The Glandular Chambers of the Placenta of the Bitch in the Second Third of Pregnancy (day 30–44): An Ultrastructural, Ultrahistochemical and Lectinhistochemical Investigation

The present study represents the first comprehensive investigation of the glandular chambers of the placenta of the bitch. We examined the glandular chambers by SEM, TEM, ultrahistochemical and lectinhistochemical methods. The glandular epithelium is a high columnar epithelium with club-shaped apical protrusions bearing short microvilli. The epithelium forms extensive folds which fill up most of the lumen of the glandular chambers. Proceeding to the placental labyrinth, the glandular chambers are covered by the tips of the chorionic tufts. The trophoblast and the glandular epithelium are separated by a thick layer of secretions. The ultrastructure cytology of the columnar epithelium is characterized by several Golgi complexes and abundant apical-located mucus vesicles with a positive dialysed iron reaction. Lectin histochemistry reveals in general a strong reaction of these mucus vesicles with all lectins used. The mucus in the lumen of the glandular chamber reacts strongly with WGA. NeuWGA, LPA and ConA. The trophoblastic villi projecting into the lumen of the glandular chambers are covered by a pseudostratified epithelium consisting of a flat basal layer and a superficial columnar one. Its cytoplasm is filled with large fusing vacuoles containing longish screw-shaped structures. No morphological equivalent of absorption is found. According to the ultrastructure of the trophoblast, the significance of the mucus in the glandular chambers in stopping the invasive growth of the trophoblast is discussed.