Nitric oxide inhibits development of embryos and implantation in mice

The objectives of this study were to evaluate the effects of a nitric oxide (NO) donor on embryo development in vitro and on implantation of embryos in vivo in mice. Mouse embryos (2-cell) were incubated in media containing different concentrations of diethylenetriamine/NO (DETA/NO), a nitric oxide donor, and development was monitored daily for 4 days. Specificity of NO effects was assessed by using DETA without NO or 48 h preincubated DETA/NO. In in-vivo studies, mated mice were continuously infused, subcutaneously, with various concentrations of DETA/NO or DETA through mini-osmotic pumps (from day 1 of pregnancy), and implantations in the uterus were assessed on day 6. None of the embryos progressed beyond 4-cell stage when exposed to 0.1 or 1.0 mM DETA/NO compared with 94.5% of central embryos that developed beyond the morula stage by day 4. Embryo development was unaffected by lower (0.001 and 0.01 mM) concentrations of DETA/NO, 48 h preincubated DETA/NO, or DETA only. Infusion of DETA/NO to mice caused inhibition of embryo implantation in a dose-dependent manner. No implantation sites were observed in mice infused with a daily dose of 20 mu mol DETA/NO rate, compared with an implantation rate of 81.8% in control or DETA-treated mice. This study demonstrates for the first time that higher concentrations of NO inhibit both embryo development in vitro and implantation in vivo in mice.