Temporal expression of inducible nitric oxide synthase in mouse and human placenta

The aim of this study is to investigate the changes in expression and activ ity of inducible nitric oxide synthase (iNOS) in the developing murine embr yo and mouse and human placenta. Using reverse transcription-polymerase cha in reaction (RT-PCR), Northern blotting, and in-situ hybridization (ISH) we identified iNOS mRNA in mouse placenta at 9.5, 12, 14, 16, 18 and 20 days post coitum. Northern blot analysis demonstrated that the quantity of murin e iNOS transcript was expressed at a stable level between days 12-20 althou gh the level of calcium-independent NOS activity declined with advancing ge station. RT-PCR detected iNOS-specific mRNA in murine embryonic stem cells, but not in embryos at later stages (4-cell or blastocyst), ISH failed to s how iNOS-specific mRNA in either murine placenta or the underlying myometri um on day 7, but did so in the trophoblast by day 9.5. Later in gestation, extensive labelling was observed in both spongiotrophoblast and trophoblast giant cells. iNOS mRNA was also detected both in immature human placentae (16-18 weeks) and at term, predominantly in syncytiotrophoblasts and placen tal artery smooth muscle. In conclusion, iNOS is constitutively expressed i n mouse and human placenta at a time and in a location that suggests a role in placentation.