progesterone shifts the pinopodes expression of mouse endometrium to pre-implantation time after ovarian hyperstimulation

background: the aim of this study was to determine the correlation between ultrastructural studies for pinopodes expression after ovarian hyperstimulation and progesterone injection in mice. materials and methods: adult nmri mice were superovulated using human menopasual gonadotropic (hmg) and human chorionic gonadotropic (hcg) hormones; after that, daily injection of progesterone (1 mg/mouse) was performed. animals were sacrificed by cervical dislocation 3.5 and 4.5 days after hcg injection. tissues of uterine horns were obtained and processed for scanning (sem) and transmission (tem) electron microscopy studies. the pseudopregnant control samples were studied same as experimental groups. results: the sem and tem observations showed that in control groups on 3.5 days of pregnancy, there were some pinopodes. all apical cell surfaces expressed these projections on the forth day. in progestrone-injected group, well developed pinopods were expressed 3.5 days after hcg injection and they were transformed to small projections on the fourth day following hcg injection. also, the life span of pinopods was limited to a short time. at the tem levels, the pinopods were seen as swelling process on the apical surface, which were more pronounced on day 3.5 of hcg injection in hyperstimulated and progestrone injection. conclusion: the progestrone may cause premature expression of pinopodes and the implantation failure after ovarian induction may be due to these timing changes.