Development of uteroplacental vasuclature, granulated metrial gland cells and trophoblasts in the uterine wall of the mouse during pregnancy

ABSTRACT

The development of the uteroplacental vasculature was studied by Indian ink injection method. The non-pregnant [estrus] endometrium was supplied by radial and terminal arteries. On day 5 of pregnancy the radial arteries became spiral arteries. All these changes appeared as an indication for the increased uterine blood volume. In this early five days interval of rapid development prior to blastocyst attachment, the endometrium underwent a decidual reaction by transforming its fusiform stromal cells into large polyhedral cells [decidual cells]. Ultrastructurally, their processes appeared to penetrate the basement membranes of the uterine epithelial cells and might aid in its disintegration. In the subsequent stages [days 6-8 of pregnancy] during the initial stages of invasion of the endometrial stroma by the embryo, most trophoblastic cells surrounding the blastocyst were flat [or roughly low cuboidal]. As pregnancy proceeded [on day 8], the area occupied by the trophoblasts became larger and some of these cells became giant. This was associated with an activation of the giant cells and their aquistion of invasive behavior, to complete the process of implantation previously experienced by decidual cells. From day 8 to day 14, the products of conception continued to enlarge at the expence of th surrounding endometrium. On day 8 erosion of endometrial blood vessels became more extensive. The outward growth of the trophoblasts from the trophoblastic shell forming primary villi. When the latter villi were invaded by mesenchymal connective tissue and branches of the umbilical arteries, they were termed chorionic villi. This was the anatomical bases for the achievement of the labyrinthine hemochorial placenta which increases in size in the subsequent stages [11-14 days]. It was considered the first step towards establishing the uteroplacental circulation on which the growth of the embryo will later depend. Numerous GMG cells characterized by their PAS positive cytoplasmic granules were found to differentiate in the deciduas basalis and metrial glands of the uterine wall during the first half of pregnancy [till day 8]. By day 8 and the subsequent stages of pregnancy some of the GMG cells were lying adjacent to the labyrinthine placenta