divided into: 1) sex-\nually transmitted diseases, 2) chronic infectious en-\ndometritis, 3) persistent breeding-induced endometri-\ntis and 4) chronic degenerative endometritis (en-\ndometrosis). This paper will be devoted to the last of\nthe above-mentioned diseases, to which more atten-\ntion has been drawn recently, shedding new light on\nits pathogenesis. Proposed therapeutic methods will\nbe also discussed in this paper.\nCorrespondence to: J. Buczkowska, e-mail: justyna.gumienna@up.wroc.pl, tel.: +48 71 320 53 11\nThere are two terms: endometrosis and endomet-\nriosis used in the medical literature, which are defined\ndifferently and should not be confused. Endometriosis\nmeans extra-uterine implantation of endometrial tis-\nsue and refers to women (Snider et al. 2011), whereas\nthe term endometrosis was introduced by Kenney in\n1992 and means changes in the mare’s uterus previ-\nously referred to as chronic degenerative endometritis\n(Allen 1993). At present, endometrosis is defined as\nactive or inactive perigrandular and/or stromal en-\ndometrial fibrosis including glandular alterations\nwithin fibrotic foci (Hoffmann et al. 2009b). This pro-\nPolish Journal of Veterinary Sciences Vol. 17, No. 3 (2014), 547–554\n\nTable 1. Types of endometrosis and histopathological view of endometrium (Lehmann et al. 2011).\nTypes of endometrosis Histopathological changes in the endometrium\nactive glands with several disordered fibrotic stromal cells showing a metabolically active dif-\nferentiation with medium to large, ovoid hypochromatous nuclei and a pale cytoplasm\ninactive glandular nest with periglandular stromal cells showing a metabolically inactive differen-\nNondestructive tiation, characterized by spindle shaped, hyperchromatous nuclei and an elongated\ncytoplasm\nmixed glands with periglandular stromal cells showing both 50% metabolically active and 50%\ninactive differentiation\nactive glands surrounded by metabolically active stromal cells, in addition to the disordered\nappearance of different layers, the fibrotic stromal cells are invasive and they penetrate\nthe lumen of the gland; different degenerated epithelial cells are visible\nDestructive inactive glands with metabolically inactive fibrotic stromal cells which lie parallely arranged to\nthe axis of the adjacent gland, multifocal destruction of single epithelial cells and con-\ngestion of the uterine secretions in the lumina are visible\nmixed glands surrounded by active and inactive periglandular stromal cells which penetrate the\nglandular epithelia\ncess may affect single glands and/or glandular nests\n(Kenney 1978). The degree of endometrosis in mares\nincreases with age; however, it is thought that this is\nnot connected with the number of foalings (Ricketts\nand Alonso 1991, Kenney 1993, Hoffmann et al.\n2009b, Aresu et al. 2012). Endometrosis is one of the\ncauses of infertility in mares. Structural changes in the\nendometrium include the occurrence of progressive\nfocal proliferation of the uterine glands, which are\nconcentrated in the glandular nests encircled by more\nand more numerous layers of fibrous tissue as the pro-\ncess progresses. Inside the nests, glandular cysts oc-\ncur, whereas the number of normal endometrial\nglands decreases. Stromal fibrosis is a dominating dis-\nease process, which results in disturbance of lymph\ncirculation, as a result of which lymphatic extension\noccurs (Katkiewicz et al. 2007).\nBased on the morphology of the periglandular\nstromal cells, the fibrosis can be divided into different\ntypes, which can be classified as either destructive or\nnon-destructive, with biopsies displaying more than\n75% of the fibrotic foci of one of these groups being\ntermed “active” or “inactive” fibrosis respectively. Bi-\nopsy with approximately equal ratios of active and in-\nactive periglandular stromal cells are termed “mixed”\nendometrosis (Table 1) (Lehmann et al. 2011). In all\nof the above-mentioned types, single uterine glands\nand/or glandular nests may be affected by the process\n(Hoffmann et al. 2009b). Additionally, we can deter-\nmine the degree of endometrosis describing it from\nmild to severe (Kenney and Doig 1986, Hoffmann et\nal. 2009b). In severe endometrosis a significantly high-\ner incidence of glandular nest development was ob-\nserved. Furthermore, a significant association of in-\nactive endometrosis and cystic dilatation of the\naffected glands could be seen. However, within active\nnon-destructive endometrosis, an asynchronous cycle,\nin particular irregular differentiation of the affected\nglandular epithelia, was most pronounced (Hoffmann\net al. 2009b).