It has been found that in the majority of cases the injection of oil into the uterus of mice on the 4th day of pseudopregnancy results in the formation of several discrete decidual swellings along the length of the uterus. Histochemical and histological examination on the 6th day of pseudopregnancy reveals that a structure closely resembling an implantation chamber is formed in the middle of the swellings. There is a down-pushing of the lumen from the mesometrial side into the centre of the swelling and breakdown of epithelium on the antimesometrial side of the chamber. The decidual tissue around the base of the chamber contains both glycogen and pas-positive diastase-fast material, similar to that found around an implanting blastocyst.
The lumen of the artificial implantation chamber contains relatively large quantities of a secretion rich in protein and a diastase-fast pas-positive material, probably a neutral mucopolysaccharide-protein complex. This secretion is also found in natural implantation chambers on the 6th day of pregnancy, though in much smaller quantities. It is suggested that it is a nutritive substance secreted by the uterus as part of the implantation reaction and normally taken up by the blastocyst. It is concluded that the 4-day pseudopregnant mouse uterus has the competence to react to a natural or unnatural decidual stimulus with the formation of implantation chambers.
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