The bovine intercaruncular placenta throughout gestation

The attachment of chorion to uterine epithelium which results in a functional placenta began in the middle of the ipsilateral horn near the embryonic disc and spread towards the tip of each uterine horn. The intercaruncular union was fragile but perfusion and careful tissue processing preserved contact between chorion and intercaruncular epithelium from the fourth week until late in gestation. The adhesion-attachment process included binucleate cell migration from the chorion and remodelling of the maternal tissue. In areas where attachment was occurring or maintained, maternal epithelial height was reduced from columnar to cuboidal or squamous. Multinucleated cells and syncytium, which resulted from fusion of migrant binucleate cells with uterine epithelium, were common in the earlier stages of placentation. Extensive syncytium did not persist beyond the second month but some multinucleates were found throughout gestation. Attachment involved substantial areas in the bodies and middle regions of both horns but was not universal. Very limited attachment was found in the tip of the ipsilateral horn and none in the tip of the contralateral horn. In sections where contact could not be preserved the uterine epithelium was composed of tall columnar cells and no binucleate cell migration was detected. Intraepithelial lymphocytes were common in the tall columnar epithelium but almost totally absent where attachment and migration were occurring. Preservation of contact between the chorion and intercaruncular uterine epithelium throughout gestation demonstrated the diffuse nature of bovine placental attachment.