\nPathogenesis\nAtypical morphological and functional differenti-\nation of periglandular endometrial stromal cells are\nthe first sign of endometrosis. The first stage of fi-\nbrosis is characterised by large, polygonal periglandu-\nlar stromal cells which synthesize collagen fibres,\nwhereas in advanced fibrosis metabolic active or in-\nactive stromal cells, without signs of collagen syn-\nthesis, as well as myofibroblasts, predominate (Walter\net al. 2001, Hoffmann et al. 2009a,b). Periglandular\nfibrosis in endometrial tissue is not characterized by\nan increased incidence of collagen fibres, but by perig-\nlandularly arranged fibroblasts in one or more layers,\nwhich produce the extracellular matrix proteins col-\nlagen IV, laminin, and fibronectin. In addition, these\nfibroblasts express h-smooth muscle actin,\ntropomyosin and occasionally desmin, which confirms\ntheir differentiation into myofibroblasts. It remains to\nbe elucidated whether the above-mentioned differen-\ntiation has further consequences on the uterine gland\nepithelium or the stromal cells, as has been shown for\nvarious pathological processes (Walter et al. 2001).\nDuring the fibrosis process, the stromal cells of\nthe basal lamina are capable of collecting collagen un-\nder the influence of different stimulating factors. The\ncollection of collagen occurs most often around the\nglands or in connection with the basement membrane\n548 J. Buczkowska et al.\n\nof the luminal epithelium (Kenney and Doig 1986).\nFibrosis occurs most often without the presence of\ninflammatory cells (Kenney 1978). The first evidence\nof impending deposition of collagen is the loss of ran-\ndomization of stromal cells (and their nuclei) in the\nstratum compactum and stratum spongiosum, particu-\nlarly visible around the glands. The advancement of\nfibrosis may be evaluated by the degree (the number\nof periglandular layers) and frequency (the number of\nfibrotic foci per linear field) (Kenney and Doig 1986).\nFrom one to three layers of perigrandular fibrosis is\nconsidered to be a slight reaction, from four to ten\n– a moderate reaction, and more than ten layers indi-\ncate a severe degree of fibrosis (Kenney 1978).\nPotential etiological factors which may affect de-\nvelopment of the disease are morphological and im-\nmunohistochemical changes of the endometrium,\nwhich occur in endometrosis (Table 1) (Hoffmann et\nal. 2009b, Lehmann et al. 2011). In the unaffected\nendometrium, cyclical and seasonal endocrine\nchanges result in cycle-synchronous morphological al-\nterations to epithelial and stromal cells. With regard\nto the morphology of the periglandular stromal cells\nwithin the fibrotic foci of the endometrosis an active\nand inactive differentiation can be distinguished (Hof-\nfmann et al. 2009b, Lehmann et al. 2011). However, in\ncontrast to the unaltered stromal cells, neither sea-\nsonal nor cyclic endocrine changes seem to have a sig-\nnificant influence on the activity of the fibrotic\nstromal cells (Hoffmann et al. 2009b). Hoffmann et al.\n(2009b) showed that, in the biopsy material collected\nduring the breeding/non-breeding season or on de-\nfined days during the oestrous cycle, both seasonal\nand cycle-associated endocrinological changes do not\ndetermine the activity of stromal cells.\nIn explaining the connection between endometri-\ntis and endometrosis, both the impact of the endomet-\nritis on further development of degenerative changes\nin the endometrium and the process of activation of\ninactive fibrotic foci were taken into account, and pre-\ndispositions for the occurrence of endometritis in\na mare with endometrosis were examined (Lee et al.\n2001, Atamas 2002, Keller et al. 2006, Hoffmann et al.\n2009b). A higher frequency of endometritis in a mare\nwith a destructive type of endometrosis was described\n(Hoffmann et al. 2009b), which indicates an important\nrole of uterine glands in the physiological clearance of\nthe endometrium, and disturbance of this function\nmay cause endometritis (Hoffmann et al. 2009b). It\nwas also shown that mares with a higher biopsy grade\nmore frequently retain fluid in the uterus after insemi-\nnation (Woodward et al. 2012). It is suggested that\ntemporary activation of fibrotic stromal cells, which\ncould be observed as a result of experimentally in-\nduced bacterial endometritis, is presumably caused by\nprofibrotic growth factors and cytokines released from\ninflammatory cells (Lee et al. 2001, Atamas 2002,\nHoffmann et al. 2009b). However, it was shown that\ninflammation is poorly correlated with grade of en-\ndometrosis, and bacterial infection does not increase\nintensification of this disease (Keller et al. 2006, Ar-\nesu et al. 2012). Additionally, in mares experimentally\ninfected with Streptococcus equi subsp.