HYPERSTIMULATION AFFECTS VASCULAR-PERMEABILITY AT IMPLANTATION SITES IN THE RAT ENDOMETRIUM

Purpose: It has previously been shown that deleterious changes occur i n the epithelium and stroma of the endometrium of the rat following ov arian hyperstimulation by exogenous gonadotropins. The purpose of the present study was to investigate the formation of possible implantatio n sites following hyperstimulation. Female rats (n = 8) were injected in phase with their estrous cycle with follicle stimulating hormone (F SH), followed by human chorionic gonadotropin (hCG), and mated at proe strous. Control rats (n = 6) were uninjected and mated at proestrous. Animals were killed at 5.5 days of pregnancy. The pontamine blue techn ique was used to demonstrate the permeability of the uterine vessels. Implantation sites were demonstrated in the uterine horns of all contr ol animals by segmental blue banding. Results: Blue staining occurred only in a portion of one horn of one hyperstimulated animal. While fen estrations were found in the walls of capillaries of control animals, similar fenestrations were not observed in the vessels of hyperstimula ted animals. Conclusion: As the walls of vessels in the hyperstimulate d animals failed to become permeable, and as no implanting embryos wer e found in these animals, it is concluded that there was an inability of the endometrium to form implantation sites. These changes may imped e attachment and implantation of the embryo.