Reproduction Abstracts

Introduction: The sex steroid hormone progesterone (P) is the most important hormone in the canine estrous cycle for initiation and preservation of pregnancy. The responsiveness of the endometrial cells to P depends on progesterone receptors (PGRs). In recent studies alternatives to the classical progesterone receptor were identified as membrane-associated progesterone receptors (MAPGRs). Progesterone receptor membrane component-1 (PGRMC-1) is a representative of the MAPGRs which was identified in human, monkey, bovine and murine endometrium so far. The distinct function of PGRMC-1 is not yet clarified but it is supposed that PGRMC-1 is important in cell-cycle regulation and stromal cell decidualization. Furthermore, in the murine endometrium PGRMC-1 deficiency leads to development of cystic endometrial hyperplasia (CEH). In the canine endometrium CEH is a common pathological alteration leading to infertility and inflammatory processes which predispose the endometrium to a secondary, potential life-threatening bacterial infection (pyometra).

Material and methods: In the present study PGRMC-1 expression in the healthy (n=20), CEH-affected (n=8) and pyometra-affected (n=8) canine endometrium was demonstrated by means of immunohistochemistry. Additionally PGR-B expression and proliferative activity were determined to demonstrate distinct expression patterns of PGRMC-1 from PR-B and the involvement of PGRMC-1 in endometrial cell-cycle regulation.

Results and discussion: Five of the CEH-affected endometria lacked of PGRMC-1 whereas in the healthy uteri PGRMC-1 protein was identified in cycle-dependent expression patterns in endothelial, epithelial, stromal and myometrial cells. This study is the first to determine PGRMC-1 in the canine endometrium and suggests a role of PGRMC-1 in the development of canine CEH.