\nZooepidemicus, the degree of endometrosis did not\nchange during the 2-year period of the observation\n(Hoffmann et al. 2009b). Recently it was shown that\nintrauterine enrofloxacin infusion in mares induced\nsevere acute uterine mucosal necrosis, inflammation,\nand a significant increase in endometrial fibrosis\n(Rodriguez et al. 2012).\nAmong other changes in the mare endometrium,\na negative correlation between mild endometrosis and\nchanges in vessels of severe angiosclerosis type was\nalso observed, yet such a correlation between en-\ndometrosis and inflammation of the perivascular\nsheath and surrounding tissue (perivasculitis) was not\nnoted (Hoffmann et al. 2009b). It was observed that\na large percentage of both barren and foaling mares\nshow angiosclerosis; however, this does not have an\nimpact on the degree of endometrosis (Lehmann et\nal. 2011).\nAn immunohistochemical study showed that\nstromal maldifferentiation which could be seen in all\nfibrotic foci is independent of the degree of endomet-\nrosis, and that the cells show a lower expression of\nsteroid hormone receptors compared to unchanged\nstromal cells (Hoffmann et al. 2009b). Moreover,\nmetabolically inactive stromal cells exhibited a de-\ncreased proliferation activity as compared to the unal-\ntered endometrium, whereas no differences could be\nobserved within active fibrotic foci (Hoffmann et al.\n2009b). A considerable reduction of estrogen and\nprogesterone receptor expression of fibrotic stromal\ncells as compared to the normal stroma is one of the\nhallmarks of endometrosis (Hoffmann et al. 2009b).\nThis reduction indicates advanced changes in the\nstromal cells within a fibrotic focus, which lead to the\nloss of specialization in the cell structure and function.\nAs a result, fibrotic stromal cells are unable to react to\ncyclic endocrine changes and become independent of\nhormonal control mechanisms in the uterus (Hof-\nfmann et al. 2009b).\nMaldifferentiation of the epithelial cells of the\nuterine glands within fibrotic foci was also character-\nized by a distinct variability in glandular steroid hor-\nmone receptor expression. In active endometrosis, an\nincrease in expression of estrogen and progesterone\nreceptors dominates, as compared to the unchanged\nglands, whereas glandular epithelia in inactive en-\ndometrosis show a decrease in expression of the\nEndometrosis – significance for horse reproduction... 549\n\nearly stages of fibrosis\nactive fibrosis\ndestruction\nmechanical stressincrease of myofibroblasts and\nextracellular matrix\nendometritis\n?\n?\nperiglandular fibrosis\ninactive fibrosis\ninactive destructive fibrosisactive destructive fibrosis\nstromal fibrosis\nendocrine changes\nFig. 1. Schematic picture of the possible pathogenesis of endometrosis (adopted from Hoffmann et al., 2009b).\nabove-mentioned receptors (Hoffmann et al. 2009b).\nMoreover, the concentrations of steroid receptors in\nthe destructive type of endometrosis are also lower.\nA mild increase in expression of estrogen and proges-\nterone epithelial receptors was observed in active\nnon-destructive fibrotic foci, whereas in the other\ntypes of endometrosis, a decrease in expression of the\nabove-mentioned receptors was visible. This phenom-\nenon can be explained by paracrine mechanisms be-\ncause the effect of the impact of steroid hormones on\nthe glandular epithelium is physiologically mediated\nby the adjacent stromal cells (Cooke et al. 1997,\nKurita et al. 1998, Pierro et al. 2001). These cells are\nmaldifferentiated in endometrosis and presumably re-\nlease other paracrine signals. Therefore, the asyn-\nchronous cycle differentiation of the affected glands\nis, initially, most likely the consequence of maldif-\nferentiation of the stroma, and the decreased express-\nion of steroid hormone receptors is likely to be caused\nby distinct degeneration of the epithelial cells. An-\nother possible explanation of the asynchronous cycle\ndifferentiation of glandular epithelia within fibrotic\nfoci is the severe damage of the basal lamina