Abstract
Embryos explanted at 10.5 days were cultured for 24 h with the visceral yolk sac intact and with the parietal yolk sac intact or opened. The culture medium was undiluted rat serum or rat serum diluted with an equal volume of Hanks balanced saline solution. Ca concentration of the medium was modified by the addition of CaCl2. Optimum growth was achieved when the explants, with or without the parietal yolk sac intact, were cultured in medium containing 0.5-2.0 mM added Ca. Ca concentration affected proliferation of trophoblast cells in the ectoplacental cone, the number of the trophoblastic giant cells in the parietal yolk sac and the expansion of the parietal yolk sac. Histochemical tests on the decidua and embryonic tissue demonstrated high concentrations of Ca around the ectoplacental cone of 10.5 day rat embryos in vivo.