Cumulus cell dispersion induced by estradiol in mouse oviduct in vitro.

Dispersion of cumulus cells in nonmated mice is completed in the oviduct 15-20 h after ovulation. Oviducts, isolated 1 h after ovulation (13 h post-human chorionic gonaditropin), were cultured in vitro for 40 h. In these oviducts, denuded oocytes were first seen at 30 h of culture, indicating that cumulus dispersion proceeded at a slower rate in vitro. Oocyte denudation was accelerated in a dose-dependent manner by the addition of estradiol to the culture medium in which oviducts were incubated. The addition of progesterone or cycloheximide to the culture medium strongly inhibited oocyte denudation even in the presence of estradiol. When isolated cumuli were incubated in the absence of oviductal tissue, the rate of cell dispersion was slower than that of cumuli incubated inside the oviduct and the addition of estradiol to the culture failed to accelerate this process. On the basis of these data, we propose that cumulus cell dispersion is accelerated by an estrogen-dependent protein produced by the oviduct and that this effect of estrogen is antagonized by progesterone.

High potassium concentration improves preimplantation development of mouse embryos in vitro.

Embryo growth in vitro in culture media containing potassium (K) ions at the concentration found in common extracellular fluids proceeds at a slower pace than in vivo. Considering that oviductal fluid has an unusually high concentration of K, the effect of various concentrations of this ion on development of mouse embryos in vitro was investigated. Two-cell to 4-cell preimplantation mouse embryos were cultured in vitro for 47 hours in a medium in which NaCl was partially replaced by KCl at concentrations ranging from 4.7 to 60 mM. The number of cells per embryo increased in a dose-related fashion when the embryos were cultured in the presence of 4.7, 10, and 25 mM of K. Higher K concentrations were detrimental for development. Embryos developed in vitro under different concentrations of K were transferred to pseudopregnant recipient foster mothers as a test of viability. The highest rate of implantation was observed with embryos cultured in medium containing 25 mM K. The results indicate that a high concentration of K in the culture medium (25 mM), comparable to that found in the genital tract of the female mouse, is required for a rate of development in vitro similar to the one observed in vivo.