Sodium ion concentrations in uterine flushings from "implanting" and "delayed implanting" mice.

The uteri of mice were flushed with isotonic mannitol (1) on the day of implantation during normal pregnancy or (2) during delay of implantation. The Na+ concentration in flushings was reduced during diapause but had increased by 65% 24 h after progesterone-treated ovariectomized mice received estrogen injections. The results suggest that the apparent metabolic quiescence of diapausing blastocysts may, in part, be a consequence of lower (Na+) in the uterus during delay of implantation.