Development of the implantation chamber in the pregnant bitch

Abstract

Uteri taken from 25 bitches at various times during the early stages of pregnancy were studies cytologically to determine how the implantation chamber developed and how fetal-maternal relations were established. On day 13 after the end of estrus, knobs of trophoblastic syncytium formed and became wedged between cells of the uterine luminal epithelium. The syncytium quickly spread along the uterine lumen and into the mouths of the glands, dislodging and surrounding maternal cells. As invasion continued trophoblastic villi, consisting of cores of cytotrophoblast covered by a continuous layer of syncytium, penetrated deeper into the endometrium. The syncytium spread to surround maternal vessels and decidual cells. By day 26 the trophoblast had extended down to the large lacunae. Here syncytial trophoblast covering tips of the villi degenerated, leaving cytotrophoblast exposed to the necrotic zone. These cells possessed characteristics of absorbing cells. Hematomas were formed by focal necrosis of fetal and endometrial tissue at the poles of the implantation sites. Large pools of extravasated blood accumulated and red blood cells were phagocytized by surrounding trophoblastic cells. Therefore, the endotheliochorial relationship in the canine placenta appeared to be established by syncytial trophoblast invading a cellular endometrium. In the necrotic zone and hematomas, cellular trophoblast may have lost its syncytial covering, but elsewhere maternal vessels and decidual cells in the placenta were in direct contact only with syncytial trophoblast.

An ultrastructural study of interstitial implantation in captive-bred, short-tailed fruit bats, Carollia perspicillata : trophoblastic adhesion and penetration of the uterine epithelium

“…In this respect, at least these bats and some rodents (rats, mice and hamsters) Schlafke 1967, 1979;Parkening 1976;Blankenship et al 1990) differ from many other mammals. In primates (Enders et al 1983;Smith et al 1987), lagomorphs (Enders and Schlafke 1971;Steer 1971), carnivores (Enders and Schlafke 1972;Barrau et al 1975;Leiser 1982;Enders and Mead 1996), and some rodents (caviids and sciurids) (Enders and Schlakfe 1969;Enders et al 1995) initial adhesion to and penetration of the uterine luminal epithelium is accomplished by syncytiotrophoblast.…”

Characterization of Foamy Epithelial Surface Cells in the Canine Endometrium

“…Furthermore, Barrau et al (1975b) described the growth of the endometrial crypts inducing the formation of lacunae in the canine pregnant endometrium by day 12 after the end of oestrus forming the implantation chamber. These observations are comparable to the morphological appearance of the endometrial surface tissue formation observed in this study.…”

Immunolocalization of E-cadherin and β-catenin in the cyclic and early pregnant canine endometrium

“…The pregnancy samples were staged on the basis of cumulative information gathered from a diestrus-compatible cytology, the date of documented coitus plus the histological changes observed in the endometrium, according to the histological descriptions of canine early pregnancy events [39,43], and aligned to the day from pre-ovulatory LH surge. Up to day 17 the embryo was not yet adhered to the endometrium, although some changes are found in the superficial layers of the endometrium, including increased interstitial edema and deepening of the endometrial crypts.…”

“…Of particular interest is the relatively long estrous phase and a remarkable long luteal phase which is of similar length in pregnant and non-pregnant cycles [38]. The dog presents an endotheliochorial placenta type, where the invasive trophoblast destroys the luminal epithelium and the underlying lamina propria in the process of implantation and placentation [39,40]. Consequently, the spatiotemporal pattern in E-cadherin and β-catenin molecules in the canine endometrium may differ from those established in other species with a shallower non-invasive placentation.…”