connec-\nted with altered expression of laminin. All of the\nstromal cells of fibrotic foci, in particular in active\ndestructive fibrosis, show intracellular laminin ex-\npression (Hoffmann et al. 2009b). Only an intact basal\nlamina is able to ensure complex paracrine interaction\nbetween the epithelia and the underlying stroma (Lin\nand Bissel 1993, Arnold et al. 2001), which inhibits\ndirect stromal-epithelial contacts as well as an interac-\ntion between epithelial cell surface integrins and the\nfibrotic extracellular matrix. Furthermore, large dis-\ncontinuities of the glandular basal lamina were deter-\nmined predominantly in destructive endometrosis. Fi-\nbrosis activity visibly affects the expression of estrogen\nreceptors; however, it does not have an influence on\nthe concentration of intermediate filaments in the\nglandular epithelium, although in the destructive type\nof endometrosis the expression of filaments increases\nconsiderably compared to the non-destructive type\n(Hoffmann et al. 2009b).\nThe immunohistochemical study of stromal cells\nindicates that distinct variability in all types of en-\ndometrosis regards coexpression of vimentin and de-\nsmin intermediate filaments as well as h-actin in my-\nofilaments. The stromal cells in destructive endomet-\nrosis, in particular in active destructive endometrosis,\ntended to express more h-actin. In addition, in the\nlatter type of endometrosis, expression of laminins in\nthe stromal cells is greater (Hoffmann et al. 2009b).\nThe immunohistochemical study of extracellular\nmatrix in fibrotic foci indicated the presence of more\nexpression of proteoglycans and fibronectin in the de-\nstructive type of endometrosis, in particular in severe\nactive endometrosis, compared to other types (Hof-\nfmann et al. 2009b). Therefore, the observed accumu-\nlation of proteoglycans and fibronectin is probably\ndue to an increased number of secretively active my-\nofibroblasts (Hoffmann et al. 2009b).\n550 J. Buczkowska et al.\n\nSumming up, partial thinning of a fragment of the\nbasal lamina initiates changeability and activity of the\nglandular epithelium (Fig. 1). A few etiological factors\nmay cause this process e.g. a periglandular localised\nendometritis, a local deficiency of oxygen caused by\nsevere angiosclerosis, wound healing processes follow-\ning mechanical damage, and disorders regarding\nphysiological regeneration of the basal lamina. How-\never, only the intact basal lamina is able to suppress\nactivation of epithelial cells and synthesis of profibrotic\ngrowth factors (Streuli et al. 1993). Endometritis which\noccurs simultaneously with endometrosis causes activa-\ntion of the metabolism of fibrotic stromal cells. In con-\ntrast with the above, cyclical and seasonal endocrine\nchanges seem to have no affect on the disease process.\nFurther studies are necessary to determine the factors\nwhich are able to maintain active fibrosis. The pro-\ngressive nature of the disease is likely to be attributed\nto an increase in the number of myofibroblasts leading\nt ot h ed a m a g eo fu t e r i n eg l a n d si nt h ef i n a ls t a g eo f\nfibrosis. On the other hand, the ability of these cells to\nrelease enzymes which regulate matrix homeostasis\nmay contribute to progressive damage of the basal\nlamina and may lead to the collection of extracellular\nmatrix, which in turn causes maintenance of the fi-\nbrosis process (Ramos et al. 2001). For the develop-\nment of metabolically inactive fibrosis, etiological fac-\ntors are particularly interesting, although they have not\nyet been determined. The contractibility of myofibrob-\nlasts and their arrangement parallel to the adjacent\nglands improves the ability of the fibrotic tissue to con-\ntract. Mechanical stress may explain cystic expansion of\nthe glands and focal damage of the epithelium, which\no c c u r sm o r eo f t e ni nt h i st y p eo fe n d o m e t r o s i s .I ti s\nassumed that activation of inactive fibrosis may occur\nat any time during endometritis and, probably, via\nother, still unknown, factors (Hoffmann et al. 2009b).