Effects of calcium on the growth of the rat conceptus during organogenesis in vitro.

Embryos explanted at 10 1/2 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. The calcium concentration of the medium was modified by the addition of calcium chloride. 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 calcium. The calcium concentration was shown to affect the 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 calcium around the ectoplacental cone of 10 1/2 day rat embryos in vivo.