EFFECT OF OESTRADIOL-17 ON FERTILIZED RABBIT EGGS IN VITRO

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Abstract
The effect of estradiol-17[beta] on fertilized rabbit eggs in vitro was studied following its inclusion in the culture medium. When estradiol is present at a concentration of 25 [mu]g/ml and several hrs. remain between the time of exposure and the expected time of first cleavage, single-celled eggs typically fail to cleave and amphimixis appears to be inhibited. If the concentration of estradiol is reduced to 10 [mu]g/ml, or if the first cleavage is imminent at the time of exposure, the eggs tend to fragment instead of undergoing normal cleavage, presumably an effect on the cell membrane. Most eggs are apparently unaffected by an estradiol concentration of 5 [mu]g/ml. A minimal exposure time of about 30 min. is necessary to achieve an estradiol response. Two- and four-celled stages are much more resistant to the estrogen than are single-celled ones. The degree of fragmentation is reduced when progesterone is added equimolarly with estradiol, suggesting that some antagonistic interaction occurs. Under incubator conditions the concentration of estradiol remains constant throughout the time of these experiments but that of estrone appears to decrease.