The nutritional requirements for the development in vitro of 2-celled mouse embryos into blastocysts have been extensively investigated by Brinster (1965a, b, c). It was found that most 2-celled embryos will develop normally in a culture medium consisting of bicarbonate-buffered Krebs-Ringer solution, containing bovine serum albumin as a protein source, and pyruvate and lactate as energy sources. Since there are always some 2-celled embryos which will not develop into blastocysts in this medium, the possibility exists that some other growth factors might increase the percentage of normally developing embryos. It is known that synthesis of DNA takes place throughout the cleavage stages and that RNA synthesis also occurs, especially after the 4-cell stage (Mintz, 1964). Thus it was thought that the addition of nucleic acid components
JOAN THOMSON TenBROECK and RALPH L. BRINSTER
The effect of an antifertility agent, U-11100A, on the development in vitro of early mouse embryos and on pregnancy in mice was studied in order to examine the mode of action of the compound.
It was found that development in vitro was blocked at a concentration of 20 μg/ml of U-11100A and that pregnancy was terminated by the oral administration of 10 mg/kg on any of the first 4 days after mating.
When the compound was administered while the embryos were still in the oviducts, acceleration of tubal transport occurred. If it was given after the embryos had reached the uterus, implantation failed to occur, and the embryos were lost through the vagina.
Thus it appears that, in mice, the compound acts on the maternal reproductive tract rather than on the embryo itself.
R. L. BRINSTER and JOAN THOMSON TenBROECK
Fertilized one- and two-cell mouse embryos were transferred to the rabbit Fallopian tube. No blastocysts developed from 730 one-cell embryos transferred. A total of 141 blastocysts developed from 540 two-cell embryos transferred.