IMMUNOHISTOCHEMICAL AND ULTRASTRUCTURAL-LOCALIZATION OF PROSTAGLANDIN-H SYNTHASE IN THE PREIMPLANTATION MOUSE EMBRYO

The immunohistochemical and ultrastructural localization of prostaglan din H synthase (PGH synthase) was studied in the Albino Swiss CF-I mou se at different stages of embryonic development (two-cell stage, four- eight cell stage, morula and blastocyst). Flushed embryos and sections of uteri and oviducts containing embryos were treated with a mouse Ig G monoclonal anti-PGH synthase antibody. The second antibody (rabbit a nti-mouse) was conjugated with peroxidase or fluorescein isothiocyanat e for light microscopy, fluorescence microscopy and confocal scanning. For reflection contrast microscopy and transmission electron microsco py a second antibody, goat anti-mouse, was conjugated with ultrasmall gold particles. Controls without anti-PGH synthase were used concurren tly. All embryos demonstrated PGH synthase reactivity. Immunostaining appeared to be more intense at the two-cell stage, four-eight cell sta ge embryos and morulae than in blastocysts. Further examination indica ted an intracytoplasmic location for PGH synthase, which was confirmed by stereoscopic photographs made during confocal scanning microscopy and by the immunostaining patterns observed with reflection contrast m icroscopy and transmission electron microscopy. Transmission electron microscopy immunostaining patterns support the localization of PGH syn thase in the endoplasmic reticulum. This is the first demonstration of the ultrastructural localization of PGH synthase in the mouse embryo. Its presence before the apposition with the endometrial epithelium su pports the hypothesis that arachidonic acid metabolism via the PGH syn thase pathway may be crucial for implantation.