Progesterone and ovarian stimulation control endometrial pinopode expression before implantation in mice

Endometrial epithelial pinopodes are considered as markers of endometrial receptivity and seem to be directly involved in the adhesion of the blastocysts to the endometrial surface. The aim of the study was to assess the effects of ovarian stimulation and progesterone injection on pinopode expression, and compare morphological characteristics in the preimplantation stage in mice. Adult female mice (n = 30) were divided into three groups: control, superovulated and superovulated-progesterone injected. In experimental groups the mice received 7.5 I.U human menopausal gonadotropin (HMG) and then after 48 h 7.5 I.U human chorionic gonadotropic (HCG) hormone. After that every two females were put with one male in one cage for mating. Superovulated-progesterone group were injected with progesterone (1 mg/mouse) in 24, 48, 72 h interval after the HMG injection. Animals were sacrificed in 96 h after HMG injection, and their uterines (the middle one-third) were prepared for transmission electron microscope studies. That demonstrated that all groups differed from each other. In most of the controls and hyperstimulated-progesterone mice 4 days after HMG injection, long and short microvilli were seen, but they had no developed pinopodes, while in hyperstimulated mice, well developed pinopodes were expressed 4 days after HMG injection.In conclusion: hyperstimulated mice without progesterone injection may be useful for the studies of pinopodes and implantation.

► Progesterone had no positive effects on luminal epithelium of the mice that stimulated for ovulation.
► Ultrastructurally, in the groups receiving HCG/HMG, pinopodes were better comparing to the others.
► The best method for obtaining blastocyst immediately before implantation is uterine flashing.