Ultrastructural Aspects of the Appositional Stage of Interstitial Blastocyst Implantation

Abstract

The ultrastructural aspects of the appositional phase of interstitial blastocyst implantation in the guinea pig have been investigated using scanning and transmission electron microscopy. Blastocysts measured 28–34 µm in diameter and were encased in the zona pellucida. Trophoblast pseudopodia which penetrated the zona made contact with the underlying uterine epithelium and served, along with uterine epithelial contact with the zona, to hold the blastocyst over the subsequent site of implantation. Pseudopodia emanated from the embryonic pole of the blastocyst measured 2–4 µm in diameter and initiated uterine-blastocyst contact. Pseudopodia contained a cytoplasm rich in tubular mitochondria, rough endoplasmic reticulum, and Golgi apparatus and usually were found directed toward a sub-epithelial capillary plexus. These results suggest that the trophoblast pseudopodia are very active metabolically and may serve to align the blastocyst over stroma regions possessing a rich subepithelial vascular supply and high nutrient availability.

Scanning electron microscopic and morphometric analysis of the guinea pig uterine luminal surface: Cyclic and ovarian steroid-induced modifications

“…The demonstration that similar surface structures could be produced in ovariectomized hormone-treated animals as were observed in normal cyclic animals indicates that progesterone and estrogen, alone or in combination, (Table 1), it is concluded that the day 2 and 12 specimens are under the primary influence of progesterone, the day 0 (ovulation) uterus under a combined P ϩ E control, while the surface of the day 6 (nidatory) uterus simulated that of the chronic P/acute E-treated specimens. Thus, depending on cyclic state, the uterine surface structure changes in relation to the hormonal milieu (Garris, 1984d).…”

“…These steroid-induced changes in uterine endocrine milieu are well recognized to modulate mitotic, vascular and structural factors that have been implicated in the initiation of interstitial blastocyst implantation in both humans and the guinea pig (Garris, 1983(Garris, , 1984aGarris and Whitehead, 1981;Garris et al, 1983Garris et al, , 1986Garris and Foreman, 1984). The cyclic fluctuations in plasma steroid levels may also induce the alterations in uterine luminal surface structure during the estrous cycle, which have been previously observed to occur in association with blastocyst implantation in this species (Garris, 1984d). The present studies were undertaken to determine the cyclic changes which occur in the ultrastructure of the guinea pig uterine luminal surface throughout the estrous cycle and to determine the independent and synergistic effects of estrogen and progesterone on altering luminal surface topography.…”

“…and perfused with Karnovsky's formaldehyde-glutaraldehyde solution via intracardiac puncture as previously described (Garris, 1984d). The length of the uterus was measured in situ, removed and pinned at its original length to a wax plate which was submerged in fresh fixative.…”

“…Scanning electron microscopy (SEM) has been used to study the luminal surface morphology of the oviduct (Dirksen and Satir 1972;Ferenczy et al, 1972;Kanagawa et al, 1972;Ludwig et al, 1972;Patek et al, 1972a,b;Dirksen, 1974;Rumery and Eddy, 1974), uterus (Psychoyos and Mandon,1971;Hafez, 1972Hafez, , 1973Johnnisson and Nilsson, 1972;Anderson et al, 1975;Jones and Hamer, 1975;Ferenczy, 1974Ferenczy, ,1976Motta and Andrews, 1976;Garris, 1984d), and vagina (Kanagawa et al, 1972;Parakkal, 1974) in a number of species, including human (Ludwig et al, 1972, at various stages of the reproductive cycle. Cyclic changes in the rat uterine surface structure are recognized to be under ovarian steroid hormone control (Anderson et al, 1975).…”

“…The guinea pig is a well-recognized animal model for studying early blastocyst-uterine changes associated with interstitial implantation, a characteristic that is shared by the human nidatory process (Garris, 1984d). A functional corpus luteum develops in the guinea pig following ovulation, which results in the maintenance of elevated plasma progesterone levels throughout the luteal phase of the cycle (Garris and Whitehead, 1981;Garris, 1984a,e;Garris and Foreman, 1984;Garris et al, , 1986Blandau,1949;Blatchley et al, 1976, Croix andFranchimont,1975).…”