The resistance of the mouse uterine lumen to flushing and possible contamination of samples by plasma and interstitial fluid.

The hydrostatic pressures generated during controlled flushing of the mouse uterus increased at implantation and under conditions of uterine closure. These pressures may be responsible for inducing tissue damage during flushing. The possibility that samples collected by flushing might be contaminated with interstitial fluid or plasma was studied using intravenously administered 51Cr-labelled EDTA and 125I-labelled human serum albumin as markers. The presence of both tracers was detected in all flushings and was greatest in flushings from uteri with luminal closure and early implantation sites. These observations raise serious doubts about the validity of the flushing technique for analysing uterine luminal constituents in mice.