\nDiagnosis\nMost degenerative changes typical for endometro-\nsis can be diagnosed only through the histological\nevaluation of an endometrial biopsy (Kenney 1978,\nKenney and Doig 1986, Ricketts and Alonso 1991,\nRicketts and Barrelet 1997, Katkiewicz et al. 2007,\nZajac et al. 2008, Schlafer 2009, Snider et al. 2011,\nAresu et al. 2012). Endometrial biopsy has been a stan-\ndard procedure for evaluation of the health of the\nmare’s uterus for more than 40 years. It is a safe, prac-\ntical and very useful method (Kenney 1978, Ricketts\nand Barrelet 1997). Nevertheless, it should be noted\nthat some researchers draw the conclusion that collec-\ntion of an endometrial specimen from one uterine por-\ntion does not necessarily reflect the state of its remain-\ning areas, as significant differences were observed re-\ngarding both the size of a fibrosis area and the grade of\nendometrosis in a biopsy collected from the same mare\nyet from different portions of its uterus. In more than\nhalf of the mares variation in the endometrial grade in\nbiopsies collected from different uterine portions was\nrevealed (Fiala et al. 2010). Keller et al. (2006) also\nobserved that a single biopsy does not represent the\nwhole endometrium in the diagnostics of degenerative\nchanges. However, according to the other researchers,\na single biopsy reflects very well the condition of the\nwhole uterus if the biopsy material has proper size and\ns h a p e ,a n di ti sp r e p a r e da n de v a l u a t e di nt h ea p p r o -\npriate way (Kenney 1978, Kenney and Doig 1986).\nThe purpose of performing the biopsy is to detect\nchanges in the endometrium and to determine the fer-\ntility potential of the mare. The biopsy should be taken\nfrom barren mares, “repeat breeder” mares, from\nmares showing anoestrus during the breeding season,\nand from mares with a pathologic content of the uterus\n(Kenney and Doig 1986, Schlafer 2007, Snider et al.\n2011). Another group consists of mares with a history\nof early embryonic or foetal death, mares with poor\nperineal conformation before surgical correction, and\nrecipient mares in the embryotransfer programme.\nPregnancy is the only known contraindication for the\nperformance of the biopsy (Kenney and Doig 1986,\nSchlafer 2007, Snider et al. 2011).\nIn the image of the uterine wall, seven components\ncan be distinguished: the uterine lumen, endometrial\nepithelial interface, superficial stroma (stratum com-\npactum), the glands and the glandular epithelium, the\nstroma – the mid and deep endometrium (stratum\nspongiosum), vessels (arteries, veins and lymphatics),\nmyometrium and larger vessels. An assessment of these\ncomponents helps the pathophysiology of the uterine\nwall to be determined. Apart from microscopic examin-\nation of the biopsy material, immunohistochemical\nexamination can be also performed (Schlafer 2007).\nEvaluation of the degree of endometrial fibrosis is\nessential as, in contrast to the inflammatory changes,\nfibrosis is of a permanent nature and, if it is intense, it\nbecomes the main factor that reduces the reproductive\nperformance of the mare (Kenney and Doig 1986). De-\npending on the degree of intensification of structural\nchanges in the endometrium, Kenney and Doig (1986)\ndivided endometrosis into four categories (Table 2).\nInflammation, fibrosis, lymphatic system and atrophic\nchanges may coexist, and the more changes occur and\nthe more advanced they are, the higher the category is.\nFor example, an occurrence of inflammatory changes\nor fibrosis signifies category IIA; however, if they occur\nsimultaneously, it will signify category IIB. If the in-\nflammatory condition is eliminated, the endometrium\nmay return to category IIA. Moreover, if inflammatory\nEndometrosis – significance for horse reproduction... 551\n\nTable 2. Standard classification system for histologic changes in the endometrium (Kenney and Doig 1986).\nPercentage\nof altered glandsCategory Structural changes in the endometrium\nI Healthy mares; no pathologic changes or any existing changes (such as inflammation or fibrosis)\nare slight and sparsely scattered –\nIIA A small degree of stromal fibrosis around the individual gland branches; a lack of glandular nests\nin 4 adjacent fields; slight to moderate inflammatory changes, lymphatic lacunae occurs; partial\nendometrial atrophy\n10-35%\nIIB Fibrotic changes are more severe and extensive than in IIA; an average of 2-4 fibrotic nests of\nglands, usually with 2-4 layers in 4 adjacent fields; inflammatory and lymphatic changes are\nwidespread, diffuse and moderately severe\n35-60%\nIII Widespread, diffuse, severe inflammatory changes; widespread fibrosis of gland branches of 5 or\nmore fibrotic nests; severe lymphatic lacunae > 60%\nTable 3. Expected foaling rates of mares according to categorization of endometrium (Kenney and Doig 1986).