A STUDY OF THE EARLY STAGES OF IMPLANTATION IN MICE

Abstract

In order to study the changes taking place in the blastocyst and locally in the uterus at the site of the blastocyst attachment, pregnant mice were killed at intervals between 3 days 21 hr. and 4 days 16 hr. post coitum. The uteri were tested for the presence of Pontamine Blue areas (indicating increased permeability of capillaries) and histochemically for alkaline phosphatase in the stroma, and also examined histologically. By classifying each female for the various features studied, the following order of ap-pearance was established Pontamine Blue reactivity, "W-bodies" [Wilson''s[image]primary invasive cells''] emerging from blastocyst, local oedema of the uterine stroma, alkaline phosphatase in the uterine stroma, histological decidualization. Giant cell transformation of the trophoblast occurred at about the same time as the emergence of W-bodies from the blastocyst. Blastocyst elongation began after the appearance of Pontamine Blue reactivity and before histological decidualization, but was not sequentially related to the other features studied.