Temporal Aspects of Rabbit Uterine Vascular and Decidual Responses to Blastocyst Stimulation

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Abstract
Measurements were made of the permeability of rabbit uterine blood vessels to protein-bound Evans blue (EB) dye at implantation sites relative to nonimplant regions of the uterus. Results, expressed as a permeability ratio (implant EB/nonimplant EB), showed that a vascular response was present at some implant sites as early as 6.5 days after mating, while higher permeability ratios (> 3.0) were obtained at 7 and 8 days. Assay of tissue water (edema) in implantation sites correlated well with changes in the degree of bluing. On day 6.5 or 7, several intact blastocysts from sites exhibiting bluing were flushed from the uterus. Light microscopic analysis of the blastocysts revealed intact blastocyst coatings suggesting that the vascular response was initiated prior to direct attachment of trophoblast to uterine epithelium in rabbits. The duration of blastocyst-uterine contact required for maximal stimulation of decidual development was assessed by destruction of blastocysts at 6.5, 6.75, 7, 7.5 or 8 days after mating. Maximal decidual development, measured on day 14, was obtained only in uteri of females where blastocysts were destroyed at, or after, 7.5 days. For most females a period of blastocyst-uterine contact approaching 24 h is required for full commitment to decidual development.