Estrogen, progesterone, and chromosome abnormalities in rabbit blastocysts

The chromosome complement of blastocysts recovered from rabbits injected with estradiol or progesterone during the time of ovum maturation or the first cleavage division was studied. One chromosome anomaly, a triploid, was found in 72 control blastocysts analyzed; two, a triploid and a 44/45 mosaic, were found in 28 blastocysts from rabbits given estradiol 1 h after mating; and two trisomies in 48 blastocysts analyzed were recovered from rabbits treated with progesterone at 4 or 20 h after mating. An increased number of small blastocysts, which could not be analyzed, was found after estradiol treatment near the time of the first cleavage division. A lower mitotic index than normal was found in whole mounts of these blastocysts.