\nCategory Degree of endometrial change Expected foaling rate\nI Absent 80-90%\nIIA Mild 50-80%\nIIB Moderate 10-50%\nIII Severe 10%\nchanges, fibrosis, and lymphatic changes coexist, the\nendometrium belongs to category III. The more\nchanges occur in the endometrium, the worse the prog-\nnosis of pregnancy and maintenance of pregnancy is\n(Table 3) (Kenney and Doig 1986).\nThe lymphatic lacunae observed in the biopsy are\nderived from dilated lymphatic vessels and can occur in\nthe lamina propria or core of the endometrium folds\nsingly or in clusters and they can be focal or diffuse.\nWhen single lacunae are joined and expand, they be-\ncome endometrial cysts, which achieve a size of even\nup to a few centimetres in diameter (Kenney 1978,\nKenney and Doig 1986). Large uterine cysts may dis-\nturb embryo mobility, and consequently the process of\nmaternal recognition of pregnancy (Kenney 1978).\nCyst-like expanded glands are often noticed within\nthe fibrotic nests. This phenomenon can be also ob-\nserved during the seasonal atrophy; however, in that\ncase, there is a thick secretion inside. Cystic distention\nwithout fibrosis and without inspissation also occurs\nduring the physiological breeding season. When the\nabove-mentioned changes are intensified to a great ex-\ntent, they seem to have a negative impact on reproduc-\ntion (Kenney 1978, Kenney and Doig 1986).\nIn about 30% of cases of fibrosis, acute and/or\nchronic inflammation is observed (Ricketts and Bar-\nrelet 1997). Then, in the biopsy, inflammatory cells\n(mainly lymphocytes and neutrophils, and a lower\nnumber of eosinophils and mastocytes which are\nconcentrated around the glandular nests and vessels,\nand dispersed within the stroma) are observed (Kenney\n1978, Zajac et al. 2008, Aresu et al. 2012).\nImpact of endometrosis on fertility\nFertility impairment is the main problem connec-\nted with endometrosis, and therefore Lehmann et al.\n(2011) decided to use histopathological and im-\nmunocytochemical examination of the endometrium in\norder to determine reproductive abilities in fertile and\nbarren mares. They showed abnormal secretion of the\nendometrial glands during endometrosis. In the barren\nmares, there was lower expression of proteins: uterog-\nlobin and uterocalin were detected in the fibrosis areas,\nespecially in those mares which suffered from moder-\nate destructive endometrosis. Uterocalins take part in\nthe supply of proteins to the embryo (Crossett et al.\n1998) and deficiency of this protein can contribute to\nearly embryonic death (Lehmann et al. 2011), whereas\ndeficiency of uteroglobins may lead to inhibition of the\nembryo protection against a maternal immune re-\nsponse which results in pregnancy loss (Zhang et al.\n2000). In the destructive type of endometrosis, both\nquantity expression and quality expression of endomet-\nrial proteins are decreased (Hoffmann 2009a). In re-\nsearch into the fertility of mares suffering from en-\ndometrosis, Lehmann et al. (2011) showed that mild\n552 J. Buczkowska et al.\n\nnon-destructive endometrosis dominates in fertile\nmares, whereas most barren mares show a moderate\ndegree of endometrosis. In addition, destructive\nchanges in the fibrotic foci are observed in most barren\nmares. Thus, barren mares much more often suffer\nfrom moderate destructive endometrosis compared to\nfertile mares. It seems that whether fibrosis is active or\ninactive does not affect fertility. Recently, Szostek et al.\n(2012) showed that changes in mRNA transcription of\nprostaglandin synthases and prostaglandin production\nwhich occur in the equine endometrium during the\ncourse of fibrosis may lead to early embryonic death.\nTreatment\nIt is difficult to provide satisfactory treatment for\nendometrosis. It is commonly thought that changes\ncaused by this disease are irreversible (Kenney and\nDoig 1986). For its treatment, mechanical curettage or\nchemical agents (kerosene, DMSO, isotonic salt) can\nbe applied (Keller et al. 2006).