Immunohistochemical localization of prostaglandin H synthase in the embryo and uterus of the mouse from ovulation through implantation

Prostaglandins (PGs) in the embryo and endometrium are involved in processes that are important for implantation. Although the presence of PGs (PGE2, PGF2 alpha, PGI2) in decidualized endometrium has been widely reported, less is known about the capacity of the pre-implantation embryo to synthesize PGs. Prostaglandin H (PGH) synthase is necessary for the production of PGs. Using an immunohistochemical method, PGH synthase was localized in the mouse embryo and uterus from superovulation through embryo implantation. No PGH synthase was detected in oocytes at the time of ovulation or in single-cell embryos 1 day post-fertilization (PF). Circular areas of immunostaining became evident in the cytoplasm of blastomeres at the morula stage (day 3 PF). After implantation (day 5 PF), a low level of PGH synthase reactivity was observed in embryonic cells; no PGH synthase was detected in the embryo by day 7 PF. The endometrial glands exhibited maximal immunostaining by day 3 PF, and after implantation, PGH synthase appeared in decidual cells along the border of placentation. Low levels of PGH synthase reactivity were detected in myometrial cells during the period after superovulation through day 7 PF. This is the first demonstration of PGH synthase in the mouse embryo prior to apposition with glandular endometrial epithelium, supporting the hypothesis that the embryo has the potential to produce PGs that may mediate autocrine and/or paracrine responses at the time of nidation.