Cyclical endometrial steroid hormone receptor expression and proliferation intensity in the mare.
Authors: Aupperle H, Ozgen SSchoon H A, Schoon D, Hoppen H O, Sieme H, Tannapfel A
Journal: Equine veterinary journal
Summary
# Cyclical endometrial steroid hormone receptor expression and proliferation intensity in the mare Oestrogen and progesterone receptors, along with markers of cellular proliferation, follow a distinct pattern throughout the equine oestrous cycle that is tightly coupled to circulating hormone concentrations. Using immunohistological examination of endometrial biopsies collected serially from seven mares over a complete cycle, researchers tracked the location and intensity of oestrogen receptor (ER), progesterone receptor (PR), and the proliferation antigen Ki-67 in relation to blood steroid levels. Rising 17β-oestradiol during preoestrus triggered synchronous expression of both receptors and Ki-67 in stromal tissue, whilst the transition to early dioestrus—marked by declining oestradiol and peak progesterone—produced the most intense proliferation activity and strongest receptor expression in epithelial cells. Critically, endometrial tissue affected by fibrotic changes (endometrosis) displayed asynchronous receptor expression and proliferation kinetics, suggesting that degenerative endometrial disease disrupts the normal cyclical responsiveness to steroid hormones. These findings provide a mechanistic framework for understanding how endometrial pathology compromises fertility, and indicate that receptor expression patterns could potentially serve as a diagnostic marker of endometrial health status and cyclical competence in problem mares.
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Practical Takeaways
- •Understanding cyclical endometrial receptor expression helps explain physiological changes during the mare's reproductive cycle and may inform breeding soundness evaluations
- •Endometrosis (fibrotic changes) disrupts normal hormone receptor cycling, which could explain subfertility in affected mares and guides consideration for biopsy interpretation
- •Timing of endometrial biopsies relative to cycle stage is important for accurate histological assessment, as hormone receptor expression and proliferation activity vary significantly
Key Findings
- •Rising 17beta-oestradiol in preoestrus induces synchronous expression of oestrogen receptors, progesterone receptors, and Ki-67 antigen in stromal cells
- •Early dioestrus correlates with decreased oestradiol, maximal progesterone levels, intense epithelial proliferation, and highest hormone receptor expression
- •Fibrotic endometrial areas (endometrosis) demonstrate asynchronous glandular differentiation with out-of-phase epithelial hormone receptor expression