Interaction of uterine flushings with mouse blastocysts in vitro as assessed by the incorporation of [3H]uridine.

Culture of mouse blastocysts in medium supplemented with uterine flushings from mice at random stages of the oestrous cycle resulted in a depression of [3H]uridine incorporation. This depression was maintained for up to 12 h, but by 24 h of culture, inhibition of uterine incorporation was no longer apparent. The loss of inhibition wa due to a change in the activity of the flushings and not to a change in the ability of blastocysts to respond to the inhibitory influence. The inhibition of [3H]uridine incorporation was maintained for at least 24 h when blastocysts were transferred every 6 h to fresh uterine flushings.