Nitric oxide synthase distribution during implantation in the mouse

The peri-implantation period is a critical time during murine development, Although the importance of nitric oxide has been demonstrated during gestat ion, its role in implantation has not been fully defined. The aim of this s tudy was to quantify (by Western blotting) two prominent nitric oxide synth ase (NOS) isoforms, inducible (iNOS) and endothelial (eNOS) and localize al l three forms [iNOS, eNOS, and neuronal (nNOS)] by immunohistochemistry in uterine tissue from days 4 through 8 of pregnancy. By day 6, iNOS values we re significantly elevated in implantation sites compared with interimplanta tion regions and continued to rise through day 8, Analysis of eNOS was simi lar, but implantation site values peaked by days 6 and 7. Labelled iNOS cel ls were within the decidua, around myometrial vessels, and within the ectop lacental cone, At implantation, eNOS was conspicuous, displaying label adja cent to the embryo in vessels of the primary decidual zone, nNOS was locali zed mainly in the mesometrium and myometrium and did not appear to change t hroughout the peri-implantation period. The increased iNOS and eNOS values following implantation in the embryonic site may imply roles in tissue remo delling, immunosuppression and vasoregulation. Nitric oxide may play an imp ortant role in the mechanisms of implantation where these factors are keys to successful pregnancy.