[Morphological changes in the fetal part of the allantoic placenta in rats exposed to acute hypoxia].

The aim of this study was to analyze the response of cyto- and syncytiotrophoblast elements of fetal part of allantoic placenta to general acute hypoxia and to determine their morphologic characteristics, which provide the basis for structural changes in placenta and for the disturbances in placental blood flow. Female Wistar rats on day 16 of gestation were exposed to hypoxia (8% oxygen concentration in the gas mixture) for 1 hr. Placenta was studied 1 and 3 days later. Short-term acute hypoxia during pregnancy was shown to induce an impairment of formation and maturation of the fetal part of placenta. In the labyrinth zone, apoptosis was enhanced and a significant number of hyperchromatic nuclei appeared in cyto- and syncytiotrophoblast, which lead to the loss of some cells of cytotrophoblast and resulted in the retardation of its development and transformation into syncytiotrophoblast. One day following hypoxia, a stimulation of adaptive processes was evident as demonstrated by a dramatic rise of mitotic activity in the cytotrophoblast of the labyrinth zone of placental fetal part. However, a delay of the labyrinth zone development persisted till the end of pregnancy. Number and volume of fetal blood vessels were decreased as compared to those in control. A sharp decline of number and size of sinusoids containing maternal blood as well as a significant decrease of blood volume in the sinusoids, suggest a spasm of the uterine and placental vessels causing an impairment of utero-placental blood circulation and development of placental insufficiency.