ICR albino mouse embryos (n=4lS0) were used to determine production of progesterone and estradiol. In Experiment I, cultures containing 20 (n=lO), 40 (n=lO) or 60 (n=6) early blastocysts were incubated in 13 X 100 rom tubes with .25 ml BMOC-2 for 20 h under 5% CO2 and air at 37C. Also, 20 (n=4) , 40 (n=7) and 60 (n=6) control embryos were frozen at -90C after flushing. Viability was determined by culturing 20 (n=5) , 40 (n=7) and 60 (n=6) for 24 h at which time percent normal development was microscopically evaluated.

In Experiment II, 40 embryos at either morula, early blastocyst or late blastocyst (n=lO) stage were cultured similarly. Viability and control steroid levels were determined on n=5, n=7 and n=7 cultures. Incubated and control cultures were extracted with diethyl ether and progesterone and estradiol isolated on Sephadex LH-20 columns prior to quantification by radioimmunoassay.

Viability for all cultures was 95.6 + .05% (~+SD). In Experiment I, incubated progesterone and estradiol were .31 + .17 and .13 ± .12 ng/culture compared to .33 ± .16 and .12 + .10 ng/culture for controls. In Experiment II, incubated progesterone and estradiol were .21 + .13 and .11 + .10 ng compared to .32 ± .16 and .10 ± .10 ng/culture for controls. There were no effects of embryo numbers, stage of development or treatment on hormone content. These data suggest that the early mouse embryo does not produce progesterone or estradiol when cultured in a defined medium, though viability is maintained.