Influence of cycle stage, age and endometrial biopsy score on oxytocin receptor distribution and gene expression in the cervix and uterus of non-pregnant mares

Abstract

Persistent breeding-induced endometritis (PBIE) or delayed uterine clearance (DUC) are major causes of mare subfertility. Oxytocin and its receptor are thought to play significant roles in the pathogenesis of DUC but the specific roles of oxytocin receptor (OR) distribution and gene expression remain undefined. In this study both OR distribution and gene expression in the endometrium, myometrium and cervix during both luteal and non-luteal phases in non-pregnant mares (n = 27) of differing age (young: 2-9 years, n = 17; old: > 10 years, n = 10) and endometrial biopsy score were described using immunohistochemistry (IHC) and quantitative reverse-transcription polymerase chain reaction (RT-qPCR), respectively. Immunohistochemistry showed a similar pattern of OR distribution in uterus and cervix, with the exception of the glandular epithelium, absent in the cervix. Uterine ORs were localized in endometrial luminal and glandular epithelia, transmural vascular endothelium, sub-epithelial and peri-glandular stromal cells and myometrial smooth muscle cells. The OR labeling intensity was consistently greatest in the vascular endothelium. Real-time qPCR showed a higher OR gene expression in myometrium compared to cervix (P = 0.001) and endometrium (P = 0.009). There was no difference in OR gene expression between cervix and endometrium (P = 1.0). Oxytocin receptor gene expression was significantly higher during the non-luteal phase in both combined uterine tissues (endometrium and myometrium) and myometrium. Oxytocin receptor distribution and gene expression were not influenced by a mare's age or endometrial biopsy score. As endometrial biopsy score and mare age were not predictors of OR gene expression, deficient OR gene expression is unlikely to be associated with DUC.

Exploring Hyperprolific Sows: A Study of Gross Morphology of Reproductive Organs and Oxytocin Receptor Distribution across Parities

“…In the present study, oxytocin receptor immunolocalization was detected in various cell types, including surface epithelial cells of the endometrium, endometrial glandular cells, myocytes of the myometrium, vascular endothelial cells, vascular smooth muscles, and endometrial stromal cells. Similar results have been reported in non-pregnant mares [19] and pregnant canines [23]. Among the five layers of the uterus, the present study identified the greatest H-score of oxytocin receptors in the deep uterine glands, while the circular muscle layer of the myometrium exhibited the lowest H-score.…”

“…The present study was conducted to undertake an investigation into various aspects related to hyperprolific sows, with a particular focus on the morphology of their reproductive organs and the distribution of oxytocin receptors in uterine tissue across different parities and stages of the estrous cycle. The presence of oxytocin receptors in uterine tissue has been well established across several mammalian species [17,19,23]. In the present study, oxytocin receptor immunolocalization was detected in various cell types, including surface epithelial cells of the endometrium, endometrial glandular cells, myocytes of the myometrium, vascular endothelial cells, vascular smooth muscles, and endometrial stromal cells.…”

“…This indicated that the level of the oxytocin receptor diminishes with the age of muscle stem cells. In contrast, a study conducted in non-pregnant mares revealed that age (2-9 years versus >10 years) did not have an impact on uterine oxytocin receptor distribution or gene expression [19]. Until now, there has been no research on the relationship between sow parity and the oxytocin receptor in various layers of their uterine tissue.…”

Cyclical cervical function in the mare involves remodelling of collagen content, which is correlated with modification of oestrogen receptor 1 abundance

“…Alternatively, oestrogen (via ESR1) could be exerting an indirect effect on collagen synthesis and degradation via other hormones and receptors for these hormones. Oxytocin receptors in the mare cervix, for example, are in a relatively greater abundance during the follicular phase of the oestrous cycle (Annandale et al 2018). Furthermore, topical application of oxytocin to the mare cervix induces an increase in the height, width and area of the cervix (Klewitz et al 2014).…”

Female age and parity in horses: how and why does it matter?

“…Most studies showed that severe endometrial changes are more frequent in endometrial biopsies from old and/or multiparous mares in comparison to biopsies from young and/or nulliparous mares (Ricketts 1975;Doig et al 1981;Waelchli 1990;Ricketts and Alonso 1991;Brinsko et al 1994;Grüninger et al 1998;Woodward et al 2012;Esteller-Vico et al 2012Ferreira et al 2015). Only one study did not find any differences according to age (Annandale et al 2018). Observed changes were related to inflammatory and fibrotic modifications (Kenney 1978) with severity of uterine fibrosis being positively correlated with mares' age (Doig et al 1981;Siemieniuch et al 2017).…”