\nOn the proceedings of J.P. Hughes international\nworkshop on equine endometritis different therapeutic\nmethods were presented and summarised by Allen\n(1993). For example, one of the authors analyzed the\neffect of physical curettage applied to mares with vari-\nous degrees of endometrosis, leading to hyperaemia\na n dm i l da c u t ee n d o m e t r i t i s ,c o m b i n e dw i t hi n -\ntrauterine administration of antibiotics to prevent in-\nfection. After treatment they noticed improvement in\nendometrial biopsy grade in 44% of mares, in 51% of\nmares there was no effect, and in 5% of mares it was\nworse. Additionally, there was no significant effect on\nthe fertility rates. It was also showed that irrigating the\nuterus with 250-500 ml of kerosene, which causes uter-\nine oedema lasting for 1-2 days and results in expulsion\nof retained excretions from the uterine glands, is able\nto improve fertility rates. The best results were ob-\ntained when mares were mated during the first oestrus\nafter treatment. Other research, in which kerosene was\nalso used, showed that the application of this therapy\nbrings rather a short-term effect, as half of the mares\nwhich were pregnant after treatment with kerosene\nmiscarried later (Allen 1993). On the other hand, Ley\net al. (1989) studied the effect of intrauterine adminis-\nt r a t i o no f1 0 - 3 0 %D M S Oi ns t e r i l es a l i n es o l u t i o n ,\ncompared to the control group i.e. mares treated with\nsterile saline solution alone. This therapy was carried\nout during oestrus for five consecutive days. No nega-\ntive changes were found in the endometrium after any\ntreatment protocols. It was shown that 30% DMSO\nsolution caused a reduction of inflammation and/or\na reduction of periglandular fibrosis. However, no sig-\nnificant difference was found in pregnancy rates be-\ntween mares treated with 30% DMSO solution and\nmares treated with saline solution alone, although\na growing tendency was observed following DMSO\ntherapy. Furthermore, Griffin and Bennet (2002) ob-\nserved an improvement of fertility following photoabla-\ntion of endometrial cysts in barren mares.\nConclusion\nContinuous progress and modern laboratory\nmethods enable a more in-depth analysis of changes in\nthe process of endometrosis, and they also make it\npossible to understand accurate genesis and show the\nimpact of different factors on the development and\nprogression of degenerative changes in the mare’s\nuterus. However, further studies are still needed to ex-\nplain the etiology of endometrosis process initiation,\nand the improvement of knowledge concerning eti-\nology and pathogenesis of endometrosis will enable the\ndevelopment of both prevention and more effective\ntreatment of this disease.\nConflict of interests\nThe authors declare that there is no conflict of in-\nterests regarding the publication of this article.\nAcknowledgments\nThis paper was supported by NCN grant,\nDEC-2011/01/B/NZ5/04173.\nReferences\nAllen WR (1993) Proceedings of the John P. Hughes interna-\ntional workshop on equine endometritis. Equine Vet J\n25: 184-193.\nAresu L, Benali S, Giannuzzi D, Mantovani R, Castagnaro M,\nFalomo ME (2012) The role of inflammation and matrix\nmetalloproteinases in equine endometriosis. J Vet Sci\n13: 171-177.\nA r n o l dJ T ,K a u f m a nD G ,S e p p a l aM ,L e s s e yB A(2001)E n -\ndometrial stromal cells regulate epithelial cell growth in\nvitro: a new co-culture model. Hum Reprod 16: 836-845.\nAtamas SP (2002) Complex cytokine regulation of tissue fi-\nbrosis. Life Sci 72: 631-643.\nCooke PS, Buchanan DL, Young P, Setiawan T, Brody J,\nKorach KS, Taylor J, Lubahn DB, Cunha GR ( 1997)\nStromal estrogen receptors mediate mitogenic effects of\nestradiol on uterine epithelium. Proc Natl Acad Sci USA\n94: 6535-6540.\nCrossett B, Suire S, Herrler A, Allen WR, Stewart F ( 1998)\nTransfer of a uterine lipocalin from the endometrium of\nthe mare to the developing equine conceptus. Biol Rep-\nrod 59: 483-490.\nEndometrosis – significance for horse reproduction... 553\n\nFiala SM, Esmeraldino A, Jobim MIM, Garbade P, Wolf\nCA, Richter G, Gregory RM, Mattos RC ( 2010)\nEndometrial fibrotic changes. Is one biopsy enough\nto diagnose degenerative changes? Anim Reprod Sci\n121S: 89-90.\nGriffin RL, Bennett SD (2002) Nd: YAG laser photoablation\nof endometrial cysts: a review of 55 cases (2000-2001).\nP AAEP 48: 58-60.\nHoffmann C, Bazer FW, Klug J, Aupperle H, Ellenberger C,\nSchoon HA ( 2009a) Immunohistochemical and his-\ntochemical identification of proteins and carbohydrates\nin the equine endometrium. Expression patterns for\nmares suffering from endometrosis. Theriogenology\n71: 264-274.\nHoffmann C, Ellenberger C, Mattos RC, Aupperle H, Dhein\nS, Steif B, Schoon HA (2009b) The equine endometrosis:\nnew insights into the pathogenesis. Anim Reprod Sci\n111: 261-278.\nKatkiewicz M, Witkowski M, Zajac S ( 2007) Endometrial\nbiopsy of mares: visualization of healthy and diseased\nstructure. Med Weter 63: 463-466.