Epidermal growth factor, vascular endothelial growth factor and progesterone promote placental development in rat whole-embryo culture.

The development and survival of rat embryos in whole-embryo culture is limited by the lack of any maternal blood circulation in a purely fetal placenta. If the resulting placental insufficiency could be overcome for some time by an increase of the placental exchange area, a prolonged culture period would result and facilitate the development of embryos. In the present study, several attempts to stimulate proliferation and growth of the fetal placenta were made by the addition of vascular endothelial growth factor (VEGF), epidermal growth factor (EGF) and progesterone to the culture medium. Rat embryos were routinely explanted with their embryonic membranes at 10.5 days of gestation. Decidua, parietal yolk sac, Reichert's membrane and the layer of superficial trophoblastic giant cells were removed. The explants were cultured and gassed continuously for 24 h in rotating plastic tubes containing rat serum, diluted to 50% with modified COON's F12 medium. Either of the two growth factors or progesterone were added to each culture tube and a control group was cultured without any factor. After the addition of each of these factors the stimulatory effect on placental growth was assessed by morphometric evaluation of several placental parameters from semithin cross-sections: On adding each of the factors the whole cross-sectional area of the placenta significantly increased, as did the area of the fetal placental mesenchyme. VEGF also increased the area of the trophoblast, and the area of the blood vessels enclosed within the trophoblast, by an average of 9.4% and 23.6%, respectively. Thus, VEGF treatment resulted in a measurable extension of the exchange area of the fetal placenta.