Uterine involution and endometrial function in postpartum pony mares.

This research investigates how the uterus in horse mares recovers after giving birth, specifically looking at the regrowth of the endometrium. It examines the different processes and factors at work using post-birth uterine biopsy specimens.

Methods of the Study

This research was carried out using nine postpartum pony mares. The methodology of this study included:

• Examination of the mares’ uteruses on days 1, 9, and 16 after they gave birth.
• Taking uterine biopsy specimens for histologic examination.
• Analysis of lectin binding using histochemistry, which is the study of the chemical composition of cells by staining, impregnating, or otherwise treating biological tissue with a dye.
• Studying the expressions of various markers such as Ki-67 antigen (a proliferation marker), lysozyme, and caspase 3 (an apoptosis marker) using immunohistochemistry which reveals the presence of certain proteins in tissues.
• Determining gene expressions for cytokines, cyclooxygenase 2, prostaglandin-E-synthase, and estrogen and progesterone receptors using quantitative real-time PCR assay, a laboratory technique used to amplify and simultaneously quantify a targeted DNA molecule.

Results of the Study

The study produced several notable results including:

• Appearance of neutrophils (a type of immune cell) predominately on day 1, later replaced largely by lymphocytes and macrophages.
• High numbers of cells showed staining for caspase 3 (a marker for cell death or “apoptosis”) on day 1, decreasing by day 9.
• Increasing number of cells showed staining for Kiel 67 antigen (a marker for cell proliferation) between days 1 and 9.
• Change in lectin binding to the endometrium over time, indicating alterations in the glycocalyx patterns of the endometrium.
• No significant difference in mRNA expressions for cytokines and prostaglandin-E-synthase between different days.
• Minimal expression of progesterone and estrogen receptors on day 1, increasing by day 9.

Conclusions of the Study

The study concluded that the mare’s endometrium undergoes apoptosis, or programmed cell death, in the early stage of the postpartum period. However, during the second postpartum week, cell proliferation takes over, which underscores the regrowth of the endometrium. Simultaneously, a change in binding patterns of lectin reflects the transformation in endometrial glycocalyx structures. Finally, the study findings indicate an increased expression of estrogen and progesterone receptors, allowing the endometrium to respond accordingly during the horse’s estrus cycle and subsequent diestrus.