\nKeller A, Neves AP, Aupperle H, Steiger K, Garbade P,\nSchoon HA, Klug E, Mattos RC ( 2006) Repetitive ex-\nperimental bacterial infections do not affect the degree of\nuterine degeneration in the mare. Anim Reprod Sci\n94: 276-279.\nKenney RM ( 1978) Cyclic and pathologic changes of the\nmare endometrium as detected by biopsy, with a note on\nearly embryonic death. J Am Vet Med Assoc 172: 241-262.\nKenney RM, Doig PA ( 1986) Equine endometrial biopsy.\nIn: Morrow D (ed) Current therapy in theriogenology.\n2 ed., Saunders, Philadelphia, pp 723-729.\nKurita T, Young P, Brody JR, Lydon JP, O’Malley BW,\nCunha GR ( 1998) Stromal progesterone receptors me-\ndiate the inhibitory effects of progesterone on es-\ntrogene-induced uterine epithelial cell desoxyribonucleic\nacid synthesis. Endocrinology 139: 4708-4713.\nLee CG, Homer RJ, Zhu Z, Lanone S, Wang X, Koteliansky\nV, Shipley JM, Gotwals P, Noble P, Chen Q, Senior RM,\nElias JA (2001) Interleukin-13 induces tissue fibrosis by\nselectively stimulating and activating transforming growth\nfactor β\n1. J Exp Med 194: 809-821.\nLehmann J, Ellenberger C, Hoffmann C, Bazer FW, Klug J,\nAllen WR, Sieme H, Schoon HA ( 2011) Morpho-fun-\ncional studies regarding the fertility prognosis of mares\nsuffering from equine endometrosis. Theriogenology\n76: 1326-1336.\nLey WB, Bowen JM, Sponenberg DP, Lessard PN ( 1989)\nDimethyl sulfoxide intrauterine therapy in the mare: ef-\nfects upon endometrial histological features and biopsy\nclassification. Theriogenology 32: 263-276.\nLin CQ, Bissell MJ (1993) Multi-faceted regulation of cell dif-\nferentiation by extracellular matrix. FASEB J 7: 737-743.\nPierro E, Minici F, Alesiani O, Miceli F, Proto C, Screpanti\nI, Mancuso S, Lanzone A (2001) Stromal-epithelial inter-\nactions modulate estrogen responsiveness in normal hu-\nman endometrium. Biol Reprod 64: 831-838.\nRamos C, Montano M, Garcia-Alvarez J, Ruiz V, Uhal BD,\nSelman M, Pardo A ( 2001) Fibroblasts from idiopathic\npulmonary fibrosis and normal lungs differ in growth\nrate, apoptosis, and tissue inhibitor of metalloproteinases\nexpression. Am J Respir Cell Mol Biol 24: 591-598.\nRicketts SW, Alonso S ( 1991) Assessment of the breeding\nprognosis of mares using paired endometrial biopsy tech-\nniques. Equine Vet J 23: 185-188.\nRicketts SW, Barrelet A ( 1997) A retrospective review of\nthe histopathological features seen in a series of 4241\nendometrial biopsy samples collected from UK Thor-\noughbred mares over a 25 year period. Pferdeheilkunde\n13: 525-530.\nRodriguez JS, Han S, Nielsen S, Pearson LK, Gay JM,\nTibary A ( 2012) Consequences of intrauterine enrof-\nloxacin infusion on mare endometrium. J Equine Vet Sci\n32: 106-111.\nSchlafer DH ( 2007) Equine endometrial biopsy: enhance-\nment of clinical value by more extensive histopathology\nand application of new diagnostic techniques?\nTheriogenology 68: 413-422.\nSnider TA, Sepoy C, Holyoak GR ( 2011) Equine endomet-\nrial biopsy reviewed: observation, interpretation and ap-\nplication of histopathologic data. Theriogenology\n75: 1567-1581.\nStreuli CH, Schmidhauser C, Kobrin M, Bissell MJ, Derynck\nR( 1993) Extracellular matrix regulates expression of the\nTGF-β\n1 gene. J Cell Biol 120: 253-260.\nSzostek AZ, Siemieniuch MJ, Lukasik K, Galvao AM, Fer-\nreira-Dias GM, Skarzynski DJ ( 2012) mRNA transcrip-\ntion of prostaglandin synthases and their products in the\nequine endometrium in the course of fibrosis.\nTheriogenology 78: 768-776.\nTroedsson MH ( 1999) Uterine clearance and resistance to\npersistent endometritis in the mare. Theriogenology\n52: 461-471.\nWalter I, Handler J, Reifinger M, Aurich C ( 2001) Associ-\nation of endometriosis in horses with differentiation of\nperiglandular myofibroblasts and changes of extracellular\nmatrix proteins. Reproduction 121: 581-586.\nWoodward EM, Christoffersen M, Campos J, Squires EL,\nTroedsson MH (2012) Susceptibility to persistent breed-\ning-induced endometritis in the mare: relationship to en-\ndometrial biopsy score and age, and variations between\nseasons. Theriogenology 78: 495-501.\nZajac S, Katkiewicz M, Witkowski M, Boryczko Z,\nPawlak M ( 2008) Endometrosis in mares. Med Weter\n64: 257-261.\nZhang Z, Kundu GC, Zheng F, Yuan CJ, Lee E, Westphal\nH, Ward J, Demayo F, Mukherjee AB ( 2000) Insight\ninto the physiological function(s) of uteroglobin by\ngene-knockout and antisense-transgenic approaches.\nAnn N Y Acad Sci 923: 210-233.\n554 J. Buczkowska et al.","source_license":"public-domain-us","license_restricted":false}