Progesterone Regulation of Proliferation and Regression of Rat Decidua Basalis

Abstract

During implantation mesometrial cells o f the uterine stroma become decidualized under the coordinate actions of progesterone (P4 ) and estrogen (E) [1,2]. This process is characterized by transformation o f phenotype and stromal cell proliferation between Days 8-12 of gestation, resulting ultimately in the formation o f the decidua basalis (DB) [3,4], By Day 14. however, the DB begins to regress and a reduced layer o f stromal cells persists to the end of pregnancy [5.6]. The regression of DB is accompanied by development o f two other layers, namely junctional zone (JZ) and labyrinth zone (LZ), which are fetal parts of the placenta and morphologically become predominant at the end stages o f pregnancy. Although the morphological changes have been well documented and numerous functions have been revealed for DB [3-8], the mechanism and factors involved in the regulation of proliferation and regression o f DB have not been elucidated. The transition of DB from proliferation to regression occurs in such a delicate way that the morphological integrity and functional competence of the DB and placenta are maintained even though stromal cells are being lost. The objective o f this study was to identify the intracellular signals initially favoring proliferation and synthetic processes and those promoting remodeling and regression as pregnancy progresses.