ULTRASTRUCTURAL STUDY OF IMPLANTATION IN GOLDEN-HAMSTER .1. LOSS OF ZONA PELLUCIDA AND INITIAL ATTACHMENT TO UTERINE EPITHELIUM

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  • 1 January 1976
    • journal article
    • research article
    • Vol. 121  (FEB) , 161-184
Abstract
Blastocysts (45) from 15 golden hamsters were examined in situ with light and electron microscopy between days 3-4 of pregnancy (post-ovulation). At 3 days, blastocysts remained free within the uterine lumen with their zonae pellucidae intact. At various intervals between 3 days and 3 days 6 h a gradual thinning of the zona occurred, indicating the possible presence of a lytic factor which aids in the removal of the zona pellucida. Blastocysts at 3 days 8 h had lost their zonae pellucidae; by 3 1/2 days they were completely enclosed by the uterine epithelium. By 4 days a more intimate association between the juxtaposed trophoblast and uterine epithelium occurred, leaving intermittent deposits of electron-dense material between the adjoining plasma membranes. During this 24 h period, ultrastructural changes within organelles in the blastocysts, particularly those in the trophoblast cells, possibly indicate metabolic changes necessary for the invasion of the uterine epithelium.