Cyclical endometrial steroid hormone receptor expression and proliferationintensity in the mare

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