Summary. Changes in the extracellular and blood spaces of the uterus were assessed from the distribution volumes of 51Cr-EDTA and 51Cr-labelled red blood cells during the development and regression of the artificially induced decidual cell reaction in ovariectomized, steroid-treated mice. The normally high values for uterine extra cellular space (0·35–0·40 μl/mg) fell to less than 0·20 μl/mg in association with decidual growth. Uterine blood space increased from around 0·02 μl/mg to 0·03–0·05 μl/mg with decidual development. Induction of decidual regression by removal of s.c. progesterone implants caused a rapid decline in tissue blood volume to reach control values (0·01–0·02 μl/mg) within 24 h and preceded any reduction in uterine weight. Uterine vascular permeability, as determined from the tissue accumulation of 125I-labelled human serum albumin, fell with a similar time course. Tissue extracellular space returned to the higher control values within 48 h of initiating decidual regression.
Keywords: mouse; decidual cell reaction; tissue space