| dc.description.abstract |
It has previously been demonstrated that uterine nitric oxide synthase (NOS)activity increases before embryonic implantation in rats. The aim of thepresent work was to investigate the regulation and the physiological relevanceof the nitric oxide (NO) system in ovoimplantation. The increase in NOSactivity in early pregnancy was found to be independent of the presence ofembryos in the uterus. Whereas the Ca<emph type="7">2+-dependentisoform of NOS increased gradually in the preimplantation days, theCa<emph type="7">2+-independent isoform increased just at the beginningof implantation (Day 5, 1800 hours); then the activity of both isoformsdeclined. Oestradiol, whose concentration peaks before implantation, might beregulating NOS activity in the uterus, since treatment of rats with tamoxifen,a receptor antagonist, reduces the activity of both isoforms topreimplantation levels. Intraluminal injections of L-NAME (0·5 mgkg<emph type="7">-1), a competitive inhibitor of NOS, reduced by50% the number of implanted embryos; this suggests that the NO systemplays a role during implantation. The data suggest that oestradiol might be amodulator of NOS activity during nidation and that NO production is necessaryto achieve a successful embryo implantation. |
|